Bioaccumulation of mercury in the trophic chain of flatfish from the Baltic Sea

Toxic metals in fishes, mussels, and sediments from the Puck Bay in the southern Baltic Sea

BACKGROUND

The environment of the Puck Bay is under strong pressure discharged sewage and brine.

METHODS

Toxic metals (cadmium, lead, mercury, arsenic, bromine) were determined in fishes (flounder and perch), sediments, and mussels.

RESULTS

Toxic metals in flounder and perch from the Puck Bay occurred at varying concentrations: Cd - 0.002-0.004 mg/kg; Pb - 0.011-0.029 mg/kg; Hg - 0.050-0.070 mg/kg; iAs lower than 0.02 mg/kg. The highest concentrations of metals occurred in outer bay sediments: Cd - 0.829 mg/kg dw; Pb - 21.54 mg/kg dw; Hg - 0.305 mg/kg dw; iAs - 0.02 mg/kg dw. Metal concentrations in mussels were at low levels. High Pb content (1.915 mg/kg ww) was only determined in samples collected at the station near the brine outfall.

CONCLUSIONS

Concentrations of toxic metals in the fishes, sediments, and mussels from the Puck Bay indicated that the environment of the bay was in good condition.

Comparison of Pollution Levels, Biomagnification Capacity, and Risk Assessments of Heavy Metals in Nearshore and Offshore Regions of the South China Sea

Seawater and fish were collected from nearshore (Pearl River Estuarine, PRE) and offshore (middle of the South China Sea, MSCS) regions of the South China Sea (SCS) to determine the heavy metals (HMs) pollution status and biomagnification characteristics. Results show that Cu in PRE seawater was moderately contaminated. Overall pollution risk of seawater were PRE (3.32) > MSCS (0.56), whereas that of fish was MSCS (0.88) > PRE (0.42). δ¹³C and δ¹⁵N exhibited distinguished characteristics for PRE and MSCS fish, indicating the diverse energy sources, nitrogen sources, and food web structures of nearshore and offshore regions. Cu was biomagnified whereas Pb and Ni were biodiluted in offshore fish. Hg presented significant biomagnification in both of nearshore and offshore fish. Finally, the target hazard quotient of Hg (1.41) in MSCS fish exceeded the standard limit, which was posed by high Hg concentration and consumption rate of offshore fish.

Trace Metals (As, Cd, Cr, Cu, Hg, Ni, Pb, Zn) and Stable Isotope Ratios (δ13C and δ15N) in Fish from Wulungu Lake, Xinjiang, China

Wulungu Lake is a vital fishery area in Xinjiang. However, the concentration, enrichment rules, and sources of As, Cd, Cr, Cu, Hg, Ni, Pb, and Zn in the aquatic organisms, have rarely been investigated. The results suggest that the concentrations of As, Ni, Pb, and Zn were higher than those recommended by the national standards for edible fish in some species. Hg, Ni, Cu, Pb, Cr, and Zn in the fish were dependent on the concentration of trace metals in the water environment (p < 0.05). The body weights of the fish were significantly negatively correlated with only Hg (p < 0.05); however, their body lengths were significantly positively correlated with As, Cu, Zn, and Hg contents. Values of δ¹³C ‰ (δ¹⁵N ‰) for the entire fish food web was found to range from -19.9‰ (7.37‰) to -27.7‰ (15.9‰), indicating a wide range of trophic positions and energy sources. Based on the linear correlation, As, Cu, Cd, and Zn contents were positively correlated with δ¹⁵N (p < 0.05), and bioaccumulation was observed in the fish. The target hazard quotient (THQ) of all fish species was less than 1, indicating the absence of potential risks to human health.

