Ecotoxicology (2014) 23:1439–1446 DOI 10.1007/s10646-014-1286-7
Changes in polychlorinated biphenyl (PCB) exposure in tree swallows (Tachycineta bicolor) nesting along the Sheboygan River, WI, USA Christine M. Custer • Thomas W. Custer Sean M. Strom • Kathleen A. Patnode • J. Christian Franson
•
Accepted: 27 June 2014 / Published online: 24 July 2014 Ó Springer Science+Business Media New York (outside the USA) 2014
Abstract Exposure to polychlorinated biphenyls (PCBs) in tree swallow (Tachycineta bicolor) eggs on the Sheboygan River, Wisconsin in the 1990s was higher at sites downstream (geometric means = 3.33–8.69 lg/g wet wt.) of the putative PCB source in Sheboygan Falls, Wisconsin than it was above the source (1.24 lg/g) with the exposure declining as the distance downstream of the source increased. A similar pattern of declining exposure was present in the 2010s as well. Although exposure to PCBs in eggs along the Sheboygan River at sites downstream of Sheboygan Falls has declined by *60 % since the mid1990s (8.69 down to 3.27 lg/g) there still seems to be residual pockets of contamination that are exposing some individuals (*25 %) to PCB contamination, similar to exposure found in the 1990s. The exposure patterns in eggs and nestlings among sites, and the changes between the two decades, are further validated by accumulation rate information.
C. M. Custer (&) T. W. Custer U.S. Geological Survey, 2630 Fanta Reed Rd, La Crosse, WI 54603, USA e-mail: [email protected] S. M. Strom WI Department of Natural Resources, 3369 W. Brewster St, Appleton, WI 54914, USA K. A. Patnode U.S. Fish and Wildlife Service, 315 South Allen Street, Suite 322, State College, PA 16801, USA J. Christian Franson U.S. Geological Survey, 6066 Schroeder Road, Madison, WI 53711, USA
Keywords Historic changes Polychlorinated biphenyls PCBs Sheboygan River Tree swallows Tachycineta bicolor
Introduction The Sheboygan River on the eastern coast of Wisconsin, USA was designated as an Area of Concern (AOC) in 1987 primarily because of contamination by polychlorinated biphenyls (PCBs), polycyclic aromatic hydrocarbons (PAHs), and trace elements. Areas of Concern were designated in annex 2 of the 1987 U.S.—Canada Great Lakes Water Quality Agreement and identified locations that had experienced environmental degradation. Management actions for this AOC are summarized by Shrank et al. (1997). It is believed that the PCBs came from an industrial site in Sheboygan Falls that used hydraulic fluids containing PCBs (Bzdusek et al. 2006), whereas the PAHs originated from highway dust, gasification plants, and coke oven emissions (Lu et al. 2005). One of several beneficial use impairments (BUIs) identified as part of the AOC process was possible adverse effects of contaminants on avian reproduction. The concern about potential reproductive effects was partially in response to a study which documented high PCBs in several bird species collected on the Sheboygan River in 1979 (Heinz et al. 1984). Our objectives were to document both historic and current exposure to total PCBs in tree swallows which nest along the Sheboygan River, quantify changes between the decades of the 1990s and 2010s, and finally to quantify differences among reaches within the river system. Tree swallows (Tachycineta bicolor) are being widely used as a model species to understand exposure to and effects of contaminants on bird populations (see review in
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Custer CM 2011). They offer two main advantages over other aquatic species, such as great blue herons (Ardea herodias), belted kingfishers (Ceryle alcyon), and herring gulls (Larus argentatus) that are also used for these types of studies: (1) their nests are more accessible than nests of these other species which increases the ability to acquireadequate sample sizes and (2) their feeding ecology simplifies data interpretation. Nest boxes (usually 10–20 per site) can be placed along specific reaches or areas of interest rather than having to rely on chance to have enough pairs nesting for adequate sample size. Because swallows feed on the aerial stage of benthic aquatic invertebrates (Blancher and McNicol 1991, Mengelkoch et al. 2004) their tissues reflect sediment contamination in a relatively straight forward manner, especially for organic contaminants (Jayaraman et al. 2009). Because they generally feed within 1 ± km of their nest box (Quinney and Ankney 1985), contaminant exposure reflects the local area and not more distant aquatic habitats. A third advantage is that there are published data available for comparative purposes for multiple endpoints, including reproductive and physiological effects, and exposure to various contaminant classes (see review in Custer CM 2011).
Methods and materials Field work Tree swallow nest boxes (15–20 per site) were deployed at five locations 1995–1997 (hereafter referred to as 1990s) and two locations in 2010–2012 (hereafter referred to as 2010s) along the Sheboygan River (Fig. 1). Because the feeding radius overlapped for the two sites in both the Middle Reach and Above the contaminant source in the 1990s, they each are considered as one location. The sites include:one site upstream of the putative PCB contaminant source (1990s only) and at two locations downstream in the1990s and again in 2010s. Nest boxes were placed approximately 20 m apart paralleling the river. In the 1990s, a double box configuration, to reduce competition for nest boxes with other cavity-nesting species, was used with each double box placed approximately 20 m apart. Egg and 12-day-old nestling samples were collected from nest boxes and analyzed for PCBs following standard analytical protocols (see sections below). Eggs were collected shortly after the clutch was completed during the last week in May and the first week in June, the contents placed in chemically-clean jars, and frozen at -20 °C until chemically analyzed. The specific eggs collected were taken haphazardly from the completed clutch; there is no evidence that laying order or stage of incubation affects total PCB concentrations in a predictable manner (Custer
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et al. 1997, 2010b). In 1990s, eggs, ‘pippers’ consisting of pipping eggs or just-hatched nestlings within a day of hatching, and 12-day-old nestlings (±1 day of age) were collected, whereas in 2010s, eggs and 12-day-old nestlings were collected. The date nestlings reached 12 days of age was determined by multiple methods. Generally the date the clutch hatched was known, and the nestling age further validated by feather length (CMC unpubl. data). Pippers and nestlings were euthanized by decapitation (AVMA 2013) under an approved Animal Care and Use protocol. The stomach contents were removed, and the carcass remainder frozen until chemically analyzed. For eggs and nestlings, because of relatively small sample mass (\20 g), the entire egg contents or nestling carcass, sans stomach contents, was homogenized and aliquots (nestlings only) further processed as indicated below. Analytical chemistry Samples were analyzed by the Wisconsin State Laboratory of Hygiene (WSLH), Madison, WI USA (1990s samples plus four nestlings from 2012) and by Axys Analytical Services, Ltd., British Columbia, Canada (Axys, 2010s samples). Axys analyzed the egg samples by high resolution (HR) methods, whereas the nestling samples were analyzed by both HR (2010) and low-resolution (LR, 2012) methods for PCB congeners. Wisconsin State Laboratory of Hygiene analyses were HR and LR, depending on the congener. Axys methods For PCB congeners, the tissue was homogenized with anhydrous powdered sodium sulphate and extracted with dichloromethane. The extracts were cleaned with a Biobead SX-3 gel permeation column with 1:1dichloromethane:hexane and eluted with 1:1 dichloromethane:hexane. A Florisil column cleanup was then used followed by LR or HR gas chromatograph [GC]/mass spectrometer [MS]. For HR, the extract was further cleaned in a 4.5 % (0.22 g) carbon AX-21/Celite 545 mixture column with hexane rinses and eluted with cyclohexane:dichloromethane (1:1) followed by 10:1 ethyl acetate:toluene (2 ml) and then analyzed with HR GC/MS. Blanks, duplicates, and spikes were analyzed at a frequency of one per analytical batch (n = *11 samples) or approximately 9 % of samples. Average percent recover was 97.2 ? 0.46 [1 standard error (SE)]. Certified reference material (CRM) was extracted and analyzed with each analytical batch. The CRM selected for this study was EDF-2525 (Cambridge Isotope Laboratories, Contaminated Fish Tissue). This CRM has certified values for 38 PCB congeners. Detection limits, also referred to as reporting limits and are defined as the
Changes in polychlorinated biphenyl (PCB) exposure Fig. 1 Map of Sheboygan River, WI tree swallow study sites in the 1990s and 2010s. The putative source of the polychlorinated biphenyls was located in Sheboygan Falls in the area designated as the Upper reach. The number of nest boxes at each site in the 1990s from upstream to downstream were 8, 11, 15, 10, and 10. There were 20 nest boxes in the Middle reach and 17 nest boxes in the Lower reach in the 2010s
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1995-97 sampling sites
Wisconsin
2010-12 sampling sites 0
1 km
Sheboygan
Kohler Sheboygan Falls
Above contaminant source
Upper
Middle
Lower
Sheboygan River reach designations
level above which quantitative results can be obtained with a high degree of confidence, were \0.01 ng/g wet wt. for the HR analyses and \0.10 ng/g for the LR analyses. WSLH methods Samples were homogenized with dry ice, allowed to sublime overnight and then combined with 60 g of sodium sulfate. The sample (10 g) was extracted with 230 ml of dichloromethane using a 20 mm ID chromatographic column. After concentrating to less than 5 ml, the final extract was diluted 1:1 with cyclohexane to 10 ml. A two-stage extract cleanup procedure was used. First, the lipid fraction was removed using an automated gel-permeation chromatography system manufactured by Gilson. Activated florisil cleanup was then performed using a 6 % ethyl ether/94 % hexane elution followed by a 3.5 % deactivated silica-gel cleanup using hexane elution. Sample extracts were concentrated to 5 ml. An aliquot of the extract was injected into a HP-5890 dual column GC equipped with an electron capture detector (ECD). Congener results were determined utilizing an Agilent 60 m DB-5 column. Congeners were confirmed using an Agilent 60 m DB-1 column. Blanks, laboratory control spikes and sample duplicates (when adequate sample amounts allowed) were extracted and analyzed with each batch of approximately ten samples. Average percent recover was 93.6 ± 0.73 (SE). Most congeners were assessed by LR, but HR was used for congeners which express toxicity through the aryl hydrocarbon receptor (Ah-active) (Maack and Sonzogni 1988). Detection limit was 1.0 ng/g wet wt.
