THE MERCURY CYCLE AND FISH IN THE ADIRONDACK LAKES

ES&T

THE MERCURY CYCLE AND

Mercury in fish occurs almost entirely as methylmercury in muscle tissue (5, 9), w h e r e it is associated with protein sulfhydryl groups [10, 11). Ingestion of fish muscle is an important exposure pathway of mercury to h u m a n s . Methylmercury is highly toxic; it is thought to inhibit enzyme activity in the cerebellum, w h i c h is re­ sponsible for n e u r o n growth in early developmental stages. Chronic exposure to organomercurials can result in mental retardation (12). As a result, the U.S. Food and Drug Administration (FDA) has set an Action Level of 1 μg/g (wet weight) for concentration of mercury in fish. Fish containing concentrations of mercury above this level are considered to be hazardous for h u m a n c o n s u m p t i o n a n d c a n n o t be sold in interstate com­ merce. Canada and several U.S. states have developed c o n s u m p t i o n advisories of 0.5 μg/g for mercury in fish. In the 1980s, the n u m b e r of fish consumption adviso­ ries increased in several states a n d the province of On­ tario. More recently, the n u m b e r of advisories has in­ creased because of the imposition of a blanket advisory covering m o r e t h a n 11,000 lakes in Michigan. This trend is probably the result not of an increase in the n u m b e r s of fish w i t h elevated mercury, but of increased monitoring and awareness of the problem. The mercury cycle in aquatic ecosystems is compli­ cated because of the myriad of species and pathways (Figure 1). Our understanding of the biogeochemistry of mercury has increased markedly over the past 10 years w i t h the development of clean protocols for the sam­ pling and analysis of mercury (13, 14). There is little confidence in measurements of aqueous mercury prior to 1985 because of the likelihood of sample contamina­ tion (15). Atmospheric deposition of mercury to lakes occurs largely as inorganic mercury (16), although inputs of methylmercury occur (17). Within oxygenated waters, Hg(II) will complex w i t h inorganic ligands (e.g., Cl~, OFT), b i n d w i t h dissolved organic carbon (DOC), or sorb to particulate matter. Mercuric ion can be reduced microbially to form ele­ mental mercury [Hg(0)]. Most waters are oversaturated w i t h respect to the solubility of atmospheric Hg(0), and Hg(0) is volatilized to the atmosphere (18). Within an­ oxic zones, mercury forms strong aqueous complexes w i t h sulfide and precipitate as HgS. Within anaerobic environments or within anoxic microzones in aerobic environments, Hg(II) can be converted to methylmer­ cury. Sulfate-reducing bacteria appear to be important in the methylation of mercury (19, 20). Methylmercury may b i n d to DOC or be demethylated by microbial pro­ cesses. Methylmercury is generally thought to be the form of mercury that bioconcentrates in fish. Gill and Bruland (21) reported a strong relationship between concentrations of organomercurials in lakes and mer­ cury concentrations in fish. High concentrations of mercury in fish tissue have been reported in remote, low-ionic-strength lakes. Sev­ eral studies have reported a correlation between fish mercury concentration and lake pH (16, 5, 22, 23). A linkage b e t w e e n surface water acidification a n d fish m e r c u r y c o n t e n t has b e e n inferred. Several mecha­ nisms have been hypothesized to explain this phenom­ enon (8), including: • increased inputs of mercury from atmospheric depo­ sition, • increased inputs of mercury from adjacent terrestrial ecosystems, • increased partitioning of mercury to the water col­ u m n in acidic waters,

FISHINTHE ADIRONDACK

H

istorically high c o n c e n ­ t r a t i o n s of m e r c u r y (Hg) i n fish h a v e been attrib­ uted to point sources of mercury generally as­ sociated w i t h industrial discharge (1-3). In recent years, there has been renewed inter­ est in the transport and fate of mercury in the environ­ ment because of 'widespread reports of elevated concen­ trations of mercury in fish caught in remote lakes {4-8).

LAKES

C H A R L E S T. D R I S C O L L

Syracuse University, CARL

L.

