Concentrations and amounts of methylmercury in water and fish in the limed and acid basins of a small lake

Three months after neutralization concentrations of methylmercury (MeHg) were higher in the water of the limed than in the control basin of a small lake. After two years, the concentrations in the limed basin were somewhat lower than in the control (0.056–2.19 ng L^?1 and 0.129–2.65 ng L^?1, respectively). The highest concentrations were found in the anoxic hypolimnia. The total amount of MeHg in the water mass of the lake varied from 19 to 68 mg, showing a drop after spring and autumn overturns and a maximum during stratification periods. The total Hg concentrations of fish in L. Iso Valkjärvi varied from 0.06 to 0.14 μg g^?1 (ww) in whitefish to 0.1 to 0.7 μg g^?1 in perch and to 0.2 to 1.4 μg g^?1 in pike. The total amount of MeHg bound in the fish of the lake was quite similar to that in the water column, 43 to 59 mg in 1990–1993, 33 to 47 mg of which was in the perch population.     

A Preliminary Assessment of Wet Deposition and Episodic Transport of Total and Methyl Mercury from Low Order Blue Ridge Watersheds,S.E. U.S.A.

Results from a preliminary sampling program designed to investigate total (THg) and methyl Hg (MeHg) deposition, cycling and transport at the Coweeta Hydrologic Laboratory western North Carolina are presented. Wet deposition samples were collected in June and July 1994 and throughfall, seep and streamwaters were intensively collected during and after a rainfall event in June 1994. All water samples were collected using ultra clean trace sampling protocol. Low elevation Watershed 18 streamwater THg concentrations peaked with discharge, increasing 6 fold to 9 ng L^-1. High elevation Watershed 27 which received less than one half the precipitation Watershed 18 received during the event, exhibited THg concentrations only 1.3 times over base flow conditions. Methyl Hg concentrations remained near detection limits (≤ 0.025 ng L^-1) in both streams. Dissolved MeHg concentrations were higher in shallow seep (0.097 ng L^-1), throughfall (0.135 ng L^-1) and precipitation (0.16 – 0.035 ng L^-1) than streamwaters. Initial estimates of annual THg and MeHg deposition and transport indicate >90% retention of Thg and a >80% retention or demethylation of wet deposition MeHg is occurring in these low order watersheds.     

Methylmercury Production and Accumulation in Sediments and Soils of an Amazonian Floodplain – Effect of Seasonal Inundation

This study investigated the spatialand seasonal variations of MeHg concentrations andburdens of different sediments and soils of theTapajós river floodplain, one of the majorclear-water tributaries of the Amazon. The smallfloodplain of the Tapajós is typical of Amazonianfloodplain ecosystems. The studied lakes are borderedby inundated forest (igapó), while floatingmacrophyte mats (Paspalum sp.) develop at themargin of lakes during the flooded season. During theflood, we observed very low MeHg concentrations in theopen water lake sediments (<0.5 ng g^-1 d.w or<0.5 μg m^-2 cm^-1 d.w.) as compared to thesemi-aquatic sediments of the macrophyte zone (0.2–1.4 ng g^-1 d.w or 1–3 μg m^-2cm^-1 d.w.) and the igapó semi-terrestrial soils (0.2–3 ng g^-1 d.w or2–12 μg m^-2 cm^-1 d.w.). The litter horizon fromthe igapó soils showed the highest value of MeHg(4–8 ng g^-1 d.w.) representing 0.2–2 μg m^-2cm^-1 d.w. at the sediment/water interface during theaquatic phase. The inundation had no effect on theconcentrations and burdens of MeHg in the sediment ofthe central part of the lake. The inundation had aclear effect on the methylation of Hg at the surfaceof semi-aquatic shoreline sediments (macrophyte zone)and semi-terrestrial forest soils, where MeHgconcentrations and burdens appeared to be 3 timesgreater following inundation. In all cores, total Hgconcentrations follow those of Fe and Aloxy-hydroxides, whereas the MeHg concentrations arelinked to organic matter quality and quantity. It issuggested that organic matter and inundation controlMeHg production and accumulation at the benthicinterface. These results confirm previousobservations, in the same study area, of net²⁰³Hg methylation potentials. The fresh andlabile organic matter in the litter of the igapóforest appears as the most important factor leading tosignificant enrichment of MeHg in these particularterrestrial/aquatic sedimentary environments.     

