Journal of Toxicology and Environmental Health
ISSN: 0098-4108 (Print) (Online) Journal homepage: http://www.tandfonline.com/loi/uteh19
Control of mercury pollution O. R. Noyes , M. K. Hamdy & L. A. Muse To cite this article: O. R. Noyes , M. K. Hamdy & L. A. Muse (1976) Control of mercury pollution, Journal of Toxicology and Environmental Health, 1:3, 409-420, DOI: 10.1080/15287397609529340 To link to this article: http://dx.doi.org/10.1080/15287397609529340
Published online: 20 Oct 2009.
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CONTROL OF MERCURY POLLUTION O. R. Noyes, M. K. Hamdy, L. A. Muse
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Department of Food Science, University of Georgia, Athens, Georgia
When a 2 0 3 Hg(NO 3 ) 2 solution was kept at 25°C in glass or polypropylene containers, 50 and 80% of original radioactivity was adsorbed to the containers' walls after I and 4 days, respectively. However, no loss in radioactivity was observed if the solution was supplemented with HgCI2 as carrier (100 μg Hg2+ /ml) and stored in either container for 13 days. When2 0 3 H g 2 + was dissolved in glucose basal salt broth with added carrier, levels of 2 0 3 H g 2 + in solution (kept in glass) decreased to 80 and 70% of original after 1 and 5 days and decreased even more if stored in polypropylene (60 and 40% of original 203 2+ activity after 1 and 4 days, respectively). In the absence of carrier, decreases of Hg activities in media stored in either container were more pronounced due to chemisorption (but) not diffusion. The following factors affecting the removal of mercurials from aqueous solution stored in glass were examined: type and concentration of adsorbent (fiber glass and rubber powder); pH; pretreatment of the rubber; and the form of mercury used. Rubber was equally effective in the adsorption of organic and inorganic mercury. The pH of the aqueous 2 0 3 Hg 2 + solution was not a critical factor in the rate of adsorption of mercury by the rubber. In addition, the effect of soaking the rubber in water for 18 hr did not show any statistical difference when compared with nontreated rubber. It can be concluded that rubber is a very effective adsorbent of mercury and, thus, can be used as a simple method for control of mercury pollution.
INTRODUCTION While conducting mercury analysis using flameless atomic absorption spectrophotometry (FAAS), it was observed that the concentration of Hg 2 + in standard HgCI2 solutions did not remain constant, but in fact decreased rapidly during storage at room temperature. Furthermore, during studies involving microbial production of methyl mercury (MM) using 2 0 3 H g 2 + , the radioactivity decreased during incubation beyond the half-life decay or the volatilization rate of the 2 0 3 Hg 2 + -containing compounds from the media. Ballard and Thornton (1941) stated that mercuric ions are adsorbed onto glass from dilute solutions, but no data were presented to support the authors' statement. Other investigators (Munns and Holland, 1971; Thorpe, 1971; Townshend and Vaughan, 1970) reported that standard solutions of mercury should be prepared just before use and special care should be exercised in cleaning glassware prior to reuse. Hinkle and Learned (1969) This research was supported by grant no. B-069-GA from the Office of Water Resources Research, Department of the Interior, Washington, D.C. We thank Dr. M. M. Duncan, Head, Physics and Astronomy Department, University of Georgia, Athens, for his helpful suggestions and review of this manuscript. O. R. Noyes's present address is Food Industries Department, California Polytechnic State University, San Luis Obispo, California 93407. Requests for reprints should be sent to this address. 409 Journal of Toxicology and Environmental Health, 1:409-420, 1976 Copyright © 1976 by Hemisphere Publishing Corporation
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reported that loss of mercury during storage caused serious errors in mercury analysis and that colloidal particles present in water contained from 5 to 25 times more mercury than the aqueous solution. Coyne and Collins (1972) showed that the loss of mercury from solution was related to the initial mercury concentration and to the presence or absence of a preservative such as nitric acid, which tended to keep the mercury in solution. These authors indicated that the effectiveness of the preservative can be achieved only if the acid was present before the addition of mercury to the container. In the present investigation, some factors affecting the chemisorption of mercury were examined and the possible movement of 2 0 3 H g 2 + through the container walls was also determined. If mercury is indeed adsorbed on solid surfaces, this principle can be utilized for the effective removal of mercury compounds from aquatic environments. This study would then have a practical value in the treatment of industrial mercury-polluted waters. METHODS Counting Systems Unless otherwise stated, all experiments were performed using mercury isotope as methyl mercury chloride ([ 2O3 Hg]CH 3 HgCI) or mercury nitrate [ 2 0 3 Hg(NO 3 ) 2 ] obtained from New England Nuclear Corp., Boston, Mass. The 2 0 3 Hg(NO 3 ) 2 was dissolved in 0.5 N HNO 3 and had a specific activity of 11.3 mCi/mg, whereas the [203 Hg] CH 3 HgCI was dissolved in 0.5 M Na2 CO 3 and had a specific activity of 1.19 mCi/mg. Aliquots of either solution were used for the preparation of saline working standard solutions. The low energy beta emitted from 2 0 3 H g 2 + in samples was determined using a Beckman model LS-100 C liquid scintillation spectrometer. A known volume of a sample was placed in a plastic scintillation vial containing 10 ml of the Beckman liquid scintillation fluor (fluoralloy dry mix in toluene containing Biosolv BBS solubilizer). Most samples were counted to ± 1 % error and those containing less than 500 were counted to not less than 5% error. The gamma energy of 2 0 3 H g 2 + in samples was counted using a Baird Atomic well-type Nal (TI) crystal shielded with 3-in. lead and equipped with a single-channel pulse-height analyzer using the integral mode. All counting data were corrected for background and half-life. Chemisorption Time-loss studies using 2 0 3 Hg(NO 3 ) 2 with and without added mercury carrier in the form of HgCI2 were conducted at 25°C in glass or in polypropylene scintillation vials. Loss of 2 0 3 H g 2 + counts from 10 ml of deionized distilled water (DDW) or from 10 ml of glucose basal salt broth (GBSB) media containing HgCI2 as a H g 2 + carrier (100 jug H g 2 + /ml), or in the absence of H g 2 + carrier, were determined. The DDW or GBSB were supplemented with standard solution of 2 0 3 Hg(NO 3 ) 2 to yield a count rate of 6 X 10 s cpm/ml. The GBSB consisted of 6.8 g KH 2 PO 4 , 0.09 g
CONTROL OF MERCURY
411
CaCI2 •4H 2 O,0.06gMgSO 4 ,0.007gZnSO 4 ,0.025gFeSO 4 • 7 H 2 O, 0.001 g (NH 4 ) 2 SO 4 , 0.001 g N a 2 M o O 4 • 7 H 2 O,and 10 g glucose/liter. During storage, the entire 10-ml sample was shaken well in the vial and the chemisorption evaluated from the differences of radioactivities in 0.1-ml samples obtained after specific elapsed time intervals. g MnSO 4 ,0.25gNH 4 CI,0.25
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Diffusion Possible movement of H g 2 + by diffusion through the container's wall was also examined at 25°C using sterile-sealed flint glass ampules containing either 1 ml sterile DDW or GBSB supplemented with 2O3 Hg(NO3 )2 to yield a count rate of 5 X 105 cpm/ml. Four groups (A, B,C, D) of nine glass ampules in each were used. The first group of ampules (A) contained DDW, and three of these ampules had no additional H g 2 + , three contained 50 jug H g 2 + ; and three had 100 ng Hg2 + / m l , both in the form of HgCI 2 . All ampules were fire-sealed, and the gamma activity in each was determined with a solid scintillation counting system. The second group of ampules (B) was prepared in a similar manner as group A, except that the beta activity in each ampule was detected after placing the entire ampule in 15 ml of scintillation fluor in the liquid scintillation system. The third and fourth groups (C) and (D) were prepared in a similar manner to groups A and B, respectively, except that GBSB media replaced the DDW. At intervals during 90 days of storage, three ampules from every group (one at each H g 2 + level used) were washed with dilute HCI, wiped with tissue, and then assayed for their radioactivity. Assuming a loss of 2O3 H g 2 + due to diffusion through the walls of the ampule, the net radioactivity (after half-life correction) counted by solid scintillation would decrease, whereas a loss of 2 0 3 H g 2 + from an ampule immersed in liquid scintillation cocktail would increase the radioactivity observed. The ampule counted by liquid scintillation was removed from the scintillation fluor and subsequently counted by solid scintillation after wiping the surface with tissue. The scintillation fluor mixture alone was also counted by liquid scintillation to detect any 2 0 3 H g 2 + that had diffused through the glass ampule. Again, the ampule analyzed previously by the solid scintillation counter was also placed in 15 ml of scintillation fluor and counted by liquid scintillation (Fig. 1). Thus, comparative analyses of the radioactivity assayed in each vial were achieved using the two types of counting systems. The ampules of each group were then broken and both aliquots and empty ampules counted by liquid and/or solid scintillation. The data were then corrected for background and half-life and reported as percent radioactivity compared with initial. Removal of Hg2 + and Factors Involved Effect of adsorbent type. Mercury losses from solutions stored in glass or polypropylene scintillation vials prompted further studies on the possible
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ScintiMotionF'luor
Nol(TI) Crystal
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Liquid
Scintillation
I ml Ampuls Solid
Scintillation
FIGURE 1. Diagram representing the experimental design used to detect diffusion of mercury nitrate, through glass (see Methods).
