G15 Mercury in Fish

Total mercury concentrations were determined in seven tissues of thirty eight fish samples comprising six species from the Kpong Hydroelectric Reservoir in Ghana by the Cold Vapour Atomic Absorption Spectrometry (CVAAS) technique using an automatic mercury analyzer. Mercury concentration in all the tissues ranged from 0.005 to 0.022µg/g wet weight. In general the concentration of mercury in all the tissues were in the order; liver > muscle > intestine > stomach > gonad > gill > swim bladder. Mercury concentration was generally greater in the tissues of high trophic level fish such as Clarotes laticeps, Mormyrops anguilloides and chrysichthys aurutus whereas low trophic level fish such as Oreochromis niloticus recorded low mercury concentration in their tissues. The results obtained for total mercury concentration in the muscle tissues analysed in this study are below the WHO/FAO threshold limit of 0.5µg/g. This suggests that the exposure of the general public to Hg through fish consumption is not significant.

In January 2006 it was reported from Russia that Greenland halibut (Reinhardtius hippoglossoides) caught in the Barents Sea had shown mercury levels exceeding the EU’s upper limit of 0.5 mg/kg wet weight for this species. These findings were confirmed in a small study from the same area. To gain more knowledge on the mercury accumulation in this species, a more extensive survey was initiated by determining the levels of mercury in 320 Greenland halibut caught at eight stations off the coast of northern Norway. Individual fish were measured for physical data (i.e. length, weight and gender). The otoliths were removed for age determination. Fillet samples of approximately 100 g each were taken from the upper side of the fish and with a cut from the middle of the fish towards the tail. The fillet samples were homogenised and then kept frozen at -20°C prior to analyses for lipids and metals. For the determination of mercury subsamples of approximately 0.2 g dry weight were used for microwave-assisted wet digestion. The mercury determinations were carried out on an Agilent quadrupole ICPMS according to Julshamn et al. 2007. Round weight of the fish varied between 1.1 and 8.1 kg. Fish age varied between 12 and 29 years. The highest mercury concentration measured in muscle tissue was 1.1 mg/kg wet weight. Female fish were larger and showed higher mercury concentrations than male fish. Mercury concentration was positively correlated with fish size and negatively correlated with fat content. Fish captured in the easternmost stations towards the Russian part of the investigated area had significantly lower mercury concentrations than those caught further west. Fish captured at one of the positions had particularly high average mercury concentrations, 0.52 mg/kg wet weight., possibly due to a combination of large size and low fat content. Further studies are warranted to conclude on the mechanisms of the rather high mercury accumulation in this species.

Julshamn K; Maage A; Norli HS; Grobecker KH; Jorheim L, Fecher P. Determination of arsenic, cadmium, mercury, and lead by ICPMS in foods after pressure digestion. J AOAC Int 2007;90: 844-56.

Desman (Desmana moschata Linnaeus) is a relic endemic species of Russia. Natural habitats of desman are Dnepr, Volga, Don and Ural river basins. Desman is a small animal (body length 180 – 215 mm, weight 380 – 520 g) with long tail and short extremities. Inhabits stagnant or slowly flowing waters, former river-beds, floodland marshes and lakes. Optimal life conditions for the desman are in the reservoirs 1 – 2 m deep, more shallow reservoirs are unfit because of the winter frost penetration. Desman feeds on small water animals: mollusks, insects and larvae, leeches, minute fish, frogs, and also willingly eats the rhizomes of water plants. The composition of desman food changes depending on the reservoir type and the time of year. Desman is active the whole year round. Life duration is 4 – 5 years.

In 2003 – 2009 nine dead individuals of desman have been gathered in the fishing nets or in the littorals of Lipetsk region rivers. Mercury analysis has been made by the mercury analyzer RA-915+ (PYRO). The precision of analytic methods of measurements have been controlled using the certified biological material DORM-2 and DOLT-2.