C H E N G VAN

Syracuse, NY 13244 SCHOFIELD

Cornell University, Ithaca, NY 14853 •

RON

MUNSON

Tetra Tech, Inc., Hadley MA 01035 JOHN

HOLSAPPLE

Empire State Electric Energy Research Corp. Schenectady, NY 12303 136 A

Environ. Sci. Technol., Vol. 28, No. 3, 1994

0013-936X/94/0927-136A$04.50/0 © 1994 American Chemical Society

• low production of fish in acidic lakes, • increased production of monomethylmercury with decreases in pH, ' • decreased rates of demethylation with decreases in pH, and • increased permeability of fish gills to methylmercury. Federal and state environmental protection and natural resource management agencies are particularly interested in mercury cycling in the environment. With the passage and subsequent implementation of the 1990 Clean Air Act Amendments, Congress directed EPA to develop a research agenda and schedule that would provide information on sources, transport, and fate and effects of mercury, including risks to human health and the environment. Title III (Hazardous Air Pollutants) of the amendments modifies Section 112 of the Act and provides a list of hazardous air pollutants (e.g., mercury) for control from major sources (those emitting 10 tons per year of a single pollutant or 25 tons per year aggregate). Lesser quantities may be considered for control based on their persistence in an ecosystem, bioconcentration factors, and health risk implications. Numerous studies are currently under way across the country that will provide information for specific Section 112 requirements. Provisions include deposition monitoring, source apportionment, and evaluation of public health and environmental effects. The assessment includes an evaluation of fish, wildlife, and other biota. In addition, a special report on mercury is being prepared by EPA. Information such as the results from the current study will complement efforts by the electric utility industry to characterize mercury emissions as well as the environmental fate and transport of mercury, and to perform risk analyses. It is expected that EPA will rely heavily on this and other work when it prepares the Section 112 mercury study and a more comprehensive Utility Hazardous Air Pollutant Study scheduled to be delivered to Congress in November 1995. Following receipt of the information provided by the regulated and scientific communities, EPA will make recommendations regarding the need for future mercury emission controls. The Adirondack region of New York has the most acidic lakes of any area in the United States (24).

FIGURE 1

Schematic diagram summarizing the mercury cycle in lake ecosystems

Many of the lakes there are characterized by low-ionic-strength water. Undoubtedly, many of these waters are naturally acidic because of inputs of organic acids [25-27). However, superimposed on naturally acidic conditions are inputs of strong acids from atmospheric deposition (28), which contribute to the acidity of surface waters [25, 29). Recently, Simonin et al. (23) investigated concentrations of mercury in fish tissue in 12 Adirondack lakes and found relatively high concentrations and increasing concentrations with decreasing pH. However, these lakes were generally neutral-pH waters with low concentrations of DOC. The objectives of this study were to determine concentrations of total and methylmercury in lake water and concentrations of mercury in fish tissue in Adirondack lakes, and to evaluate mechanisms regulating the concentration of mercury in fish. Methods The Adirondack region is a large (2,400,000 ha), predominately forested area in northern New York state (29). The bedrock material is primarily granitic gneisses and metasedimentary rocks. The mountains and uplands are mantled glacial till, thicker in the valleys and becoming progressively more shallow upslope. Soils of the region are generally acidic Spodosols developed from glacial till. The Adirondack region receives large inputs of precipitation (—100 cm/year) and, as a result, has high stream runoff

138 A Environ. Sci. Technol., Vol. 28, No. 3, 1994

(~60 cm/year). Within the Adirondack Ecological Zone, there are 2796 lakes and ponds covering >0.2 ha in surface area. From 1984 to 1987, the Adirondack Lakes Survey Corporation (ALSO surveyed 1469 lakes within the Adirondack Ecological Zone (30, 24). Physical, chemical, and biological data were collected on each lake and its watershed. From this detailed survey, a classification system was developed for Adirondack lakes based on characteristics of hydrologie flowpaths, surficial geology, and concentrations of organic solutes (i.e., DOC; 24, 29, 31). For the present study, 16 lakes that represent many of the ALSC classes were selected. These lake classes are thought to represent conditions in which high concentrations of mercury might occur in fish tissue (i.e., seepage lakes, acidic lake classes such as thin till drainage lakes, and high-DOC lakes). These lakes are located throughout the Adirondack Park, but many are in the Oswegatchie-Black drainage area of the southwestern Adirondacks. The Oswegatchie-Black watershed is characterized by many low-pH and high-DOC lakes. Two of the study sites are seepage lakes (Oregon Pond and North Pond); the remainder are drainage lakes. Two of the lakes (Sunday Lake and Halfmoon Lake) exhibit complete or nearly complete depletion of O z in the hypolimnion during summer stratification. The ALSC data base contains information on physical factors, water chemistry, and fish prey species that help interpret pat-

