Baseline activities of four biomarkers in three life-stages of the amphipod,Leptocheirus plumulosus

This study investigated differences in baseline levels of four cellular biomarkers (glutathione (GSH), lipid peroxidation (LPx), acetylcholinesterase (AChE), and cholesterol (CHL)) in the larval, juvenile, and adult stages of the estuarine amphipod, Leptocheirus plumulosus. Glutathione, LPx, and AChE exhibited the same pattern of decreasing levels with increasing developmental stage. Cholesterol showed an inverse relationship of increasing levels with increasing developmental stages. This research provides valuable background information that may be used in future assessments of amphipod biomarker research.     

Baseline activities of four biomarkers in three life-stages of the amphipod, Leptocheirus plumulosus

This study investigated differences in baseline levels of four cellular biomarkers (glutathione (GSH), lipid peroxidation (LPx), acetylcholinesterase (AChE), and cholesterol (CHL)) in the larval, juvenile, and adult stages of the estuarine amphipod, Leptocheirus plumulosus. Glutathione, LPx, and AChE exhibited the same pattern of decreasing levels with increasing developmental stage. Cholesterol showed an inverse relationship of increasing levels with increasing developmental stages. This research provides valuable background information that may be used in future assessments of amphipod biomarker research.     

Distribution of total and methylmercury in different ecosystem compartments in the Everglades: implications for mercury bioaccumulation

We analyzed Hg species distribution patterns among ecosystem compartments in the Everglades at the landscape level in order to explore the implications of Hg distribution for Hg bioaccumulation and to investigate major biogeochemical processes that are pertinent to the observed Hg distribution patterns. At an Everglade-wide scale, THg concentrations were significantly increased in the following order: periphyton相似文献   

Cadmium and methylmercury bioaccumulation by nymphs of the burrowing mayflyHexagenia rigida from the water column and sediment

Based on a three compartment microcosm-water column, natural sediment,Hexagenia rigida nymphs-an experimental study was set up to compare cadmium (Cd) and methylmercury (MeHg) bioaccumulation by a burrowing mayfly species, after exposure via the water column or the sediment as initial contamination sources. Results from a wide concentration range for each exposure condition revealed very marked differences between the two metals: MeHg was readily accumulated from the two contamination sources, leading to important metal concentrations in the nymphs after the 2 weeks’ exposure; Cd bioaccumulation, on the other hand, was negligible when the metal was added to the water compartment, even though significant transfers were observed from the sediment source. The average Cd concentrations in the nymphs were proportional to the sediment contamination levels. Turbidity measurements in the water column, reflecting the bioturbation activity of the nymphs, revealed that the effect of Cd was significant, but only when the metal was initially added to the sediment. The results are discussed according to the uptake routes and the structural and functional properties of the biological barriers involved (gills and gut).     

Accumulation of mercury and methylmercury by mushrooms and earthworms from forest soils

Accumulation of total and methyl-Hg by mushrooms and earthworms was studied in thirty-four natural forest soils strongly varying in soil physico-chemical characteristics. Tissue Hg concentrations of both receptors did hardly correlate with Hg concentrations in soil. Both total and methyl-Hg concentrations in tissues were species-specific and dependent on the ecological groups of receptor. Methyl-Hg was low accounting for less than 5 and 8% of total Hg in tissues of mushrooms and earthworms, respectively, but with four times higher concentrations in earthworms than mushrooms. Total Hg concentrations in mushrooms averaged 0.96 mg Hg kg⁻¹ dw whereas litter decomposing mushrooms showed highest total Hg and methyl-Hg concentrations. Earthworms contained similar Hg concentrations (1.04 mg Hg kg⁻¹ dw) whereas endogeic earthworms accumulated highest amounts of Hg and methyl-Hg.     

Patterns of mercury and methylmercury bioaccumulation in fish species downstream of a long-term mercury-contaminated site in the lower Ebro River (NE Spain)

Since the 19th century, large amounts of industrial waste were dumped in a reservoir adjacent to a chlor-alkali plant in the lower Ebro River (NE Spain). Previous toxicological analysis of carp populations inhabiting the surveyed area have shown that the highest biological impact attributable to mercury pollution occurred downstream of the discharge site. However, mercury speciation in fish from this polluted area has not been addressed yet. Thus, in the present study, piscivorous European catfish (Silurus glanis) and non-piscivorous common carp (Cyprinus carpio) were selected, to investigate the bioavailability and bioaccumulation capacities of both total mercury (THg) and methylmercury (MeHg) at 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 fitted in order to assess the relationship between both Hg species in fish and different variables of interest. Mercury levels in fish inhabiting the dam at the discharge site were found to be approximately 2-fold higher than those from an upstream site; while mercury pollution progressively increased downstream of the hot spot. In fact, both THg and MeHg levels at the farthest downstream point were 3 times greater than those close to the waste dump. This result clearly indicates downstream transport and increased mercury bioavailability as a function of distance downstream from the contamination source. A number of factors may affect both the downstream transport and increased Hg bioavailability associated with suspended particulate matter (SPM) and dissolved organic carbon (DOC).     