Mercury content in all organs and tissues varied strongly and increased in the line: brain<muscles< kidneys<liver. The lower mercury concentrations were registered in the individual with the smallest weight (95 g): from 0.005 mg Hg/kg of wet weight in brain to 0.03 in liver. The least difference between the animals have been observed on the levels of metal accumulation in brain (0.005 – 0.070 mg Hg/kg ), while the content in liver was higher (1.0 – 60.0 mg Hg/kg). The remained tissues of heart muscle, intestine and spleen in some animals contained more mercury than brain and muscles, but less than kidneys and liver.

Analysis taken gives the opportunity to distinguish a few features that differ accumulation and distribution of mercury in organs and tissues of desman from those in other mammals. It is the considerable variability of accumulation level in liver and muscles compared to those in kidneys. Big difference in mercury accumulation by different organs and tissues. Extraordinary high levels of mercury accumulation in liver in some individuals (10 – 60 mg/kg), which is significantly higher than in mink and otter that inhabit European part of Russia.

Mercury concentrations have been investigated in whitefish (Coregonus lavaretus, n=42), European smelt (Osmerus eperlanus, n=29), Arctic char (Salvelinus alpinus, n=50), perch (Perca fluviatilis, n=26), brown trout (Salmo trutta, n=30), Atlantic salmon (Salmo salar, n=14), northern pike (Esox lucius, n=11), tench (Tinca tinca, n=4) and crucian carp (Carassius carassius, n=2), in Lake Norsjø, southern Norway. In addition, the stable isotope ratios d¹⁵N and d¹³C have been analyzed to reveal variations in trophic position and carbon source, within and between fish species.

The mercury levels varied both within and between the fish species. Totally 23 fish had Hg-concentrations above the consumption limit of 0,5 µg Hg/L: 10 Arctic char, 7 brown trout, 5 northern pike and 1 European smelt. The highest concentrations were measured in brown trout (1,95 mg Hg/kg ww) and northern pike (1,44 mg Hg/kg ww).

The results on d¹⁵N indicate a food web consisting of 4 consumer levels. The d¹³C signatures indicate that Arctic char, European smelt and sub-populations of whitefish primarily feed in the pelagic zone, while the d¹³C in perch, brown trout and the other sub-population of whitefish had heavier d¹³C signatures, indicating fish feeding in the littoral zone of the lake.

All fish species (except Atlantic salmon) exhibit significant correlations (p < 0,05) between Hg and age, weight and length. Within each species, no significant correlations were found between Hg and d¹⁵N, but a weak and significant (r² = 0,074, p < 0,001) positive linear relationship was found when plotting all the fish species together, indicating biomagnification along the food web.

Concentrations of mercury (Hg) have increased slowly in landlocked Arctic char over a 10- to 15-year period in the Arctic. Fluxes of Hg to sediments also show increases in most Arctic lakes. Correlation of Hg with trophic level (TL) was used to investigate and compare biomagnification of Hg in food webs from lakes in the Canadian Arctic sampled from 2002 to 2007. Concentrations of Hg (total Hg and methylmercury [MeHg]) in food webs were compared across longitudinal and latitudinal gradients in relation to d¹³C and d¹⁵N in periphyton, zooplankton, benthic invertebrates, and Arctic char of varying size-classes. Trophic magnification factors (TMFs) were calculated for the food web in each lake and related to available physical and chemical characteristics of the lakes. The relative content of MeHg increased with trophic level from 4.3 to 12.2% in periphyton, 41 to 79% in zooplankton, 59 to 72% in insects, and 74 to 100% in juvenile and adult char. The d¹³C signatures of adult char indicated coupling with benthic invertebrates. Cannibalism among char lengthened the food chain. Biomagnification was confirmed in all 18 lakes, with TMFs ranging from 3.5±1.1 to 64.3±0.8. Results indicate that TMFs and food chain length (FCL) are key factors in explaining interlake variability in biomagnification of [Hg] among different lakes.