203
Hg 2 + , as
application of this observation to remove organic or inorganic mercury compounds from aqueous solutions using different concentrations of adsorbents: fiber glass (FG), rubber stopper powder (RS), and rubber latex foam (RL). Glass vials containing aqueous solution (15 ml, pH 6.0) and the various concentrations of the adsorbent test substances were used. In all the following experiments the solution used was supplemented with 203 Hg(NO 3 ) 2 or [ 2 0 3 Hg]CH 3 HgCI, as deemed necessary, to yield a count rate of 7 X 10 6 cpm/ml in presence or absence (control) of the solid material. During storage at 25°C and prior to analysis, the entire content of each vial was shaken manually for 10 sec; the adsorbent was then allowed to settle. The rate of removal of 2 0 3 H g 2 + by the adsorbent was evaluated from differences of the beta radioactivities in 0.1-ml samples obtained at intervals during storage. Effect of pH. Effect of pH of the aqueous solution on the rate of removal of 203 Hg(NO3 )2 by 1.0 g RS was examined. This was performed by repeating the above experiment except for adjusting the pH of the DDW with 0.01 N HCI or NaOH to 3, 6, 10, and 12. The RS was prepared by drilling holes in rubber stoppers and collecting the resulting fine powder. No attempt was made to obtain a uniform size powder by seiving. Effect of type of mercury. Effect of RS on the removal of 203 Hg2 + from mercury nitrate [ 2 0 3 Hg(NO 3 ) 2 ] or methyl mercury chloride ([ 2 0 3 Hg]CH 3 HgCI) solution was examined. In this experiment, glass vials containing 1.0 g RS and aqueous solution (15 ml, pH 6.0) containing the radioactive mercury compound were stored at 25°C, and the rate of 2 O 3 H g 2 + removal by the RS from organic or inorganic mercury solution was followed. Effect of presoaking the adsorbent. This was conducted in the exact manner as the aforementioned experiments, except that 1.0 g RS was presoaked for 18 hr in DDW adjusted to pH 3.0. The treated or untreated RS was added to vials containing 15 ml aqueous solution (pH 3.0), supplemented with 2 0 3 Hg(NO 3 ) 2 . Vials with the same solution (pH 3.0) and no RS served as control.
CONTROL OF MERCURY
413
The data of all the previous experiments were normalized for background half-life, losses to containers' walls (control), and compared with initial radioactivity. The results reported herein represent the average of four to six experiments. RESULTS 203
Hg2 + during Storage
In DDW (pH 7.0) kept in glass vials (Fig. 2a) with no added H g 2 + carrier (line B), the radioactivity decreased to 51 and 25% of initial after 5 and 13 days, respectively; in presence of 100 jug H g 2 + carrier/ml (line A) no significant loss was detected during the entire duration of the experiment. Storage of 2 0 3 H g 2 + in polypropylene vials in absence of added H g 2 + carrier (Fig. 2b) resulted in 80% loss within 2 days (line B), with little change thereafter. On the other hand, no losses were noted during storage in the
100
F O
y
• —• A
©
50
o
B-no carrier
1-
n
LJ_100
©
O 1-
PERC
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Factors Affecting Losses of
^
^
3
6
^-B
9
12
15 0
3
6
STORAGE (days) FIGURE 2. Factors affecting losses of 2 0 3 Hg 2 + , as mercury nitrate, during storage in presence (A) or absence (B) of 100 ßg Hg2 + carrier (HgCI,). (a) DDW in glass, (b) DDW in polypropylene vials, (c) GBSB media in glass, and (d) GBSB media in polypropylene vials. The vials containing DDW and GBSB (10 ml) were each supplemented with 203 Hg(NO 3 ) 2 to yield 6 X 10s cpm/ml. Results are reported as specific activity (percent of initial) corrected for background and half-life.
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O. R. NOYES ET AL.
