Trace Element Concentrations and Bioindicator Responses in Tree Swallows from Northwestern Minnesota

Extremely high concentrations of cadmium (3.5 μg/g dry wgt.) and elevated concentrations of chromium (>10 μg/g dry wgt.) and mercury (1.6 μg/g dry wgt.) were reported in waterbird tissues at Agassiz National Wildlife Refuge in northwestern Minnesota in 1994. Tree swallows (Tachycineta bicolor) were studied during 1998–2001 at three drainages into the Refuge, two pools on the Refuge, and at a nearby reference location to document whether high levels of contaminants were still present, and if so to quantify the source and severity of the contamination. Trace elements were measured in tree swallow eggs, livers, and diet. Reproductive success and bioindicator responses were monitored. In 2000, water was drawn down on Agassiz Pool, one of the main pools on the Refuge. This presented an opportunity to evaluate the response of trace element concentrations in the diet and tissues of tree swallows after reflooding. High concentrations of trace elements were not detected in swallow tissues, nor were there differences among locations. Less than 20% of swallow samples had detectable concentrations of cadmium or chromium. Mercury concentrations were low and averaged <0.25 μg/g dry wgt. in swallow tissues. Trace elements, including mercury, did not increase in tree swallows following the 2000 drawdown at Agassiz Pool. Hatching success and survival of nestlings to 12 days-of-age for tree swallows on the Refuge were similar to the national average and consistent with background trace element concentrations. Bioindicator measurements were within the normal ranges as well.     

Controls on Mercury and Methylmercury Deposition for Two Watersheds in Acadia National Park, Maine

Throughfall and bulk precipitation samples were collected for two watersheds at Acadia National Park, Maine, from 3 May to 16 November 2000, to determine which landscape factors affected mercury (Hg) deposition. One of these watersheds, Cadillac Brook, burned in 1947, providing a natural experimental design to study the effects of forest type on deposition to forested watersheds. Sites that face southwest received the highest Hg deposition, which may be due to the interception of cross-continental movement of contaminated air masses. Sites covered with softwood vegetation also received higher Hg deposition than other vegetation types because of the higher scavenging efficiency of the canopy structure. Methyl mercury (MeHg) deposition was not affected by these factors. Hg deposition, as bulk precipitation and throughfall was lower in Cadillac Brook watershed (burned) than in Hadlock Brook watershed (unburned) because of vegetation type and watershed aspect. Hg and MeHg inputs were weighted by season and vegetation type because these two factors had the most influence on deposition. Hg volatilization was not determined. The total Hg deposition via throughfall and bulk precipitation was 9.4 μg/m²/year in Cadillac Brook watershed and 10.2 μg/m²/year in Hadlock Brook watershed. The total MeHg deposition via throughfall and bulk precipitation was 0.05 μg/m²/year in Cadillac Brook watershed and 0.10 μg/m²/year in Hadlock Brook watershed.     

Extreme Spatial Variability and Unprecedented Methylmercury Concentrations Within a Constructed Wetland

We began monitoring concentrations of both total mercury (THg) and methylmercury (MeHg) in surface water at Stormwater Treatment Area-2 (STA) on July 20, 2000. This 2602 hectare STA was constructed with three independent marshes to remove phosphorus from agricultural runoff and reduce eutrophication in the northern Everglades. However, there was concern that in doing so, STA-2 might inadvertently worsen the existing mercury problem in the Everglades. Accordingly, operating permits stipulated that flow-through operation of these treatment cells could not begin until concentrations of THg and MeHg in the interior marsh were not significantly greater than corresponding concentrations in the supply canal. Cells 2 and 3 quickly met the start-up criteria in the fall of 2000. In contrast, Cell 1 exhibited anomalously high MeHg concentrations in the fall of 2000 and 2001, and the summer of 2002. During the last such event, water-column concentrations in Cell 1 reached 32 ng THg/L and an unprecedented 20 ng MeHg/L. Tissue Hg in resident fishes reached levels as high as 430 ng/g in mosquitofish, Gambusia holbrooki, 930 ng/g in sunfish, Lepomis spp., and 2000 ng/g in largemouth bass, Micropterus salmoides. Guided by results from the monitoring program, flow rate and water depth were managed as a means to alter sulfur biogeochemistry and, thereby, reduce in situ mercury methylation. This adaptive management strategy likely played a role in the decline in water-column concentrations of THg and MeHg in Cell 1 by late 2002 and the subsequent declines in tissue Hg levels in resident fishes. Cell 1 finally met formal start-up criteria on November 26, 2002.     