Mercury is a heavy metal that bioaccumulates in living organisms, and its concentration increases along subsequent trophic levels; being highly toxic to humans and wildlife. It is naturally present in aquatic environments but is also released by human activities such as industrial and mining waste, amplified by increasing deforestation and erosion in drainage basins. Mercury methylation determines the toxicological consequences of antropic-induced release and the increase of mercury levels in the environment. Mercury levels are assessed in muscular tissues of fishes, which are consumed by humans as an important protein source. Samples of muscle, liver and kidney of 46 individuals of Pygocentrus nattereri, 20 from Paraguay River, locality of Descalvados(Cáceres – MT) and 26 from Bento Gomes River, Pantanal Mato-Grossense River (Poconé – MT); and 30 individuals of Crenicichla lepidota, collected in Bento Gomes River (Poconé – MT), during two seasons (rainy and dry). Samples (0.05g) were conditioned separately, kept frozen and subsequently undergone acid digestion; THg concentrations were determined by atomic absorption spectrometry with Flow Injection Mercury System (FIMS) and FIAS 400 with AS90 auto-sampler (Perkin Elmer, USA). All samples had THg concentrations below 0.500 µg.g^-1, which is the safe level established by the World Health Organisation (WHO). THg concentrations in Pygocentrus nattereri, however, varied from 0.044 µg.g^-1 to 0.468 µg.g^-1, indicating recent mercury contamination in sampled places with potential danger to human health. The highest mercury concentrations in Crenicichla lepidota were quantified with similar values in muscles (112.87 ± 46.3) and livers (110.86 ± 46.26) in the rainy season. During the dry season, the highest concentrations were found in sampled livers (0.253 ± 0.098). It is worth noting that, even though THg concentrations are below the safe level established by WHO, monitoring this metal is extremely relevant because riverside people in Pantanal of Mato Grosso have a daily diet of more than 400g of fish.

Muscle and liver samples of 93 and 38 yellowfin tuna (Thunnus albacores), respectively, caught by two Taiwanese long-line fishing vessels in Seychelles, Indian Ocean from April to December 2006, were used to analyze total mercury (THg) and organic mercury (OHg) contents. The overall THg and OHg concentrations were 0.206 ± 0.154 and 0.166 ± 0.125 mg kg^-1 wet weight for the muscles, and 0.250 ± 0.264 and 0.158 ± 0.153 mg kg^-1 wet weight for the livers. Highest THg and OHg of muscles were found for yellowfin tuna worldwide ever. Liver and muscle ratio were calculated for discussing the dietary shift and Hg pollution status. The linear relationships between liver and muscle were both established in THg and OHg. None of the samples contained the OHg levels above 1 mg kg^-1 wet weight and only 2 out of 93 muscle samples of the tuna from the Indian Ocean had levels of OHg above 0.5 mg kg^-1 wet weight set by US FDA and WHO for predatory and most fish meats, respectively.

There is a lack of studies on complex Hg dynamics and biogeochemical cycling in aquatic environments of Korea, especially in estuarine systems. The objective of this study was to examine distribution, historical trends, and trophic transfer of Hg in the Masan Bay. The Masan Bay, located in the southeastern coastal region of Korea, is a semi-enclosed bay with a sluggish water exchange and one of the most contaminated sites with various organic pollutants and heavy metals in Korea. Surface sediment samples were collected on five occasions from March of 2009 to May of 2010, while biota (invertebrates and fishes) samples were collected by SCUBA divers in August and September of 2009. Surface water samples were collected in August of 2009. For historical trends of Hg in sediments, about 1 m-long sediment cores were collected in September of 2009. Subsamples of biota and sediment cores were analyzed for carbon and nitrogen stable isotopes. THg and MeHg in surface water averaged 0.75±0.21 ng/L and 40.8±25.1 pg/L, respectively. THg and MeHg (% MeHg) in surface sediments ranged from 10.4 to 145 and from 0.05 to 0.38 (0.04 – 1.46 %) ng/g dw, respectively. While THg concentration in the Masan Bay was lower than other estuarine sediments, % MeHg was comparable, suggesting that MeHg production appeared to be high. For biota, MeHg concentration increased as trophic position increased. Food web magnification factors (FWMFs) for both THg (0.107) and MeHg (0.164) were slightly lower than what others found and this difference was likely due to the length of trophic levels and Hg concentrations in biota on a dry weight basis. Historical trends of THg in sediment cores indicated that Hg inputs increased with increasing anthropogenic activities. The overall results suggest that further studies are necessary for better understanding of Hg dynamics and trophic transfer in the Masan Bay.