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presence of 100 jug Hg 2 + /ml. When the 2 0 3 Hg(NO 3 ) 2 , in the presence of HgCI2 (carrier), was added to sterile GBSB media (pH 7.0) and kept in glass vials (Fig. 2c), 2 0 3 H g 2 + activity (line A) reached 83, 69, and 52% of initial value after 1, 5, and 13 days, respectively. In the absence of carrier Hg2 + (line B), further decreases were observed reaching 58, 35, and 3 1 % after 1, 5, and 13 days, respectively. Storage of mercury in GBSB media in polypropylene vials (Fig. 2d), with no added carrier (line B), resulted in decreases of original activity to 34, 16, and 19% after 1, 5, and 13 days, respectively. In the presence of 100 /ig H g 2 + carrier (line A), the trend of 2 0 3 H g 2 + losses was similar but less in magnitude (i.e., 6 1 , 28, and 34% of original activities remained after 1, 5, and 13 days, respectively). Possible Diffusion of
203
Hg 2 + through Container's Walls
When glass ampules containing carrier-free 2 0 3 H g 2 + in DDW were counted by liquid scintillation, no changes were noted (Table 1, Group A). However, when these ampules were counted by solid scintillation (Group B), losses averaging 19 and 24% of the radioactivity were noted after 60 and 90 days storage, respectively. In the presence of 50 /ig and 100 jug Hg2 + carrier/ml, no changes in counts were detected using both counting systems. After the removal of these ampules from the scintillation vial, no radioactivity was detected in the scintillation fluor, indicating that 203 Hg2 + did not diffuse through the wall of the ampule into the scintillation cocktail. No losses of 203 Hg2 + activities occurred from GBSB media containing 0, 50, or 100 jug H g 2 + carrier/ml solution during the entire period of storage (Table 1, Groups C and D). The ampules were then broken, and the solution as well as the empty glass were checked for their radioactivity. In the absence of HgCI2 as H g 2 + carrier, 12 and 74% of the original radioactivity were detected on the empty glass ampules containing DDW after 30 and 90 days storage, respectively (Table 2). Only 4.6 and 4.3% of the original radioactivity were found on the glass when DDW had 50 jug and 100 jug H g 2 + carrier/ml, respectively. Adsorption of 2 0 3 H g 2 + to the glass wall of ampules containing GBSB media with no carrier was 15, 14, and 28% of initial level after 30, 60, and 90 days storage, respectively. At both levels of carrier H g 2 + (50 and 100 jug Hg 2 + /ml), the adsorption of 2 0 3 H g 2 + from media to the glass wall oí the ampule was found to be inconsistent during the 90-day storage period and did not follow a definite pattern. Effect of Adsorbent Type Results (Fig. 3a) revealed that in the presence of 2 0 3 Hg(NO 3 ) 2 and 0.5 g FG in 15 ml solution, 85 and 32% of the initial 2 0 3 H g 2 + activity were detected in water after 2 and 72 hr storage, respectively. However, when the level of 2 0 3 Hg(NO 3 ) 2 was kept constant and the concentration of FG increased threefold (1.5 g), 52 and 25% of the initial radioactivity were found after 2 and 72 hr storage, respectively. The removal of 2 0 3 Hg 2 + from water at pH 6.0 was more pronounced when rubber was used. It was noted that 0.5
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TABLE 1. Effect of Added Carrier (HgClä) on Diffusion of *° 3 Hg 2 + from Sealed Glass Ampules Containing DDW orGBSB during Extended Storage"
Storage time (days) Group B
Group A "
GroupC
Group D
Carrier (MgHg I+ /ml)
Sample no.
30
60
90
30
60
90
30
60
90
30
60
90
None
1 2 3 4 5 6 7 8 9
100 100 100 100 100 100 100 100 100
_c 100 100 — 100 100 100 100 100
_ 100 -
100 88 83 100 100 100 100 100 100
82 80 100 100 — 100 100
76 — 100 — 100
100 100 100 100 100 100 100 100 100
100 100 — 100 100 — 100 100
— 100 — 100 — 100
100 100 100 100 100 100 100 100 100
100 100 — 100 100 — 100 100
— 100 — — — — 100
50 100
-
-
-
100
•
"Results are expressed as percent of initial 2 0 3 Hg 2 + radioactivity. ^Four groups (A, B, C, D) of nine ampules in each were used: group A had DDW and three of these ampules contained no carrier Hg 2 + , three with + + 50 ßg HgJ+/Vnl, and three ampules had 100 /ig Hg J+ /ml. The radioactivities in ampules were determined by liquid scintillation. Group B was prepared as group A except that the ampules were counted by solid scintillation; groupsCand D were duplicates of A and B except GBSB media replaced the DDW. c Ampule was broken, solution and empty ampule counted (see Table 2).
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O. R. NOY ES ET AL.
TABLE 2. Comparative Effect of Added Carrier (HgCIJ on Adsorption of of the Sealed Ampules Containing DDW or GBSB during Storage0'6
203
Hg 2 + onto Walls
GBSB
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DDW
Carrier (Mg/ml)
.Storage days
Sealed ampule
Solution only
Empty ampule
Solution only
Empty ampule
0
30 60 90
100 100 100
87.7 79.5 25.9
12.3 20.5 74.1
84.9 85.9 72.2
15.1 14.1 27.8
50
30 60 90
100 100 100
99.7 97.9 95.4
0.3 2.1 4.6
24.7 88.1 43.3
75.3 11.9 56.7
100
30 60 90
100 100 100
99.8 99.8 95.7
0.2 0.2
45.0 84.9 65.4
55.0 15.1 34.6
4.3
"Each ampule was broken, solution and empty ampule counted. 6 Results are expressed as percent of initial activity (cpm).
75
k©
O
i •O
o • 0.5 g FS • • I.Sg FG o>05gRL
• • PH 12 i.pn i • pH 10 • • pH 6 o • Control (no B)
• • I.OgRS
— —
w
"
25-
—i
0 20
O •-;
40
;
o • .
SO
60
TIME (hrs)
0
ZO
40
60
TIME (min)
TIME (min)
TIME (min) 203
I+
FIGURE 3. Factors affecting the removal of H g from aqueous solution, (a) Effect of type and concentration of adsorbent (fiber glass, FB; rubber latex foam, RL; rubber stopper, RS), (b) effect of pH of solution, (c) effect of type of Hg 2 + (inorganic vs. organic), and (d) effect of presoaking rubber (pH 3.0). The solution in vials (15 ml, pH 6.0, unless otherwise indicated) was supplemented with " 3 Hg(NO 3 )j or [ 203 Hg]CH 3 HgCI (as necessary) to yield 7 X 106 cpm/ml in presence or absence (control) of adsorbent. Results are reported as specific activity (percent of initial) corrected for background, half-life, and loss to container.
CONTROL OF MERCURY
417
g RL removed 72% of the initial 2 0 3 H g 2 + level of the mercury nitrate within 2 hr and adsorbed 80 and 93.5% after 6 and 72 hr storage, respectively. However, in presence of 1.0 g RS, 16 and 3% of initial 2 0 3 H g 2 + activity remained in the water after 2 and 72 hr of storage, respectively.
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Effect of pH Results (Fig. 3b) indicated that there was no statistical difference (p < 0.05) in the amount of 2 0 3 H g 2 + adsorbed by 1 g RS kept in the 203 Hg(NO 3 ) 2 solution at pH 3, 6, or 10. It was noted that 43, 2 1 , and 14% of the initial 2 0 3 H g 2 + activity remained after 1, 20, and 43 min of storage, respectively. However, the removal of 2 0 3 H g 2 + by RS at pH 12 was less than that noted at pH 3, 6, and 10. After 1 and 60 min storage, 49 and 26% of initial activity was detected, respectively. Effect of Type of Mercury Compound The comparative effects of removal rates of inorganic [ 2 0 3 Hg(NO 3 ) 2 ] and organic ([ 2 0 3 Hg]CH 3 HgCI) mercury compounds by 1 g RS from aqueous solution at pH 6.0 (Fig. 3c) indicated no statistical difference between the compounds. After 5 min, 29% of initial activity of both forms of mercury remained. This value decreased to 19 and 9% after 20 and 60 min, respectively. Effect of Presoaking the Adsorbent The effect of soaking 1 g RS in water (pH 3.0) for 18 hr showed very little difference on the rate of removal of 2 0 3 H g 2 + from water (Fig. 3d). It was found that in the presence of nonsoaked rubber, 43 and 15% of the initial level of 2 0 3 H g 2 + remained in solution after 1 and 60 min, respectively, whereas 39 and 6% of the original activity was found after the same periods of time for the presoaked rubber.