A risk assessment of the effects of mercury on Baltic Sea, Greater North Sea and North Atlantic wildlife, fish and bivalves

A wide range of species, including marine mammals, seabirds, birds of prey, fish and bivalves, were investigated for potential population health risks resulting from contemporary (post 2000) mercury (Hg) exposure, using novel risk thresholds based on literature and de novo contamination data. The main geographic focus is on the Baltic Sea, while data from the same species in adjacent waters, such as the Greater North Sea and North Atlantic, were included for comparative purposes. For marine mammals, 23% of the groups, each composing individuals of a specific sex and maturity from the same species in a specific study region, showed Hg-concentrations within the High Risk Category (HRC) and Severe Risk Category (SRC). The corresponding percentages for seabirds, fish and bivalves were 2.7%, 25% and 8.0%, respectively, although fish and bivalves were not represented in the SRC. Juveniles from all species showed to be at no or low risk. In comparison to the same species in the adjacent waters, i.e. the Greater North Sea and the North Atlantic, the estimated risk for Baltic populations is not considerably higher. These findings suggest that over the past few decades the Baltic Sea has improved considerably with respect to presenting Hg exposure to its local species, while it does still carry a legacy of elevated Hg levels resulting from high neighbouring industrial and agricultural activity and slow water turnover regime.

A Machine Learning Approach in Analyzing Bioaccumulation of Heavy Metals in Turbot Tissues

Metals are considered to be one of the most hazardous substances due to their potential for accumulation, magnification, persistence, and wide distribution in water, sediments, and aquatic organisms. Demersal fish species, such as turbot (Psetta maxima maeotica), are accepted by the scientific communities as suitable bioindicators of heavy metal pollution in the aquatic environment. The present study uses a machine learning approach, which is based on multiple linear and non-linear models, in order to effectively estimate the concentrations of heavy metals in both turbot muscle and liver tissues. For multiple linear regression (MLR) models, the stepwise method was used, while non-linear models were developed by applying random forest (RF) algorithm. The models were based on data that were provided from scientific literature, attributed to 11 heavy metals (As, Ca, Cd, Cu, Fe, K, Mg, Mn, Na, Ni, Zn) from both muscle and liver tissues of turbot exemplars. Significant MLR models were recorded for Ca, Fe, Mg, and Na in muscle tissue and K, Cu, Zn, and Na in turbot liver tissue. The non-linear tree-based RF prediction models (over 70% prediction accuracy) were identified for As, Cd, Cu, K, Mg, and Zn in muscle tissue and As, Ca, Cd, Mg, and Fe in turbot liver tissue. Both machine learning MLR and non-linear tree-based RF prediction models were identified to be suitable for predicting the heavy metal concentration from both turbot muscle and liver tissues. The models can be used for improving the knowledge and economic efficiency of linked heavy metals food safety and environment pollution studies.

Development of fish age normalization technique for pollution assessment of marine ecosystem, based on concentrations of mercury, copper, and zinc in dorsal muscles of fish

Correlation between metal concentrations in fish tissues and fish body size poses certain challenge when comparing concentration levels encountered at different locations or time periods by degrading performance of statistical tests due to variable age composition of fish sample pool. In order to overcome this, the concentrations of Hg, Cu, and Zn, measured in tissues of five fish species, were normalized to selected age group. Computed species-specific equations, based on empirically obtained exponential relationship, provided accurate estimates of the normalized concentrations under the conditions of substantial metal and fish age covariation. Obtained normalized and measured concentrations were then compared among sampling stations by means of commonly used analysis of variance (ANOVA) in combination with Tuckey's HSD test, where 11 out of 18 considered cases showed significant smoothing of the observed differences. The applied method worked well in the case of locally distributed coastal species populations where transformed data allowed clearer separation of spatial areas exhibiting different levels of pollution. At the same time, application of the method on pelagic fish species was less successful due to high mobility of specimens and mixed impact on the population originating from variable pollution levels at different areas of the entire migration region; therefore, attribution of a sample pool to a specific catchment area can cause a bias in assessment results.