Measurement of methylmercury and mercury in run-off,lake and rain waters

During one year, samples from eight drainage lakes, seven run-off stations and three deposition sites from various geographical areas in Sweden were collected and analyzed for methyl Hg (MeHg) and total Hg (Hg-tot). The MeHg concentrations ranged from 0.04 to 0.64 ng L^?1, 0.04 to 0.8 ng L^?1, and <0.05 to 0.6 ng L^?1 in run-off, lake water and rain water, respectively. The corresponding Hg-tot concentrations were found in the range 2 to 12 ng L^?1, 1.35 to 15 ng L^?1, and 7 to 90 ng L^?1, respectively. A Hg-tot level of about 60 ng Hg L^?1 was found in throughfall water. The MeHg and Hg-tot concentrations are positively correlated in both run-off and lake water, but not in rain and throughfall water. A strong positive correlation between the MeHg, as well as the Hg-tot concentration, and the water color is observed in both run-off and lake waters, which suggests that the transport of MeHg and other Hg fractions from soil via run-off water to the lake is closely related to the transport of organic substances; and is a consequence of the biogeochemical processes and the water flow pathway. The ratio between the mean values of MeHg and Hg-tot seems to be an important parameter, with an indicated negative coupling to the mean value of pH for run-off water, but a strong positive correlation to Hg-content in fish, the ratio between the area of the catchment and the lake, as well as to the retention time of lake.     

Mercury Cycling in Lake Gordon and Lake Pedder,Tasmania (Australia). II: Catchment Processes

The sources and concentrations of total mercury (total Hg) and methylmercury (MeHg) in the upper catchment of the Lake Gordon/Lake Pedder system in Tasmania, Australia were investigated. The catchment area, which contains over 50% wetlands, is located in a temperate region with no obvious point sources of mercury. Surface waters in the region had concentrations of total Hg ranging from 1.2 to 14.4 ng L^-1 and MeHg from < 0.04 to 1.4 ng L^-1. MeHg concentrations were seasonally dependent, with the highest concentrations occurring in summer. Sediments/soils in the catchment had concentrations of total Hg ranging from 4.0 to 194 ng g^-1 and MeHg from <0.02 to 20.1 ng g^-1. The low concentrations of total Hg confirmed that this region is pristine as regards mercury and has no geological enrichment of total Hg. The highest total Hg and MeHg concentrations in both sediment/soils and waters were found in bogs whereas the lowest concentrations typically occurred on the wetlandplains. MeHg concentrations, in bog and swamp sediments were correlatedwith the organic matter content (r = 0.942, P < 0.001). Acid volatile sulfide (AVS) measurements indicate that in most sediments AVS was greater than total Hg. Given the high reactivity of inorganic mercury and sulfide, this suggests that most of the particulate mercury in sediments is present as mercuric sulfide. The yield of MeHg from the catchment was estimated to be 3.2 mg ha^-1 yr^-1 and is higher than published rates measured in non-contaminated temperate catchments in the northern hemisphere. The higher yield was attributed to the generally warmer climatic conditions that favour net methylation and the relatively high rainfall (2–3 m yr^-1) of the region, which supplies reactive inorganic mercury to the active zones ofmercury methylation and also flushes MeHg from the catchment.     

Methylmercury in Flood-Control Impoundments and Natural Waters of Northwestern Minnesota, 1997–99