Since the 19^th century, large amounts of industrial waste containing high concentrations of mercury (up to 436 µg/g) were dumped in a reservoir adjacent to a chlor-alkali plant in the lower Ebro River (NE Spain). Previous toxicological analysis of carp (Cyprinus carpio) populations inhabiting the surveyed area have shown that the highest biological impact occurs downstream of the discharge site. In the present study, various fish species were selected in order to investigate the bioavailability and bioaccumulation capacities of both total mercury (THg) and methylmercury (MeHg) in the discharge site and downstream points. Multiple Correspondence Analysis (MCA) was applied to reduce the dimensionality of the data set, and Multiple Linear Regression (MLR) models were conducted in order to assess the relationship between both THg and MeHg concentrations in fish and different variables of interest, namely sampling site, fish species, gender and length.

Experimental results showed that mercury levels in fish inhabiting the highly polluted dam where the discharge site is located were about twofold higher than those in the upstream site. Moreover, although the THg concentrations indicated that Hg in fish increased significantly with increasing trophic position, surprisingly, MeHg percentages were higher for non-piscivorous species than for piscivorous ones. This was an unexpected but and important finding, since the most efficient bioaccumulators of MeHg should be the piscivorous species located at the top of the food chain. Data suggest that MeHg contamination in aquatic organisms from a highly Hg-polluted environment might be explained by the habits, i.e. food, prey and ecology of the species, and is thus dominated by the amount of bioavailable MeHg rather than by differences in trophic level.

On the other hand, mercury pollution increased progressively downstream of the hot spot. In this sense, both THg and MeHg levels found in the farthest downstream point were three times greater than those close to the waste dump. This result clearly indicated a downstream transport and an increase of the bioavailability of mercury according with the distance to the source of contamination, which may ultimately affect the Ebro Delta Natural Park, the second most important wetland in Spain.

Overall recruitment of European eel (Anguilla anguilla) remarkably decreased since the early 1980ies, with observed losses of up to 99%. Although a coherent explanation for this phenomenon is still missing, several possible causes are under suspicion, among others: overfishing, oceanographic / climatic changes, migration inhibitors, parasites and infectious diseases and contamination of aquatic habitats with xenobiotics. Industrial contamination of river systems with toxic metals can have long-term effects on the metal body burdens. This is particularly true in the case of mercury which is not only converted from a relatively toxic inorganic specie to a very toxic organometal species (methylmercury, MeHg), but also bioaccumulates and biomagnifies in aquatic biota. The leptocephalus stage of eels is a key stage, characterized by the accumulation of energy stores for metamorphosis and estuarine migration. When they reach the continental shelf, they metamorphose into glass eels which enter estuaries on the French Atlantic coast and then migrate up estuaries without feeding.. They progressively acquire green and brown pigments to become yellow eels which colonized the watershed for a long fresh-water growth phase. Then, eels undergo a second metamorphosis into silver eels, and return to the Sargasso Sea to reproduce and die.