Total Mercury Levels in Commercial Fish in Market of the Republic of Srpska, Bosnia and Herzegovina

The mercury concentration was quantified in frozen and canned fish found in the market of the Republic of Srpska, Bosnia and Herzegovina. Using the method of amalgamation by atomic absorption spectrophotometry with a direct mercury analyzer (DMA-80), significant differences in mercury concentrations among the analyzed fish were found. Frozen pangasius and canned tuna had the highest mercury concentration (59.1 μg/kg and 54.1 μg/kg, respectively). Also, fish from Vietnam had the highest level of total mercury in comparison to fish from other countries. Determined levels of mercury in our samples were below the limit set by the European and Bosnian and Herzegovinian legislation (500 μg/kg wet weight). We have concluded that consumption of commercial fish in the market of the Republic of Srpska does not present any health risk for the average consumer. Nevertheless, a surveillance system of mercury content in fishery products, especially in certain species that concentrate mercury, is crucial for public health protection.

Trophic transfer, biomagnification and risk assessments of four common heavy metals in the food web of Laizhou Bay, the Bohai Sea

This study investigated the trophic transfer of four common toxic metals (Cd, Cr, Cu and Hg) in the food web and assessed their potential ecological risks in Laizhou Bay, a spawning area for fishery populations in the Bohai Sea, North China. Based on the predation relations of 43 species that were representatives of the main trophic levels (TLs), a simplified food web was constructed using stomach content analysis and stable nitrogen isotope ratio (δ¹⁵N) analysis. Using copepods as the baseline species (TL = 2.00), the TLs of the organisms ranged from 1.96 (Polychaeta) to 4.47 (Japanese flounder) and showed the following ranking order: predatory pelagic or demersal fish > medium demersal fish > crustacean, cephalopod, small pelagic or demersal fish > zooplankton and Polychaeta. The metals showed different trophic transfer behaviors in the food web. Hg and Cr tended to be efficiently biomagnified between TLs, along the main food chains and in the food web. Cu biodiluted significantly with increasing TLs, while Cd showed no biomagnification or biodilution trends in the food web. At low or moderate levels of Cd and Hg, potential ecological risks were detected in the water and sediments at only a few sites, indicating their overall low ecological risks in the environment. The metals in the important fishery species (four top predatory fish, two cephalopods and eight crustaceans) were below the permissible limits, except for Cd in octopus and paddle crab, which reached or exceeded the most restrictive criteria. Based on the provisional tolerable weekly intake (PTWI) criteria, the safe weekly human consumption levels by humans of the predatory fish, cephalopods and crustaceans were species-specific (0.20-4.44 kg) and should be cautiously assessed.

Dynamics of mercury content in adult sichel (Pelecus cultratus L.) tissues from the Baltic Sea before and during spawning

This study compares the content of mercury in the muscles, liver, kidneys, gonads and gills of male and female individuals of sichel (Pelecus cultratus). Moreover, the trend of changes of mercury concentration before (March) and during (May) the spawning season was examined. Sichel brooders were caught in the Vistula Lagoon during commercial fishing. The mercury content in tissues was determined by atomic absorption using a Milestone DMA-80. The tests revealed a statistically higher mercury concentration in muscles, liver and gonads in male vs. female fish. Moreover, significantly higher mercury concentration was found in male and female fish caught during the spawning season (May) than in those caught before this season (March). Moreover, testes (0.011 ± 0.007 mg kg^-1 w/w) were found to contain 12 times, and ovaries (0.004 ± 0.001 mg kg^-1 w/w) - approx. 19 times less mercury than the muscular tissue of those same fish. This may suggest the existence of a protective barrier, defending future offspring against the transfer of toxic mercury from the parent body to gonads and gametes.