Adjustment between laboratories The specific congeners included in the total PCB analysis varied by laboratory and to a lesser degree by whether the chemical analysis was done using HR or LR analysis methods (Table 1). Of the 179 congeners (counting a coeluted group as one congener), there were 72 congeners analyzed in common, i.e. by both labs and both HR and LR. An additional 82 congeners were analyzed only by Axys and three congeners only by WSLH. Eight congeners were not detected by either lab. Total PCBs was the sum of the congeners in the pool of congeners common to both laboratories. A congener was not included in the common pool for analysis if differences in detection limits would bias the results from either decade. For example, a congener would not be included in the common pool if a higher detection limit in one decade resulted in mostly all non-detectable values, even though in the other decade there were detectable values at a lower detection limit. Also, if [50 % of the samples were below the detection limit in one or the other of the decades then that congener was also eliminated from the ‘common’ pool. Both measures were taken to reduce any possible bias in the data analysis. Even though WSLH analyzed fewer PCB congeners they captured an average of between 68 % (n = four paired nestling samples analyzed by both labs, multiplier = 1.48) and 78 % of the total PCBs (concentration of congeners in common divided by concentration of all congeners, n = 17 Axys data points; multiplier = 1.29). Concentrations from WSLH, therefore, should be multiplied by 1.3–1.5 to make the concentrations reported by the
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Table 1 Polychlorinated biphenyl (PCB) congeners analyzed by Axys analytical, either by high (HR) and low resolution (LR) analyses, and by the Wisconsin State Laboratory of Hygiene (WSLH) from the Sheboygan River in the 1990s and in the 2010s Congener group
Axys HR
WSLH LR
10, 20/28, 32, 34, 60, 64, 68, 73, 109, 120, 121, 127, 144, 164, 190, 192
XX
1, 2, 3, 11, 12/13, 17, 21/33, 23/34, 38, 39, 42/59, 43/49, 54, 55, 57, 58, 59/62/75, 67, 72, 78, 79, 81, 94, 96, 103, 104, 107/109/124, 111/115, 112, 114, 122, 129/138/160/163/164, 131/142, 132/168, 133, 134, 139/149/140, 145, 148, 150, 152, 155, 159, 161, 165, 175, 176, 179, 184, 186, 188, 189, 191, 195, 197, 204, 205, 207, 209
XX
XX
4/10, 5/8, 6, 7/9, 15/17, 16/32, 18/30, 19, 22, 24/27, 25, 26/29, 28/31, 37/42, 40/41 seriesa, 44/47/65, 45/51, 46, 47/48, 49/69, 50/53, 52/73, 56/60, 61/70/74/76, 63, 66/80/95, 77, 82, 83/99/108, 84/92, 85 series, 86 series, 88 series, 89 series, 92, 93/95/98/100/102, 105/127, 110/115, 106/118, 123, 126, 128/166, 130, 135/144/151/154, 136, 137/176, 141, 146, 147/149, 153/132, 156/157, 158, 167, 170/190, 171/173/202, 172/192/197, 174/181, 177, 178, 180, 182/187, 183/185, 194, 196/203, 198/199, 201, 202/171, 206, 208/195
XX
XX
8, 27 33, 163/138, 99
XX
80, 106, 142
ND
XX
XX XX
14, 35, 36, 161
ND
ND
169
ND
ND
ND
Congeners separated by a slash were reported as a coelution by at least one lab a congener combinations in series are: 41 series = 40/41/71 (HR), 40 ? 41/64/68/71 (LR), 40/10 ? 41/71/64 (WSLH); 85 series = 85/ 116/117 (HR), 85/120 (LR), 85 (WSLH); 86 series = 86/87/97/108/ 119/125 (HR), 86/97 ? 87/115/116 ?119 ? 125 (LR), 87 ? 97 (WSLH); 88 series = 88/91 (HR), 88/121 ? 91 (LR), 91 (WSLH); 89 series = 89 ? 90/101/113 (HR), 89/90/101 ? 113 (LR), 101 ? 89 (WSLH)
WSLH comparable to estimated total PCBs when all possible congeners were included in the chemical analysis. All PCB concentration data presented in text, tables, and figures are the sum of the 72 congeners in common and have not been corrected for laboratory unless specifically indicated, mainly in the discussion when comparing to literature values. The total PCBs from HR and LR from Axys are equivalent (Pillay per. comm). Statistical analyses Differences in PCB exposure were compared between decades and among sites using analysis of variance
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(ANOVA) on log transformed data. The sites are identified in text and tables with the reach designation. Decadal and site statistical comparisons were made within each matrix type (i.e. egg, nestling, etc.) individually. Two-way ANOVAs (decade, site, and decade * site interaction) were run on the egg and nestling data from the Middle and Lower reaches. One-way ANOVAs compared among sites for the 1990s so that the Above reach could be included in the assessments. Bonferroni multiple comparison method was used to determine differences among means when ANOVAs were significant. Data were log transformed to meet the homogeneity of variance assumptions of ANOVA methods. Geometric means (antilog of log means) and 95 % confidence intervals (CI) are provided in text and tables. Accumulation rate (lg of PCBs accumulated per day, calculated as the PCB mass in nestlings minus the mass in eggs divided by age of nestling) was calculated and compared among sites with ANOVA similar to the concentration assessments above. The mass of a contaminant was calculated by multiplying the concentration in the sample by the sample mass. Accumulation rate factors out any exposure in eggs that may have occurred at wintering or migration areas, although this is usually negligible. Accumulation rate calculations also improve clarity in understanding exposure in nestlings that can be obscured by growth dilution in rapidly growing nestlings. When possible, eggs and 12-day old nestlings from the same nest were used to calculate accumulation rates. However, because only two sibling pairs were available for the site in the Middle reach and none from the site in the Lower reach in the 1990s, mean concentration in the pooled egg samples from the nests from which 12-day old nestlings were collected were used to calculate the PCB mass in eggs. The reach designations were mainly used to provide discrete, equidistant sampling units downstream of the putative PCB source in Sheboygan Falls, however, the reaches in this study correspond to segments used in previous ecological risk assessments of the Sheboygan River (Burzynski 2000). The Middle reach site was approximately 3 km downstream from the putative PCB source, in a straight linear line, and the Lower reach site was approximately 7 km downstream of the source.