Habitat-specific bioaccumulation of methylmercury in invertebrates of small mid-latitude lakes in North America

We examined habitat-specific bioaccumulation of methylmercury (MeHg) in aquatic food webs by comparing concentrations in pelagic zooplankton to those in littoral macroinvertebrates from 52 mid-latitude lakes in North America. Invertebrate MeHg concentrations were primarily correlated with water pH, and after controlling for this influence, pelagic zooplankton had significantly higher MeHg concentrations than littoral primary consumers but lower MeHg than littoral secondary consumers. Littoral primary consumers and pelagic zooplankton are two dominant prey for fish, and greater MeHg in zooplankton is likely sufficient to increase bioaccumulation in pelagic feeders. Intensive sampling of 8 lakes indicated that habitat-specific bioaccumulation in invertebrates (of similar trophic level) may result from spatial variation in aqueous MeHg concentration or from more efficient uptake of aqueous MeHg into the pelagic food web. Our findings demonstrate that littoral-pelagic differences in MeHg bioaccumulation are widespread in small mid-latitude lakes.     

A chronic bioassay with the estuarine amphipod Corophium volutator: test method description and confounding factors

Methods of conducting a chronic sediment toxicity test with the estuarine amphipod Corophium volutator are described. They consist of a 49-day exposure, after which mortality, growth and reproduction are determined. Pilot experiments were used to optimize test design parameters such as temperature, duration, feeding and refreshing regimes, and effects of indigenous organisms. By way of further validation, the present study focused on the effects of four different parameters: oxygen saturation, salinity, ammonium and nitrite. These confounding factors might play an important role especially if the test is used for risk assessment of field-contaminated sediments. It is concluded that the present experimental design is well suited for chronic sediment exposures with C. volutator. The test can be performed at a broad range of salinity values, provided that controls are performed at the same salinity. Results further demonstrate that with the endpoints growth and reproduction this chronic test procedure is a factor 7-18 more sensitive to ammonium and nitrate than the standardized acute bioassay (endpoint mortality).     

Reproduction of the estuarine and marine amphipod Corophium volutator (Pallas) in laboratory for toxicity testing

The acute whole sediment bioassay with the estuarine and marine amphipod Corophium volutator (Pallas) is broadly used within Europe. Hitherto, the test is carried out with field-collected animals. In order to provide a more standardized and continuously available test organism reproduction and growth experiments were performed for a period of one year in laboratory under simulated summer conditions (light/dark 16:8 at 15, 19, and 23 degrees C). C. volutator was the first time reproduced successfully in laboratory for several generations and independent from its natural life cycle also in winter. The females produced two to three broods with a mean number of 96 offspring. A mean growth rate of 0.07 mm per day was determined at 15 degrees C. The reproduction and growth experiments provide consequently the essential base for the development of a chronic toxicity test with C. volutator.     

Dietary mercury exposure and bioaccumulation in amphibian larvae inhabiting Carolina bay wetlands

Inorganic mercury and methylmercury concentrations were measured both in guts and remaining carcasses of southern leopard frog (Rana sphenocephala) larvae from 10 Carolina bay wetlands in South Carolina, USA. Significant variation among bays in methylmercury and inorganic mercury concentrations existed both in guts and carcasses. There was a moderate negative correlation between dissolved organic carbon concentration in bays and mean inorganic mercury concentrations in guts. There was also a weak positive correlation between pH in bays and mean methylmercury concentrations in carcasses. The ratio of methylmercury to inorganic mercury decreased with increasing total mercury concentration in guts and in larvae, but the rate of decrease was highly variable among bays. Ratios of concentrations in carcasses to concentrations in guts were inversely related to gut concentration. Mercury concentrations in carcasses in some bays were within the range of concentrations at which adverse effects have been observed in laboratory studies of R. sphenocephala.     