Environmental genotoxicity and cytotoxicity levels in herring (Clupea harengus), flounder (Platichthys flesus) and cod (Gadus morhua) inhabiting the Gdansk Basin of the Baltic Sea

Frequencies of eight nuclear abnormalities (NAs) reflecting environmental genotoxicity and cytotoxicity, were examined in 739 specimens of herring (Clupea harengus), flounder (Platichthys flesus) and cod (Gadus morhua) collected between 2009 and 2017 at 50 study stations located in the Gulf of Gdansk and the southern part of the Gdansk Deep (the Baltic Sea). The highest levels of geno-cytotoxicity were recorded in fish caught at stations located in close proximity to chemical and conventional munitions dumping sites or in zones polluted by Chemical Warfare Agents (CWAs). The values of NAs were significantly higher (up to 51-fold compared with the reference level) in herring caught at seven stations and in cod from one station located close to the munitions dumping sites. Exceptionally high total genotoxicity (∑Gtox) risk was found for flounder collected from 18 (72.0%) stations, herring caught at 12 (38.7%) stations and cod caught at four (17.4%) studied stations.

Organotropism of methylmercury in fish of the southeastern of Brazil

This is one of the first studies to evaluate the effect of biometric variables (total length and weight), diet, and abiotic matrices (sediment and water column) on the bioaccumulation of methylmercury in tissues (muscle, liver, and gills) of four fish (two carnivore-invertivores, Pimelodus fur and Pachyurus adspersus; one carnivore-piscivore, Oligosarcus hepsetus; and one omnivore, Pimelodella lateristriga) in the lower section of a river in southeastern Brazil. Samples of fish (n = 120), water (n = 5) and sediment (n = 5) were collected at five sites characterized by pollution with mercury due to the use of organomercury fungicides and stream bed gold mining, commonly carried out in that section of the river in the 1980s. The results show that biometric variables are strongly correlated with methylmercury levels in muscle (r = 0.61, p < 0.0005) of P. fur. As a rule, concentrations of total mercury and methylmercury did not vary considerably between the organs of the species of different food habits, because of the environmental conditions in the study area. Despite the low concentrations of mercury in sediments (<0.05 mg kg^-1 wet. wt), this compartment is a representative source of this pollutant for the organisms investigated, due to the close contact these animals keep with it in view of the low water columns in that section of the river.

The impact of military activities on the concentration of mercury in soils of military training grounds and marine sediments

Military activities have been conducted on land and at sea. Both during conflicts and in peace time, some regions served as a military training ground which included firing positions and bunkers. Mercury fulminate has been used in ammunition primers and detonators. Certain amount of ammunition was dumped into the Baltic Sea after the Second World War. Because of corroded containers, mercury can be released into the marine environment. The soil and sediment samples were taken from military training grounds, southern Baltic in 2014 and 2015. The concentration of mercury was determined by AMA-254 analyzer. Hg concentration was higher in the places of military activities, as compared to other areas. Ten times increased concentration of Hg was determined in soil sample collected in area of active gun range compared to the reference station. The significant higher concentration of mercury was detected in stations where chemical warfare agents were found.

Arsenic, lead, mercury and cadmium: Toxicity, levels in breast milk and the risks for breastfed infants

Metals are ubiquitous in nature, being found in all environmental compartments, and have a variety of applications in human activities. Metals are transferred by maternal blood to the fetus via the placenta, and exposure continues throughout life. For the general population, exposure comes mainly from water and food consumption, including breast milk. In this paper, we reviewed studies on the toxicity of arsenic, lead, mercury and cadmium, the toxic metals of most concern to human health, focusing on the potential risks to newborns and infants. A total of 75 studies published since 2000 reporting the levels of these metals in breast milk were reviewed. Lead was the metal most investigated in breast milk (43 studies), and for which the highest levels were reported (up to 1515µg/L). Arsenic was the least investigated (18 studies), with higher levels reported for breast milk (up to 149µg/L) collected in regions with high arsenic concentrations in water (>10µg/L). Data from 34 studies on mercury showed that levels in breast milk were generally higher in populations with high fish consumption, where it may be present mainly as MeHg. Cadmium levels in breast milk were the lowest, with means <2µg/L in most of the 29 studies reviewed. Results of risk assessments indicated that the intake of arsenic, lead and mercury by infants through breastfeeding can be considered a health concern in most regions of the world. Although the potential risks to infants are mostly outweighed by the benefits of breast milk consumption, it is essential that contaminants be continuously monitored, especially in the most critical regions, and that measures be implemented by health authorities to reduce exposure of newborns and infants to these metals, and thus avoid unnecessary health risks.