Results Geometric mean PCB concentrations in tree swallow eggs collected from the site in the Middle reach of the Sheboygan River significantly decreased by *60 % between the decades of the 1990s and 2010s (8.69 down to 3.27 lg/ g), but did not decline statistically for nestlings (5.50 vs. 4.71 lg/g Table 2). One nestling in the 2010s contained
Changes in polychlorinated biphenyl (PCB) exposure
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Table 2 Geometric mean concentration and 95 % confidence intervals (CIs) for total polychlorinated biphenyls (PCBs) based on the sum of congeners that were common to both analytical chemistry Site locations and sampling matrix
n
laboratories for tree swallows nesting along the Sheboygan River, WI in the 1990s compared to the 2010s
Geometric mean concentrations (lg/g wet wt.), 95 % CI, and minimum and maximum values {in brackets} by decade 1990s
2010s
Above PCB source Egg
10
1.24
0.49–3.18
{0.32–19.8}
Pipper
8
0.44
0.24–0.82
{0.22–1.60}
Nestling
13
0.22
0.14–0.35
{0.07–1.01}
Egg
11, 4a
8.69 Ab
6.15–12.3
{3.40–18.3}
Pipper
15
4.51
3.20–6.34
{1.04–12.9}
Nestling
16, 4
5.50 ac
3.90–7.77
Middle 3.27 B
1.05–10.22
{2.00–9.48}
{1.34–12.9}
4.71 a
2.10–10.55
{3.67–10.1}
Lower Egg
6, 5
3.33 B
2.07–5.38
{1.99–5.42}
0.48 C
0.26–0.89
{0.32–0.95}
Pipper Nestling
4 6, 3
2.41 4.24 a
1.15–5.03 2.16–8.33
{1.57–3.67} {1.31–7.46}
0.64 b
0.23–1.75
{0.64–1.44}
Among site differences—1990s only a
P \ 0.001 (eggs); P \ 0.001 (nestling); P \ 0.001 (pipper)
First number is sample size for the 1990s and the second number is the sample size for the 2010s
b
Means for eggs sharing same capital letter are not different between decades and among sites in the named reaches (Middle and Lower) (F3,22 = 34.11, P \ 0.001 [decades P \ 0.001, site P \ 0.001, decades * site interaction P = 0.043]). See text for differences with above source in 1990s c
Means for nestlings sharing same lower case letter are not different between decades and among sites in the named reaches (Middle and Lower) [F3,25 = 10.47, P \ 0.001 (decade = 0.002, site = 0.006, decade * site interaction = 0.004)]. See text for differences with above source in 1990s
10.1 lg/g PCBs, compared to \3.99 lg/g for the other three nestlings which accounted for this lack of statistical difference between decades. For eggs, pippers and nestlings in the 1990s, the site Above the PCB source had significantly less contamination than at least one of the downstream locations. For nestlings, the two downstream locations did not differ from one another and both were significantly higher than the site in the Above reach. For pippers, the Above site had significantly less PCBs than either of the sites in the Middle and Lower reaches. For eggs, however, the site in the reach Above the putative PCB source had significantly less PCB contamination than the site in the Middle reach, but the site in the reach Above (1.24 lg/g) and the site in the Lower reach (3.33 lg/g) were not different from one another. In the 2010s, the site in the Lower reach had significantly less PCB contamination than the site in the Middle reach for both eggs and nestlings (Table 2). In both decades, the accumulation rate (mass in the nestling minus mass in egg divided by the age of the nestling) of total PCBs, was *6 times higher at the site in the Middle reach compared to the site in the Lower reach [13.6 vs. 8.6 lg/day (1990s) and 8.7 vs. 1.4 lg/day (2010s), (decade P = 0.014, site P = 0.014, decade * site = 0.608, Fig. 2]. The accumulation rate at the
site Above the putative PCB source was 0.08 lg/day and statistically differed from both the sites in the Middle and Lower reaches in the 1990s. The site in the Middle reach, where data were available for both decades, accumulated PCBs at approximately half the rate in the 2010s (8.7 lg/ day) compared to the earlier decade (13.6 lg/day, 1990s), but was not statistically different (Bonferroni mean separation) because of small samples sizes and high within site variability. The difference between the two decades is actually more than reflected by the mean accumulation rate, however, because one of four rates in 2010s was similar to the 1990s rates (Fig. 2). The mean accumulation rate for the 2010s without that one nest was 6.2 lg/day, approximately half the rate in the 1990s.
Discussion The current exposure of tree swallows to PCBs on the Sheboygan River is about half of what it was in the mid1990s, based on concentrations in eggs [geometric mean = 8.6 lg/g wet wt. (1990s) compared to 3.3 (2010s)]. Interestingly, the difference between the two decades in nestling exposure was less (5.5 vs. 4.7) and not statistically different. This smaller difference for nestlings
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Accumulation rate – 1990s
µg PCBs
Middle = 13.6 µg/day
Lower = 8.6 µg/day
Above = 0.08 µg/day; n=3 lines
µg PCBs
Accumulation rate – 2010s
Middle = 8.7 µg/day
Lower = 1.4 µg/day
Egg
Days of age
Fig. 2 Accumulation rate (lg/day) of total polychlorinated biphenyls (PCBs) in the 1990s (upper panel) and 2010s (lower panel) along the Sheboygan River, WI
may be because there still seems to be some ‘hot spots’ on the Sheboygan River near the sites in the Middle reach and that is producing significant exposure to some (*25 %), but not all tree swallows. This high variability in exposure in the 2010s is consistent with high variability at the sites within the Middle reach in the 1990s, as well as, in other tree swallow studies (Custer et al. 2003). Additional sampling is planned to further investigate this level of variability and what proportion of the nesting swallows are still feeding in ‘hot spots’, or on more contaminated food items. The *50 % decline in exposure to PCB on the Sheboygan River was similar to the magnitude of the decline from the mid-1990s to the current decade in tree swallows sampled at the mouth of the Fox River in lower Green Bay, WI (Custer et al. 2014). Calculation of accumulation rates can provide a clearer assessment of exposure during the nestling period. Interpretation of concentration values are often confounded by growth dilution during that period. Body mass in nestling tree swallows increases by a factor of thirteen (1.5 g at hatching to 20 g at 12 days of age). Concentrations in nestling can go down in spite of significant exposure that is masked by the large increase in body mass. By only looking
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at concentration, the appearance of little to no exposure can be erroneously concluded even though considerable exposure is actually occurring. The accumulation rate in nestlings further illustrates the decadal decline in exposure to PCBs along the Sheboygan River. There was less, but not significantly less, accumulation of PCBs at the site in the Middle reach in the 2010s (8.7 lg/day) compared to the 1990s (13.6 lg/day). This lack of significance was because there was one nest box where the accumulation rate in the 2010s was similar to the 1990s (Fig. 2). The accumulation rate at the site in the Lower reach in the 2010s was only 1.4 lg/day, but still more than the 1990s rate at the site Above the PCB source (0.08 lg/day). Mean accumulation rates at other PCB-contaminated sites were between 33.7 and 75.9 lg/day along the Housatonic River, MA (Custer et al. 2003), 1.3–6.7 in 1994–95 along the Fox River and lower Green Bay, WI (Custer et al. 1998) and 27 lg/day in New Bedford Harbor, MA (Jayaraman et al. 2009). Background accumulation rates for PCBs for comparative purposes were between and 0.37–0.68 lg/day along the Wisconsin River, WI (Custer et al. 2002), 0.18–0.21 lg/day in Pool 15 of the upper Mississippi River in Iowa (Custer et al. 2000), 0.06–0.42 lg/day at the two reference locations for the Fox River/Green Bay study (Custer et al. 1998), and a -0.3–0.7 lg/day at the reference location for the Housatonic River study (Custer et al. 2003). Comparing to literature values, the average egg and nestling PCB exposure at the site in the Middle reach of the Sheboygan River in the 1990s [means = 13.1 lg/g wet wt. (eggs) and 8.3 lg/g (nestlings)]and in the 2010s [mean = 4.9 lg/g (eggs) and 7.1 lg/g (nestlings)], using the 1.5 multiplier to correct for unmeasured PCB congeners, here and for the following Sheboygan River data, were elevated but considerably lower than at the most known PCB-contaminated site (Housatonic River). Mean egg and nestling PCB concentrations from tree swallows collected on the Housatonic River, MA in the late 1990s ranged between 31 and 101 lg/g (eggs) and 21–45 lg/g (nestlings, Custer et al. 2003). Mean eggs concentrations from the Sheboygan River were similar, however, to other sites sampled during that same time frame such as on the Akwesasne Reserve, NY in the early 1990s (11.2 lg/g wet wt., Bishop et al. 1999) and the Hudson River both in the mid-1990s (means between 9.3 and 29.5 lg/g wet wt., Secord et al. 1999) and in the early 2000s (6.8 lg/g Custer et al. 2010a). The Sheboygan River had higher exposure than on the lower Fox River and Green Bay in the mid1990s [2–3 lg/g (eggs) and 1–4 lg/g (nestlings) Custer et al. 1998]. Background PCB concentrations typically are 1 lg/g or less in eggs and nestlings (Custer et al. 1998, Bishop et al. 1999) in the Great Lakes, but reference areas can be elevated above 1 lg/g such as was the case at the Housatonic River reference site (Custer et al. 2003).
