RADIOSILVER
(AG-110M) CONCENTRATIONS
IN C H E S A P E A K E MAINTAINED
BAY OYSTERS
NEAR A NUCLEAR
A STATISTICAL
POWER PLANT:
ANALYSIS
K. A. ROSE *, J. K. S U M M E R S
Versar, Inc., ESM Operations, 9200 Rumsey Road, Columbia, MD 21045, U.S.A.
R. I. M c l e a n and S. L. D O M O T O R
Maryland Power Plant Research Program, Department o f Natural Resources, Tawes State Office Building, Annapolis, MD 21041, U.S.A.
(Received November 1987) Abstract. An ongoing biomonitoring program using oysters (Crassostrea virginica) was implemented in 1978 to monitor radionuclide releases from the Calvert Cliffs Nuclear Power Plant located on Chesapeake Bay. The program involves quarterly removal and replenishment of oysters located in a tray about 0.2 km from the effluent discharge. Radiosilver (Ag-ll0m) concentrations in tray oysters (pCi/kg ww) were analyzed using ANCOVA-like models with plant releases of Ag-110m in the present and immediately preceding quarters and season of exposure as explanatory variables. Hypothesis testing based on the estimated models and comparison among model predictions under hypothetical release scenarios showed that season of exposure was important in influencing Ag-110m concentrations, with exposure during the Fall and Summer seasons resulting in significantly higher Ag-110m concentrations in tray oysters than exposure during the Winter and Spring seasons. From a management perspective of minimizing Ag-110m concentrations in oysters located near the plant, Winter and Spring are the preferred seasons for plant releases.
1. Introduction The extremely low concentrations of many contaminants often observed in natural waters makes direct measurement difficult. With biomonitoring approaches, biota, because of their bioaccumulation properties, serve as a medium that allows for monitoring of the low concentrations of contaminants found in natural waters. Biomonitoring has been used to assess contaminant dose to humans (e.g., Salo and Leet, 1969) and as a general indicator of water quality (e.g., Goldberg, 1986; De Kock, 1986; Huggett et al., 1973). As part of a comprehensive radiological impact assessment program at the Calvert Cliffs Nuclear Power Plant, located on the Chesapeake Bay (Figure 1), an ongoing biomonitoring program was implemented in 1978 utilizing oysters (Crassostrea virginica) maintained in the vicinity of the plant effluent for known quarterly exposure periods. Oysters were selected because of the advantages associated with * Present address: Environmental Sciences Division, P.O. Box 2008, MS-036, Oak Ridge National Laboratory, Oak Ridge, TN 37831, (615) 574-4815. Address all correspondance to: K. A. Rose at present address.
Environmental Monitoring and Assessment 10 (1988) 205-218. 9 1988 by Kluwer Academic Publishers.
206
K.A.ROSE
ET A L ,
Peflfls ivanu MIryland
"~Ot ~"~ I~ /~-GCNPP
o,
km
,,2
~ d: J
%
j
0r 20 40
60
80
Scale in km
Fig. 1.
Location of the Calvert Cliffs Nuclear Power Plant (CCNPP). Insert shows location of (A) unaffected area from which initial tray oysters are obtained and (B) effluent discharge.
the use of bivalves as biomonitoring organisms (see Goldberg, 1986; Phillips, 1977), because oysters are commercially and recreationally harvested in the vicinity of Calvert Cliffs, and because radioactivity dose to man via consumption of oysters is a concern (McLean, 1984). Available data indicate that the annual total body
STATISTICAL ANALYSIS OF RADIOSILVER CONCENTRATIONS IN OYSTERS
207
radiation dose to a maximally exposed human due to consumption of oysters from the Calvert Cliffs area is < 10~ of the allowed limit (McLean, 1984). Season of exposure potentially plays an important role in the uptake and elimination (excretion) of contaminants in oysters. Seasonal variation in water temperature affects metabolic activity (Galstoff, 1964) and biological processes of oysters (growth, reproduction) exhibit seasonal patterns that can greatly affect observed contaminant concentrations (Frazier, 1975; 1976). In this paper, we present the results of a statistical analysis of the data from the Calverts Cliffs biomonitoring program. The analyses were conducted to examine the relationship between radiosilver (Ag-ll0m) concentrations measured in oysters maintained near the power plant and power plant releases of Ag-110m. The objectives of this analysis were to (1) develop predictive models that could be used if the biomonitoring program were interupted, and (2) elucidate any relationships between the magnitude and seasonal timing of plant releases and resulting Ag-110m concentrations in oysters. While all results in this paper are based on releases of radiosilver from a nuclear power plant, the general statistical approach used is also applicable to other biomonitoring programs that involve known and measurable contaminant discharges.
