Application of stable isotopes to the bioaccumulation and trophic transfer of arsenic in aquatic organisms around a closed realgar mine

Biodilution of Organic Species of Arsenic in Freshwater Food Webs

Arsenic can accumulate in freshwater biota, sometimes reaching potentially harmful levels. However, the toxicity of arsenic strongly depends on which arsenic species are present. Although organic species are considered less harmful than inorganic ones, they have not been extensively studied in freshwater environments, and drivers of variation in arsenic speciation among sites and taxa remain unclear. We assessed concentrations of two organic arsenic species, arsenobetaine (AsB) and dimethylarsinic acid (DMA), in fish and invertebrates from three lakes near Sudbury, Ontario, Canada-a region with widespread mining impacts. Both AsB and DMA were detected in most samples (n = 212), varying across a wide range of concentrations (<0.001-30.144 and <0.006-5.262 mg/kg dry wt, respectively). The lake with the most severe mining impacts typically had the highest concentrations (designated by square brackets []) of AsB and DMA. In contrast, the percentage of total arsenic made up by AsB (%AsB) and DMA (%DMA) did not vary significantly between lakes. Arsenic speciation in fish muscle varied with fish size, selenium concentrations, and trophic elevation (inferred from nitrogen stable isotope ratios δ15 N), but relationships with dietary carbon source (inferred from carbon stable isotope ratios δ13 C) were more varied. Within all three lake food webs, [AsB] and [DMA] typically underwent biodilution, decreasing with trophic elevation (i.e., δ15 N). Although the aforementioned factors explained some variation in arsenic speciation, there remains considerable unexplained variation. Further studies on arsenic speciation in freshwater biota should target a wider diversity of taxa to better understand drivers of variation in arsenic speciation. In addition, research emphasizing the percentage of inorganic arsenic and other organic arsenic species is needed to improve environmental and human health risk assessments. Environ Toxicol Chem 2024;00:1-14. © 2024 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Determining the trophic transfer of metal(loid)s and arsenic speciation in freshwater aquatic organisms by quantifying diet compositions

Bioaccumulation through diet is the predominant source of metal(loid)s in fishes; however, the trophic transfer of metal(loid)s from the diet to aquatic organisms remains largely unclear. In this study, aquatic organisms and five potential food sources (leaf litter, coarse and fine particulate organic matter (CPOM and FPOM, respectively), epilithon and fish) were collected around the Shimen Realgar Mine of China. Stomach content analysis and stable nitrogen and carbon isotope analysis, combined with a new Bayesian mixing model (MixSIAR), were used to quantify diet compositions of aquatic organisms. The δ¹³C and δ¹⁵N values varied among fish sizes and sampling sites and were probably related to the diet shift of aquatic organisms. The MixSIAR modelling results showed that the aquatic organisms' food sources were mainly composed of FPOM (9%-68%) and epilithon (15%-65%), with leaf litter, CPOM and fish accounting for smaller proportions (2%-30%). Concentrations ranged from 0.91 to 1298 mg/kg for As, 0.01-1.30 mg/kg for Cd, 0.12-37.79 mg/kg for Pb, 0.63-1158 mg/kg for Cr, 1.22-411 mg/kg for Cu, 0.82-1772 mg/kg for Mn, 0.31-542 mg/kg for Ni and 21.84-1414 mg/kg for Zn in all the collected samples, including the aquatic organisms and the relevant food sources. The metal(loid) concentrations in the CPOM, FPOM and epilithon were significantly higher than those in aquatic organisms and leaf litter. In addition, the biomagnification factors were all less than 1, indicating a biodilution from diet to freshwater organisms. The predominant As species were organic As in aquatic organisms, while inorganic As was common in their food sources, indicating that As biotransformation occurred within the freshwater food chain.

Concentrations of heavy metals in water, sediments and aquatic organisms from a closed realgar mine

Mining activities can result in severe heavy metal contamination in freshwater ecosystems and lead to significant health risks. In this study, eight heavy metal concentrations in the water, sediments and aquatic organisms, including eighteen fish species, two shrimp species, one crab species and one amphibian frog species of the abandoned Shimen Realgar Mine area, were analysed. The results showed that most of the heavy metals detected in water, sediments and fish from the mine area were at relatively high levels, and historical realgar mining activities were a major source of arsenic (As) contamination in this area. We concluded that heavy metal bioaccumulation is species- and tissue-specific and is different for each element and sampling site. The concentration of heavy metals in fish was generally lower than that of the other aquatic organism species; these concentrations varied among different species with different feeding habits and habitats. The study showed that heavy metal concentrations were lower in muscle tissue than in other tissues (e.g. liver, skin, exoskeleton). A significant positive correlation between the As concentrations in sediment and fish was observed, indicating that sediment is an important factor affecting As accumulation in fish; thus, for fish protection, controlling the sources of water and sediment contamination is essential. Furthermore, the estimated daily intake (EDI) of all metals was acceptable, and the corresponding target hazard quotient (THQ) and total target hazard quotient (TTHQ) values were less than 1; hence, there was no serious health risk through fish consumption in this area.