In this work, marine and estuarine glass eels were collected in different locations along the French Atlantic coast (Biscay Bay, France) Seasonal variations have been evaluated by different marine and estuarine sampling during the fishing season and the global temporal evolution was investigating with annual sampling from 2004 to 2009. A performant analytical method using GC-ICPMS for the determination of mercury species in glass eels has been used. The developed methodology is able to analyse the mercury species accurately and precisely using multiple species-specific isotope dilution, allowing to correct for species transformations during the analytical procedure. Low detection limits are achieved (0.007 - 0.17 mg Hg kg-1 for MeHg and IHg respectively) allowing the individual low mass sample analysis, even in the case of young state where the sample weighed some tens of mg. The mercury species concentrations levels determined for the different collected individual glass eels will be presented with regards to their morphological parameters, their growing state, and the seasonal, temporal and spatial distribution. The evaluation of the impact of MeHg bioaccumulation on their migratory behaviour will be also discussed by comparing bioaccumulation between glass eels presenting a high or low propensity to migrate.

The temporal trends of total mercury (THg) in four fish species in Lake Erie were evaluated based on 35 years of fish contaminant data. Our Bayesian statistical approach consists of three steps aiming to address different questions. First, we used the exponential and mixed-order decay models to assess the declining rates in four intensively studied fish species, i.e., the walleye (Stizostedion vitreum), the yellow perch (Perca flavescens), the smallmouth bass (Micropterus dolomieui), and the white bass (Morone chrysops). Because the two models postulate monotonic decrease of the THg levels, we included first- or second-order random error terms in our statistical formulations to accommodate non-monotonic patterns in the data time series. Our analysis reveals an increasing trend in the THg concentrations, which becomes particularly evident after the mid-90s. In the second step, we used double exponential models to quantify the relative magnitude of the THg trends depending on the type of data used (skinless-boneless fillet versus whole fish data) and the fish species examined. The observed THg concentrations were significantly higher in skinless boneless fillet than in whole fish portions, while the whole fish portions of walleye exhibited faster decline rates and slower rates of increase relative to the skinless boneless fillet data. Our analysis also shows lower decline rates and higher rates of increase in walleye relative to the other three fish species. Using skinless boneless fillet data, we introduced a double exponential hierarchical model to infer about the THg trends in four locations of the Lake Erie (Western Basin, Central Basin, Long Point Bay and Eastern Basin). Our results revealed that the contaminant decline rates were higher in Eastern Basin and Central Basin followed by Western Basin and Long Point Bay, whereas the fish samples collected from Eastern Basin exhibited relatively higher rate of increase in THg concentration as compared to other locations. The food web structural shifts induced by the invasive species (dreissenid mussels and round goby) may be associated with the recent THg trends in Lake Erie fish.

In the 80s, was the built the Port of Vila do Conde in the city of Barcarena, State of Pará, Brazil. Near the port was installed a industrial complex. In the last decade, numerous environmental accidents were recorded in this region. Two years ago, was implanted in a region to monitoring and control program that studies the accumulation of contaminants in sediments and possible absorption in biological materials into the aquatic ecosystem. Previous studies have shown that near industrialized regions has been occurring accumulation of toxic metals, as mercury, based mainly on atmospheric emissions or composition of the wastes carried into rivers. In 2009 and 2010, the possible accumulation of mercury in sediments and fish in the river Para, near the industrial complex and port Barcarena, were investigated. Were made four sediment sampling (16 points) and muscle tissue of 259 fish specimens. Sediments and fish samples were analyzed by CV-AAS (Akagi, 2004). For quality control were analyzed IAEA-SL-1 and DORM-2. The average levels of total mercury in sediments ranged from 0.064 to 0.346 µg/g, with higher levels found in November/2009. These results demonstrate that mercury in sediments of the Para River showed significant variations over two sampling years, a factor that may be indicative of a greater accumulation of mercury in sediments of this region over the years. The average total mercury in five species of carnivorous fish ranged from 0.020 to 0.250 µg/g in the first (N=65) and 0.070 to 0.160 µg/g in the second sampling (N=146). In the three carnivorous species not investigated the average levels of total mercury ranged from 0.050 to 0.180 µg/g in the first (N=21) and 0.020 to 0.130 µg/g in the second sampling (N=27). These results demonstrate that average mercury in carnivorous species is higher than the levels found in those non-carnivores. However, average levels for carnivorous species are below the limits recommended by WHO. Despite being a large river, the average levels of mercury in sediments of the Para river have been increasing, but not anomalous were recorded for fish in the region.