terns of fish mercury concentration. The percentage of wetland area was estimated from topographic maps of individual watersheds. These val­ ues should be considered as only approximate representations of wet­ land area. Subsequent analysis (Kretser, unpublished data) of areal photographs indicates that the wet­ l a n d areas d e r i v e d from topo­ graphic maps may be more repre­ sentative of near-shore wetland areas and may under-represent up­ land wetlands. The yellow perch [Perca flavescens) was selected as an index species because it is widely distrib­ uted throughout lakes in the Adirondacks, as well as the upper Mid­ west and southeastern Canada. From Sept. 16 to Oct. 29, 1992, 977 yellow perch were collected from the 16 study lakes. Fish were cap­ tured using variable-mesh experi­ mental gill nets and Alaska-style net traps. Nets were fished until a minimum of 60 yellow perch were collected from each lake. Live, un­ damaged perch, representative of the size distribution in the catch, were selected for analysis. Length and weight measurements were ob­ tained from each selected fish, and scale samples and opercular bones were removed for age and growth analysis. Fish were individually wrapped in aluminum foil, placed in Ziploc bags, and kept on ice until they could be frozen (within 4-8 h after collection). After the ages of all perch were determined, utilizing both scales and opercular bones, a sample of 30 fish, representative of the age distri­ bution, was selected for tissue sam­ pling for mercury analysis. A sec­ tion of the dorsolateral muscle tissue was removed from the same location on each fish using the pro­ tocol described by Gloss et al. {32). Tissue samples 1.0 g wet weight were first homog­ enized with a stainless steel tissue homogenizer. All samples were kept frozen until analyzed for mer­ cury. Mean annual growth rates [G = log(Wt)-log(Wl)/t-l, where W = weight in g, t = age in years] were determined from weights at ages ob­ tained from back-calculated lengths using opercular bones [In (total length, mm) = 3.17 + 0.88* In (oper­ cular length, mm), Ν = 931, r 2 = 0.96] and length/weight relation­ ships for individual lengths. Water samples were collected from the lakes between Oct. 15 and 22,1992. Clean techniques were fol­

lowed during all phases of sample collection and handling. Lake water was collected by grab-sampling over the side of a nonmetallic boat into 1-L Teflon bottles for mercury analysis and into 1-L polypropylene bottles for the analysis of major sol­ utes. Care was taken to avoid sam­ pling water over which the boat had passed. Sampling personnel wore full clean-suits w i t h shoulderlength plastic gloves and collected water from about 0.25 m below the lake surface. Sampling bottles were opened and closed at depth to avoid sampling the surface film, and were rinsed three times with water prior to collecting the final sample. The bottles were hermetically sealed and double-bagged immediately af­ ter sample collection. Upon transport to the laboratory, samples were filtered through an acid-cleaned 0.2-μπι disposable ni­ trocellulose filter for analysis of to­ tal dissolved mercury. For analysis of total and total dissolved mercury, samples were first oxidized with BrCl. After oxidation, samples were pre-reduced with NH 2 OHHCl, re­ duced further with SnCl 2 , purged to Au traps, and thermally desorbed as Hg(0) with He carrier gas for detec­ tion by cold vapor atomic fluores­ cence spectrometry (CVAFS). Total methylmercury was processed by first extracting samples from a HC1/ KCl matrix into CH2C12 followed by back extraction into pure water (by solvent evaporation). Determina­ tion of methylmercury was accom­ plished by aqueous-phase ethylation with NaB(C2H5)4, cryogenic gas chromatograph separation, and CVAFS detection. Bloom (33) pro­ vides details of the procedure used to fractionate aqueous samples for mercury. The water samples col­ lected were also measured for major water chemistry parameters using the p r o c e d u r e s s u m m a r i z e d in Driscoll and van Dreason (32). Water chemistry results The lakes evaluated in this study exhibited diverse physical charac­ teristics and water chemistry, and r e p r e s e n t 12 of the ALSC lake classes. The lakes contain generally acidic, low-ionic-strength waters. Values of acid-neutralizing capacity ranged from below 0 to above 200 μeq/L, with pH values from below 5 to near 7.0. The study lakes also covered a range of DOC concentra­ tions (from 3.4 to 26.5 mg C/L). Lake DOC concentrations were influ­ enced by the presence of near-shore wetlands within the drainage basin