2. Data Collection
2.1. SITE DESCRIPTION The Calvert Cliffs Nuclear Power Plant is located on the western shore of Chesapeake Bay just north of the mouth of the Patuxent River (Figure 1). After suitable holdup periods to allow for physical decay of short-lived radionuclides, fission and activation products from the operation of the nuclear plant are combined with cooling water effluent and discharged 260 m offshore at a depth of 2 m in water 6-7 m deep. Typically, radionuclides are released almost daily for a period of 3-4 hr. Data on cumulative quarterly releases are compiled and regularly reported. 2.2.
TRAY
OYSTERS
All oysters are initially obtained from an unaffected area 10 km north of the plant site that has temperature and salinity conditions similar to those at the Calvert Cliffs site. Approximately 50 mature oysters (-- 8 cm shell length) are placed into each of four compartments of 91 x 41 x 13 cm stainless steel vinyl mesh covered trays. Trays are placed approximately 0.3 km from the effluent discharge location on a platform approximately 1 m from the bottom in water 6-7 m deep. Oysters are removed from compartments of the trays and radionuclide concentrations and oysters wet weight are measured quarterly. The schedule of oyster removal and replacement from the four compartments of the trays is depicted in Figure 2 for a typical 12-month period. This schedule results in 8-9 observations per year (4 after one quarter of exposure, 2 after two quarters
208
K.A.ROSIE ET AL.
< Start
>|-
/
Year I End of "[ Quarter I
C~ D~
.~-i
(AG-110M) CONCENTRATIONS
IN C H E S A P E A K E MAINTAINED
BAY OYSTERS
NEAR A NUCLEAR
A STATISTICAL
POWER PLANT:
ANALYSIS
K. A. ROSE *, J. K. S U M M E R S
Versar, Inc., ESM Operations, 9200 Rumsey Road, Columbia, MD 21045, U.S.A.
R. I. M c l e a n and S. L. D O M O T O R
Maryland Power Plant Research Program, Department o f Natural Resources, Tawes State Office Building, Annapolis, MD 21041, U.S.A.
(Received November 1987) Abstract. An ongoing biomonitoring program using oysters (Crassostrea virginica) was implemented in 1978 to monitor radionuclide releases from the Calvert Cliffs Nuclear Power Plant located on Chesapeake Bay. The program involves quarterly removal and replenishment of oysters located in a tray about 0.2 km from the effluent discharge. Radiosilver (Ag-ll0m) concentrations in tray oysters (pCi/kg ww) were analyzed using ANCOVA-like models with plant releases of Ag-110m in the present and immediately preceding quarters and season of exposure as explanatory variables. Hypothesis testing based on the estimated models and comparison among model predictions under hypothetical release scenarios showed that season of exposure was important in influencing Ag-110m concentrations, with exposure during the Fall and Summer seasons resulting in significantly higher Ag-110m concentrations in tray oysters than exposure during the Winter and Spring seasons. From a management perspective of minimizing Ag-110m concentrations in oysters located near the plant, Winter and Spring are the preferred seasons for plant releases.