DISCUSSION AND CONCLUSIONS The results presented in this report demonstrated the losses of 2 0 3 Hg 2 + from solution by chemisorption onto the container walls and the amount of H g 2 + adsorbed seems to be correlated with the initial concentration of the H g 2 + ion, the chemical composition of container, the chemical nature of the solution used and storage time. Shimomura et al. (1968, 1969) showed that loss of 2 0 3 H g 2 + from solution depended on pH and that this loss was due to vaporization of the mercury. Coyne and Collins (1972) established that loss of H g 2 + was related to initial concentration of mercury and presence of a preservative/These authors recommended that HNO 3 be added to the container prior to the addition of the mercury solution. In this investigation, when DDW was used, the presence of Hg2 + carrier in the form of HgCI2 (100 jug Hg 2 + /ml) minimized losses of 2 0 3 H g 2 + in both glass and polypropylene containers. On the other hand, when GBSB media was used, adding Hg2 +
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O. R. NOYES ET AL.
carrier did not minimize the loss of 2 0 3 H g 2 + activity in both containers. Webb (1966) reported that H g 2 + forms strongly ionic covalent bonds with ligand atoms capable of donating electron pairs, both CI" and O H " being simple examples of this. We would expect that H g 2 + might complex readily with anions in the walls of the container as well as with the various ions present in the media. The differences in chemisorption rates between glass and polypropylene containers suggested that there are a finite number of adsorption sites for the H g 2 + ions, which vary considerably between containers. Recent results from our lab showed that very little ( < 0.5%) 203 H g 2 + in either organic ([ 2 0 3 Hg]CH 3 HgCI) or inorganic [such as 203 Hg( N O 3 ) 2 ] compounds was adsorbed by the walls of Teflon containers. Greenwood and Clarkson (1970) stated that losses of H g 2 + were highest in tubes made of flint glass, cellulose nitrate, polyethylene, and Butyrex and lowest in Pyrex, polycarbonate, and Teflon tubes. Chau and Saitoh (1970) noted that losses of 82% of added mercury were encountered in unpreserved natural water samples. Benes (1969) and Benês and Rajman (1969) found that in aqueous solutions of Hg 2 + , aged no more than 5 days, pseudocolloidal particles of mercury were found between pH 2 and 7 and pH 12 and 14, probably due to adsorption on and/or coprecipitation with foreign impurities in the solution. Shimomura et al. (1968, 1969) established that the loss of 2 0 3 H g 2 + from solutions during storage was due to vaporization of mercury. Greenwood and Clarkson (1970) reported that losses of H g 2 + occurred following storage of dilute HgCI2 solution and that H g 2 + may be removed by diffusion across the walls or by volatilization and subsequent binding to the upper part of the container. However, our data did not support their suggestion as no diffusion of 2 0 3 H g 2 + occurred through the sealed ampules. The apparent loss indicated by solid scintillation counting in ampules containing DDW with no added H g 2 + carrier may be due to changes that took place in ionic arrangement (geometry) of the atoms of 2 0 3 H g 2 + with respect to the sodium iodide crystal of the detector. The initial count expressed the total activity found in solution at a particular geometry; during storage the 2 0 3 H g 2 + ions were adsorbed onto the wall of the ampule leading to a change in the position of the 2 0 3 H g 2 + atoms in the counter used. Several methods are currently being investigated to remove mercury compounds from the aquatic environment. These include dredging of mercury-containing sediment followed by roasting or leaching (Smith, 1972) and a microbial cell-reutilization process (Suzuki et al., 1968). These processes, while quite efficient, still require trapping and collecting mercury vapor. Jernelöv (1970) and Smith (1972) suggested using sand or other overlay materials to cover mercury-containing sediment. However, current shifts within the body of the treated water could remove the "protective" covering as fast as it is laid down.
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CONTROL OF MERCURY
419
Several ¡on exchange column procedures, such as Chelex 100 chelating resin, are very effective in removing inorganic mercury compounds but not the organic mercurials (Law, 1971). Another anion exchange resin, Saffrion NMRR, has been suggested by Law (1971) as an effective means for the removal of both inorganic and organic (MM) mercurials from aqueous solution. The use of Dowex A-1 (a chelating resin) and chitosan (obtained from shells of crabs) was reported by Muzzarelli and Isolati (1971) to be very effective in removal of both inorganic and organic mercury compounds from aqueous solutions. We believe that the ¡deal material to be used for removing H g 2 + from water should be inert so that further pollution of the water does not occur. This material should also remove the H g 2 + compounds from H g 2 + polluted water quickly and efficiently in large enough concentrations to make its use practical and inexpensive. Fiber glass meets some of these requirements; it is inert and inexpensive. However, the use of rubber meets all criteria and removes both inorganic and organic mercury compounds from water with reasonable efficiency. The cost of pure rubber, admittedly, might be expensive. However, an inexpensive and ready source of rubber might be found in old wornout automobile and truck tires that are now either thrown away or burned. The pH of the aqueous solution was not a critical factor in the removal of H g 2 + by rubber. In addition, the effect of soaking the rubber did not show any differences on the removal of 2 0 3 Hg 2 + when compared with the nontreated rubber. This characteristic would then lend itself to the use of rubber in a column or trickling filter apparatus over which the Hg 2+ -containingsolution could be passed prior to its discharge into any body of water.
REFERENCES Ballard, A. E. and Thornton, C. D. W. 1941. Photometric method for estimation of minute amounts of mercury. Ind. Eng. Chem. Anal. Ed. 13:893-897. Benes, P. 1969. On the state of mercury (II) traces in aqueous solutions. Colloidal behaviour of mercury. J. Inorg. Nucl. Chem. 31: 1923-1928. Benes, P. and Rajman, I. 1969. Radiochemical study of the sorption of trace elements. V. Adsorption and desorption of bivalent mercury on polyethylene. Collection Czechoslov. Chem. Commun. 34:1375-1386. Chau, Y. -K. and Saitoh, H. 1970. Determination of submicrogram quantities of mercury in lake waters. Environ. Sci. Technol. 4:839-841. Coyne, R. V. and Collins, J. A. 1972. Loss of mercury from water during storage. Anal. Chem. 44:1093-1096. Greenwood, M. R. and Clarkson, T. W. 1970. Storage of mercury at submolar concentrations. Am. Ind. Hyg. Assoc. J. 31:250-251. Hinkle, M. E. and Learned, R. E. 1969. Determination of mercury in natural waters by collection on silver screens. U.S. Geol. Survey Prof. Papers 650-D, pp. D251-D254. Jernelov, A. 1970. Release of methyl mercury from sediments with layers containing inorganic mercury at different depths. Limnol. Oceanogr. 15:958-960. Law, S. L. 1971. Methyl mercury and inorganic mercury collection by a selective chelating resin. Science 174:285-287.