[DOC concentration (mg C/L) = 1.42* % wetland + 0.56, r2 = 0.88; where % wetland is the percentage of the total watershed area that is near-shore wetlands]. Consistent with the sundry physi­ cal and chemical characteristics were diverse concentrations of total mercury. The seepage lakes (North and Oregon Ponds) had the lowest concentrations of total mercury of the study lakes, less than 1 ng/L. The concentrations of total mercury in drainage lakes ranged from below 1 ng/L to above 5 ng/L. Most of the total mercury was in the dissolved fraction (mean dissolved Hg/total Hg = 0.61), although there was con­ siderable lake-to-lake variability in the fraction of particulate mercury. There was no relationship with the fraction of dissolved mercury and water chemistry parameters, such as pH or DOC concentration. Considerable variability was also evident in concentrations of meth­ ylmercury (0.068-0.61 ng/L). The seepage lakes (North and Oregon Ponds) showed low concentrations of methylmercury. Lakes with an­ oxic hypolimnion during summer stratification (Sunday Lake and Halfmoon Lake) had very high concentrations of methylmercury, consistent with the formation of methylmercury under anaerobic c o n d i t i o n s . In the A d i r o n d a c k lakes studied, there was generally a good relationship between con­ centrations of total methylmercury and total mercury for oxic lakes [methylmercury (ng/L) = 0.1* total Hg (ng/L) - 0.033, r2 = 0.84]. There­ fore, total m e t h y l m e r c u r y was about 10% of total mercury in most Adirondack lakes. An exception was evident for the lakes with an­ oxic h y p o l i m n i o n , w h i c h h a d about 20% of total mercury as total methylmercury. In the Adirondack lakes, there was a pattern of increasing concen­ trations of both total mercury and total methylmercury with decreas­ ing pH. Moreover, for a given pH value, lakes with DOC concentra­ tions > 6 mg C/L had higher concen­ trations of both total mercury and total methylmercury than did lakes with DOC concentrations 0.05) age effects b e t w e e n lake compari­ sons of m e a n m e r c u r y concentra­ tions. Further increases in fish mer­ cury above age 5+ probably reflect a shift to p i s c i v o r y . T h e latter i n ­ crease in mercury concentration of older age fish occurred at a length of a p p r o x i m a t e l y 200 m m , above w h i c h piscivory or cannibalism is c o m m o n to yellow p e r c h p o p u l a ­ tions (34). In Oregon P o n d , c o n c e n t r a t i o n s of fish mercury increased u p to age 6+ a n d declined thereafter. This un­ usual pattern may be partly the re­ sult of a lack of fish prey species in this p o n d a n d high variability in growth rates of older fish. For exam­ ple, mercury concentrations in age 9+ perch were inversely related to growth rates [fish Hg ^ g / g ) = 0.80 1.872*growth rate, r = 0.86, ρ = 0.0017], a n d m e r c u r y c o n c e n t r a ­ tions in perch age 7+ to 10+ were in­ versely related to body weight [fish Hg ^ g / g ) = 0.45 - 0.001*weight (g), r 2 = 0.45, ρ = 0.0018]. These rela­ tionships suggest that growth dilu­ tion (i.e., rate of muscle tissue elab­ o r a t i o n e x c e e d s r a t e of m e r c u r y u p t a k e in food) is responsible for the decline in mercury concentra­ tion of older, faster growing perch in the Oregon Pond population. Unlike other studies (21), n o n e of the simple regressions between con­ 140 A

Lakes with anoxic conditions in the hypolimnion during summer stratification are shown with open circles.

FIGURE 3

Concentrations of mercury in the muscle tissue of different age classes of yellow perch in Adirondack study lakes, except Oregon Pond, and lakes from the Upper Peninsula of Michigan (5)

centrations of mercury in age 3+ to 5+ p e r c h a n d a q u e o u s m e a s u r e ­ ments of pH, DOC, and methylmer­ cury was significant (p > 0.05) w h e n the high-DOC (26.5 mg C/L) Rock P o n d was i n c l u d e d in the analysis. Excluding Rock Pond, significant (p < 0.05) regressions w e r e obtained b e t w e e n fish m e r c u r y a n d m e t h ­ ylmercury concentrations in the water column [fish Hg ^ g / g ) = 0.35 + 0.58*methylmercury (ng/L), r 2 = 0.32], and p H [fish Hg (\iglg) = 1.61 - 1.19*pH, r 2 = 0.37] and DOC [fish Hg ^ g / g ) = 0.13 + 0.067*DOC (mg C/L), r 2 = 0.29; Figure 4]. The only water chemistry param­ eter significantly c o r r e l a t e d w i t h fish mercury w h e n all 16 lakes were