Mercury Contamination of Biota from Acadia National Park, Maine: A Review

We reviewed literature reporting both total and methylmercury from biota from Acadia National Park, Maine, USA. Our review of existing data indicates that 1) mercury contamination is widespread throughout the Park’s various aquatic ecosystems; 2) mercury pollution likely represents a moderate to high risk to biota inhabiting the Park; and 3) biota at all trophic levels possess elevated concentrations of both total and methylmercury. Watershed fire history and the resulting post-fire forest succession patterns are an important landscape attribute governing mercury cycling at Acadia National Park. Therefore, park service personnel should consider these factors when planning and implementing Hg biomonitoring efforts. Additional baseline funding from the National Park Service for Hg research and biomonitoring will likely be required in order to further evaluate the spatial and temporal patterns of mercury contamination in the park’s biota. An erratum to this article can be found at     

Transfer of mercury in the marine food web of West Greenland

Total mercury (THg), methylmercury (MeHg) and stable isotopes of nitrogen (delta(15)N) and carbon (delta(13)C) were measured in three invertebrate, five fish, three seabird and three marine mammal species of central West Greenland to investigate trophic transfer of mercury in this Arctic marine food web. The food web magnification factor (FWMF) estimated as the slope of the regression between the natural logarithm of THg or MeHg concentrations (mg kg(-1) dw) and tissue delta(15)N ( per thousand) was estimated to 0.183 (SE = 0.052) for THg and 0.339 (SE = 0.075) for MeHg. The FWMFs were not only comparable with those reported for other Arctic marine food webs but also with quite different food webs such as freshwater lakes in the sub-Arctic, East Africa and Papua New Guinea. This suggests similar mechanisms of mercury assimilation and isotopic (delta(15)N) discrimination among a broad range of aquatic taxa and underlines the possibility of broad ecosystem comparisons using the combined contaminant and stable isotope approach.     

Heavy metal and selenium levels in birds at Agassiz National Wildlife Refuge,Minnesota: Food chain differences

The levels of heavy metals and selenium in the eggs and in breast feathers of adult doublecrested cormorant (Phalacrocorax auritus), black-crowned night heron (Nycticorax nycticorax), and franklin's gull (Larus pipixcan) nesting at Agassiz National Wildlife Refuge in Marshall County, northwestern Minnesota were examined. Also examined were metal levels in the feathers of fledgling night herons and gulls, in the feathers of adult and fledgling American bittern (Botaurus lentiginosus), in eggs of American coot (Fulica americana) and eared grebe (Podiceps caspicus), and in feathers of adult Canada geese (Branta canadensis). These species represent different levels on the food chain from primarily vegetation-eating species (geese, coot) to species that eat primarily fish (cormorant). A clear, positive relationship between level on the food chain and levels of heavy metals occurred only for mercury in feathers and eggs. Otherwise, eared grebes had the highest levels of all other metals in their eggs compared to the other species. No clear food chain pattern existed for feathers for the other metals. For eggs at Agassiz: 1) lead, selenium, and manganese levels were similar to those reported in the literature, 2) mercury levels were slightly higher for cormorants and night herons, 3) all species had higher chromium and cadmium levels than generally reported, and 4) eared grebes had significantly higher levels of cadmium than reported for any species from elsewhere. For adult feathers: 1) gulls had higher levels of lead than the other species, 2) cadmium levels were elevated in gulls and adult herons and cormorants, 3) mercury levels showed an increase with position on the food chain, 4) selenium and chromium levels of all birds at Agassiz were generally low and 5) manganese levels in adults were generally higher than in the literature for other species. Adults had significantly higher mercury levels than fledgling gulls, night herons, and bitterns.     

