Hg Levels In Fish Research Articles

Fish mercury concentration in the Alto Pantanal, Brazil: influence of season and water parameters

The tropical flood plain Pantanal is one of the world’s largest wetlands and a wildlife sanctuary. Mercury (Hg) emissions from some upstream gold mining areas and recent findings of high natural Hg levels in tropical oxisols motivated studies on the Hg cycle in the Pantanal. A survey was made on total Hg in the most consumed piscivorous fish species from rivers and floodplain lakes in the north (Cáceres and Barão de Melgaço) and in the south part of Alto Pantanal (around the confluence of the Cuiabá and Paraguai rivers). Samples were collected in both the rainy and dry seasons (March and August 1998) and included piranha ( Serrasalmus spp.), and catfish ( Pseudoplatystoma coruscans, pintado, and Pseudoplatystoma fasciatum, cachara or surubim). There was only a small spatial variation in Hg concentration of the 185 analyzed fish samples from the 200×200 km large investigation area, and 90% contained total Hg concentration below the safety limit for regular fish consumption (500 ng g −1). Concentration above this limit was found in both Pseudoplatystoma and Serrasalmus samples from the Baı́a Siá Mariana, the only acid soft-water lake included in this study, during both the rainy and dry seasons. Concentration above this limit was also found in fish outside Baı́a Siá Mariana during the dry season, especially in Rio Cuiabá in the region of Barão de Melgaço. The seasonal effect may be connected with decreasing water volumes and changing habitat during the dry season. The results indicate that fertile women should restrict their consumption of piscivorous fishes from the Rio Cuiabá basin during the dry season. Measures should be implanted to avoid a further deterioration of fish Hg levels.

Simple direct method for the determination of total mercury levels in blood and urine and nitric acid digests of fish by inductively coupled plasma mass spectrometry

A simple direct method was developed to determine Hg by ICP-MS in diluted urine, diluted blood and HNO3 digests of fish. Wash-out times of <130 s for Hg concentrations ≤30 µg l–1 were achieved by complexing Hg with (NH4)2H2EDTA and the presence of ammonia. A novel disinfection procedure for urine and blood utilised dilution with a virucidal agent, Virkon. Virkon precipitated blood proteins, requiring subsequent dissolution using tetramethylammonium hydroxide. More than 85% of internal QC results were within ±1 µg l–1 of their target values for blood and >80% within 5% for urine. There was successful participation in three QA schemes for urine and one for blood. NIST Albacore Tuna gave 95% recovery of the target, 0.95 µg g–1, and good precision, 0.90±0.01 µg g–1 (n=3). The method did not discriminate between inorganic and organic Hg. Detection limits for Hg, using 3σ at or near the blank level, were 0.13 µg l–1 in blood, 0.27 µg l–1 in urine and 0.004 µg g–1 in fish. The developed methods were used to analyse samples collected from four sites in the Tapajos Valley of Brazil in an EC funded study of exposure to Hg as a result of gold mining. All but one of the subjects (n=106) had Hg levels in either blood or urine that exceeded the upper 95% limits for non-exposed subjects, 55% had blood Hg levels above the 95% limit in industrial workers (19 µg l–1) and 17% exceeded the urine Hg limit at which industrial workers should be removed from exposure (50 µg l–1). Subjects living in a fishing village, Jacareacanga, 100 km from mining activities, had significantly higher blood Hg levels (mean 81 µg l–1) than the other three groups (p<0.004), presumed to be related to fish consumption. Fish Hg levels were similar to those found in other polluted areas, mean 0.379 mg kg–1 (n=52). The EC study provided the strongest evidence to date in 1991 that Hg in fish in the Amazon basin posed much more of a general health problem than Hg vapour since it affected a larger proportion of the population than just the gold miners, ancillary workers and traders. The methods were also used in the routine clinical analysis of blood and urine samples within the UK National Health Service. Investigations included a case of acute mercury poisoning in a 28-month-old boy who had swallowed a battery who had an initial blood Hg of 394 nmol l–1 and urine Hg of 16 nmol mmol–1 creatinine. He was successfully treated with the chelating agent British Anti-Lewisite.

DDE mercury, and selenium in Biota, sediments, and water of the Rio Grande-Rio Bravo Basin, 1965-1995.