Environ. Sci. Technol., Vol. 28, No. 3, 1994

i n c l u d e d w a s t o t a l d i s s o l v e d Al [fish Hg ^ g / g ) = 0.27 + 0.001*total diss Al ^ g / L ) , r 2 = 0.59; Figure 5]. Total dissolved Al tends to be high­ est in low-pH lakes w i t h high DOC (35) a n d appears to be a better indi­ cator of fish mercury concentrations than either pH or DOC alone. This o b s e r v a t i o n suggests t h a t funda­ mental hydrologie and geochemical processes controlling the transport a n d solubility of Al also influence t h e b i o a v a i l a b i l i t y of m e r c u r y in these lakes. H y p o l i m n e t i c anoxia is a n o t h e r factor that may influence mercury bioavailability in Adirondack lakes. For example, concentrations of mer­ cury in age 3+ to 5+ yellow perch

Sunday Lake and Halfmoon Lake. In multiple regression analysis, mean mercury concentrations for age 3+ to 5+ yellow perch increased with increasing total dissolved Al and decreased with increasing DOC. Although aqueous total meth­ ylmercury concentrations were higher in lakes with high DOC con­ centrations (Figure 2), bioavailable methylmercury appears to be regu­ lated primarily by the extent of mer­ cury binding with organic ligands. Aluminum may compete with me­ thylmercury for organic binding sites, thus leading to greater bio­ availability of methylmercury in lakes with high Al/DOC ratios [fish Hg ^ g / g ) = 0.01 χ Al/DOC (μ δ Al/mg C) + 0.21, r2 = 0.73].

FIGURE 4

Concentrations of mercury in muscle tissue of age 3+ to 5+ yellow perch as a function of dissolved organic carbon (DOC) concentration in study lakes

FIGURE 5

Concentrations of mercury in muscle tissue of age 3+ to 5+ yellow perch as a function of dissolved AI concentration in study lakes

were high in both Sunday Lake and Halfmoon Lake, lakes with anoxic hypolimnion and high concentra­ tions of methylmercury in the water column, In Adirondack lakes, concentra­ tions of mercury in age 3+ to 5+ yel­ low perch increased with increas­ ing concentrations of DOC (Figure 4) and percentage of near-shore wet­ lands in the drainage basin [fish Hg i^g/g) = 0.08*% wetland + 0.19, r 2 = 0.67], w i t h o u t considering the highly dystrophic Rock Pond. The Rock Pond data suggest that with in­ creases in DOC concentration at some value above 8 mg C/L, concen­ trations of fish mercury decrease. The bioconcentration factor (BF)

of methylmercury is defined as the ratio of methylmercury concentra­ tion in fish tissue to the methyl mer­ cury concentration in water. For age 3+ to 5+ yellow perch, the log BF ranged from 5.73 to 7.03. The log BF decreased significantly with in­ creasing concentrations of DOC, but showed no significant (p > 0.05) pH effect. For given concentrations of DOC, the presence or absence of po­ tential fish prey species also signifi­ cantly influences the methylmer­ cury BF [log BF = 6.1 - 0.044*DOC (mg C/L) + 0.35*prey presence/ absence, r2 = 0.48]. For the Adiron­ dack lakes studied, the log BF was lowest in dystrophic Rock Pond and the lakes with anoxic hypolimnion,

Discussion Like other remote lake districts in eastern North America (5, 22), con­ centrations of mercury were ele­ vated in fish tissue in Adirondack lakes, with patterns of increasing mercury concentrations with de­ creasing pH. Concentrations of mer­ cury in muscle tissue of yellow perch obtained from remote Adirondacks lakes were higher than values reported in the detailed study of lakes from the Upper Pen­ insula of Michigan (5; Figure 3). For example, length-adjusted least squares mean mercury concentra­ tion in muscle tissue of age 3+ to 5+ yellow perch obtained from 14 Ad­ irondack drainage lakes (0.46 μg/g) was significantly higher (p < 0.004) than age 3+ to 5+ yellow perch mean mercury concentration from 12 drainage lakes (0.27 μg/g) in the Upper Peninsula of Michigan (5). However, there was no significant difference (p = 0.65) in the adjusted least squares means (Adirondacks = 0.38 μg/g; Michigan = 0.36 μg/g) when regional differences in the to­ tal Al/DOC ratio were accounted for by covariance analysis (r2 = 0.76). Regional comparison of least squares mean Al/DOC ratios, ad­ justed for pH, indicated that the ra­ tio was significantly (p < 0.004) higher in the Adirondack drainage lakes. In the Adirondacks, 26% of the yellow perch caught exceeded the 0.5 μg/g Action Level, and 7% exceeded the FDA Action Level of 1.0 μg/g. Additionally, at least one perch with mercury concentrations exceeding the 0.5 μg/g level was found in 14 of the 16 study lakes, and at least one perch exceeding the 1.0 μg/g level was found in 9 of the 16 study lakes. It is not clear why mercury con-