We studied methylmercury (MeHg) and totalmercury (Hg_T) in impounded and natural surface waters innorthwestern Minnesota, in settings ranging from agriculturalto undeveloped. In a recently constructed (1995) permanent-pool impoundment, MeHg levels typically increased from inflowto outflow during 1997; this trend broke down from late 1998 toearly 1999. MeHg levels in the outflow reached seasonal maximain mid-summer (maximum of 1.0 ng L^-1 in July 1997) andlate-winter (maximum of 6.6 ng L^-1 in February 1999), andare comparable to high levels observed in new hydroelectricreservoirs in Canada. Spring and autumn MeHg levels weretypically about 0.1–0.2 ng L^-1. Overall, MeHg levels inboth the inflow (a ditch that drains peatlands) and outflowwere significantly higher than in three nearby referencenatural lakes. Eleven older permanent-pool impoundments andsix natural lakes in northwestern Minnesota were sampled fivetimes. The impoundments typically had higher MeHg levels(0.071–8.36 ng L^-1) than natural lakes. Five of six lakesMeHg levels typical of uncontaminated lakes (0.014–1.04 ngL^-1) with highest levels in late winter, whereas ahypereutrophic lake had high levels (0.37–3.67 ng L^-1)with highest levels in mid-summer. Seven temporary-poolimpoundments were sampled during summer high-flow events. Temporary-pool impoundments that retained water for about 10–15days after innundation yielded pronounced increases in MeHgfrom inflow to outflow, in one case reaching 4.6 ng L^-1,which was about 2 ng L^-1 greater than the mean inflowconcentration during the runoff event.     

Effect of pH on the bioaccumulation of low level,dissolved methylmercury by rainbow trout (Oncorhynchus mykiss)

An inverse relationship has been observed between pH and McHg concentration in freshwater fish. Many hypotheses exist regarding the mechanisms which lead to elevated levels of organic Hg in fish from low pH lakes. To determine if pH has a direct effect on the rate of McHg bioaccumulation in fish, rainbow trout fingerlings (Oncorhynchus mykiss) were exposed to a low concentration of aqueous methylmercuric chloride (1.38 ± 0.49 ng·L^?1) at four pH-levels (8.2, 7.0, 6.3, 5.8) for eight weeks. McHg and total Hg were specifically determined on whole fish homogenates and water samples. The pH was found to have a significant: inverse effect on the rate of McHg bioaccumulation in the fish only in the lowest exposure level. Fish held at pH 5.8 had an uptake rate of 1.11 ± 0.07 ng·g^?1·d^?1, while those at pH ≥ 6.3 had a MeHg tissue uptake rate of ≤ 0.64 ± 0.07 ng·g^?1·d^?1. Total body burden of MeHg in the fish held at pH 5.8 also showed an elevated level of MeHg when compared with fish held at higher pH-levels, but the difference was less dramatic. These results suggest that a portion of the Hg burden in fish from low pH systems may be due to the direct effects of low pH on bioaccumulation, but that a threshold may exist above which pH does not play a significant role.     

Methylmercury in runoff from the Svartberget Catchment in northern Sweden during a stormflow episode

The dynamics of MeHg during rain-driven runoff episodes are important in calculating the output of MeHg from forested catchments. These dynamics may also provide insight into the processes controlling MeHg output from soils to surface waters. The concentrations of MeHg, Hg-tot, TOC and associated chemistry were observed during a rain-driven, July runoff episode on two forested tributaries of the Svartberget Catchment, as well as at the outlet of a mire in the headwaters of that catchment. TOC concentrations in runoff increased during the episode. Hg-tot concentrations also tended to increase (from 3 to between 4 and 7 ng L^?1), though the timing of that increase varied. MeHg concentrations, on the other hand, tended to decrease. The decrease was slight in the two forested tributaries (ca. 0.1 ng L^?1), but greater in the mire runoff (from 0.8 to ca 0.3 ng L^?1). These data are set in relation to a hypothesis about the processes which control MeHg output.     

Mercury Cycling in Lake Gordon and Lake Pedder,Tasmania (Australia). I: In-lake Processes