Methylmercury and Total Mercury in Eels, Anguilla anguilla, from Lakes in Northeastern Poland: Health Risk Assessment

In the aquatic environment, mercury is readily methylated into its most toxic form of methylmercury. In this form, it enters the aquatic food chain and its concentrations increase in subsequent links, which decreases the quality of fish meat and poses risks to consumer health. Concentrations of methylmercury (MeHg) and total mercury (THg) were determined in the muscle tissues of 64 eel specimens measuring from 59 to 95 cm in length as functions of specimen size and weight. Risks posed to consumers by eel from different length classes were also assessed. The mean concentration of THg in all of the eel examined was 0.179 mg kg^-1, but the range was from 0.028 to 0.487 mg kg^-1. The mean concentration of MeHg was 0.147 mg kg^-1, and the range was also wide from 0.023 to 0.454 mg kg^-1. Accumulated MeHg and THg increased with eel body length. The percentage share of MeHg in THg also changed with specimen length, and there was a positive correlation between the concentrations of MeHg and THg. Risk assessment was performed based on the doses of THg and MeHg ingested with fish for several specimen length classes. Consuming the meat of eel measuring 80 cm in length increased the estimated weekly intake (EWI) of THg and MeHg twofold in comparison to that from specimens 60 cm in length and fourfold in specimens exceeding 90 cm in length. The percentage shares of the EWI in the tolerable weekly intake and the target hazard quotient coefficient also increased proportionally. Generally, concentrations of MeHg and THg in eel are below current limits and pose no risk to consumer health as long as the consumption of larger specimens is avoided.

Dose-response analysis indicating time-dependent neurotoxicity caused by organic and inorganic mercury-Implications for toxic effects in the developing brain

A latency period preceding neurotoxicity is a common characteristic in the dose-response relationship induced by organic mercury. Latency periods have typically been observed with genotoxicants in carcinogenesis, with cancer being manifested a long time after the initiating event. These observations indicate that even a very small dose may cause extensive adverse effects later in life, so the toxicity of the genotoxic compound is dose and time-dependent. In children, methylmercury exposure during pregnancy (in utero) has been associated with delays in reaching developmental milestones (e.g., age at first walking) and decreases in intelligence, increasing in severity with increasing exposure. Ethylmercury exposure from thimerosal in some vaccines has been associated, in some studies, with autism and other neurological disorders in children. In this paper, we have examined whether dose-response data from in vitro and in vivo organic mercury toxicity studies fit the Druckrey-Küpfmüller equation c·t(n)=constant (c=exposure concentration, t=latency period), first established for genotoxic carcinogens, and whether or not irreversible effects are enhanced by time of exposure (n≥1), or else toxic effects are dose-dependent while time has only minor influence on the adverse outcome (n<1). The mode of action underlying time-dependent toxicity is irreversible binding to critical receptors causing adverse and cumulative effects. The results indicate that the Druckrey-Küpfmüller equation describes well the dose-response characteristics of organic mercury induced neurotoxic effects. This amounts to a paradigm shift in chemical risk assessment of mercurial compounds and highlights that it is vital to perform toxicity testing geared to investigate time-dependent effects.

Sex-related mercury bioaccumulation in fish from the Madeira River, Amazon

Sex plays an important role in the kinetics and dynamics of methylmercury in some animals. Although fish is the main source of mercury exposure to consumers, the role of sex in fish-Hg bioaccumulation is less known. We studied total Hg (THg) concentrations in 2538 samples (males=1052, females=1486) of fish from different trophic levels (herbivorous, planctivorous, detritivorous, omnivorous, carnivorous, piscivorous); for each species we made a post hoc estimation of the minimum number of samples required to detect variance-based differences between sexes. Only five of the 41 studied species showed significant difference between sexes; but, no consistent dominant pattern of THg concentrations favored either sex. When grouped by trophic levels, overall mean difference in THg concentrations between males and females were not statistically significant. Correlation analysis showed sex-dependent THg bio-accumulation as a function of condition factor was statistically significant and negative for all trophic levels (detritivorous, herviborous, omnivorous, planctivorous, carnivorous, and piscivorous).