1. Introduction The extremely low concentrations of many contaminants often observed in natural waters makes direct measurement difficult. With biomonitoring approaches, biota, because of their bioaccumulation properties, serve as a medium that allows for monitoring of the low concentrations of contaminants found in natural waters. Biomonitoring has been used to assess contaminant dose to humans (e.g., Salo and Leet, 1969) and as a general indicator of water quality (e.g., Goldberg, 1986; De Kock, 1986; Huggett et al., 1973). As part of a comprehensive radiological impact assessment program at the Calvert Cliffs Nuclear Power Plant, located on the Chesapeake Bay (Figure 1), an ongoing biomonitoring program was implemented in 1978 utilizing oysters (Crassostrea virginica) maintained in the vicinity of the plant effluent for known quarterly exposure periods. Oysters were selected because of the advantages associated with * Present address: Environmental Sciences Division, P.O. Box 2008, MS-036, Oak Ridge National Laboratory, Oak Ridge, TN 37831, (615) 574-4815. Address all correspondance to: K. A. Rose at present address.
Environmental Monitoring and Assessment 10 (1988) 205-218. 9 1988 by Kluwer Academic Publishers.
206
K.A.ROSE
ET A L ,
Peflfls ivanu MIryland
"~Ot ~"~ I~ /~-GCNPP
o,
km
,,2
~ d: J
%
j
0r 20 40
60
80
Scale in km
Fig. 1.
Location of the Calvert Cliffs Nuclear Power Plant (CCNPP). Insert shows location of (A) unaffected area from which initial tray oysters are obtained and (B) effluent discharge.
the use of bivalves as biomonitoring organisms (see Goldberg, 1986; Phillips, 1977), because oysters are commercially and recreationally harvested in the vicinity of Calvert Cliffs, and because radioactivity dose to man via consumption of oysters is a concern (McLean, 1984). Available data indicate that the annual total body
STATISTICAL ANALYSIS OF RADIOSILVER CONCENTRATIONS IN OYSTERS
207
radiation dose to a maximally exposed human due to consumption of oysters from the Calvert Cliffs area is < 10~ of the allowed limit (McLean, 1984). Season of exposure potentially plays an important role in the uptake and elimination (excretion) of contaminants in oysters. Seasonal variation in water temperature affects metabolic activity (Galstoff, 1964) and biological processes of oysters (growth, reproduction) exhibit seasonal patterns that can greatly affect observed contaminant concentrations (Frazier, 1975; 1976). In this paper, we present the results of a statistical analysis of the data from the Calverts Cliffs biomonitoring program. The analyses were conducted to examine the relationship between radiosilver (Ag-ll0m) concentrations measured in oysters maintained near the power plant and power plant releases of Ag-110m. The objectives of this analysis were to (1) develop predictive models that could be used if the biomonitoring program were interupted, and (2) elucidate any relationships between the magnitude and seasonal timing of plant releases and resulting Ag-110m concentrations in oysters. While all results in this paper are based on releases of radiosilver from a nuclear power plant, the general statistical approach used is also applicable to other biomonitoring programs that involve known and measurable contaminant discharges.
2. Data Collection
2.1. SITE DESCRIPTION The Calvert Cliffs Nuclear Power Plant is located on the western shore of Chesapeake Bay just north of the mouth of the Patuxent River (Figure 1). After suitable holdup periods to allow for physical decay of short-lived radionuclides, fission and activation products from the operation of the nuclear plant are combined with cooling water effluent and discharged 260 m offshore at a depth of 2 m in water 6-7 m deep. Typically, radionuclides are released almost daily for a period of 3-4 hr. Data on cumulative quarterly releases are compiled and regularly reported. 2.2.
TRAY
OYSTERS
All oysters are initially obtained from an unaffected area 10 km north of the plant site that has temperature and salinity conditions similar to those at the Calvert Cliffs site. Approximately 50 mature oysters (-- 8 cm shell length) are placed into each of four compartments of 91 x 41 x 13 cm stainless steel vinyl mesh covered trays. Trays are placed approximately 0.3 km from the effluent discharge location on a platform approximately 1 m from the bottom in water 6-7 m deep. Oysters are removed from compartments of the trays and radionuclide concentrations and oysters wet weight are measured quarterly. The schedule of oyster removal and replacement from the four compartments of the trays is depicted in Figure 2 for a typical 12-month period. This schedule results in 8-9 observations per year (4 after one quarter of exposure, 2 after two quarters
208
K.A.ROSIE ET AL.
< Start
>|-
/
Year I End of "[ Quarter I
C~ D~
.~-i