The processes affecting the concentrations of total mercury (total Hg) and methylmercury (MeHg) in a freshwater system comprising two connected reservoirs in southwest Tasmania were investigated. Surface concentrations of total mercury (total Hg)were temporally and spatially uniform in both Lake Gordon (2.3±0.4 ng L^-1, n = 27) and Lake Pedder (2.3±0.3 ng L^-1, n = 11). The surface concentrations of MeHg in Lake Gordon (0.35±0.39 ng L^-1, n = 25) were more variable than total Hg and MeHg typically comprised 10–20% of total Hg. The relatively high amount of total mercury present as MeHg in Lake Gordon was attributed to the high proportion of wetlandsin the upper catchment (50% of total area) and in-lake contributions (ca. 40% of total MeHg). Despite the close proximity of the two lakes, MeHg concentrations in Lake Pedder were consistently lower than in Lake Gordon. This phenomenon canbe explained in part by the greater contribution of direct rainfall to Lake Pedder leading to the dilution of MeHg. Water column MeHg concentrations were higher in warmer months in bothlakes, reflecting increased net methylation of inorganic mercury.Unlike previous studies of seasonally anoxic lakes, depth profiles of total mercury and MeHg in Lake Gordon were uniform and were not affected by water column stratification occurringin the summer months, and oxygen depletion with depth. This suggests that redox cycling and accumulation of MeHg in the hypolimnion following seasonally-induced anoxia is not a significant part of the mercury cycle in Lake Gordon. The primary location of MeHg production within the lake's water column is not conspicuous. Mercury speciation measurements made above and below the lake system over a period of 19 months indicates that after 20 yr of impoundment, the reservoirs are not significantly affecting MeHg concentrations in the downstreamriverine environment.     

Influence of Sediment Preservation on Total Mercury and Methylmercury Analyses

Estuarine and riverine sediments from fourlocations showing different sediment structures wereanalysed as fresh, thawed and lyophilised samples fortotal mercury (TotHg) and methylmercury (MeHg)concentrations, and results were compared to addresseffects of sample preservation on Hg speciation. TotHg was measured by cold vapour atomic absorptionspectrometry (CVAAS). MeHg was isolated bydistillation and ion-exchange and analysed by coldvapour atomic fluorescence spectrometry (CVAFS) afterpreconcentration on a gold trap. No loss of TotHg norMeHg due to lyophilisation was found. Concentrationsof TotHg and MeHg respectively ranged from 92 to 267ng g^-1 dw and 1.1 to 2.9 ng g^-1 dw in freshsamples, from 94 to 215 ng g^-1 dw and 1.1 to 2.8ng g^-1 dw in thawed samples, and from 100 to 256ng g^-1 dw and 1.2 to 3.1 ng g^-1 dw inlyophilised samples. Lyophilised samples showedbetter homogeneity and better MeHg analysisreproducibility compared with wet samples.     

Seasonal variability in the Mercury speciation of Onondaga Lake (New York)

Dissolved and particulate Hg speciation was determined on four occasions in the Spring to Fall interval of 1989, at three depths of the water column of Onondaga Lake, New York; an urban system in which the sediments and fish flesh are contaminated with H_g. Species determined included total Hg (Hg_t), reactive (‘ionic’) Hg (Hg_i), monomethylmercury (CH₃HgX), elemental Hg (Hg°) and dimethylmercury (CH₃)₂Hg). Onondaga Lake was found to contain very high levels of Hg_t (2 to 25 ng L^?1 Hg), Hg_j (0.5 to 10 ng L^?1 Hg), and CH₃HgX (0.3 to 7 ng L^?1 Hg), which generally increased with depth in the lake. These concentrations represent a significant level of contamination, based upon comparisons with other polluted and pristine sites. Elemental Hg levels were typically about 0.05 ng L^?1 and (CH₃)₂Hg was near the limits of detection (?0.001 ng) L^?1 in most samples. The greatest CH₃HgX concentrations in the hypolimnion, as well as the largest gradients of both CH₃HgX and (Hg_t), were observed upon the first onset of stratification, in early summer. These concentrations did not become more pronounced, however, as stratification and H₂S levels in the hypolimnion increased throughout the summer. The very low concentrations of (CH₃)₂Hg in these MeHg and sulfide-rich waters calls into question the belief that CH₃HgX and H₂S will react to yield volatile dimethyl-mercury, which can then escape to the atmosphere by diffusion. Mercury speciation was highly dynamic, indicating active cycling within the lake, and an apparent sensitivity to changes in attendant Iimnological conditions that track the stratification cycle.     