CONCLUSIONS

Sex is not the main driver of Hg bioaccumulation in most Amazonian fish species; however, studies have to consider the minimum number of samples required to ascertain sex effects on THg bioaccumulation. Therefore, neither the surveillance of environmental pollution nor the current food advisories based on muscle THg need to change because of fish sex.

Mercury toxicity and the protective role of selenium in eel, Anguilla anguilla

The aim of the study was to determine the impact trace metals, mainly toxic ones, on the condition of eel (Anguilla anguilla) inhabiting four regions of Poland. Metal concentrations in eel muscle tissues were studied as functions of size, region, and season 2011-2012. The levels of metals were also used for risk assessment on consumer health. Copper and zinc occurred at concentrations that could only have positive impacts on eel condition. Low levels of cadmium and lead did not impair the condition of the fish. However, mercury occurred at high levels and increased with fish length and season. The mercury levels in eels were compared with the threshold of toxicity (500-1,200 μg kg(-1)), which can cause changes in biochemical processes and impair fish reproduction. The concentration of mercury was 1,010 μg kg(-1) in one specimen of the 120 samples examined, and in 16 specimens, it exceeded 500 μg kg(-1). The toxic effects of the mercury could have been attenuated by the selenium in the muscles of the eel, especially in the muscles of smaller specimens in which the Se/Hg molar ratio was higher than 1 with a positive correlation between these two elements. In larger specimens measuring in excess of 70 cm, this coefficient was below 1, and the mercury to selenium correlation was negative, which meant that the protective effects of selenium were weaker. The mercury in the muscles of large specimens at levels exceeding 500 μg kg(-1) could have weakened eel condition and also posed a threat to consumer health. The cadmium and lead in the muscles of the eel did not affect the condition of the fish. Mercury weakened the condition of large eel, A. anguilla. Selenium protected small- and medium-sized eel against the toxic effects of mercury.

Genotoxicological response of the common carp (Cyprinus carpio) exposed to spring water in Tlaxcala, México

This study evaluated the genotoxic impact of anthropic activities in Huactzinco Spring, using Cyprinus carpio as a biomonitor. In situ and in vivo experimental designs were compared by means of simultaneous 2-week exposures. The water from the spring generated mean micronuclei frequency values (108.6 ± 32 MN/1,000) and DNA fragmentation values (143.4 ± 35 au) which were statistically higher than those for the negative control (10.9 ± 6 MN/1,000 and 67.6 ± 23 au). The in situ and in vivo experiments supported one another. The comet assay proved to be the most sensitive test, with an EC50 value (11.4 % ± 3.4 %) being less than that determined for the micronuclei test (54.8 % ± 3.2 %). The results of this study confirm the usefulness of C. carpio as an environmental contamination biomonitor, and suggest that Huactzinco Spring water constitutes a latent risk to human health and the environment.

Concentrations of mercury in tissues of striped dolphins suggest decline of pollution in Mediterranean open waters

The Mediterranean is a semi-enclosed sea subject to high mercury (Hg) pollution from both natural and anthropogenic sources. With the objective of discerning temporal changes in marine Hg pollution in the oceanic waters of the northwestern Mediterranean Sea, we analysed liver and kidney from striped dolphins (Stenella coeruleoalba) collected during 2007-2009 and compared them with previous results from a similar sample from 1990-1993. The effect of body length and sex on tissue Hg concentrations was investigated to ensure an unbiased comparison between the periods. The Hg concentrations did not show significant sex-related differences in any tissue or period but were correlated positively with body length. Using body length as a covariate, Hg concentrations in liver and kidney were higher in 1990-1993 than in 2007-2009. This result suggests that measures to reduce emissions in Western European countries have been effective in reducing mercury pollution in Mediterranean open waters.