Assessment of metals in down feathers of female common eiders and their eggs from the Aleutians: arsenic, cadmium, chromium, lead, manganese, mercury, and selenium

Concentrations of arsenic, cadmium, chromium, lead, manganese, mercury and selenium were examined in the down feathers and eggs of female common eiders (Somateria mollissima) from Amchitka and Kiska Islands in the Aleutian Chain of Alaska to determine whether there were (1) differences between levels in feathers and eggs, (2) differences between the two islands, (3) positive correlations between metal levels in females and their eggs, and (4) whether there was more variation within or among clutches. Mean levels in eggs (dry weight) were as follows: arsenic (769 ppb, ng/g), cadmium (1.49 ppb), chromium (414 ppb), lead (306 ppb), manganese (1,470 ppb), mercury (431 ppb) and selenium (1,730 ppb). Levels of arsenic were higher in eggs, while chromium, lead, manganese, and mercury were higher in feathers; there were no differences for selenium. There were no significant interisland differences in female feather levels, except for manganese (eider feathers from Amchitka were four times higher than feathers from Kiska). Levels of manganese in eggs were also higher from Amchitka than Kiska, and eider eggs from Kiska had significantly higher levels of arsenic, but lower levels of selenium. There were no significant correlations between the levels of any metals in down feathers of females and in their eggs. The levels of mercury in eggs were below ecological benchmark levels, and were below human health risk levels. However, Aleuts can seasonally consume several meals of bird eggs a week, suggesting cause for concern for sensitive (pregnant) women.     

Mercury and methyl mercury ratios in caimans (Caiman crocodilus yacare) from the Pantanal area, Brazil

The Pantanal region is the largest floodplain area in the world and of great biological importance due to its unique flora and fauna. This area is continuously undergoing increasing anthropogenic threats, and has also experienced mercury contamination associated with gold mining and other anthropogenic activities. Pantanal caimans are top-level predators, and, as such, show great potential to accumulate mercury (Hg) by biomagnification. In this study 79 specimens from four locations in the Pantanal were analyzed for total Hg and methyl mercury (MeHg) by cold vapor atomic absorption spectrometry. Total Hg contents ranged from 0.02 to 0.36 μg g(-1) (ww), and most specimens presented MeHg ratios above 70%. One of the sites, impacted by anthropogenic activities, presented significantly higher total Hg in comparison to three less impacted sites, supporting the hypothesis that caimans can, in fact, be considered effective bioindicators of ecosystem health.     

Methyl mercury in fish—a case study on various samples collected from Ganges river at West Bengal

This study investigated the presence of total mercury (Hg) and organic mercury levels in the muscle of 19 common fresh water fish species captured from river Ganges, West Bengal, India. The total mercury level found in our study may not cause any toxic effect, but the methyl mercury (MeHg) level in some freshwater fish species was surprisingly very high and toxically unacceptable. The results of mercury analysis in various specimens indicated that some fish muscles tended to accumulate high levels of Hg, and approximately 50–84% of Hg was organic mercury. A strong positive correlation between mercury levels in muscle with food habit and fish length (age) was found. Wallago attu possessed the highest amount of organic mercury in their muscle tissues, and it was 0.93 ± 0.61 μg Hg/g of wet weight. Whereas in small-sized fishes Eutropiichthys murius, Puntius sarana, Cirrhinus mrigala, Mystus vittatus or Mystus gulio, and Tilapia mossambicus, it was below the detection limit. Contamination in Catla catla (0.32 ± 0.11), Anguilla bengalensis bengalensis (0.26 ± 0.07 μg Hg/g), Chitala chitala (0.25 ± 0.18), Rita rita (0.34 ± 0.14), and Ompok pabda (0.26 ± 0.04) was also above the 0.25 μg Hg/g of wet weight, the limit set by the PFA for the maximum level for consumption of fish exposed to MeHg. Though in Labeo rohita (0.12 ± 0.03), Mastacembelus armatus (0.17 ± 0.02), Pangasius pangasius (0.12 ± 0.16), Bagarius bagarius (0.12 ± 0.01), and Clupisoma garua (0.1 ± 0.01), concentration was below the recommended level, in Lates calcarifer (0.23 ± 0.0) and Mystus aor (0.23 ± 0.1), it was threatening. Interestingly, a low concentration of Hg was found in post-monsoon samples.     