Environ. Sci. Technol., Vol. 28, No. 3, 1994 141 A

centrations are high in yellow perch in Adirondack lakes in comparison to other lake districts in eastern North America. Concentrations of total mercury in Adirondack lakes were also generally higher than val­ ues reported for other remote lakes in the literature (Table 1). The high­ est concentrations of total mercury measured for Adirondack lakes were comparable to concentrations reported for urban lakes or lakes with a point source of mercury from mining or industrial activity. The most obvious factor regulat­ ing the concentration and availabil­ ity of both total and methylmercury in Adirondack lakes is DOC. A number of investigators have re­ ported relationships between mer­ cury and concentrations of DOC or color in surface waters [36, 37). However, correlations between DOC concentrations and fish tissue mercury have been inconsistent. Concentrations of DOC explained a significant amount of the variation of mercury in lake trout in Ontario [4). Likewise, Haines et al. [8) ob­ served a positive correlation be­ tween lake color and concentrations of mercury in perch in the former Soviet Union. In contrast, Grieb et al. (5) reported that the mercury content of yellow perch decreased with increasing DOC concentra­ tions in seepage lakes. The results of our study suggest that DOC plays a complicated role in the transport and bioavailability of mercury in lake ecosystems. The transport of total and methylmer­ cury to Adirondack lakes seems to be linked to DOC, which is released from wetlands within the basin. This pattern has also been observed for lakes in Sweden [38). Therefore, DOC concentrations seem to be im­ portant in regulating lake concen­ trations of both total and methylmercury, and ultimately the supply to fish. On the other hand, DOC appears to bind with methylmercury, limit­ ing its bioavailability. This conflict­ ing role of DOC is shown by the increase in fish mercury concentra­ tions with increasing DOC up to concentrations of about 8 mg C/L followed by lower concentrations of mercury in yellow perch caught from highly dystrophic Rock Pond (DOC = 26.5 mg C/L; Figure 4), and the observed decreases in the BF of methylmercury with increasing DOC. In addition, inputs of other metals, such as Al, that complex with DOC appear to alter the bind­ ing of mercury with organic ligands, 142 A

TABLE 1

Summary of Hg concentrations in lakes Lake systems

Location

Total Hg (ng/L)

Reference

Remote lakes Drainage (14) Seepage (2) Seepage (4) Drainage Alpine Drainage (3)

Adirondacks Adirondacks Wisconsin Washington (state) California Manitoba

0.8-5.3 0.8 0.9-1.9 0.2 0.6 0.2-1.1

this study this study 15 33 21 3

Urban lakes Lake Union

Washington (state)

1.7

33

3.9 0.9

21 21

3.6-104 5.2-6.4

21 21

7-19 5-80

3 2

Great Lakes Erie United States/Canada Ontario United States/Canada Mining contaminated lakes Clear Lake California Davis Creek Reservoir California Chlor-Alkali contaminated lakes New York Onondaga Clay Lake Ontario