Shark populations globally have suffered recent declines due to overfishing, finning, and habitat degradation. Methylmercury (MeHg) is a contaminant suspected to affect reproduction of teleosts and, by extension, potentially elasmobranchs such as sharks. Here, we present data on mercury (Hg) and MeHg in sharks sampled near the coasts of Belize, Central America, and Florida, USA. We sampled muscle from 620 sharks (17 species) that included 171 individuals near Belize and 449 offshore of Florida. In 95% of the shark muscles sampled, total Hg concentrations exceeded the U.S. Environmental Protection Agency’s action level of 0.3 µg/g. Eighty-three percent exceeded the Florida Department of Environmental Protection human health advisory of 0.5µg/g and 63% exceeded both the World Health Organization (WHO) advisory level and the Federal Drug Administration (FDA) action level of 1.0 µg/g. A subset of muscle samples from Florida sharks (n = 41) contained greater than 95% of total Hg as MeHg. These concentrations of total Hg and MeHg exceed published effects levels for teleost fishes known to cause physiological, behavioral and reproductive harm. This study provides a baseline of total Hg and MeHg in shark muscle for these two regions of the Caribbean and points to the need for future research focused on impacts of MeHg and other contaminants on shark populations and individuals. Sharks have an important influence on human exposure to MeHg and, as top predators, in balancing food web dynamics. Sharks may be useful biomonitors of ecosystem health and human exposure in many coastal and open-ocean fisheries.

The aim of this study was to evaluate the Hg biomagnification in fishes of the Madeira River Basin (RO). Three fish species were selected for study, Rhaphiodon vulpinus (piscivorous) and two species of the genus Potamorhina spp (detritivorous). Fish were collected with gillnets and working out in four local stations (Belmont and Jatuarana Igarapés; Puruzinho and Cuniã Lakes). Approximately 200 mg (WW) of the fishes samples were digested with acid and total Hg determination by atomic absorption spectroscopy with cold vapor generation (CV-AAS, Flow Injection Mercury System-FIMS-400, Perkin-Elmer, Germany). The results for total mercury Rhaphiodon vulpinus (n = 23) ranged from 0.964 ± 0.090 mg.kg^-1 and 1.844 ± 1.304 mg.kg^-1 in the Belmont Igarapé and Cuniã Lake, respectively. The Potamorhina altamazonica (n = 51) ranged from 0.044 ± 0.011 mg.kg^-1 and 0.130 ± 0.068 mg.kg^-1 in the Cuniã Lake and Belmont Igarapé, respectively. The Potamorhina latior (n= 88) ranged from 0.056 ± 0.028 mg.kg^-1 to 0.167 ± 0.052 mg.kg^-1 in the Cuniã Lake and Belmont Igarapé, respectively. Biomagnification Factor (BMF) above of 1 indicates the occurrence of amplification along the food chain, which was observed in this study in relation to predator and prey. In the Belmont Igarapé the BMF ranged between 6 and 7; in Jatuarana Igarapé between 18 and 29; in Puruzinho Lake was 8 and Cuniã Lake between 31 and 39. The study shows that in all areas assessed biomagnification processes are occurring, including those more isolated as the Cuniã and Puruzinho Lakes.