Factors affecting food chain transfer of mercury in the vicinity of the Nyanza Site,Sudbury River,Massachusetts

The influence of the Nyanza Chemical Waste Dump Superfund Site on the Sudbury River, Massachusetts, was assessed by analysis of sediment, fish prey organisms, and predator fish from four locations in the river system. Whitehall Reservoir is an impoundment upstream of the site, and Reservoir #2 is an impoundment downstream of the site. Cedar Street is a flowing reach upstream of the site, and Sherman Bridge is a flowing reach downstream of the site. Collections of material for analysis were made three times, in May, July, and October. Sediment was analyzed for acid-volatile sulfide (AVS), simultaneously-extracted (SEM) metals (As, Cd, Cr, Hg, Pb, Sb, Zn), and total recoverable Hg. The dominant predatory fish species collected at all sites, largemouth bass (Micropterussalmoides), was analyzed for the same suite of metals as sediment. Analysis of stomach contents of bass identified smallfish (yellow perch Perca flavescens, bluegill Lepomismacrochirus, and pumpkinseed Lepomis gibbosus), crayfish,and dragonfly larvae as the dominant prey organisms. Samples of the prey were collected from the same locations and at the sametimes as predator fish, and were analyzed for total and methyl mercury. Results of AVS and SEM analyses indicated that sediments were not toxic to aquatic invertebrates at any site. The SEM concentrations of As, Cd, and Cr were significantly higher at Reservoir #2 than at the reference sites, and SEM As and Cdwere significantly higher at Sherman Bridge than at Cedar St. Sediment total Hg was elevated only at Reservoir #2. Hg washigher at site-influenced locations in all fish speciesexcept brown bullhead (Ameiurus nebulosus). Cd washigher in bluegill, black crappie (Pomoxis nigromaculatus),and brown bullhead, and Cr was higher in largemouth bass filletsamples but not in whole-body samples. There were no seasonal differences in sediment or prey organism metals, but some metalsin some fish species did vary over time in an inconsistent manner. Predator fish Hg concentration was significantly linearlyrelated to weighted prey organism methyl Hg concentration. Largemouth bass Hg was significantly lower at Reservoir #2 in our study than in previous investigations in 1989 and 1990. High concentrations of inorganic Hg remain in river sediment asa result of operation of the Nyanza site, and fish Hg concentrations in river reaches downstream of the site areelevated compared to upstream reference sites. However, thedifferences are relatively small and Hg concentrations inlargemouth bass from the site-influenced locations are nohigher than those from some other, nearby uncontaminatedsites. We hypothesize that this results from burial ofcontaminated sediment with cleaner material, which reducesbioavailability of contaminants and possibly reducesmethylation of mercury.     

Mass Balances of Mercury and Nitrogen in Burned and Unburned Forested Watersheds at Acadia National Park, Maine, USA

Precipitation and streamwater samples were collected from 16 November 1999 to 17 November 2000 in two watersheds at Acadia National Park, Maine, and analyzed for mercury (Hg) and dissolved inorganic nitrogen (DIN, nitrate plus ammonium). Cadillac Brook watershed burned in a 1947 fire that destroyed vegetation and soil organic matter. We hypothesized that Hg deposition would be higher at Hadlock Brook (the reference watershed, 10.2 μg/m²/year) than Cadillac (9.4 μg/m²/year) because of the greater scavenging efficiency of the softwood vegetation in Hadlock. We also hypothesized the Hg and DIN export from Cadillac Brook would be lower than Hadlock Brook because of elemental volatilization during the fire, along with subsequently lower rates of atmospheric deposition in a watershed with abundant bare soil and bedrock, and regenerating vegetation. Consistent with these hypotheses, Hg export was lower from Cadillac Brook watershed (0.4 μg/m²/year) than from Hadlock Brook watershed (1.3 μg/m²/year). DIN export from Cadillac Brook (11.5 eq/ha/year) was lower than Hadlock Brook (92.5 eq/ha/year). These data show that ∼50 years following a wildfire there was lower atmospheric deposition due to changes in forest species composition, lower soil pools, and greater ecosystem retention for both Hg and DIN.     

Biogeochemistry of mercury and methylmercury in sediment cores from Sundarban mangrove wetland, India—a UNESCO World Heritage Site