increasing its bioavailability. This process is particularly relevant for lake districts, such as the Adiron­ dacks, that have been impacted by acidic deposition and exhibit ele­ vated concentrations of Al. In addition to DOC concentration, other factors such as lake pH and Al concentration, anoxic hypolimnion, fish age, and food sources appear to be important in the regulation of mercury concentrations in fish tis­ sue. These myriad factors undoubt­ edly contribute to the weak rela­ tionship between methylmercury in lake water and mercury concentra­ tions in fish tissue. Elevated concentrations of mer­ cury in fish tissue may have impli­ cations for higher trophic levels within the Adirondack and other re­ mote regions. Mclntyre et al. [39) in­ vestigated mercury concentrations in eggs of the common loon [Gavia immer). They found that concentra­ tions were higher in eggs collected in the Adirondacks than in other lake districts in New Hampshire and Saskatchewan. They reported very high mercury concentrations in common loon eggs from Stillwa­ ter Reservoir in the Adirondacks (1.58 μg/g), near levels found to in­ duce reproductive problems in mal­ lards [Anas platyrhynchos; 40). Although our study provides im­ portant data on concentrations of mercury in fish tissue in Adiron­ dack lakes and factors that influ­ ence this accumulation, critical in­ f o r m a t i o n is m i s s i n g for t h e management of this important wa­ ter quality problem. First, there is

Environ. Sci. Technol., Vol. 28, No. 3, 1994

little time-series information on concentrations of mercury in the Adirondacks. Mclntyre et al. [39) re­ ported that concentrations of mer­ cury have declined in common loon eggs from 1978 to 1986; however, there is no historical information on trends in mercury in water or fish in the Adirondack region. Second, it is unclear whether the source of mer­ cury in the Adirondacks or other drainage lakes in eastern North America is atmospheric deposition, or whether the mercury is derived from mercury-bearing minerals in soil. Fitzgerald and Watras [15) con­ ducted a mass balance for a seepage lake in Wisconsin and reported that inputs of mercury were largely the result of atmospheric deposition. In an earlier study, Bloomfield et al. [41) developed a mass balance on mercury for Cranberry Lake in the Adirondacks and found that lake mercury was largely derived from within the lake watershed. Note, however, that watershed sources could still represent atmospheric deposition in a watershed followed by remobilization to drainage wa­ ters. The strong relationship be­ tween DOC and water column mer­ cury observed in our study could support either perspective (i.e., at­ mospheric or mineral sources). Moreover, wetlands play an impor­ tant role in the transport of mercury to lake ecosystems. However, the ultimate source of lake mercury (at­ mospheric vs. mineral release) and the way in w h i c h i n p u t s have changed over time is unclear, re­ sulting in a critical uncertainty for

management decisions on controls of a t m o s p h e r i c e m i s s i o n s of m e r ­ cury through the Clean Air Act A m e n d m e n t s of 1 9 9 0 . Acknowledgments This study w a s funded by the Empire State Electric Energy Research Corpora­ tion, t h e N e w York State Energy Re­ search Development Authority, and t h e Electric Power Research Institute. We thank Walt Kretser and Jim Gallagher of the A d i r o n d a c k Lake Survey Corpora­ tion for h e l p w i t h fish collection a n d data analysis, Carl Watras for h e l p in sample collection, and Nick Bloom for help in sample analysis. We also appre­ ciate the assistance of Sean Tenney, Wei Wang, D a w n Long, a n d Kim P o s t e k . This is contribution No. 128 of the Up­ state Freshwater Institute. References (1) (2) (3) (4) (5) (6) (7) (8) (9) (10) (11) (12) (13) (14) (15) (16) (17) (18) (19) (20) (21) (22) (23) (24)