Although fish mercury (Hg) levels have declined in portions of the Everglades over the past 20 years, levels remain a concern and mercury hotspots remain. One such hotspot is the Shark River in Everglades National Park (ENP). The Shark River Slough transitions from a shallow vegetated freshwater marsh into a series of interconnected mangrove lined creeks, which merge to form the Shark River extending to the Gulf of Mexico. Within the transitional zone creeks, previous monitoring indicates fish Hg levels that exceed all other areas within ENP. During the past decade, at North Prong Creek (site NP) in Shark Slough, annual mean Hg ranged from 0.91 to 2.37 µg/g for largemouth bass (LMB; Micropterus salmoides); from 0.60 to 1.73 µg/g for common snook (Centropomus undecimalis); and from 0.47 to 0.55 µg/g for grey snapper (Lutjanus griseus). No significant temporal trends (seasonal Kendall analyses; r = -0.018; P = 0.9164) were evident for LMB.

We report on fish Hg along a transect downstream from site NP to mid-river at Tarpon Bay (TB) and near the mouth at Little Shark River (LS). During September 2011, we collected two species with different feeding strategies (grey snapper and common snook) that occur across a range of salinities. Both demonstrated size-dependent bioaccumulation of Hg. For snapper, the only species collected at all three sites (n=39), differences in mercury bioaccumulation among the sites were evaluated by comparing slopes and elevations of regression lines of Hg vs TL using ANCOVA with TL as a covariate. There were no significant differences (P=0.732) in the slopes of regression lines indicating similar rates of mercury bioaccumulation. But site means differed significantly (df=1,2; P <0.001 ), declining seaward indicating similar gradients in ambient methyl-mercury. Mean snapper Hg was 0.45 µg/g (range; 0.19 – 0.76 µg/g) at upstream site NP; 0.15 µg/g (0.06 – 0.25 µg/g) at midstream site TB; and 0.05 µg/g (0.03 – 0.09 µg/g) at downstream site LS. Mean snook Hg was 0.74 µg/g (range; 0.33 – 1.25 µg/g) at upstream site NP and 0.41 µg/g (range; 0.18 – 0.68 µg/g) at site TB. None were collected from LS. Current results were consistent with previously reported values from NP and nearby Florida Bay.

To explain the observed gradients in fish Hg levels, additional fish, water, and sediment sampling is proceeding to better understand mercury transport and transformation processes and food web interactions in this estuarine system.

Methylmercury contamination in fish is of particular concern because consumption of fish is the primary source of mercury to humans and other wildlife. Mercury from both natural and anthropogenic sources accumulates in fish tissue at concentrations which are influenced by a large number of factors. For example, disturbance in the watershed by forest management or wildfire alters hydrologic and soil processes and plant communities thereby increasing the risk of altering the cycling and bioavailability of mercury in the terrestrial and aquatic ecosystem. The objective of this study is to evaluate how watershed characteristics, particularly disturbance within watersheds, are associated with the concentration of methylmercury in fish. Information on fish contamination levels, fish community structure and lake characteristics was collected by the Broadscale Fisheries Management Program (BSFM), a collaboration between the Ontario Ministries of Natural Resources and Environment. The BSFM program has been monitoring fish community diversity, sport fish abundance, invasive species and fish contaminant levels on a large number of lakes across Ontario since 2008. Watershed characteristics, including forest harvesting and fire disturbance, geology, wetland area, topography and forest type, will be summarized using a geographic information system (GIS) analysis of provincial spatial databases. The study will focus on lakes in the boreal region where forest management and fire are the primary disturbance agents and where many remote lakes have fish with unacceptably high levels of mercury. Preliminary results will be presented for the most abundant sport fish in the area: lake trout (Salvelinus namaycush), northern pike (Esox lucius), and walleye (Sander vitreus). It is hypothesized that a portion of the variability in mercury levels in these fish species can be explained by watershed characteristics, particularly disturbance, and that these characteristics can be used to identify mercury sensitive lakes. Improved decision making regarding future land use prescriptions could be developed based on consideration of these sensitive ecosystems.