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Munns, R. K. and Holland, D. C. 1971. Determination of mercury in fish by flameless atomic absorption: A collaborative study. J. Assoc. Off. Agric. Chem. 54:202-205. Muzzarelli, R. A. A. and Isolati, A. 1971. Methyl mercury acetate removal from waters by chromatography on chelating polymers. Water Air Soil Pollut. 1:65-71. Shimomura, S., Nishihara, Y. and Tanase, Y. 1968. Escape of mercury from diluted mercury (II) solutions. Jap. Anal. 17:1148-1149. Shimomura, S., Nishihara, Y. and Tanase, Y. 1969. Decrease of mercury radioactivity in the dilute mercury (II) solutions. Jap. Anal. 18:1072-1077. Smith, I. C. 1972. Control of mercury pollution in sediments. Environ. Protect. Technol. Ser. EPA-R2-72-043, 56 pp. Washington, D.C.: Office of Research and Monitoring, U.S. Environmental Protection Agency. Suzuki, T., Furukawa, K. and Tonomura, K. 1968. Studies on the removal of inorganic mercurial compounds in waste by the cell-reused method of mercury-resistant bacterium. J. Ferment. Technol. 46:1048-1055. Thorpe, V. A. 1971. Determination of mercury in food products and biological fluids by aeration and flameless atomic absorption spectrophotometry. J. Assoc. Off. Agric. Chem. 54:206-210. Townshend, A. and Vaughan, A. 1970. Applications of enzyme-catalysed reactions in trace analysis-Vl. Determination of mercury and silver by their inhibition of yeast alcohol dehydrogenase. Talanta 17:299-304. Webb, J. L. 1966. Enzymesand metabolic inhibitors, vol. 2, 732 pp. New York: Academic Press. Received March 3, 1975 A ccepted June 30, 1975
ISSN: 0098-4108 (Print) (Online) Journal homepage: http://www.tandfonline.com/loi/uteh19
Control of mercury pollution O. R. Noyes , M. K. Hamdy & L. A. Muse To cite this article: O. R. Noyes , M. K. Hamdy & L. A. Muse (1976) Control of mercury pollution, Journal of Toxicology and Environmental Health, 1:3, 409-420, DOI: 10.1080/15287397609529340 To link to this article: http://dx.doi.org/10.1080/15287397609529340
Published online: 20 Oct 2009.
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CONTROL OF MERCURY POLLUTION O. R. Noyes, M. K. Hamdy, L. A. Muse
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Department of Food Science, University of Georgia, Athens, Georgia
When a 2 0 3 Hg(NO 3 ) 2 solution was kept at 25°C in glass or polypropylene containers, 50 and 80% of original radioactivity was adsorbed to the containers' walls after I and 4 days, respectively. However, no loss in radioactivity was observed if the solution was supplemented with HgCI2 as carrier (100 μg Hg2+ /ml) and stored in either container for 13 days. When2 0 3 H g 2 + was dissolved in glucose basal salt broth with added carrier, levels of 2 0 3 H g 2 + in solution (kept in glass) decreased to 80 and 70% of original after 1 and 5 days and decreased even more if stored in polypropylene (60 and 40% of original 203 2+ activity after 1 and 4 days, respectively). In the absence of carrier, decreases of Hg activities in media stored in either container were more pronounced due to chemisorption (but) not diffusion. The following factors affecting the removal of mercurials from aqueous solution stored in glass were examined: type and concentration of adsorbent (fiber glass and rubber powder); pH; pretreatment of the rubber; and the form of mercury used. Rubber was equally effective in the adsorption of organic and inorganic mercury. The pH of the aqueous 2 0 3 Hg 2 + solution was not a critical factor in the rate of adsorption of mercury by the rubber. In addition, the effect of soaking the rubber in water for 18 hr did not show any statistical difference when compared with nontreated rubber. It can be concluded that rubber is a very effective adsorbent of mercury and, thus, can be used as a simple method for control of mercury pollution.
INTRODUCTION While conducting mercury analysis using flameless atomic absorption spectrophotometry (FAAS), it was observed that the concentration of Hg 2 + in standard HgCI2 solutions did not remain constant, but in fact decreased rapidly during storage at room temperature. Furthermore, during studies involving microbial production of methyl mercury (MM) using 2 0 3 H g 2 + , the radioactivity decreased during incubation beyond the half-life decay or the volatilization rate of the 2 0 3 Hg 2 + -containing compounds from the media. Ballard and Thornton (1941) stated that mercuric ions are adsorbed onto glass from dilute solutions, but no data were presented to support the authors' statement. Other investigators (Munns and Holland, 1971; Thorpe, 1971; Townshend and Vaughan, 1970) reported that standard solutions of mercury should be prepared just before use and special care should be exercised in cleaning glassware prior to reuse. Hinkle and Learned (1969) This research was supported by grant no. B-069-GA from the Office of Water Resources Research, Department of the Interior, Washington, D.C. We thank Dr. M. M. Duncan, Head, Physics and Astronomy Department, University of Georgia, Athens, for his helpful suggestions and review of this manuscript. O. R. Noyes's present address is Food Industries Department, California Polytechnic State University, San Luis Obispo, California 93407. Requests for reprints should be sent to this address. 409 Journal of Toxicology and Environmental Health, 1:409-420, 1976 Copyright © 1976 by Hemisphere Publishing Corporation
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reported that loss of mercury during storage caused serious errors in mercury analysis and that colloidal particles present in water contained from 5 to 25 times more mercury than the aqueous solution. Coyne and Collins (1972) showed that the loss of mercury from solution was related to the initial mercury concentration and to the presence or absence of a preservative such as nitric acid, which tended to keep the mercury in solution. These authors indicated that the effectiveness of the preservative can be achieved only if the acid was present before the addition of mercury to the container. In the present investigation, some factors affecting the chemisorption of mercury were examined and the possible movement of 2 0 3 H g 2 + through the container walls was also determined. If mercury is indeed adsorbed on solid surfaces, this principle can be utilized for the effective removal of mercury compounds from aquatic environments. This study would then have a practical value in the treatment of industrial mercury-polluted waters. METHODS Counting Systems Unless otherwise stated, all experiments were performed using mercury isotope as methyl mercury chloride ([ 2O3 Hg]CH 3 HgCI) or mercury nitrate [ 2 0 3 Hg(NO 3 ) 2 ] obtained from New England Nuclear Corp., Boston, Mass. The 2 0 3 Hg(NO 3 ) 2 was dissolved in 0.5 N HNO 3 and had a specific activity of 11.3 mCi/mg, whereas the [203 Hg] CH 3 HgCI was dissolved in 0.5 M Na2 CO 3 and had a specific activity of 1.19 mCi/mg. Aliquots of either solution were used for the preparation of saline working standard solutions. The low energy beta emitted from 2 0 3 H g 2 + in samples was determined using a Beckman model LS-100 C liquid scintillation spectrometer. A known volume of a sample was placed in a plastic scintillation vial containing 10 ml of the Beckman liquid scintillation fluor (fluoralloy dry mix in toluene containing Biosolv BBS solubilizer). Most samples were counted to ± 1 % error and those containing less than 500 were counted to not less than 5% error. The gamma energy of 2 0 3 H g 2 + in samples was counted using a Baird Atomic well-type Nal (TI) crystal shielded with 3-in. lead and equipped with a single-channel pulse-height analyzer using the integral mode. All counting data were corrected for background and half-life. Chemisorption Time-loss studies using 2 0 3 Hg(NO 3 ) 2 with and without added mercury carrier in the form of HgCI2 were conducted at 25°C in glass or in polypropylene scintillation vials. Loss of 2 0 3 H g 2 + counts from 10 ml of deionized distilled water (DDW) or from 10 ml of glucose basal salt broth (GBSB) media containing HgCI2 as a H g 2 + carrier (100 jug H g 2 + /ml), or in the absence of H g 2 + carrier, were determined. The DDW or GBSB were supplemented with standard solution of 2 0 3 Hg(NO 3 ) 2 to yield a count rate of 6 X 10 s cpm/ml. The GBSB consisted of 6.8 g KH 2 PO 4 , 0.09 g