This study was performed to elucidate the distribution, concentration trend and possible sources of total mercury (Hg(T)) and methylmercury (MeHg) in sediment cores (<63 μm particle size; n?=?75) of Sundarban mangrove wetland, northeastern part of the Bay of Bengal, India. Total mercury was determined by atomic absorption spectrometry (AAS) in a Leco AMA 254 instrument and MeHg by gas chromatography-atomic fluorescence spectrometry (GC-AFS). A wide range of variation in Hg(T) (0.032-0.196 μg g(-1) dry wt.) as well as MeHg (0.04-0.13 ng g(-1) dry wt.) concentrations revealed a slight local contamination. The prevalent low Hg(T) levels in sediments could be explained by sediment transport by the tidal Hugli (Ganges) River that would dilute the Hg(T) values via sediment mixing processes. A broader variation of MeHg proportions (%) were also observed in samples suggesting that other environmental variables such as organic carbon and microbial activity may play a major role in the methylation process. An overall elevated concentration of Hg(T) in surface layers (0-4 cm) of the core is due to remobilization of mercury from deeper sediments. Based on the index of geoaccumulation (I (geo)) and low effects-range (ER-L) values, it is considered that the sediment is less polluted by Hg(T) and there is less ecotoxicological risk. The paper provides the first information of MeHg in sediments from this wetland environment and the authors strongly recommend further examination of Hg(T) fluxes for the development of a detailed coastal MeHg model. This could provide more refine estimates of a total flux into the water column.     

Watershed Nitrogen and Mercury Geochemical Fluxes Integrate Landscape Factors in Long-term Research Watersheds at Acadia National Park, Maine, USA

This paper is an overview of this special issue devoted to watershed research in Acadia National Park (Acadia NP). The papers address components of an integrated research program on two upland watersheds at Acadia NP, USA (44° 20′ N latitude; 68° 15′ E longitude). These watersheds were instrumented in 1998 to provide a long-term foundation for regional ecological and watershed research. The research was initiated as part of EPA/NPS PRIMENet (Park Research and Intensive Monitoring of Ecosystems Network), a system of UV-monitoring stations and long-term watershed research sites located in US national parks. The initial goals at Acadia NP were to address research questions about mercury, acid rain, and nitrogen saturation developed from prior research. The project design was based on natural differences in forests and soils induced by an intense wildfire in one watershed in 1947. There is no evidence of fire in the reference watershed for several hundred years. We are testing hypotheses about controls on surface water chemistry, and bioavailability of contaminants in the contrasting watersheds. The unburned 47-ha Hadlock Brook watershed is 70% spruce-fir mature conifer forest. In contrast, burned 32-ha Cadillac Brook watershed, 4 km northeast of the Hadlock watershed, is 20% regenerating mixed northern hardwoods and 60% shrub/rocky balds. Differences in atmospheric deposition are controlled primarily by forest stand composition and age. The watersheds are gauged and have water chemistry stations at 122 m (Cadillac) and 137 m (Hadlock); watershed maximum elevations are 468 and 380 m, respectively. The stream water chemistry patterns reflect, in part, the legacy of the intense fire, which, in turn, controls differences in forest vegetation and soil characteristics. These factors result in higher nitrogen and mercury flux from the unburned watershed, reflecting differences in atmospheric deposition, contrasting ecosystem pools of nitrogen and mercury, and inferred differences in internal cycling and bioavailabilty.     

Mercury and other metals in eggs and feathers of glaucous-winged gulls (Larus glaucescens) in the Aleutians

Levels of mercury and other contaminants should be lower in birds nesting on isolated oceanic islands and at high latitudes without any local or regional sources of contamination, compared to more urban and industrialized temperate regions. We examined concentrations of arsenic, cadmium, chromium, lead, manganese, mercury and selenium in the eggs, and the feathers of fledgling and adult glaucous-winged gulls (Larus glaucescens) nesting in breeding colonies on Adak, Amchitka, and Kiska Islands in the Aleutian Chain of Alaska in the Bering Sea/North Pacific. We tested the following null hypotheses: 1) There were no differences in metal levels among eggs and feathers of adult and fledgling glaucous-winged gulls, 2) There were no differences in metal levels among gulls nesting near the three underground nuclear test sites (Long Shot 1965, Milrow 1969, Cannikin 1971) on Amchitka, 3) There were no differences in metal levels among the three islands, and 4) There were no gender-related differences in metal levels. All four null hypotheses were rejected at the 0.05 level, although there were few differences among the three test sites on Amchitka. Eggs had the lowest levels of cadmium, lead, and mercury, and the feathers of adults had the lowest levels of selenium. Comparing only adults and fledglings, adults had higher levels of cadmium, chromium, lead and mercury, and fledglings had higher levels of arsenic, manganese and selenium. There were few consistent interisland differences, although levels were generally lower for eggs and feathers from gulls on Amchitka compared to the other islands. Arsenic was higher in both adult feathers and eggs from Amchitka compared to Adak, and chromium and lead were higher in adult feathers and eggs from Adak compared to Amchitka. Mercury and arsenic, and chromium and manganese levels were significantly correlated in the feathers of both adult and fledgling gulls. The feathers of males had significantly higher levels of chromium and manganese than did females. The levels of most metals in feathers are below those known to be associated with adverse effects in the gulls or their predators. However, levels of mercury in some gull eggs are within a range suggesting that several eggs should not be eaten in one day by sensitive humans.     