Furutani, Α.; Rudd, J.W.M. Appl. En­ viron. Microbiol. 1980, 40, 770. Parks, J. W.; Lutz, Α.; Sutton, J. A. Can. /. Fish. Aquat. Sci. 1989, 46, 2184. Bloom, N. S.; Effler, S. W. Water Air SoilPollut. 1990, 53, 251. McMurty, M. J. et al. Can. J. Fish. Aquat. Sci. 1989, 46, 426. Grieb, T. M. et al. Environ. Toxicol. Contam. 1990, 9, 919. Hakanson, L.; Nilsoon, Α.; Andersson, T. Environ. Pollut. 1990, 49, 145. Wiener, J. G. et al. Environ. Toxicol. Chem. 1990, 9, 909. Haines, Τ. Α.; Komov, V.; Jagoe, C. H. Environ. Pollut. 1992, 78, 1. Bloom, N. S. Can. /. Fish. Aquat. Sci. 1992, 49, 1010. Montoura, R.F.C. et al. Estuar. Coast. Mar. Sci. 1978, 6, 387. Morel, F. M. M. Principles of Aquatic Chemistry, Wiley: New York, 1983. Klaassen, C. D.; Amdur, M. O.; Doull, J. Toxicology: The Basic Science of Poisons; Macmillan: New York, 1986. Gill, G. Α.; Fitzgerald, W. F. Deep-Sea Res. 1985, 32, 287. Gill, G. Α.; Fitzgerald, W. F. Mar. Chem. 1987, 20, 227. Fitzgerald, W. F.; Watras, C. J. Sci. To­ tal Environ. 1989, 87/88, 223. Winfrey, M. R.; Rudd, J.W.M. Envi­ ron. Toxicol. Chem. 1990, 9, 853. Bloom, N. S.; Watras, C. J. Sci. Total Environ. 1989, 87/88, 199. Vandal, G. M.; Mason, R. P.; Fitzger­ ald, W. F. Water Air Soil Pollut. 1991, 56, 791. Compeau, G C ; Bartha, R. Appl. En­ viron. Microbiol. 1985, 50, 498. Gilmour, C. C ; Henry, Ε. Α.; Mitchell, R. Environ. Sci. Technol. 1992, 26, 2281. Gill, G. Α.; Bruland, K. W. Environ. Sci. Technol. 1990, 24, 1392. Suns, K.; Hitchin, G. Water Air Soil Pollut. 1990, 650, 255. Simonin, H. A. et al. In Trace Sub­ stances in the Environment; Lewis Publishers: Chelsea, MI, in press. Baker, J. P. et al. In Adirondack Lake Survey: An Interpretive Analysis of Fish Communities and Wafer Chemis­ try, 1984-87; Adirondack Lakes Sur­

vey Corporation: Ray Brook, NY, 1990. (25) Driscoll, C. T.; Newton, R. M. Envi­ ron. Sci. Technol. 1985, 19, 716. (26) Munson, R. K.; Gherini, S. A. Water Resour. Res. 1993, 29, 891. (27) Driscoll, C. T.; Lehtinen, M. D.; Sulli­ van, T. J. Wafer Resour. Res., in press. (28) Shepard, J. P. et al. Water Air Soil Pol­ lut. 1989, 48, 225. (29) Driscoll, C. T. In Acidic Deposition and Aquatic Ecosystems: Regional Case Studies; Charles, D. F., Ed.; SpringerVerlag: New York, 1991; pp. 133-202. (30) Kretser, W. J.; Gallagher, J.; Nicolette, J. An Evaluation of Fish Communities and Water Chemistry; Adirondack Lakes Survey Corporation: Ray Brook, NY, 1989. (31) Driscoll, C. T.; van Dreason, R. Water Air Soil Pollut. 1993, 67, 319. (32) Gloss, S. P. et al. "Mercury Levels in Fish From the Upper Peninsula of Michigan (ELS Subregion 2B) in Rela­ tion to Lake Acidity"; Environmental Protection Agency: Washington, DC, 1990; EPA 600/3-90/028. (33) Bloom, N. S. Can. /. Fish. Aquat. Sci. 1989, 46, 1131. (34) Tarby, M. J. Trans. Am. Fish. Soc. 1974, 103, 462. (35) Driscoll, C. T. In The Environmental Chemistry of Aluminum; Sposito, G , Ed.; CRC Press: Boca Raton, FL, 1989; pp. 241-78. (36) Mierle, G ; Ingram, R. Water Air Soil Pollut. 1991, 56, 349. (37) Lindqvist, O. et al. Water Air Soil Pol-

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Carl L. Schofield is a fishery biologist and senior research associate in the De­ partment of Natural Resources at Cor­ nell University. His research has fo­ cused on lake acidification effects on fish populations in the Adirondack re­ gion of New York state.

Charles T. Driscoll is distinguished pro­ fessor of civil and environmental engi­ neering at Syracuse University. His re­ search interests include element cycling in terrestrial, wetland, and aquatic eco­ systems, and environmental quality modeling.

Ronald K. Munson is a senior engineer and project manager for Tetra Tech, Inc. He holds an M.S. degree from Brigham Young University. His research interests include mercury cycling and acid depo­ sition modeling, and evaluation of nonpoint sources of pollution.

Cheng Yan is research assistant and graduate student in the Department of Civil and Environmental Engineering at Syracuse University. He holds a B.S. de­ gree from Nanjing University. His re­ search interests include heavy metal contamination in natural water systems and soil.

John G. Holsapple is the administrator of water quality programs for the Empire State Electric Energy Research Corp. He holds an M.S. degree from the Univer­ sity of Massachusetts. His research in­ terests include the relationship between electric generation activities and aquatic ecosystems.

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