Speciation of methylmercury in rice grown from a mercury mining area

Monomethylmercury (CH₃Hg⁺ and its complexes; MeHg hereafter) is a known developmental neurotoxin. Recent studies have shown that rice (Oryza sativa L.) grain grown from mercury (Hg) mining areas may contain elevated MeHg concentrations, raising concerns over the health of local residents who consume rice on a daily basis. An analytical method employing high performance liquid chromatography (HPLC) - inductively coupled plasma mass spectrometry (ICP-MS) following enzymatic hydrolysis was developed to analyze the speciation of MeHg in uncooked and cooked white rice grain grown from the vicinity of a Hg mine in China. The results revealed that the MeHg in the uncooked rice is present almost exclusively as CH₃Hg-l-cysteinate (CH₃HgCys), a complex that is thought to be responsible for the transfer of MeHg across the blood-brain and placental barriers. Although cooking does not change the total Hg or total MeHg concentration in rice, no CH₃HgCys is measurable after cooking, suggesting that most, if not all, of the CH₃HgCys is converted to other forms of MeHg, the identity and toxicity of which remain elusive.     

Comparison of total mercury and methylmercury cycling at five sites using the small watershed approach

The small watershed approach is well-suited but underutilized in mercury research. We applied the small watershed approach to investigate total mercury (THg) and methylmercury (MeHg) dynamics in streamwater at the five diverse forested headwater catchments of the US Geological Survey Water, Energy, and Biogeochemical Budgets (WEBB) program. At all sites, baseflow THg was generally less than 1ng L(-1) and MeHg was less than 0.2ng L(-1). THg and MeHg concentrations increased with streamflow, so export was primarily episodic. At three sites, THg and MeHg concentration and export were dominated by the particulate fraction in association with POC at high flows, with maximum THg (MeHg) concentrations of 94 (2.56)ng L(-1) at Sleepers River, Vermont; 112 (0.75)ng L(-1) at Rio Icacos, Puerto Rico; and 55 (0.80)ng L(-1) at Panola Mt., Georgia. Filtered (<0.7microm) THg increased more modestly with flow in association with the hydrophobic acid fraction (HPOA) of DOC, with maximum filtered THg concentrations near 5ng L(-1) at both Sleepers and Icacos. At Andrews Creek, Colorado, THg export was also episodic but was dominated by filtered THg, as POC concentrations were low. MeHg typically tracked THg so that each site had a fairly constant MeHg/THg ratio, which ranged from near zero at Andrews to 15% at the low-relief, groundwater-dominated Allequash Creek, Wisconsin. Allequash was the only site with filtered MeHg consistently above detection, and the filtered fraction dominated both THg and MeHg. Relative to inputs in wet deposition, watershed retention of THg (minus any subsequent volatilization) was 96.6% at Allequash, 60% at Sleepers, and 83% at Andrews. Icacos had a net export of THg, possibly due to historic gold mining or frequent disturbance from landslides. Quantification and interpretation of Hg dynamics was facilitated by the small watershed approach with emphasis on event sampling.     

Total mercury and methylmercury in freshwater and salt marsh soils of the Mississippi river deltaic plain

Mercury entering wetland environments can be microbially methylated to methylmercury. The purpose of this study was to investigate the historical rate of mercury accumulation and distribution of total and methylmercury in soil profile of Louisiana coastal marshes. Two sediment cores each were taken from Louisiana freshwater marsh and salt marsh. Vertical accretion was determined using the 137Cs dating technique. Total and methylmercury were determined with depth in the soil profiles. The fresh marsh soil on a dry weight basis contained more total and methylmercury than the salt marsh. Average vertical accretion rates in freshwater marsh and salt marsh were 0.90 and 0.75 cm year(-1), respectively. Average total and methylmercury content (to a depth of 30 cm) was 140 and 4.19 microg kg(-1) and 80 and 1.34 microg kg(-1) for the fresh and salt marsh, respectively. Due to greater sediment input resulting in a higher bulk density the salt marsh contained more total mercury per m2 (to 30 cm depth) than the fresh water marsh (5340 microg m(-2) as compared to 2929 microg m(-2)). The amount of methylmercury per m2 to depth of 30 cm was approximately the same for each marsh.     