Mercury proxies and mercury dynamics in a forested watershed of the US Northeast

Although many studies focus on mercury (Hg) and methylmercury (MeHg) dynamics in streams, challenges remain in identifying the relative importance of land cover and seasonality at regulating Hg and MeHg dynamics at the watershed scale. Developing robust proxies for Hg and/or MeHg determination also remains a challenge. Our study used Hg, MeHg, and dissolved organic carbon (DOC) concentration measurements and various DOC fluorescence indices to characterize Hg and DOC dynamics in a forested watershed of the US Northeast. Principal component analysis indicated that land cover/landscape position (i.e., headwater vs. wetland-influenced area vs. lake-influenced area) explained 44 % of the variance in Hg, MeHg, DOC concentrations, and DOC quality during the snow-free season, while seasonality (i.e., air temperature and discharge) explained only 21 % of the variance in the results. Furthermore, finding a good proxy for Hg that is valid across a range of landscape positions remains a challenge; however, regression analysis indicated that the fluorescence peak Humic C (excitation?=?350 nm; emission?=?max (420–480)), which corresponds to the presence of melanoidins in water, explained 21 % of the variability in MeHg concentrations across both space and time (p?=?0.001), and thus appears to be a possible proxy for MeHg determination in our study watershed. From a management perspective, land cover modifications (lake, reservoir, and wetland) are likely to play more important roles at regulating Hg, MeHg, and DOC exports at the watershed scale than long-term changes in the climate of this region.     

Little Egrets (Egretta Garzetta) and Trace-Metal Contamination in Wetlands of China

The rapidly developing Asian countries may face threatening environmental contamination, that however remains largely unassessed. We studied persistent trace elements in three wetlands, Poyang Lake, relatively unpolluted, and Tai Lake, and Pearl River Delta, selected as hotspots of pollution in Central China. We adopted as indicator the Little Egret, a widespread colonial waterbird, and during 1999 and 2000 we collected and analysed the same samples as for a parallel study we conducted in Pakistan, e.g. eggs, body feathers of chicks, prey spontaneously regurgitated by the chicks, and sediments at the areas most used by foraging egrets. The levels of trace-metals at our three study areas were similar, or within the range, of those found in the few other studies for East Asia, with few exceptions. The concentrations of the various elements were below the threshold that may affect the survival or reproduction of the birds, and even the highest concentrations relative to background, i.e. Se in eggs, and Hg in feathers at Pearl Delta, do not pose toxic hazards. In sediments, the levels of trace elements were lower than the critical levels assumed for contaminated soil, except for alarming high levels of As at Poyang. These results do not confirm our expectation, that Poyang was relatively uncontaminated, while Tai and Pearl were polluted. Although trace metal concentration differed significantly among the three study areas, these differences were minor and were not consistent among elements and samples. The bioaccumulation ratios from sediments through prey, feather and egg, were consistent with our previous findings for Pakistan. Only Hg exhibited high bioaccumulation, while Se and Zn had low accumulation, and the other elements no accumulation. This reasserts that feathers of predators such as egrets, may be more sensitive indicators of environmental contamination for the elements subject to bioaccumulation, whereas the sediments or the organisms low in the food chain are better indicators for the other elements.     

The value of chick feathers to assess spatial and interspecific variation in the mercury contamination of seabirds

In 1991 we compared eggs, down and body feathers of chicks of Common Terns, Herring Gulls and Black-headed Gulls in their utility to assess contamination with mercury. Like eggs feathers distinctly show interspecific and intersite differences in contamination. Highest levels were found in Common Terns, lowest in Black-headed Gulls. Chicks hatched at the Elbe had much higher mercury levels than those in other areas of the German North Sea coast. Conversion ratios between tissues have to be used with caution.     