An assessment of contaminant stressors on biota of the Rio Grande was conducted to identify relevant contaminant issues, assess exposure and ecological effects, identify data gaps, and determine potential risks. Most contaminant data were from studies conducted during 1965-1995 in the Lower Rio Grande, on the Texas side of the river, within a 100-km boundary from Falcon Dam to the mouth. Contaminants most frequently reported were organochlorine compounds (OCs) and trace elements. The number of records for OCs and trace elements was at least twofold greater for fish than for birds, mammals, or reptiles. Of the OCs, p,p'-DDE was the most commonly reported. Among the trace elements, Hg was one of the most frequently reported; however, Se, As, Pb, Cu, and Zn were also common. The highest concentrations of OCs and trace elements were reported predominantly from Lower Rio Grande Valley locations, with approximately 68% of the highest values detected from Falcon Dam to the mouth of the river. Twenty-six (20%) of the locations with maximum concentrations corresponded to portions of Llano Grande Lake and the Arroyo Colorado. Recent analyses of birds and fish indicate that levels of DDE are currently much lower than in the 1970s or 1980s in Rio Grande wildlife. This apparent decline does not apply to Hg and Se levels in birds and fish, which have remained more or less constant, but may have increased over the years in some locations. Hg was of particular concern because of high levels found recently in addled eggs of aplomado falcons and in their potential prey. Hg was elevated in fish from the Big Bend area. Also, Se in fish sampled in 1993 and 1994 was near or above the threshold for potential effects in fish-eating wildlife. Future investigations should evaluate the potential impacts of Hg and Se on aquatic and terrestrial species from selected sites of concern.

Mercuty in Precipitation and Its Relation to Bioaccumulation in Fish: A Literature Review

Increases in industrial mercury (Hg) emissions in recent years have led many researchers to believe that Hg from the atmosphere constitutes a main source of Hg to aquatic biota in the absence of point source discharges. Established background levels for fish (0.2–1.0 mg kg-1) now exceed the pre industrial level of 0.15 mg kg-1, suggesting an anthropogenic origin. This review of recent literature illustrates how levels of mercury (Hg) species in the atmosphere are effectively transported into the aquatic arena, where chemical parameters combine to determine bioaccumulation rates in fish. Limited studies on methyl mercury (MeHg) in precipitation shown that concentrations average from 5% of total-Hg (T-Hg), to 1% in industrial regions. Observations of increased Hg is snow and precipitation from the Arctic Circle, related to poleward atmospheric circulation patterns, also demonstrate a spring maximum accompanying ozone depletion. Increases in oxidants and soil derived Hg in the atmosphere during the summer best explain summer Hg maximums observed in precipitation, while increased temperatures raise fish metabolism increasing Hg uptake through respiration and ingestion rate. The major route of entry for MeHg to fish appears to be biomagnification, after input from precipitation, runoff and inlake methylation. Regions buffered against acid precipitation maintain low fish-Hg levels by reduced MeHg production and maintaining gill function. When considering the bioaccumulation of Hg in fish this study shows that there are many variables to consider, not all of which originate from inside the aquatic arena. Both catchment and atmospheric processes combine with aquatic variables to dictate the overall levels of MeHg observed in fish tissue. There now appears to be sufficient knowledge to develop an axiom for the identification of aquatic systems likely to be susceptible to bioaccumulation from atmospheric derived Hg.

Follow-up of mercury levels in fish, human hair and urine in the Madeira and Tapajós basins, Amazon, Brazil

Informal economy of gold mining has contaminated some important river basins in Amazon. Follow-up studies on critical compartments showed some areas with high Hg levels in fish as well as in human hair samples. Average Hg in piscivorous fish in the Madeira river itself was 846 ppb (N=284) with a maximum of 3921 ppb. Mercury in fish from non polluted areas in this basin shows high variability, even for single species. A seasonal variation in Hg content was observed, with higher values at the end of the dry season. In the upper Tapajos basin comparable values were found for fish but with a definite decreasing trend downstream. Average value for piscivorous fish in the whole Tapajos basin is 482 ppb (N=122) with a maximum value of 3770 ppb. Hair Hg was higher in fishing villages in the Tapajos (average: 17 ppm; with N=432 and maximum value of 176 ppm) than in the Madeira (average: 9 ppm; N=169; maximum 71 ppm), and data from some areas of the Tapajos suggest a decrease with time. Mercury was much higher in urine of goldshop workers in Santarem (low Tapajos) than in Alta Floresta (high Tapajos) and show a decreasing trend in both cases, probably related to the significant decline in gold mining activities during the study period (1986-1994).