Natural Mercury Levels in Geological Enriched and Geological Active Areas: Case Study of Katun River and Lake Teletskoye,Altai (Siberia)

Natural geological Hg deposits control the Hg levels inthe upper Katun river. Very high levels of total Hg areobserved in the watercolumn (up to 20 ng L^-1) and thesediments (up to 244 μg g^-1) close to the depositarea, but almost normal levels (1.8 ng L^-1 in the watercolumn and 0.14 μg g^-1 in the sediments) are reached60 km downstream of that zone. In general, low dissolvedmethylmercury (MMHg) concentrations were found (0.04–0.05 ngL^-1) due to unfavourable methylation conditions. The MMHgconcentrations in the sediments vary from 23.3 ng g^-1, inthe vicinity of the geological Hg deposits, to 0.17 ng g^-1 60 km downstream.Total Hg levels in Lake Teletskoye (a geological activearea) are slightly increased (1.1–1.8 ng L^-1) compared toLake Baikal and fairly constant alover the Lake, suggestingmultiple sources. High mercury concentrations in springs andsoils coincide with high radon concentrations in the samecompartments as well as high soil exhalation fluxes. Theseresults in combination with the fact that Lake Teletskoye islocated in an active fault zone suggest that the Rn and Hgsources may be fault aligned spring waters and deep seatedgases escaping through open cracks. Methylmercuryconcentrations in the Lake (0.03–0.1 ng L^-1) werecomparable to the concentrations found in Katun river butrelative to the total Hg burden this means a higher percentage.     

Influence of the Forest Canopy on Total and Methyl Mercury Deposition in the Boreal Forest

Atmospheric mercury deposition by wet and dry processes contributes mercury to terrestrial and aquatic systems. Factors influencing the amount of mercury deposited to boreal forests were identified in this study. Throughfall and open canopy precipitation samples were collected in 2005 and 2006 using passive precipitation collectors from pristine sites located across the Superior National Forest in northern Minnesota, USA. Samples were collected approximately every 2 weeks and analyzed for total (THg) and methyl mercury (MeHg). Forest canopy type and density were the primary influences on THg and MeHg deposition. Highest THg and MeHg concentrations were measured beneath conifer canopies (THg mean?=?19.02 ng L^?1; MeHg mean?=?0.28 ng L^?1) followed by deciduous throughfall (THg mean?=?12.53 ng L^?1; MeHg mean?=?0.19 ng L^?1) then open precipitation (THg mean?=?8.19 ng L^?1; MeHg mean?=?0.12 ng L^?1). The greater efficiency of conifers at scavenging THg and MeHg from the atmosphere may increase the risk of mercury related water quality issues in conifer-dominated systems.     

Evaluating the mercury distribution and release risks in sediments using high-resolution technology in Nansi Lake,China

Purpose

Mercury (Hg) and methylmercury (MeHg) are easily released from sediments to overlying water and cause secondary contamination. In general, Hg concentrations are low in natural aquatic environments, but Hg toxicity is high. Therefore, it is important to assess the mobility and release risks of Hg and MeHg from surface sediment using in situ high-resolution sampling techniques.

Methods

The profile distribution of Hg and MeHg was obtained for samples from Weishan sub-lake (WL) and Dushan sub-lake (DL) of Nansi Lake, China, by high-resolution dialysis (HR-Peeper probes) and the diffusive gradients in thin films (DGT) technique at mm-resolution. Furthermore, Hg mobility and release risks in sediments were evaluated by combining BCR (European Community Reference Bureau) extraction and DGT-measured data.

Results

The soluble concentrations of Hg in surface sediments in WL and DL were 21.70 and 19.38 ng L^?1 and the DGT-labile concentration of Hg were 8.21 and 10.30 ng L^?1, respectively. The soluble and labile Hg and MeHg concentrations were higher in the surface sediments (from??40 to 0 mm) than in deep sediments. The distribution of the labile-Hg was controlled by the ferrimanganic (hydr)oxide and total nitrogen rather than organic carbon content. The non-residual components accounted for a greater proportion of the interface, which further confirmed Hg was more active on the surface layer of the sediment. The resupply ability indicated that the release of Hg from sediment was insufficient to maintain the initial concentration in the porewater before consumption. The MeHg fluxes in WL (6.18 ng m^?2 day^?1) were twice those in DL (2.89 ng m^?2 day^?1), and the risk assessment code revealed a higher risk in the surface layer (25.21–61.88%) than in the deep layer (0–27.75%).