CONTROL OF MERCURY
411
CaCI2 •4H 2 O,0.06gMgSO 4 ,0.007gZnSO 4 ,0.025gFeSO 4 • 7 H 2 O, 0.001 g (NH 4 ) 2 SO 4 , 0.001 g N a 2 M o O 4 • 7 H 2 O,and 10 g glucose/liter. During storage, the entire 10-ml sample was shaken well in the vial and the chemisorption evaluated from the differences of radioactivities in 0.1-ml samples obtained after specific elapsed time intervals. g MnSO 4 ,0.25gNH 4 CI,0.25
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Diffusion Possible movement of H g 2 + by diffusion through the container's wall was also examined at 25°C using sterile-sealed flint glass ampules containing either 1 ml sterile DDW or GBSB supplemented with 2O3 Hg(NO3 )2 to yield a count rate of 5 X 105 cpm/ml. Four groups (A, B,C, D) of nine glass ampules in each were used. The first group of ampules (A) contained DDW, and three of these ampules had no additional H g 2 + , three contained 50 jug H g 2 + ; and three had 100 ng Hg2 + / m l , both in the form of HgCI 2 . All ampules were fire-sealed, and the gamma activity in each was determined with a solid scintillation counting system. The second group of ampules (B) was prepared in a similar manner as group A, except that the beta activity in each ampule was detected after placing the entire ampule in 15 ml of scintillation fluor in the liquid scintillation system. The third and fourth groups (C) and (D) were prepared in a similar manner to groups A and B, respectively, except that GBSB media replaced the DDW. At intervals during 90 days of storage, three ampules from every group (one at each H g 2 + level used) were washed with dilute HCI, wiped with tissue, and then assayed for their radioactivity. Assuming a loss of 2O3 H g 2 + due to diffusion through the walls of the ampule, the net radioactivity (after half-life correction) counted by solid scintillation would decrease, whereas a loss of 2 0 3 H g 2 + from an ampule immersed in liquid scintillation cocktail would increase the radioactivity observed. The ampule counted by liquid scintillation was removed from the scintillation fluor and subsequently counted by solid scintillation after wiping the surface with tissue. The scintillation fluor mixture alone was also counted by liquid scintillation to detect any 2 0 3 H g 2 + that had diffused through the glass ampule. Again, the ampule analyzed previously by the solid scintillation counter was also placed in 15 ml of scintillation fluor and counted by liquid scintillation (Fig. 1). Thus, comparative analyses of the radioactivity assayed in each vial were achieved using the two types of counting systems. The ampules of each group were then broken and both aliquots and empty ampules counted by liquid and/or solid scintillation. The data were then corrected for background and half-life and reported as percent radioactivity compared with initial. Removal of Hg2 + and Factors Involved Effect of adsorbent type. Mercury losses from solutions stored in glass or polypropylene scintillation vials prompted further studies on the possible
412
O. R. NOYES ET AL.
ScintiMotionF'luor
Nol(TI) Crystal
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Liquid
Scintillation
I ml Ampuls Solid
Scintillation
FIGURE 1. Diagram representing the experimental design used to detect diffusion of mercury nitrate, through glass (see Methods).
203
Hg 2 + , as
application of this observation to remove organic or inorganic mercury compounds from aqueous solutions using different concentrations of adsorbents: fiber glass (FG), rubber stopper powder (RS), and rubber latex foam (RL). Glass vials containing aqueous solution (15 ml, pH 6.0) and the various concentrations of the adsorbent test substances were used. In all the following experiments the solution used was supplemented with 203 Hg(NO 3 ) 2 or [ 2 0 3 Hg]CH 3 HgCI, as deemed necessary, to yield a count rate of 7 X 10 6 cpm/ml in presence or absence (control) of the solid material. During storage at 25°C and prior to analysis, the entire content of each vial was shaken manually for 10 sec; the adsorbent was then allowed to settle. The rate of removal of 2 0 3 H g 2 + by the adsorbent was evaluated from differences of the beta radioactivities in 0.1-ml samples obtained at intervals during storage. Effect of pH. Effect of pH of the aqueous solution on the rate of removal of 203 Hg(NO3 )2 by 1.0 g RS was examined. This was performed by repeating the above experiment except for adjusting the pH of the DDW with 0.01 N HCI or NaOH to 3, 6, 10, and 12. The RS was prepared by drilling holes in rubber stoppers and collecting the resulting fine powder. No attempt was made to obtain a uniform size powder by seiving. Effect of type of mercury. Effect of RS on the removal of 203 Hg2 + from mercury nitrate [ 2 0 3 Hg(NO 3 ) 2 ] or methyl mercury chloride ([ 2 0 3 Hg]CH 3 HgCI) solution was examined. In this experiment, glass vials containing 1.0 g RS and aqueous solution (15 ml, pH 6.0) containing the radioactive mercury compound were stored at 25°C, and the rate of 2 O 3 H g 2 + removal by the RS from organic or inorganic mercury solution was followed. Effect of presoaking the adsorbent. This was conducted in the exact manner as the aforementioned experiments, except that 1.0 g RS was presoaked for 18 hr in DDW adjusted to pH 3.0. The treated or untreated RS was added to vials containing 15 ml aqueous solution (pH 3.0), supplemented with 2 0 3 Hg(NO 3 ) 2 . Vials with the same solution (pH 3.0) and no RS served as control.
CONTROL OF MERCURY
413
The data of all the previous experiments were normalized for background half-life, losses to containers' walls (control), and compared with initial radioactivity. The results reported herein represent the average of four to six experiments. RESULTS 203
Hg2 + during Storage
In DDW (pH 7.0) kept in glass vials (Fig. 2a) with no added H g 2 + carrier (line B), the radioactivity decreased to 51 and 25% of initial after 5 and 13 days, respectively; in presence of 100 jug H g 2 + carrier/ml (line A) no significant loss was detected during the entire duration of the experiment. Storage of 2 0 3 H g 2 + in polypropylene vials in absence of added H g 2 + carrier (Fig. 2b) resulted in 80% loss within 2 days (line B), with little change thereafter. On the other hand, no losses were noted during storage in the
100
F O
y
• —• A
©
50
o
B-no carrier
1-
n
LJ_100
©
O 1-
PERC
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Factors Affecting Losses of
^
^
3
6
^-B
9
12
15 0
3
6
STORAGE (days) FIGURE 2. Factors affecting losses of 2 0 3 Hg 2 + , as mercury nitrate, during storage in presence (A) or absence (B) of 100 ßg Hg2 + carrier (HgCI,). (a) DDW in glass, (b) DDW in polypropylene vials, (c) GBSB media in glass, and (d) GBSB media in polypropylene vials. The vials containing DDW and GBSB (10 ml) were each supplemented with 203 Hg(NO 3 ) 2 to yield 6 X 10s cpm/ml. Results are reported as specific activity (percent of initial) corrected for background and half-life.