Effect of point source removal on mercury bioaccumulation in an industrial pond

A one hectare pond on the headwaters of a mercury-contaminated creek in Oak Ridge, Tennessee acted as a biochemical reactor for the production of methylmercury, increasing waterborne methylmercury concentrations in the stream below the pond discharge. The flow of the creek was diverted around the pond in order to eliminate this input. Waterborne total mercury, methylmercury, and mercury in fish, were monitored in the pond and stream before and after bypass. Waterborne methylmercury concentration in the creek downstream from the pond decreased over 800% following diversion of streamflow around the pond, but mercury in redbreast sunfish in the pond tailwater did not decline similarly. Within the pond, now isolated from fresh waterborne mercury inputs from the stream, methylmercury concentrations in the water column remained similar to levels present before bypass. However, mercury concentrations in sunfish in the pond decreased approximately 75% following bypass, despite the continued presence of highly contaminated sediments (approximately 50 mg Hg/kg dry weight). We concluded that a decrease in the fraction of 'dissolved methylmercury' in the isolated pond relative to pre-bypass conditions explained the decrease in mercury in fish within the pond. That observation also indicates that mercury associated with pond sediments was relatively unavailable for eventual bioaccumulation when compared to 'fresh' mercury contributed by upstream sources. The lack of a post-bypass decrease in mercury concentrations in tailwater fish was also likely to be associated with the particle-associated nature of waterborne methylmercury exported from the pond.     

Accumulation, subcellular distribution and toxicity of inorganic mercury and methylmercury in marine phytoplankton

We examined the accumulation, subcellular distribution, and toxicity of Hg(II) and MeHg in three marine phytoplankton (the diatom Thalassiosira pseudonana, the green alga Chlorella autotrophica, and the flagellate Isochrysis galbana). For MeHg, the inter-species toxic difference could be best interpreted by the total cellular or intracellular accumulation. For Hg(II), both I.?galbana and T.?pseudonana exhibited similar sensitivity, but they each accumulated a different level of Hg(II). A higher percentage of Hg(II) was bound to the cellular debris fraction in T.?pseudonana than in I.?galbana, implying that the cellular debris may play an important role in Hg(II) detoxification. Furthermore, heat-stable proteins were a major binding pool for MeHg, while the cellular debris was an important binding pool for Hg(II). Elucidating the different subcellular fates of Hg(II) and MeHg may help us understand their toxicity in marine phytoplankton at the bottom of aquatic food chains.     

Long-term increased bioaccumulation of mercury in largemouth bass follows reduction of waterborne selenium

Average mercury concentrations in largemouth bass from Rogers Quarry in east Tennessee were found to increase steadily following the elimination of selenium-rich discharges of fly ash to the quarry in 1989. From 1990 to 1998, mean mercury concentrations (adjusted to compensate for the covariance between individual fish weight and mercury concentration) in bass rose from 0.02 to 0.61 mg/kg. There was no indication that the rate increase was slowing or that mercury concentrations in fish were approaching a plateau or steady state. Mean selenium concentrations in bass declined from 3 to 1 mg/kg over the first five years of the study, but remained at 1-1.5 mg/kg (about twice typical concentrations in bass from local reference sites) for the last three years of the study. Gross physical abnormalities were common in fish from the site in the first three years after elimination of fly ash discharges but disappeared after two more years. Although it remains possible that other chemical or physical changes related to fly ash disposal in the system were associated with increased mercury bioaccumulation, the most likely explanation is that selenium played a critical role. It appears as though aqueous selenium enrichment was capable of having a profound effect on mercury bioaccumulation in this system but at the cost of causing a high incidence of gross abnormalities in fish. However, it is possible that selenium concentrations between the national ambient water quality criterion for the protection of aquatic life, 5 microg/l, and that now found in Rogers Quarry (<2 microg/l) could reduce mercury bioaccumulation without causing adverse effects on aquatic biota and fish-eating wildlife.     

Factors influencing the total mercury and methyl mercury in the hair of the fishermen of Kuwait

Total and methyl mercury (MeHg) levels in the hair of fishermen are described anticipating that they represent the critical group for dietary exposure. One-hundred human hair samples were collected from fishermen (Egyptians: age range 25-60), living in Doha Fishing Village, Kuwait. Thirty-five additional samples were taken from a control group working in a local construction company (age range 26-35). Overall mean concentrations in the hair of the population of fishermen are 4.181+/-3.220 and 4.025+/-3.130 microg g(-1) for total and MeHg, respectively. The equivalent values for the control are 2.617+/-1.404 and 2.556+/-1.391 microg g(-1) for total and MeHg, respectively. MeHg concentrations are strongly correlated to those of total Hg ( [Formula: see text], [Formula: see text] ) and MeHg concentrations in human hair are unrelated to age and duration of residence in Kuwait but show a positive correlation with the quantity of fish consumed. Levels of Hg in hair also show a tendency to increase in those who prefer to eat the entire fish, including the heads. In general, the concentrations of total and MeHg in fishermens' hair are twice the WHO 'normal' level (2.0 microg g(-1)) but are still less than the WHO threshold level (10.0 microg g(-1)). The results also show that grey hair contains undetectable amounts of Hg and therefore does not reflect individual exposure to this contaminant.     