Changes in polychlorinated biphenyl (PCB) exposure
PCB concentrations in a few individual eggs sampled from the site in the Middle reach of the Sheboygan River in the 1990s (max. value exceeded 25 lg/g wet wt., again using the 1.5 multiplier) exceeded the threshold (*20 lg/g wet wt. in eggs) associated with reduced hatching success in swallows (Custer et al. 2003), but by the 2010s (max. value = 14 lg/g), none exceeded that threshold value, although a few egg samples were still substantially elevated. The threshold value for when reproductive success begins to become impaired for tree swallows is similar to that found for other avian species (raptors = 35 lg/g wet wt.; gulls and terns = 23–142 lg/g wet wt., from review in Harris and Elliott 2011). In contrast, the maximum egg concentration (1.4 lg/g wet wt.) in the 2010s at the site in the Lower reach of the Sheboygan River was *14 times lower than the threshold for reduced hatching success. Comparison to other bird species The corrected concentrations in nestling tree swallow carcasses at the site in the Middle portions of the Sheboygan River in the 1990s (geometric means = 6.4 and 8.3, maximum value 19.3) were 20–30 times lower than concentrations in belted kingfisher carcasses (Heinz et al. 1984) in 1979 from that same stretch of the river. This can be partly explained because swallows feed at a lower trophic level (aquatic invertebrates) than kingfishers (small fish) and hence have lower exposure which was also found on the Hudson River, NY (Custer et al. 2010a). An additional factor was because the kingfishers that were collected by Heinz et al. (1984) were either adult or immature birds and therefore had been feeding in the contaminated habitat for a much longer period of time, months rather than *12 days, than were the nestling tree swallows. Similarly, the carcass residues in spotted sandpiper (Actitis macularia) on the Sheboygan River in the 1990s were also much higher than in tree swallows from the same reach in the 1990s, again most likely because of the additional length of time spent feeding in the contaminated stretches of the river prior to collection, and with a lesser contribution due to food habit differences. Summary Exposure to PCBs on the Sheboygan River was higher at the two sites downstream of the putative PCB source than it was upstream of the source and the exposure tended to decline as the distance downstream of the source increased. Because there was only one site sampled in both the Middle and Lower reaches in each decade, it is possible that this upstream/downstream gradient is spurious. Although exposure to PCBs along the Sheboygan River downstream of Sheboygan Falls has declined by *60 %
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since the mid-1990s, there still seems to be residual pockets of contamination that are exposing some individuals (25 %) to PCB contamination, similar to exposure found in the 1990s. The elevated exposure in eggs is further validated by the elevated accumulation rate in nestlings that effectively factors out any exposure that might have occurred at wintering or migration areas. Acknowledgments We thank River Wildlife, City of Sheboygan, Mayline Co., Sarah and Pete Gahagan,and Richard Seichter for access to their property; Diana Goldberg, Andrew Haertel, Kristina Mott, Kelsey Prestby, Darin Ripp, Josh TeSlaa, and Jocelyn Tschaikovsky for field assistance; Paul M. Dummer for field and data management assistance; David Rogers for assistance with analytical methodology; and L.K. Lohman and two anonymous reviewers for comments on earlier drafts of this manuscript. Use of trade, product, or firm names does not imply endorsement by the U.S. Government. Conflict of interest The authors declare that we have no conflict of interest. Data were collected under current laws of the United States of America. The work in 2010–2012 was funded by the Great Lakes Restoration Initiative and was approved by the Animal Care and Use Committee at the Upper Midwest Environmental Sciences Center.
References AVMA (2013) AVMA guidelines for the euthanasia of animals, 2013th edn. American Veterinary Medical Association, Schaumburg Bishop CA, Mahony NA, Trudeau S, Pettit KE (1999) Reproductive success and biochemical effects in tree swallows (Tachycineta bicolor) exposed to chlorinated hydrocarbon contaminants in wetlands of the Great lakes and St. Laurence river basin, USA and Canada. Environ Toxicol Chem 18:263–271 Blancher PJ, McNicol DK (1991) Tree swallow diet in relation to wetland acidity. Can J Zool 69:2629–2637 Burzynski, M (2000) Sheboygan river food chain and sediment contaminant assessment. Final project report U.S. EPA Grant #GL-995681, http://www.epa.gov/glnpo/sediment/FoodChain/index. html Bzdusek P, Lu J, Christensen ER (2006) PCB congeners and dechlorination in sediments of Sheboygan River, Wisconsin, determined by matrix factorization. Environ Sci Technol 40:120–129 Custer TW, Custer CM, Stromborg KL (1997) Distribution of organochlorine contaminants in double-crested cormorant eggs and sibling embryos. Environ Toxicol Chem 16:1646–1649 Custer CM, Custer TW, Allen PD, Stromborg KL, Melancon MJ (1998) Reproduction and environmental contamination in tree swallows nesting in the Fox River drainage and Green Bay, Wisconsin, USA. Environ Toxicol Chem 17:1765–1987 Custer CM, Custer TW, Coffey M (2000) Organochlorine chemicals in tree swallows nesting in pool 15 of the upper Mississippi River. Bull Environ Contam Toxicol 64:341–346 Custer TW, Custer CM, Hines RK (2002) Dioxins and congenerspecific polychlorinated biphenyls in three avian species from the Wisconsin River, Wisconsin. Environ Pollut 119:223–232 Custer CM, Custer TW, Dummer PM, Munney KL (2003) Exposure and effects of chemical contaminants on tree swallows nesting along the Housatonic River, Berkshire County, Massachusetts, USA, 1998–2000. Environ Toxicol Chem 22:1605–1621 Custer CM, Custer TW, Dummer PM (2010a) Patterns of organic contaminants in eggs of an insectivorous, omnivorous, and