Long-term study of mercury concentrations in fish following cessation of a mercury-containing discharge

Mercury-contaminated industrial effluent was discharged over a 30-year period into Princess Royal Harbour, a marine embayment on the south coast of Western Australia. The discharge of effluent was stopped in 1984 and most fish taken from the harbour at that time contained concentrations of Hg in their muscle tissue which exceeded the maximum permitted concentration (0.5 mg kg −1) set by Australian health authorities. To allay human health concerns, the contaminated portion of the harbour was closed to all forms of commercial and recreational fishing in 1984. The course of Hg contamination following cessation of the effluent discharge was monitored by determining Hg concentrations in the muscle tissue of eight teleost fish species, namely cobbler ( Cnidoglanis macrocephalus), rock flathead ( Platycephalus laevigatus), striped trumpeter ( Pelates sexlineatus), King George whiting ( Sillaginodes punctata), Australian herring ( Arripis georgianus), brown-spotted wrasse ( Pseudolabrus parilus), spiny-tailed leatherjacket ( Bigener brownii) and six-spined leatherjacket ( Meuschenia freycineti), sampled near the effluent outfall on 14 occasions from 1984 to 1993. Mercury concentration showed a significant positive relationship with length of fish for five of the species and a significant negative relationship with length for two species. Four species showed significant differences in Hg concentration depending on season (summer vs winter); summer concentrations were generally higher than those in winter. The Hg concentrations decreased with time and were about 50% of their initial values by 1993. In general, fish Hg levels had decreased to below the maximum permitted concentration by 1991 and the closed portion of the harbour was reopened in 1992. For most species, however, the rate of reduction in Hg concentration was less in the latter part of the study. The data suggest that future reductions in Hg concentrations in fish may be less than those achieved in the first 10 years, and that for some species Hg concentrations could remain elevated for many years.

Mercury in fish in the Smallwood Reservoir, Labrador, twenty one years after impoundment

The elevated mercury (Hg) levels in fish flesh found after impoundment of a reservoir, are predicted to decline as the reservoir ages. The length of time required for a return to background levels is dependent on among other things, the trophic status of the fish. Predictions for omnivorous species range between 15 and 20 years while for piscivorous species they vary from 20 to 30 years. Fish in the Smallwood Reservoir, Labrador, Canada, were sampled 6 years after impoundment when hg levels were found to be elevated in most species. Selected of the sites were re-sampled after 16 years and again after 21 years. Mercury in the flesh of omnivorous species such as lake whitefish (Coregonus clupeaformis) had returned to background levels after 16 years as predicted. However, hg in the flesh of piscivores such as northern pike (Esox lucius) and lake trout (Salvelinus namaycush) remained elevated even 21 years after impoundment. While the levels in lake trout have declined somewhat in that time, there is no evidence of decline in the northern pike either within the reservoir or at downstream stations. Models predicting decline in hg levels in piscivorous fish in reservoirs must be re-evaluated in light of this extended data set.

Mercury concentrations in an aquatic ecosystem during twenty years following abatement the pollution source

Phenyl Hg was widely used as a slimicide in Finnish pulp industry until the end of 1967. The use of Hg caused a significant increase of Hg levels in fish in several areas. High concentrations were measured in Lake Kirkkojärvi in Hämeenkyrö, SW Finland. Vast amounts of Hg are still present in the lake sediments. Since 1968 uncontaminated fibres have partly covered the contaminated layers. Since 1971 Hg has been monitored in fish, sediments and aquatic plants in the water course downstream from the pulp and paper factory. The Hg concentration of a 1-kg pike (Esox lucius) has decreased from 1.5 µg g−1 in the years 1971–74 to 0.8 µg g−1 in 1990.

Time resolution of mercury dose and lake sensitivity related to mercury content in fish

This work treats data from 75 small, mainly oligotrophic Swedish forest lakes. The aim is to study and evaluate the temporal variation of different Hg-dose and lake sensitivity parameters vs. Hg in 1-kg pike and small perch (<10 g). The lakes were treated with different remedies (such as lake liming) during 1987 in order to reduce Hg-levels in fish. Lake water chemistry has a large seasonal variation but the yearly means is clearly affected by the treatments (mean alkalinity is increased from 0.05 to 0.19 mcq*L−1). There is a marked change of Hg in perch 2 yr after treatment; the median decrease is 33%, a further time delay of about 2 yr is suggested for Hg in pike. Among the dose parameters, Hg in material from sediment traps and in water the fraction RIHg seem to be affected by the remedies with an accentuated decrease during 1988, while a slight increase of total-Hg (THg) in water can be observed. A regression model where the Hg content in perch (Hg-pe) is predicted by Hg-dose, pH and lake water retention time is presented (r2=0.71, n=22) as an example of the importance of using time compatible data with respect to the effect parameter (Hg-pe).

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.