Comparison of mercury and methylmercury in northern pike and Arctic grayling from western Alaska rivers

In western Alaska, mercury (Hg) could be a potential health risk to people whose diet is primarily fish-based. In 2000, total Hg (THg) and methylmercury (MeHg) were examined in northern pike (Esox lucius) and Arctic grayling (Thymallus arcticus) from two watersheds in western Alaska, the Yukon and Kuskokwim rivers. Whitefish (Coregonus sp.) were also examined from the Kuskokwim River. Pike from the Yukon and Kuskokwim rivers had mean concentrations of THg in muscle of 1.506 and 0.628 mg/kg wet wt, respectively. The mean concentrations of THg in grayling muscle from these rivers were 0.264 and 0.078 mg/kg, respectfully. Whitefish had a mean THg concentration in muscle of 0.032 mg/kg. MeHg, in pike and grayling constituted nearly 100% of the THg concentrations; the proportion was less in whitefish. A significant positive correlation between Hg levels and fish length was also found. Generally, there were no changes in Hg concentrations in pike or grayling over the last several years. Only pike from theYukon River had THg concentrations that exceeded the USFDA action level for human consumption of edible fish (1 mg/kg). Human hazard index for pike was > or = 1 for both adults and children, indicating a potential for toxic concern, especially among children. Further studies are needed to determine the environmental and human health impacts associated with these Hg concentrations in western Alaska, especially in the context of potentially increased consumption of resident fishes when anadromous salmon catches are reduced.     

Methylmercury and total mercury in estuarine organisms from Rio de Janeiro, Brazil

Guanabara Bay (GB), located in the Rio de Janeiro State, is still a productive estuary on the south-eastern Brazilian coast. It is an ecosystem heavily impacted by organic matter, oil and a number of other toxic compounds, including Hg. The present study aimed to comparatively evaluate the aquatic total mercury (THg) and MeHg contamination, and the ratios of MeHg to THg (% MeHg), in 3 species of marine organisms, Micropogonias furnieri-carnivorous fish (N = 81), Mugil spp.--detritivorous fish (N = 20) and Perna perna--filter-feeding bivalves (N = 190), which are widely consumed by the population. A total of 291 specimens were collected at the bay in different periods between 1988 and 1998. THg concentrations were determined by cold vapour AAS with stannous chloride as a reducing agent. MeHg was extracted by dithizone-benzene and measured by GC-ECD. Analytical quality was checked through certified standards. All organisms presented both low THg and MeHg concentrations and they were below the maximum limit of 1,000 micrograms Hg.kg-1 wet wt. as established for human intake of predatory fish by the new Brazilian legislation. Carnivorous fish showed higher THg and MeHg concentrations, and also % MeHg in muscle tissues, than organisms with other feeding habits and lower trophic levels. The average of THg concentrations in carnivorous fish was 108.9 +/- 58.6 micrograms.kg-1 wet wt. (N = 61) in 1990 and 199.5 +/- 116.2 micrograms.kg-1 wet wt. (N = 20) in 1998, but they presented different total length and body weights. The average THg content in detritivorous fish was 15.4 +/- 5.8 micrograms.kg-1 wet wt., whereas THg concentrations ranged from 4.1 to 53.5 micrograms.kg-1 wet wt. for the molluscs. The THg and MeHg contents of mussel varied according to the sampling point and water quality. MeHg concentration in detritivorous fish was similar to MeHg concentration in molluscs, but there was a significant difference in the MeHg/THg ratio: the carnivorous fish presented higher MeHg percentages (98%) than the detritivorous fish (54%) and the molluscs (33%). Weight-normalised average concentration of THg in carnivorous fish collected in 1990 (0.18 +/- 0.08 microgram.g-1/0.7 kg wet wt.) and in 1998 (0.16 +/- 0.09 microgram.g-1/0.7 kg wet wt.) presented no significant difference (t = 1.34; P < 0.5). In conclusion, the low THg and MeHg concentrations in the organisms from the GB ecosystem, are related to its eutrophic conditions and elevated amounts of suspended matter. In this situation, Hg could be strongly complexed or adsorbed by the particulate, which would dilute the Hg inputs and reduce its residence time in the water column, with a consequent decrease in its availability to organisms.