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1446 piscivorous bird nesting on the Hudson River, NY, USA. Environ Toxicol Chem 29:2286–2296 Custer CM, Gray BR, Custer TW (2010b) Effects of egg order on organic and inorganic element concentrations and egg characteristics in tree swallows, Tachycineta bicolor. Environ Toxicol Chem 29:909–921 Custer CM (2011) Swallows as a sentinel species for contaminant exposure and effect studies. In: Elliott JE, Bishop CA, Morrissey CA (eds) Wildlife ecotoxicology: forensic approaches, emerging topics in ecotoxicology, vol 3. Springer, New York, pp 45–91. doi:10.1007/978-0-387-89432-4_3 Custer TW, Dummer PM, Custer CM, Franson JC, Jones M (2014) Contaminant exposure of birds nesting in Green Bay, Wisconsin. Environ Toxicol Chem 33:1832–1839 Harris ML, Elliott JE (2011) Effects of polychlorinated biphenyls, dibenzo-p-dioxins and dibenzofurans, and polybrominated diphenyl ethers in wild birds. In: Beyer WN, Meador JP (eds) Environmental contaminants in biota interpreting tissue concentrations. CRC Press, Boca Raton, pp 477–528 Heinz GH, Swineford DM, Katsma DE (1984) High PCB residues in birds from the Sheboygan River, Wisconsin. Environ Monit Assess 4:155–161 Jayaraman S, Nacci DE, Champlin DM, Pruell RJ, Rocha KJ, Custer CM, Custer TW, Cantwell M (2009) PCBs and DDE in tree
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C. M. Custer et al. swallow (Tachycineta bicolor) eggs and nestlings from an estuarine PCB superfund site, New Bedford Harbor, MA USA. Environ Sci Technol 43:8387–8392 Lu J, Bzdusek PA, Christensen ER, Arora S (2005) Estimating sources of PAHs in sediments of the Sheboygan River, Wisconsin, by a chemical mass balance model. J Great Lakes Res 31:456–465 Maack L, Sonzogni WC (1988) Analysis of polychlorobiphenyl congeners in Wisconsin fish. Arch Environ Contam Toxicol 17:711–719 Mengelkoch JM, Niemi GJ, Regal RR (2004) Diet of the nestling tree swallow. Condor 106:423–429 Quinney TE, Ankney CD (1985) Prey size selection by tree swallows. Auk 102:245–250 Schrank CS, Cormier SM, Blazer VS (1997) Contaminant exposure, biochemical, and histopathological biomarkers in white suckers from contaminated and reference sites in the Sheboygan River, Wisconsin. J Great Lakes Res 23:119–130 Secord AL, McCarty JP, Echols KR, Meadows JC, Gale RW, Tillitt DE (1999) Polychlorinated biphenyls and 2,3,7,8-tetrachlorobidenzo-p-dioxin equivalents in tree swallows from the upper Hudson River, New York state, USA. Environ Toxicol Chem 18:2519–2525
Changes in polychlorinated biphenyl (PCB) exposure in tree swallows (Tachycineta bicolor) nesting along the Sheboygan River, WI, USA Christine M. Custer • Thomas W. Custer Sean M. Strom • Kathleen A. Patnode • J. Christian Franson
•
Accepted: 27 June 2014 / Published online: 24 July 2014 Ó Springer Science+Business Media New York (outside the USA) 2014
Abstract Exposure to polychlorinated biphenyls (PCBs) in tree swallow (Tachycineta bicolor) eggs on the Sheboygan River, Wisconsin in the 1990s was higher at sites downstream (geometric means = 3.33–8.69 lg/g wet wt.) of the putative PCB source in Sheboygan Falls, Wisconsin than it was above the source (1.24 lg/g) with the exposure declining as the distance downstream of the source increased. A similar pattern of declining exposure was present in the 2010s as well. Although exposure to PCBs in eggs along the Sheboygan River at sites downstream of Sheboygan Falls has declined by *60 % since the mid1990s (8.69 down to 3.27 lg/g) there still seems to be residual pockets of contamination that are exposing some individuals (*25 %) to PCB contamination, similar to exposure found in the 1990s. The exposure patterns in eggs and nestlings among sites, and the changes between the two decades, are further validated by accumulation rate information.
C. M. Custer (&) T. W. Custer U.S. Geological Survey, 2630 Fanta Reed Rd, La Crosse, WI 54603, USA e-mail: [email protected] S. M. Strom WI Department of Natural Resources, 3369 W. Brewster St, Appleton, WI 54914, USA K. A. Patnode U.S. Fish and Wildlife Service, 315 South Allen Street, Suite 322, State College, PA 16801, USA J. Christian Franson U.S. Geological Survey, 6066 Schroeder Road, Madison, WI 53711, USA
Keywords Historic changes Polychlorinated biphenyls PCBs Sheboygan River Tree swallows Tachycineta bicolor
Introduction The Sheboygan River on the eastern coast of Wisconsin, USA was designated as an Area of Concern (AOC) in 1987 primarily because of contamination by polychlorinated biphenyls (PCBs), polycyclic aromatic hydrocarbons (PAHs), and trace elements. Areas of Concern were designated in annex 2 of the 1987 U.S.—Canada Great Lakes Water Quality Agreement and identified locations that had experienced environmental degradation. Management actions for this AOC are summarized by Shrank et al. (1997). It is believed that the PCBs came from an industrial site in Sheboygan Falls that used hydraulic fluids containing PCBs (Bzdusek et al. 2006), whereas the PAHs originated from highway dust, gasification plants, and coke oven emissions (Lu et al. 2005). One of several beneficial use impairments (BUIs) identified as part of the AOC process was possible adverse effects of contaminants on avian reproduction. The concern about potential reproductive effects was partially in response to a study which documented high PCBs in several bird species collected on the Sheboygan River in 1979 (Heinz et al. 1984). Our objectives were to document both historic and current exposure to total PCBs in tree swallows which nest along the Sheboygan River, quantify changes between the decades of the 1990s and 2010s, and finally to quantify differences among reaches within the river system. Tree swallows (Tachycineta bicolor) are being widely used as a model species to understand exposure to and effects of contaminants on bird populations (see review in
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Custer CM 2011). They offer two main advantages over other aquatic species, such as great blue herons (Ardea herodias), belted kingfishers (Ceryle alcyon), and herring gulls (Larus argentatus) that are also used for these types of studies: (1) their nests are more accessible than nests of these other species which increases the ability to acquireadequate sample sizes and (2) their feeding ecology simplifies data interpretation. Nest boxes (usually 10–20 per site) can be placed along specific reaches or areas of interest rather than having to rely on chance to have enough pairs nesting for adequate sample size. Because swallows feed on the aerial stage of benthic aquatic invertebrates (Blancher and McNicol 1991, Mengelkoch et al. 2004) their tissues reflect sediment contamination in a relatively straight forward manner, especially for organic contaminants (Jayaraman et al. 2009). Because they generally feed within 1 ± km of their nest box (Quinney and Ankney 1985), contaminant exposure reflects the local area and not more distant aquatic habitats. A third advantage is that there are published data available for comparative purposes for multiple endpoints, including reproductive and physiological effects, and exposure to various contaminant classes (see review in Custer CM 2011).