Relationship of methyl mercury accumulation with lipid and weight in two river cat fish species, Wallagoo attu and Mystus aor, from West Bengal, India

This study focuses on mercury (Hg) bioaccumulation in Indian cat fish, Wallagoo attu and Mystus aor, from different rivers. Methyl mercury (MeHg) concentrations were determined in muscle tissue of two different parts, ventral and dorsal part, of each species and the levels of organic mercury were co-related with lipid content of each part. The MeHg concentrations increased in a linear fashion with both weight and age for these river species. The average concentration of MeHg was found to be 0.93?±?0.60 and 1.26?±?0.62 μg Hg g^?1 (expressed in wet weight basis) for ventral and dorsal parts, respectively in W. attu and this was above the 0.25 μg Hg g^?1 of wet weight, the limit set by the Prevention of Food Adulteration Act for the maximum level for consumption of fish exposed to mercury pollution. In M. Aor the concentration of MeHg was not above the standard limit but threatening, it was 0.22?±?0.07 and 0.23?±?0.08 μg Hg g^?1 (expressed in wet weight basis) in dorsal and ventral parts, respectively.     

Seasonal and Inter-Annual Variations in Methyl Mercury Concentrations in Zooplankton from Boreal Lakes Impacted by Deforestation or Natural Forest Fires

We compared the effects of natural and anthropogenic watershed disturbances on methyl mercury (MeHg) concentration in bulk zooplankton from boreal Shield lakes. MeHg in zooplankton was monitored for three years in nine lakes impacted by deforestation, in nine lakes impacted by wildfire, and in twenty lakes with undisturbed catchments. Lakes were sampled during spring, mid- and late summer. MeHg in zooplankton showed a seasonal trend: concentrations were the lowest in spring, then peaked in mid-summer and decreased in late summer. Over the three study years, MeHg concentrations observed in mid-summer in zooplankton from forest harvested lakes were significantly higher than in reference and fire-impacted lakes, whereas differences between these two groups of lakes were not significant. The pattern of distribution of MeHg in zooplankton during the different seasons paralleled that of dissolved organic carbon (DOC), which is known as a vector of Hg from watershed soils to lake water. Besides DOC, MeHg in zooplankton also showed a positive significant correlation with epilimnetic temperature and sulfate concentrations. An inter-annual decreasing trend in MeHg was observed in zooplankton from reference and fire-impacted lakes. In forest harvested lakes, however, MeHg concentrations remained higher and nearly constant over three years following the impact. Overall these results indicate that the MeHg pulse observed in zooplankton following deforestation by harvesting is relatively long-lived, and may have repercussions to the accumulation of MeHg along the food chain. Therefore, potential effects of deforestation on the Hg contamination of fish should be taken into account in forest management practices.     

Environmental contaminants in male river otters from Oregon and Washington, USA, 1994–1999

This study reports hepatic concentrations and distribution patterns of select metals, organochlorine pesticides (OCs), polychlorinated biphenyls (PCBs), polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs) in 180 male river otters (Lontra canadensis) collected from Oregon and Washington, 1994-1999. Seven regional locations of western Oregon and Washington were delineated based on associations with major population centers, industry or agriculture. Cadmium (Cd) was not found above 0.5 microg g(-1), dry weight (dw) in juveniles, but increased with age in adults though concentrations were generally low (nd-1.18 microg g(-1), dw). Regional geometric means for total mercury (THg) ranged from 3.63 to 8.05 microg g(-1), dw in juveniles and 3.46-12.6 microg g(-1) (dw) in adults. The highest THg concentration was 148 microg g(-1), dw from an apparently healthy adult male from the Olympic Peninsula of Washington. Although THg increased with age in adult otters, the occurrence of the more toxic form methylmercury (MeHg) was not evaluated. Mean OC and PCB concentrations reported in this study declined dramatically from those reported in 1978-1979 from the lower Columbia River. Organochlorine pesticide and metabolite means for both juvenile and adult river otter males were all below 100 microg kg(-1), wet weight (ww), with only DDE, DDD and HCB having individual concentrations exceeding 500 microg kg(-1), ww. Mean SigmaPCB concentrations in both juvenile and adult male otters were below 1 microg g(-1) for all regional locations. Mean juvenile and adult concentrations of non-ortho substituted PCBs, PCDDs and PCDFs were in the low ng kg(-1) for all locations studied.