414
O. R. NOYES ET AL.
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presence of 100 jug Hg 2 + /ml. When the 2 0 3 Hg(NO 3 ) 2 , in the presence of HgCI2 (carrier), was added to sterile GBSB media (pH 7.0) and kept in glass vials (Fig. 2c), 2 0 3 H g 2 + activity (line A) reached 83, 69, and 52% of initial value after 1, 5, and 13 days, respectively. In the absence of carrier Hg2 + (line B), further decreases were observed reaching 58, 35, and 3 1 % after 1, 5, and 13 days, respectively. Storage of mercury in GBSB media in polypropylene vials (Fig. 2d), with no added carrier (line B), resulted in decreases of original activity to 34, 16, and 19% after 1, 5, and 13 days, respectively. In the presence of 100 /ig H g 2 + carrier (line A), the trend of 2 0 3 H g 2 + losses was similar but less in magnitude (i.e., 6 1 , 28, and 34% of original activities remained after 1, 5, and 13 days, respectively). Possible Diffusion of
203
Hg 2 + through Container's Walls
When glass ampules containing carrier-free 2 0 3 H g 2 + in DDW were counted by liquid scintillation, no changes were noted (Table 1, Group A). However, when these ampules were counted by solid scintillation (Group B), losses averaging 19 and 24% of the radioactivity were noted after 60 and 90 days storage, respectively. In the presence of 50 /ig and 100 jug Hg2 + carrier/ml, no changes in counts were detected using both counting systems. After the removal of these ampules from the scintillation vial, no radioactivity was detected in the scintillation fluor, indicating that 203 Hg2 + did not diffuse through the wall of the ampule into the scintillation cocktail. No losses of 203 Hg2 + activities occurred from GBSB media containing 0, 50, or 100 jug H g 2 + carrier/ml solution during the entire period of storage (Table 1, Groups C and D). The ampules were then broken, and the solution as well as the empty glass were checked for their radioactivity. In the absence of HgCI2 as H g 2 + carrier, 12 and 74% of the original radioactivity were detected on the empty glass ampules containing DDW after 30 and 90 days storage, respectively (Table 2). Only 4.6 and 4.3% of the original radioactivity were found on the glass when DDW had 50 jug and 100 jug H g 2 + carrier/ml, respectively. Adsorption of 2 0 3 H g 2 + to the glass wall of ampules containing GBSB media with no carrier was 15, 14, and 28% of initial level after 30, 60, and 90 days storage, respectively. At both levels of carrier H g 2 + (50 and 100 jug Hg 2 + /ml), the adsorption of 2 0 3 H g 2 + from media to the glass wall oí the ampule was found to be inconsistent during the 90-day storage period and did not follow a definite pattern. Effect of Adsorbent Type Results (Fig. 3a) revealed that in the presence of 2 0 3 Hg(NO 3 ) 2 and 0.5 g FG in 15 ml solution, 85 and 32% of the initial 2 0 3 H g 2 + activity were detected in water after 2 and 72 hr storage, respectively. However, when the level of 2 0 3 Hg(NO 3 ) 2 was kept constant and the concentration of FG increased threefold (1.5 g), 52 and 25% of the initial radioactivity were found after 2 and 72 hr storage, respectively. The removal of 2 0 3 Hg 2 + from water at pH 6.0 was more pronounced when rubber was used. It was noted that 0.5
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TABLE 1. Effect of Added Carrier (HgClä) on Diffusion of *° 3 Hg 2 + from Sealed Glass Ampules Containing DDW orGBSB during Extended Storage"
Storage time (days) Group B
Group A "
GroupC
Group D
Carrier (MgHg I+ /ml)
Sample no.
30
60
90
30
60
90
30
60
90
30
60
90
None
1 2 3 4 5 6 7 8 9
100 100 100 100 100 100 100 100 100
_c 100 100 — 100 100 100 100 100
_ 100 -
100 88 83 100 100 100 100 100 100
82 80 100 100 — 100 100
76 — 100 — 100
100 100 100 100 100 100 100 100 100
100 100 — 100 100 — 100 100
— 100 — 100 — 100
100 100 100 100 100 100 100 100 100
100 100 — 100 100 — 100 100
— 100 — — — — 100
50 100
-
-
-
100
•
"Results are expressed as percent of initial 2 0 3 Hg 2 + radioactivity. ^Four groups (A, B, C, D) of nine ampules in each were used: group A had DDW and three of these ampules contained no carrier Hg 2 + , three with + + 50 ßg HgJ+/Vnl, and three ampules had 100 /ig Hg J+ /ml. The radioactivities in ampules were determined by liquid scintillation. Group B was prepared as group A except that the ampules were counted by solid scintillation; groupsCand D were duplicates of A and B except GBSB media replaced the DDW. c Ampule was broken, solution and empty ampule counted (see Table 2).
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O. R. NOY ES ET AL.
TABLE 2. Comparative Effect of Added Carrier (HgCIJ on Adsorption of of the Sealed Ampules Containing DDW or GBSB during Storage0'6
203
Hg 2 + onto Walls
GBSB
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DDW
Carrier (Mg/ml)
.Storage days
Sealed ampule
Solution only
Empty ampule
Solution only
Empty ampule
0
30 60 90
100 100 100
87.7 79.5 25.9
12.3 20.5 74.1
84.9 85.9 72.2
15.1 14.1 27.8
50
30 60 90
100 100 100
99.7 97.9 95.4
0.3 2.1 4.6
24.7 88.1 43.3
75.3 11.9 56.7
100
30 60 90
100 100 100
99.8 99.8 95.7
0.2 0.2
45.0 84.9 65.4
55.0 15.1 34.6
4.3
"Each ampule was broken, solution and empty ampule counted. 6 Results are expressed as percent of initial activity (cpm).
75
k©
O
i •O
o • 0.5 g FS • • I.Sg FG o>05gRL
• • PH 12 i.pn i • pH 10 • • pH 6 o • Control (no B)
• • I.OgRS
— —
w
"
25-
—i
0 20
O •-;
40
;
o • .
SO
60
TIME (hrs)
0
ZO
40
60
TIME (min)
TIME (min)
TIME (min) 203
I+
FIGURE 3. Factors affecting the removal of H g from aqueous solution, (a) Effect of type and concentration of adsorbent (fiber glass, FB; rubber latex foam, RL; rubber stopper, RS), (b) effect of pH of solution, (c) effect of type of Hg 2 + (inorganic vs. organic), and (d) effect of presoaking rubber (pH 3.0). The solution in vials (15 ml, pH 6.0, unless otherwise indicated) was supplemented with " 3 Hg(NO 3 )j or [ 203 Hg]CH 3 HgCI (as necessary) to yield 7 X 106 cpm/ml in presence or absence (control) of adsorbent. Results are reported as specific activity (percent of initial) corrected for background, half-life, and loss to container.
CONTROL OF MERCURY
417
g RL removed 72% of the initial 2 0 3 H g 2 + level of the mercury nitrate within 2 hr and adsorbed 80 and 93.5% after 6 and 72 hr storage, respectively. However, in presence of 1.0 g RS, 16 and 3% of initial 2 0 3 H g 2 + activity remained in the water after 2 and 72 hr of storage, respectively.
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Effect of pH Results (Fig. 3b) indicated that there was no statistical difference (p < 0.05) in the amount of 2 0 3 H g 2 + adsorbed by 1 g RS kept in the 203 Hg(NO 3 ) 2 solution at pH 3, 6, or 10. It was noted that 43, 2 1 , and 14% of the initial 2 0 3 H g 2 + activity remained after 1, 20, and 43 min of storage, respectively. However, the removal of 2 0 3 H g 2 + by RS at pH 12 was less than that noted at pH 3, 6, and 10. After 1 and 60 min storage, 49 and 26% of initial activity was detected, respectively. Effect of Type of Mercury Compound The comparative effects of removal rates of inorganic [ 2 0 3 Hg(NO 3 ) 2 ] and organic ([ 2 0 3 Hg]CH 3 HgCI) mercury compounds by 1 g RS from aqueous solution at pH 6.0 (Fig. 3c) indicated no statistical difference between the compounds. After 5 min, 29% of initial activity of both forms of mercury remained. This value decreased to 19 and 9% after 20 and 60 min, respectively. Effect of Presoaking the Adsorbent The effect of soaking 1 g RS in water (pH 3.0) for 18 hr showed very little difference on the rate of removal of 2 0 3 H g 2 + from water (Fig. 3d). It was found that in the presence of nonsoaked rubber, 43 and 15% of the initial level of 2 0 3 H g 2 + remained in solution after 1 and 60 min, respectively, whereas 39 and 6% of the original activity was found after the same periods of time for the presoaked rubber.