Methods and materials Field work Tree swallow nest boxes (15–20 per site) were deployed at five locations 1995–1997 (hereafter referred to as 1990s) and two locations in 2010–2012 (hereafter referred to as 2010s) along the Sheboygan River (Fig. 1). Because the feeding radius overlapped for the two sites in both the Middle Reach and Above the contaminant source in the 1990s, they each are considered as one location. The sites include:one site upstream of the putative PCB contaminant source (1990s only) and at two locations downstream in the1990s and again in 2010s. Nest boxes were placed approximately 20 m apart paralleling the river. In the 1990s, a double box configuration, to reduce competition for nest boxes with other cavity-nesting species, was used with each double box placed approximately 20 m apart. Egg and 12-day-old nestling samples were collected from nest boxes and analyzed for PCBs following standard analytical protocols (see sections below). Eggs were collected shortly after the clutch was completed during the last week in May and the first week in June, the contents placed in chemically-clean jars, and frozen at -20 °C until chemically analyzed. The specific eggs collected were taken haphazardly from the completed clutch; there is no evidence that laying order or stage of incubation affects total PCB concentrations in a predictable manner (Custer
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et al. 1997, 2010b). In 1990s, eggs, ‘pippers’ consisting of pipping eggs or just-hatched nestlings within a day of hatching, and 12-day-old nestlings (±1 day of age) were collected, whereas in 2010s, eggs and 12-day-old nestlings were collected. The date nestlings reached 12 days of age was determined by multiple methods. Generally the date the clutch hatched was known, and the nestling age further validated by feather length (CMC unpubl. data). Pippers and nestlings were euthanized by decapitation (AVMA 2013) under an approved Animal Care and Use protocol. The stomach contents were removed, and the carcass remainder frozen until chemically analyzed. For eggs and nestlings, because of relatively small sample mass (\20 g), the entire egg contents or nestling carcass, sans stomach contents, was homogenized and aliquots (nestlings only) further processed as indicated below. Analytical chemistry Samples were analyzed by the Wisconsin State Laboratory of Hygiene (WSLH), Madison, WI USA (1990s samples plus four nestlings from 2012) and by Axys Analytical Services, Ltd., British Columbia, Canada (Axys, 2010s samples). Axys analyzed the egg samples by high resolution (HR) methods, whereas the nestling samples were analyzed by both HR (2010) and low-resolution (LR, 2012) methods for PCB congeners. Wisconsin State Laboratory of Hygiene analyses were HR and LR, depending on the congener. Axys methods For PCB congeners, the tissue was homogenized with anhydrous powdered sodium sulphate and extracted with dichloromethane. The extracts were cleaned with a Biobead SX-3 gel permeation column with 1:1dichloromethane:hexane and eluted with 1:1 dichloromethane:hexane. A Florisil column cleanup was then used followed by LR or HR gas chromatograph [GC]/mass spectrometer [MS]. For HR, the extract was further cleaned in a 4.5 % (0.22 g) carbon AX-21/Celite 545 mixture column with hexane rinses and eluted with cyclohexane:dichloromethane (1:1) followed by 10:1 ethyl acetate:toluene (2 ml) and then analyzed with HR GC/MS. Blanks, duplicates, and spikes were analyzed at a frequency of one per analytical batch (n = *11 samples) or approximately 9 % of samples. Average percent recover was 97.2 ? 0.46 [1 standard error (SE)]. Certified reference material (CRM) was extracted and analyzed with each analytical batch. The CRM selected for this study was EDF-2525 (Cambridge Isotope Laboratories, Contaminated Fish Tissue). This CRM has certified values for 38 PCB congeners. Detection limits, also referred to as reporting limits and are defined as the
Changes in polychlorinated biphenyl (PCB) exposure Fig. 1 Map of Sheboygan River, WI tree swallow study sites in the 1990s and 2010s. The putative source of the polychlorinated biphenyls was located in Sheboygan Falls in the area designated as the Upper reach. The number of nest boxes at each site in the 1990s from upstream to downstream were 8, 11, 15, 10, and 10. There were 20 nest boxes in the Middle reach and 17 nest boxes in the Lower reach in the 2010s
1441
1995-97 sampling sites
Wisconsin
2010-12 sampling sites 0
1 km
Sheboygan
Kohler Sheboygan Falls
Above contaminant source
Upper
Middle
Lower
Sheboygan River reach designations
level above which quantitative results can be obtained with a high degree of confidence, were \0.01 ng/g wet wt. for the HR analyses and \0.10 ng/g for the LR analyses. WSLH methods Samples were homogenized with dry ice, allowed to sublime overnight and then combined with 60 g of sodium sulfate. The sample (10 g) was extracted with 230 ml of dichloromethane using a 20 mm ID chromatographic column. After concentrating to less than 5 ml, the final extract was diluted 1:1 with cyclohexane to 10 ml. A two-stage extract cleanup procedure was used. First, the lipid fraction was removed using an automated gel-permeation chromatography system manufactured by Gilson. Activated florisil cleanup was then performed using a 6 % ethyl ether/94 % hexane elution followed by a 3.5 % deactivated silica-gel cleanup using hexane elution. Sample extracts were concentrated to 5 ml. An aliquot of the extract was injected into a HP-5890 dual column GC equipped with an electron capture detector (ECD). Congener results were determined utilizing an Agilent 60 m DB-5 column. Congeners were confirmed using an Agilent 60 m DB-1 column. Blanks, laboratory control spikes and sample duplicates (when adequate sample amounts allowed) were extracted and analyzed with each batch of approximately ten samples. Average percent recover was 93.6 ± 0.73 (SE). Most congeners were assessed by LR, but HR was used for congeners which express toxicity through the aryl hydrocarbon receptor (Ah-active) (Maack and Sonzogni 1988). Detection limit was 1.0 ng/g wet wt.
Adjustment between laboratories The specific congeners included in the total PCB analysis varied by laboratory and to a lesser degree by whether the chemical analysis was done using HR or LR analysis methods (Table 1). Of the 179 congeners (counting a coeluted group as one congener), there were 72 congeners analyzed in common, i.e. by both labs and both HR and LR. An additional 82 congeners were analyzed only by Axys and three congeners only by WSLH. Eight congeners were not detected by either lab. Total PCBs was the sum of the congeners in the pool of congeners common to both laboratories. A congener was not included in the common pool for analysis if differences in detection limits would bias the results from either decade. For example, a congener would not be included in the common pool if a higher detection limit in one decade resulted in mostly all non-detectable values, even though in the other decade there were detectable values at a lower detection limit. Also, if [50 % of the samples were below the detection limit in one or the other of the decades then that congener was also eliminated from the ‘common’ pool. Both measures were taken to reduce any possible bias in the data analysis. Even though WSLH analyzed fewer PCB congeners they captured an average of between 68 % (n = four paired nestling samples analyzed by both labs, multiplier = 1.48) and 78 % of the total PCBs (concentration of congeners in common divided by concentration of all congeners, n = 17 Axys data points; multiplier = 1.29). Concentrations from WSLH, therefore, should be multiplied by 1.3–1.5 to make the concentrations reported by the
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Table 1 Polychlorinated biphenyl (PCB) congeners analyzed by Axys analytical, either by high (HR) and low resolution (LR) analyses, and by the Wisconsin State Laboratory of Hygiene (WSLH) from the Sheboygan River in the 1990s and in the 2010s Congener group
Axys HR
WSLH LR
10, 20/28, 32, 34, 60, 64, 68, 73, 109, 120, 121, 127, 144, 164, 190, 192
XX
1, 2, 3, 11, 12/13, 17, 21/33, 23/34, 38, 39, 42/59, 43/49, 54, 55, 57, 58, 59/62/75, 67, 72, 78, 79, 81, 94, 96, 103, 104, 107/109/124, 111/115, 112, 114, 122, 129/138/160/163/164, 131/142, 132/168, 133, 134, 139/149/140, 145, 148, 150, 152, 155, 159, 161, 165, 175, 176, 179, 184, 186, 188, 189, 191, 195, 197, 204, 205, 207, 209