The coupling of mercury and organic matter in the biogeochemical cycle — towards a mechanistic model for the boreal forest zone

In boreal forest lakes, high Hg concentrations in fish are common, even in remote areas. In this paper, the effects of atmospheric Hg pollution in Sweden are synthesized and related to a concept based on the strong interaction of Hg with biogenic matter (Hg/B). Based on this concept, a compartment model is developed to predict concentrations, pool sizes, flux rates and turnover times of Hg along the biogeochemical cycle, including atmosphere, forest soils, surface runoff, lake waters, and aquatic biota. The aim is to provide a conceptual framework, both for a comprehensive mechanistic model, and for predictions from readily available information, such as regional data on acid deposition, air temperature and surface runoff, and local data on the trophic status of lakes with respect to humus and nutrient concentrations. The model is in good agreement with observations from recent Swedish field studies in all compartments. It suggests a strong influence of climate on the susceptibility of soil and lake ecosystems in the boreal region to Hg contamination. The high Hg concentrations in fish from forest lakes can be largely attributed to the low productivity of both terrestrial and aquatic biota. The impact of historical point sources of Hg is considered, as well as the slow turnover of Hg in forest soils, both resulting in elevated fish Hg levels in humic lakes for centuries following atmospheric deposition.

Mercury in the Madeira River ecosystem, Rondônia, Brazil

A survey of mercury levels in river water and sediments, forest soils, fish, air and human hair is presented for the Madeira River watershed in southwest Amazonia, Brazil. Mercury levels appeared particularly high in tributary rivers close to major gold-mining areas. High Hg levels in fish (up to 2.7 ppm) were also found in such areas. Atmospheric Hg levels were mostly close to background, but can reach high values (3.2 mg/m 3) in the proximity of the HgAu reburning complex. Human-hair levels, however, reach values up to 26.7 ppm, indicating high exposure rates of the local population.

Mercury

New findings on the environmental fate of Hg indicate that lakes can be contaminated by long distance transport on mercury vapor in the atmosphere and that higher levels of Me Hg in fish are associated with acidification of lakes and with the creation of hydroelectric reservoirs. Considerable progress has been made in the understanding of the disposition and metabolism of mercury in the body. Inhaled mercury vapor rapidly enters cells in view of its lipid solubility. Inside the cell, it is oxidized by the enzyme, catalase, to inorganic divalent mercury. The latter may be the proximate toxic species. Me Hg also crosses cell membranes rapidly but, in this case, probably by forming water-soluble complexes whose structures mimic those of endogenous substrates that are transported on specific carriers. The mechanism of damage to the central nervous system by mercury vapor is still unknown. The kidney damage probably arises from the effect of inorganic mercury on immunocompetent cells causing them to produce antibodies that affect the glomerulus. The selective damage by Me Hg to specific anatomical areas of the brain and the long latent period are still unexplained. Most studies have focused on the earliest biochemical lesion, the inhibition of protein synthesis. Prenatal damage occurs in all areas of the developing brain. Cell division and abnormal neuronal migration are the processes primarily affected. The destruction of microtubules in neuronal and astrocystic cells offers a plausible explanation of the deranged cytoarchitecture. Prenatal effects such as delays in the normal development of prenatally exposed infants occur at exposures substantially lower than those associated with the onset of adult poisoning.

Concentrations of trace elements in yellow perch (Perca flavescens) from six acidic lakes

Yellow perch (Perca flavescens) were collected from six small acidic lakes in northwestern New Jersey. Analyses of muscle tissue identified a pattern of increased concentrations of Hg in fish from the most acidic lakes; levels of Cd and Pb were greatly elevated in livers of specimens from two of the most acidic lakes. At one site, Sunfish Pond, positive correlations between fish size and Hg levels in muscle and Cd concentrations in livers were detected. In only one case did Hg concentrations in muscle tissue exceed the U.S. FDA action level of 1 μg g−1 (wet wt).

Mercury content in some marine fish from the Alexandria coast.

The total Hg of 6 marine fish species, caught from the 3 main fishing grounds along the coast of Alexandria, was determined and the distribution among the different organs was studied. It was found that the total Hg levels in fish differed according to species, size, and organs of fish as well as fishing ground. The highest value was found in large size especially in the viscera of Mullus barbatus obtained from El-Mex fishing ground.

Mercury in fish and waters of the Irish Sea and other United Kingdom fishing grounds.

THE Ministry of Agriculture, Fisheries and Food has reported high mercury (Hg) levels in marketable fish from several United Kingdom fishing grounds1,2. My studies (Table 1) indicate accompanying high dissolved Hg concentrations in waters within the same study areas. An analysis of both sets of data has revealed a linear relationship (correlation coefficient 0.92) between the mean Hg concentrations of the water and fish. In distant waters a concentration factor of Hg from water to fish was 2.9×103 compared with 10.6×103 in coastal waters between Anglesey and St Bees Head. Fish harvested from these industrially affected waters ( > 50 ng 1−1 mean dissolved Hg) contained more than the 0.5 p.p.m. Hg limit set for edible fish in many countries.