DISCUSSION AND CONCLUSIONS The results presented in this report demonstrated the losses of 2 0 3 Hg 2 + from solution by chemisorption onto the container walls and the amount of H g 2 + adsorbed seems to be correlated with the initial concentration of the H g 2 + ion, the chemical composition of container, the chemical nature of the solution used and storage time. Shimomura et al. (1968, 1969) showed that loss of 2 0 3 H g 2 + from solution depended on pH and that this loss was due to vaporization of the mercury. Coyne and Collins (1972) established that loss of H g 2 + was related to initial concentration of mercury and presence of a preservative/These authors recommended that HNO 3 be added to the container prior to the addition of the mercury solution. In this investigation, when DDW was used, the presence of Hg2 + carrier in the form of HgCI2 (100 jug Hg 2 + /ml) minimized losses of 2 0 3 H g 2 + in both glass and polypropylene containers. On the other hand, when GBSB media was used, adding Hg2 +
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O. R. NOYES ET AL.
carrier did not minimize the loss of 2 0 3 H g 2 + activity in both containers. Webb (1966) reported that H g 2 + forms strongly ionic covalent bonds with ligand atoms capable of donating electron pairs, both CI" and O H " being simple examples of this. We would expect that H g 2 + might complex readily with anions in the walls of the container as well as with the various ions present in the media. The differences in chemisorption rates between glass and polypropylene containers suggested that there are a finite number of adsorption sites for the H g 2 + ions, which vary considerably between containers. Recent results from our lab showed that very little ( < 0.5%) 203 H g 2 + in either organic ([ 2 0 3 Hg]CH 3 HgCI) or inorganic [such as 203 Hg( N O 3 ) 2 ] compounds was adsorbed by the walls of Teflon containers. Greenwood and Clarkson (1970) stated that losses of H g 2 + were highest in tubes made of flint glass, cellulose nitrate, polyethylene, and Butyrex and lowest in Pyrex, polycarbonate, and Teflon tubes. Chau and Saitoh (1970) noted that losses of 82% of added mercury were encountered in unpreserved natural water samples. Benes (1969) and Benês and Rajman (1969) found that in aqueous solutions of Hg 2 + , aged no more than 5 days, pseudocolloidal particles of mercury were found between pH 2 and 7 and pH 12 and 14, probably due to adsorption on and/or coprecipitation with foreign impurities in the solution. Shimomura et al. (1968, 1969) established that the loss of 2 0 3 H g 2 + from solutions during storage was due to vaporization of mercury. Greenwood and Clarkson (1970) reported that losses of H g 2 + occurred following storage of dilute HgCI2 solution and that H g 2 + may be removed by diffusion across the walls or by volatilization and subsequent binding to the upper part of the container. However, our data did not support their suggestion as no diffusion of 2 0 3 H g 2 + occurred through the sealed ampules. The apparent loss indicated by solid scintillation counting in ampules containing DDW with no added H g 2 + carrier may be due to changes that took place in ionic arrangement (geometry) of the atoms of 2 0 3 H g 2 + with respect to the sodium iodide crystal of the detector. The initial count expressed the total activity found in solution at a particular geometry; during storage the 2 0 3 H g 2 + ions were adsorbed onto the wall of the ampule leading to a change in the position of the 2 0 3 H g 2 + atoms in the counter used. Several methods are currently being investigated to remove mercury compounds from the aquatic environment. These include dredging of mercury-containing sediment followed by roasting or leaching (Smith, 1972) and a microbial cell-reutilization process (Suzuki et al., 1968). These processes, while quite efficient, still require trapping and collecting mercury vapor. Jernelöv (1970) and Smith (1972) suggested using sand or other overlay materials to cover mercury-containing sediment. However, current shifts within the body of the treated water could remove the "protective" covering as fast as it is laid down.
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CONTROL OF MERCURY
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Several ¡on exchange column procedures, such as Chelex 100 chelating resin, are very effective in removing inorganic mercury compounds but not the organic mercurials (Law, 1971). Another anion exchange resin, Saffrion NMRR, has been suggested by Law (1971) as an effective means for the removal of both inorganic and organic (MM) mercurials from aqueous solution. The use of Dowex A-1 (a chelating resin) and chitosan (obtained from shells of crabs) was reported by Muzzarelli and Isolati (1971) to be very effective in removal of both inorganic and organic mercury compounds from aqueous solutions. We believe that the ¡deal material to be used for removing H g 2 + from water should be inert so that further pollution of the water does not occur. This material should also remove the H g 2 + compounds from H g 2 + polluted water quickly and efficiently in large enough concentrations to make its use practical and inexpensive. Fiber glass meets some of these requirements; it is inert and inexpensive. However, the use of rubber meets all criteria and removes both inorganic and organic mercury compounds from water with reasonable efficiency. The cost of pure rubber, admittedly, might be expensive. However, an inexpensive and ready source of rubber might be found in old wornout automobile and truck tires that are now either thrown away or burned. The pH of the aqueous solution was not a critical factor in the removal of H g 2 + by rubber. In addition, the effect of soaking the rubber did not show any differences on the removal of 2 0 3 Hg 2 + when compared with the nontreated rubber. This characteristic would then lend itself to the use of rubber in a column or trickling filter apparatus over which the Hg 2+ -containingsolution could be passed prior to its discharge into any body of water.
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Munns, R. K. and Holland, D. C. 1971. Determination of mercury in fish by flameless atomic absorption: A collaborative study. J. Assoc. Off. Agric. Chem. 54:202-205. Muzzarelli, R. A. A. and Isolati, A. 1971. Methyl mercury acetate removal from waters by chromatography on chelating polymers. Water Air Soil Pollut. 1:65-71. Shimomura, S., Nishihara, Y. and Tanase, Y. 1968. Escape of mercury from diluted mercury (II) solutions. Jap. Anal. 17:1148-1149. Shimomura, S., Nishihara, Y. and Tanase, Y. 1969. Decrease of mercury radioactivity in the dilute mercury (II) solutions. Jap. Anal. 18:1072-1077. Smith, I. C. 1972. Control of mercury pollution in sediments. Environ. Protect. Technol. Ser. EPA-R2-72-043, 56 pp. Washington, D.C.: Office of Research and Monitoring, U.S. Environmental Protection Agency. Suzuki, T., Furukawa, K. and Tonomura, K. 1968. Studies on the removal of inorganic mercurial compounds in waste by the cell-reused method of mercury-resistant bacterium. J. Ferment. Technol. 46:1048-1055. Thorpe, V. A. 1971. Determination of mercury in food products and biological fluids by aeration and flameless atomic absorption spectrophotometry. J. Assoc. Off. Agric. Chem. 54:206-210. Townshend, A. and Vaughan, A. 1970. Applications of enzyme-catalysed reactions in trace analysis-Vl. Determination of mercury and silver by their inhibition of yeast alcohol dehydrogenase. Talanta 17:299-304. Webb, J. L. 1966. Enzymesand metabolic inhibitors, vol. 2, 732 pp. New York: Academic Press. Received March 3, 1975 A ccepted June 30, 1975