XX
XX
4/10, 5/8, 6, 7/9, 15/17, 16/32, 18/30, 19, 22, 24/27, 25, 26/29, 28/31, 37/42, 40/41 seriesa, 44/47/65, 45/51, 46, 47/48, 49/69, 50/53, 52/73, 56/60, 61/70/74/76, 63, 66/80/95, 77, 82, 83/99/108, 84/92, 85 series, 86 series, 88 series, 89 series, 92, 93/95/98/100/102, 105/127, 110/115, 106/118, 123, 126, 128/166, 130, 135/144/151/154, 136, 137/176, 141, 146, 147/149, 153/132, 156/157, 158, 167, 170/190, 171/173/202, 172/192/197, 174/181, 177, 178, 180, 182/187, 183/185, 194, 196/203, 198/199, 201, 202/171, 206, 208/195
XX
XX
8, 27 33, 163/138, 99
XX
80, 106, 142
ND
XX
XX XX
14, 35, 36, 161
ND
ND
169
ND
ND
ND
Congeners separated by a slash were reported as a coelution by at least one lab a congener combinations in series are: 41 series = 40/41/71 (HR), 40 ? 41/64/68/71 (LR), 40/10 ? 41/71/64 (WSLH); 85 series = 85/ 116/117 (HR), 85/120 (LR), 85 (WSLH); 86 series = 86/87/97/108/ 119/125 (HR), 86/97 ? 87/115/116 ?119 ? 125 (LR), 87 ? 97 (WSLH); 88 series = 88/91 (HR), 88/121 ? 91 (LR), 91 (WSLH); 89 series = 89 ? 90/101/113 (HR), 89/90/101 ? 113 (LR), 101 ? 89 (WSLH)
WSLH comparable to estimated total PCBs when all possible congeners were included in the chemical analysis. All PCB concentration data presented in text, tables, and figures are the sum of the 72 congeners in common and have not been corrected for laboratory unless specifically indicated, mainly in the discussion when comparing to literature values. The total PCBs from HR and LR from Axys are equivalent (Pillay per. comm). Statistical analyses Differences in PCB exposure were compared between decades and among sites using analysis of variance
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(ANOVA) on log transformed data. The sites are identified in text and tables with the reach designation. Decadal and site statistical comparisons were made within each matrix type (i.e. egg, nestling, etc.) individually. Two-way ANOVAs (decade, site, and decade * site interaction) were run on the egg and nestling data from the Middle and Lower reaches. One-way ANOVAs compared among sites for the 1990s so that the Above reach could be included in the assessments. Bonferroni multiple comparison method was used to determine differences among means when ANOVAs were significant. Data were log transformed to meet the homogeneity of variance assumptions of ANOVA methods. Geometric means (antilog of log means) and 95 % confidence intervals (CI) are provided in text and tables. Accumulation rate (lg of PCBs accumulated per day, calculated as the PCB mass in nestlings minus the mass in eggs divided by age of nestling) was calculated and compared among sites with ANOVA similar to the concentration assessments above. The mass of a contaminant was calculated by multiplying the concentration in the sample by the sample mass. Accumulation rate factors out any exposure in eggs that may have occurred at wintering or migration areas, although this is usually negligible. Accumulation rate calculations also improve clarity in understanding exposure in nestlings that can be obscured by growth dilution in rapidly growing nestlings. When possible, eggs and 12-day old nestlings from the same nest were used to calculate accumulation rates. However, because only two sibling pairs were available for the site in the Middle reach and none from the site in the Lower reach in the 1990s, mean concentration in the pooled egg samples from the nests from which 12-day old nestlings were collected were used to calculate the PCB mass in eggs. The reach designations were mainly used to provide discrete, equidistant sampling units downstream of the putative PCB source in Sheboygan Falls, however, the reaches in this study correspond to segments used in previous ecological risk assessments of the Sheboygan River (Burzynski 2000). The Middle reach site was approximately 3 km downstream from the putative PCB source, in a straight linear line, and the Lower reach site was approximately 7 km downstream of the source.
Results Geometric mean PCB concentrations in tree swallow eggs collected from the site in the Middle reach of the Sheboygan River significantly decreased by *60 % between the decades of the 1990s and 2010s (8.69 down to 3.27 lg/ g), but did not decline statistically for nestlings (5.50 vs. 4.71 lg/g Table 2). One nestling in the 2010s contained
Changes in polychlorinated biphenyl (PCB) exposure
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Table 2 Geometric mean concentration and 95 % confidence intervals (CIs) for total polychlorinated biphenyls (PCBs) based on the sum of congeners that were common to both analytical chemistry Site locations and sampling matrix
n
laboratories for tree swallows nesting along the Sheboygan River, WI in the 1990s compared to the 2010s
Geometric mean concentrations (lg/g wet wt.), 95 % CI, and minimum and maximum values {in brackets} by decade 1990s
2010s
Above PCB source Egg
10
1.24
0.49–3.18
{0.32–19.8}
Pipper
8
0.44
0.24–0.82
{0.22–1.60}
Nestling
13
0.22
0.14–0.35
{0.07–1.01}
Egg
11, 4a
8.69 Ab
6.15–12.3
{3.40–18.3}
Pipper
15
4.51
3.20–6.34
{1.04–12.9}
Nestling
16, 4
5.50 ac
3.90–7.77
Middle 3.27 B
1.05–10.22
{2.00–9.48}
{1.34–12.9}
4.71 a
2.10–10.55
{3.67–10.1}
Lower Egg
6, 5
3.33 B
2.07–5.38
{1.99–5.42}
0.48 C
0.26–0.89
{0.32–0.95}
Pipper Nestling
4 6, 3
2.41 4.24 a
1.15–5.03 2.16–8.33
{1.57–3.67} {1.31–7.46}
0.64 b
0.23–1.75
{0.64–1.44}
Among site differences—1990s only a
P \ 0.001 (eggs); P \ 0.001 (nestling); P \ 0.001 (pipper)
First number is sample size for the 1990s and the second number is the sample size for the 2010s
b
Means for eggs sharing same capital letter are not different between decades and among sites in the named reaches (Middle and Lower) (F3,22 = 34.11, P \ 0.001 [decades P \ 0.001, site P \ 0.001, decades * site interaction P = 0.043]). See text for differences with above source in 1990s c
Means for nestlings sharing same lower case letter are not different between decades and among sites in the named reaches (Middle and Lower) [F3,25 = 10.47, P \ 0.001 (decade = 0.002, site = 0.006, decade * site interaction = 0.004)]. See text for differences with above source in 1990s
10.1 lg/g PCBs, compared to \3.99 lg/g for the other three nestlings which accounted for this lack of statistical difference between decades. For eggs, pippers and nestlings in the 1990s, the site Above the PCB source had significantly less contamination than at least one of the downstream locations. For nestlings, the two downstream locations did not differ from one another and both were significantly higher than the site in the Above reach. For pippers, the Above site had significantly less PCBs than either of the sites in the Middle and Lower reaches. For eggs, however, the site in the reach Above the putative PCB source had significantly less PCB contamination than the site in the Middle reach, but the site in the reach Above (1.24 lg/g) and the site in the Lower reach (3.33 lg/g) were not different from one another. In the 2010s, the site in the Lower reach had significantly less PCB contamination than the site in the Middle reach for both eggs and nestlings (Table 2). In both decades, the accumulation rate (mass in the nestling minus mass in egg divided by the age of the nestling) of total PCBs, was *6 times higher at the site in the Middle reach compared to the site in the Lower reach [13.6 vs. 8.6 lg/day (1990s) and 8.7 vs. 1.4 lg/day (2010s), (decade P = 0.014, site P = 0.014, decade * site = 0.608, Fig. 2]. The accumulation rate at the
site Above the putative PCB source was 0.08 lg/day and statistically differed from both the sites in the Middle and Lower reaches in the 1990s. The site in the Middle reach, where data were available for both decades, accumulated PCBs at approximately half the rate in the 2010s (8.7 lg/ day) compared to the earlier decade (13.6 lg/day, 1990s), but was not statistically different (Bonferroni mean separation) because of small samples sizes and high within site variability. The difference between the two decades is actually more than reflected by the mean accumulation rate, however, because one of four rates in 2010s was similar to the 1990s rates (Fig. 2). The mean accumulation rate for the 2010s without that one nest was 6.2 lg/day, approximately half the rate in the 1990s.