Conclusions

Dissolved Hg and MeHg accumulated on the surface of the sediments and were more active than in the deeper sediments. The DGT-labile state can be used for a better understanding of the bioavailability and mobility of Hg. The diffusion direction of Hg and MeHg was from sediment to the overlying water. The release risks of Hg and MeHg from surface sediments (especially in WL) were found to be worthy of concern.

     

In Situ partitioning and biomagnification of mercury in industrially polluted Husainsagar Lake,Hyderabad, India

The distribution of Hg in water, sediment, plankton and fish along with the in situ biomagnification of the metal in Husainsagar Lake, India were measured. The concentration of Hg in the water was 10 μg L^?1 and exceeded the water quality criteria standards. Sediments of the lake at different sites had Hg concentrations several thousand fold more than that of the overlying water column and showed relationship with the water content of the wet sediment. Sediments in the lake acted as a `sink' for the metal. The concentrations of Hg increased from nanoplankton → phytoplankton -> zooplankton. Fish, an end organism in the food chain, had Hg concentrations higher than that of nanoplankton and lower than those of phytoplankton and zooplankton. This trend did not illustrate the expected pattern of food chain enrichment in the classical sense as noted for chlorinated hydrocarbons (DDT).     

Occurrence and Geochemistry of Arsenic in Groundwater of Punjab,Northwest India

Abstract

Arsenic (As) is a deadly poison at high concentrations. It is mysterious in the sense that people are exposed to it most of the time through drinking groundwater, fortunately at much lower concentrations than the deadly levels, and usually without knowing it. Arsenic content in alluvial aquifers of Punjab varied from 3.5 to 688 µg L^?1. Arsenic status of groundwater is classified into low (<10 µg L^?1), moderate (≥10 to <25 µg L^?1), high (≥25 to <50 µg L^?1), and very high (>50 µg L^?1). In zone I, the concentration of As in groundwater varied from 3.5 to 42 µg L^?1 with a mean value of 23.4 µg L^?1. On the basis of these limits, only 8% of samples were low, whereas 51 and 41% of the total samples collected from this region fall in the moderate and high As categories. The concentration of As in groundwater of zone II varied from 9.8 to 42.5 µg L^?1 with a mean value of 24.1 µg L^?1. Arsenic concentration in the alluvial aquifers of the central plain of zone II is 2 and 52% in the low and moderate limits. In this region, 46% of groundwater sites contain high As concentrations. Arsenic concentrations in the aridic southwestern parts are significantly different from other two provinces. The As concentration ranged from 11.4 to 688 µg L^?1 with average value of 76.8 µg L^?1. Eleven percent of the aquifers of the southwestern region of zone III are in the moderate category, 54% in the high, and 35% in the very high. According to safe As limits (<10 µg L^?1), only 3 and 1% of the groundwater samples collected from zones I and II were fit for dinking purposes with respect to As content. In the aridic southwest, zone III, all water samples contained As concentrations greater than the safe limits and thus are not suitable for drinking purposes. The presence of elevated As concentrations in groundwater are generally due to the results of natural occurrences of As in the aquifer materials. The concentration of other competitive oxyanions in waters such as phosphate, sulfate, and borate also depressed the adsorption of As on the sorption sites of aquifer materials and thereby eventually elevate the As concentration in groundwaters. In groundwater of alluvial aquifers of Punjab, released from sulfide oxidation and oxyhydroxide of iron, elevated (>10 µg L^?1) concentrations of As were widespread because of high pH (>8.0) and higher concentrations of phosphate, borate, sulfate, and hydroxyl anions. It is conclusively evident that geochemical conditions, such as pH, oxidation–reduction, associated or competing ions, and evaporative environments have significant effects on As concentration in groundwater. These conditions influence how much As is dissolved or precipitated into the water and how much is bound to the aquifer materials or the solid particles in water.     