Discussion The current exposure of tree swallows to PCBs on the Sheboygan River is about half of what it was in the mid1990s, based on concentrations in eggs [geometric mean = 8.6 lg/g wet wt. (1990s) compared to 3.3 (2010s)]. Interestingly, the difference between the two decades in nestling exposure was less (5.5 vs. 4.7) and not statistically different. This smaller difference for nestlings
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Accumulation rate – 1990s
µg PCBs
Middle = 13.6 µg/day
Lower = 8.6 µg/day
Above = 0.08 µg/day; n=3 lines
µg PCBs
Accumulation rate – 2010s
Middle = 8.7 µg/day
Lower = 1.4 µg/day
Egg
Days of age
Fig. 2 Accumulation rate (lg/day) of total polychlorinated biphenyls (PCBs) in the 1990s (upper panel) and 2010s (lower panel) along the Sheboygan River, WI
may be because there still seems to be some ‘hot spots’ on the Sheboygan River near the sites in the Middle reach and that is producing significant exposure to some (*25 %), but not all tree swallows. This high variability in exposure in the 2010s is consistent with high variability at the sites within the Middle reach in the 1990s, as well as, in other tree swallow studies (Custer et al. 2003). Additional sampling is planned to further investigate this level of variability and what proportion of the nesting swallows are still feeding in ‘hot spots’, or on more contaminated food items. The *50 % decline in exposure to PCB on the Sheboygan River was similar to the magnitude of the decline from the mid-1990s to the current decade in tree swallows sampled at the mouth of the Fox River in lower Green Bay, WI (Custer et al. 2014). Calculation of accumulation rates can provide a clearer assessment of exposure during the nestling period. Interpretation of concentration values are often confounded by growth dilution during that period. Body mass in nestling tree swallows increases by a factor of thirteen (1.5 g at hatching to 20 g at 12 days of age). Concentrations in nestling can go down in spite of significant exposure that is masked by the large increase in body mass. By only looking
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at concentration, the appearance of little to no exposure can be erroneously concluded even though considerable exposure is actually occurring. The accumulation rate in nestlings further illustrates the decadal decline in exposure to PCBs along the Sheboygan River. There was less, but not significantly less, accumulation of PCBs at the site in the Middle reach in the 2010s (8.7 lg/day) compared to the 1990s (13.6 lg/day). This lack of significance was because there was one nest box where the accumulation rate in the 2010s was similar to the 1990s (Fig. 2). The accumulation rate at the site in the Lower reach in the 2010s was only 1.4 lg/day, but still more than the 1990s rate at the site Above the PCB source (0.08 lg/day). Mean accumulation rates at other PCB-contaminated sites were between 33.7 and 75.9 lg/day along the Housatonic River, MA (Custer et al. 2003), 1.3–6.7 in 1994–95 along the Fox River and lower Green Bay, WI (Custer et al. 1998) and 27 lg/day in New Bedford Harbor, MA (Jayaraman et al. 2009). Background accumulation rates for PCBs for comparative purposes were between and 0.37–0.68 lg/day along the Wisconsin River, WI (Custer et al. 2002), 0.18–0.21 lg/day in Pool 15 of the upper Mississippi River in Iowa (Custer et al. 2000), 0.06–0.42 lg/day at the two reference locations for the Fox River/Green Bay study (Custer et al. 1998), and a -0.3–0.7 lg/day at the reference location for the Housatonic River study (Custer et al. 2003). Comparing to literature values, the average egg and nestling PCB exposure at the site in the Middle reach of the Sheboygan River in the 1990s [means = 13.1 lg/g wet wt. (eggs) and 8.3 lg/g (nestlings)]and in the 2010s [mean = 4.9 lg/g (eggs) and 7.1 lg/g (nestlings)], using the 1.5 multiplier to correct for unmeasured PCB congeners, here and for the following Sheboygan River data, were elevated but considerably lower than at the most known PCB-contaminated site (Housatonic River). Mean egg and nestling PCB concentrations from tree swallows collected on the Housatonic River, MA in the late 1990s ranged between 31 and 101 lg/g (eggs) and 21–45 lg/g (nestlings, Custer et al. 2003). Mean eggs concentrations from the Sheboygan River were similar, however, to other sites sampled during that same time frame such as on the Akwesasne Reserve, NY in the early 1990s (11.2 lg/g wet wt., Bishop et al. 1999) and the Hudson River both in the mid-1990s (means between 9.3 and 29.5 lg/g wet wt., Secord et al. 1999) and in the early 2000s (6.8 lg/g Custer et al. 2010a). The Sheboygan River had higher exposure than on the lower Fox River and Green Bay in the mid1990s [2–3 lg/g (eggs) and 1–4 lg/g (nestlings) Custer et al. 1998]. Background PCB concentrations typically are 1 lg/g or less in eggs and nestlings (Custer et al. 1998, Bishop et al. 1999) in the Great Lakes, but reference areas can be elevated above 1 lg/g such as was the case at the Housatonic River reference site (Custer et al. 2003).
Changes in polychlorinated biphenyl (PCB) exposure
PCB concentrations in a few individual eggs sampled from the site in the Middle reach of the Sheboygan River in the 1990s (max. value exceeded 25 lg/g wet wt., again using the 1.5 multiplier) exceeded the threshold (*20 lg/g wet wt. in eggs) associated with reduced hatching success in swallows (Custer et al. 2003), but by the 2010s (max. value = 14 lg/g), none exceeded that threshold value, although a few egg samples were still substantially elevated. The threshold value for when reproductive success begins to become impaired for tree swallows is similar to that found for other avian species (raptors = 35 lg/g wet wt.; gulls and terns = 23–142 lg/g wet wt., from review in Harris and Elliott 2011). In contrast, the maximum egg concentration (1.4 lg/g wet wt.) in the 2010s at the site in the Lower reach of the Sheboygan River was *14 times lower than the threshold for reduced hatching success. Comparison to other bird species The corrected concentrations in nestling tree swallow carcasses at the site in the Middle portions of the Sheboygan River in the 1990s (geometric means = 6.4 and 8.3, maximum value 19.3) were 20–30 times lower than concentrations in belted kingfisher carcasses (Heinz et al. 1984) in 1979 from that same stretch of the river. This can be partly explained because swallows feed at a lower trophic level (aquatic invertebrates) than kingfishers (small fish) and hence have lower exposure which was also found on the Hudson River, NY (Custer et al. 2010a). An additional factor was because the kingfishers that were collected by Heinz et al. (1984) were either adult or immature birds and therefore had been feeding in the contaminated habitat for a much longer period of time, months rather than *12 days, than were the nestling tree swallows. Similarly, the carcass residues in spotted sandpiper (Actitis macularia) on the Sheboygan River in the 1990s were also much higher than in tree swallows from the same reach in the 1990s, again most likely because of the additional length of time spent feeding in the contaminated stretches of the river prior to collection, and with a lesser contribution due to food habit differences. Summary Exposure to PCBs on the Sheboygan River was higher at the two sites downstream of the putative PCB source than it was upstream of the source and the exposure tended to decline as the distance downstream of the source increased. Because there was only one site sampled in both the Middle and Lower reaches in each decade, it is possible that this upstream/downstream gradient is spurious. Although exposure to PCBs along the Sheboygan River downstream of Sheboygan Falls has declined by *60 %
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since the mid-1990s, there still seems to be residual pockets of contamination that are exposing some individuals (25 %) to PCB contamination, similar to exposure found in the 1990s. The elevated exposure in eggs is further validated by the elevated accumulation rate in nestlings that effectively factors out any exposure that might have occurred at wintering or migration areas. Acknowledgments We thank River Wildlife, City of Sheboygan, Mayline Co., Sarah and Pete Gahagan,and Richard Seichter for access to their property; Diana Goldberg, Andrew Haertel, Kristina Mott, Kelsey Prestby, Darin Ripp, Josh TeSlaa, and Jocelyn Tschaikovsky for field assistance; Paul M. Dummer for field and data management assistance; David Rogers for assistance with analytical methodology; and L.K. Lohman and two anonymous reviewers for comments on earlier drafts of this manuscript. Use of trade, product, or firm names does not imply endorsement by the U.S. Government. Conflict of interest The authors declare that we have no conflict of interest. Data were collected under current laws of the United States of America. The work in 2010–2012 was funded by the Great Lakes Restoration Initiative and was approved by the Animal Care and Use Committee at the Upper Midwest Environmental Sciences Center.
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