Effects of throughfall and litterfall manipulation on concentrations of methylmercury and mercury in forest‐floor percolates

The forest floor was shown to be an effective sink of atmospherically deposited methylmercury (MeHg) but less for total mercury (Hg_total). We studied factors controlling the difference in dynamics of MeHg and Hg_total in the forest floor by doubling the throughfall input and manipulating aboveground litter inputs (litter removal and doubling litter addition) in the snow‐free period in a Norway spruce forest in NE Bavaria, Germany, for 14 weeks. The MeHg concentrations in the forest‐floor percolates were not affected by any of the manipulation and ranged between 0.03 (Oa horizon) and 0.11 (Oi horizon) ng Hg L^–1. The Hg_total concentrations were largest in the Oa horizon (24 ng Hg L^–1) and increased under double litterfall (statistically significant in the Oi horizon). Similarly, concentrations of dissolved organic C (DOC) increased after doubling of litterfall. The concentrations of Hg_total and DOC correlated significantly in forest‐floor percolates from all plots. However, we did not find any effect of DOC on MeHg concentrations. The difference in the coupling of Hg_total and MeHg to DOC might be one reason for the differences in the mobility of Hg species in forest floors with a lower mobility of MeHg not controlled by DOC.     

Contaminants in Arctic Snow Collected over Northwest Alaskan Sea Ice

Snow cores were collected over sea ice from four northwest Alaskan Arctic estuaries that represented the annual snowfallfrom the 1995–1996 season. Dissolved trace metals, major cationsand anions, total mercury, and organochlorine compounds weredetermined and compared to concentrations in previous arctic studies. Traces (<4 nanograms per liter, ng L^-1) of cis- and trans-chlordane, dimethyl 2,3,5,6-tetrachloroterephthalate, dieldrin, endosulfan II, andPCBs were detected in some samples, with endosulfan I consistently present. High chlorpyrifos concentrations (70–80 ng L^-1) also were estimated at three sites. The snow washighly enriched in sulfates (69–394 mg L^-1), with highproportions of nonsea salt sulfates at three of five sites (9 of 15 samples), thus indicating possible contamination throughlong-distance transport and deposition of sulfate-rich atmospheric aerosols. Mercury, cadmium, chromium, molybdenum, and uranium were typically higher in the marine snow (n = 15) in relation to snow from arctic terrestrial studies, whereas cations associated with terrigenous sources, such as aluminum,frequently were lower over the sea ice. One Kasegaluk Lagoon site (Chukchi Sea) had especially high concentrations of totalmercury (mean = 214 ng L^-1, standard deviation = 5 ng L^-1), but no methyl mercury was detected above the method detection limit (0.036 ng L^-1) at any of the sites. Elevated concentrations of sulfate, mercury, and certain heavymetals might indicate mechanisms of contaminant loss from the arctic atmosphere over marine water not previously reported overland areas. Scavenging by snow, fog, or riming processes and thehigh content of deposited halides might facilitate the loss of such contaminants from the atmosphere. Both the mercury and chlorpyrifos concentrations merit further investigation in view of their toxicity to aquatic organisms at low concentrations.     

A Survey of Organotin Compounds in the Northern Adriatic Sea

The extent of pollution with organotin compounds was investigated in water, sediment and bivalve mussels (Mytilus galloprovincialis) from the Northern Adriatic Sea. Butyl-, phenyl- and octyltin species were quantified after extraction and derivatisation by gas chromatography–mass spectrometry in a total of 99 samples from the period from 2000 to 2006. The accuracies of the analytical procedures were checked by spiking of unpolluted water samples and by the analysis of standard reference materials (harbour sediment PACS-2 and mussel tissue ERM-CE 477). Among organotin species analysed in samples butyltins were the predominant. Tributyltin was found to be present in the highest concentrations, suggesting its recent input into the marine environment. Butyltins were detected at all sites surveyed (sum of butyltins was up to 718 ng Sn L^?1, 3,552 ng Sn g^?1 d.w. and 9,991 ng Sn g^?1 d.w. in water, sediment and mussel samples, respectively), phenytins in much lower concentrations (up to 31 ng Sn L^?1, 326 ng Sn g^?1 d.w. and 442 ng Sn g^?1 d.w. in water, sediment and mussel samples) and to a much smaller extent, while octyltins were not detected at any location. The spatial distribution of tributyltin was closely related to boating, with the highest concentrations found in marinas (up to 586 ng Sn L^?1 for water samples, 1,995 ng Sn g^?1 d.w. for sediment and 6,434 ng Sn g^?1 d.w. for mussel samples). The temporal distribution clearly indicates a decrease of organotin pollution at all sites.