Insights from the Niger Delta Region, Nigeria on the impacts of urban pollution on the functional organisation of Afrotropical macroinvertebrates

Anthropogenic activities, including urbanisation and industrialisation threaten stream ecological integrity, ecosystem community structure and ecosystem functioning of rivers and streams worldwide. However, developing sustainable monitoring strategies for ecological health remains a critical challenge in Africa. We examined the effects of urban disturbance on macroinvertebrate Functional Feeding Groups in selected streams in the Niger Delta Region of Nigeria. We sampled 11 sites between 2008 and 2012 and grouped into three site groups (Site groups 1 > 2 > 3). The groups represent an increasing gradient of urban pollution. Our result showed that urban-induced disturbances affected physicochemical variables in the study area (PERMANOVA; p < 0.05), with nutrients NO₂-N, PO₄-P, and electrical conductivity being significantly higher in impacted Site group 3 (ANOVA, p < 0.05). Predators and gatherers were the most dominant Functional Feeding Group recorded in the study area, while shredders were the least abundant macroinvertebrate Functional Feeding Groups. The multivariate RLQ analysis revealed that shredders, predators, and scrapers were tolerant of urban pollution, whereas gatherers were sensitive to increasing urban pollution. Overall, macroinvertebrates Functional Feeding Groups responded differentially to urban pollution in the Niger Delta Region. Identifying pollution indicator Functional Feeding Groups is seen as an important step towards developing a reliable, low-cost tool for riverine monitoring of urban pollution effects in Africa.

The speciation of arsenic in the muscle tissue of inland and coastal freshwater fish from a remote boreal region

Elevated concentrations of total arsenic (As) have been reported in boreal freshwater fish in both human-impacted and relatively pristine areas. We assessed the arsenic speciation profiles in muscle tissue of six fish species (n = 300) sampled from nine locations across a remote freshwater watershed in northern Ontario, Canada, extending from inland headwater lakes to the coastal marine confluence. Of the five arsenic species measured, only arsenobetaine (AsB) and dimethylarsinic acid (DMA) were detected in these fish. Riverine fish had up to 10-fold higher total [As] when compared to lacustrine fish. On average, these riverine fish also had higher percentages of AsB (%AsB, 60 ± 26%) and lower percentages of unmeasured arsenic (%UNM, 20 ± 21%), compared to lacustrine fish (28 ± 18% and 52 ± 21% %AsB and %UNM, respectively). DMA percentages (%DMA) were relatively consistent across the watershed, averaging 20 ± 21% across all fish. We examined ecological drivers of As speciation and found that %AsB increased slightly with fish weight in large-body predatory fish, but not in forage fish or insectivores. Furthermore, %AsB was positively related to trophic elevation (inferred from δ¹⁵N) in lacustrine fish across 3 out of 4 communities and within some populations. Lastly, riverine fish with a more marine-based diet had markedly higher %AsB when compared to fish with more freshwater-based diets, indicating an effect of anadromy on arsenic speciation. Overall, knowledge on arsenic speciation in freshwater fish has been limited and these results indicate potential drivers that can be considered in future studies. Furthermore, the absence of toxic inorganic As species in these boreal fish is an important consideration for future environmental monitoring practices and risk assessments, some of which assume 10-20% of total [As] in fish is present as toxic inorganic As. Additional studies on As bioaccumulation and biotransformation are needed in freshwater systems, particularly at the base of aquatic food webs.

Source appointment of potentially toxic elements (PTEs) at an abandoned realgar mine: Combination of multivariate statistical analysis and three common receptor models

Identifying pollution sources and quantifying their contributions are of great importance for proposing management and control strategies of potentially toxic elements (PTEs) in soil. In this study, multivariate statistical analysis and receptor models were combined to identify potential pollution sources and apportion their contributions at an abandoned realgar mine. Principal component analysis (PCA) result shows that three factors are responsible for PTEs, which is also supported by cluster analysis (CA). Correlation analysis and spatial analysis also show that the heavy metals from the same pollution source are of higher correlation coefficients and similar spatial distribution. Three receptor models were combined to apportion contributions of pollution sources. Three pollution sources were detected by absolute principal component analysis-multiple linear regression (APCA-MLR). In contrast, four sources were identified by positive matrix factorization (PMF) and UNMIX. Soil parent material was heavily loaded on Cr, Cu, Ni and Zn, occupying the largest average contribution (30%-43%). Cadmium was mainly derived from agricultural activities with contribution higher than 60%. Arsenic accumulation was mainly associated with mining and smelting activity with contribution higher than 80%. PMF and UNMIX models showed that more than half of Pb concentrations were influenced by industrial activities. Comparatively speaking, APCA-MLR was a well-performing model for all PTEs even though it only detected three pollution sources. The study showed that it was a good choice to apply multiple receptor models in order to achieve more reliable and objective conclusions of source appointment.

Pollution characteristics and environmental availability of toxic elements in soil from an abandoned arsenic-containing mine

Understanding the pollution characteristics and assessing the ecological risk of toxic metals in mine soil are crucial to controlling and managing risks in abandoned mine areas. In this study, the profile soil pollution characteristics and modified ecological risk of As, Cd, Hg, Pb, Sb, and Tl for both the different mining functional areas and the downstream impacted areas at a large-scale abandoned arsenic-containing mine were studied. Results showed that both the profile soils at the mining functional areas and the surface layer in downstream sites are heavily polluted by As, Cd, Hg, Sb, and Tl. As, Hg, Sb, and Tl mainly accumulated on soils with a depth of 0-1.5 m. In contrast, these metals in the mining site were gradually increased with soil depth above the bedrock strata. Cd and Pb were mainly concentrated at depth of 2.5-3.5 m in the smelting with by-product processing site. The speciation of metals in the profile soils mainly occurred in residual fraction. However, high levels of potential mobile As and Sb were found in mining soils and smelting surface soils, as well as Tl in deep soils at mining functional sites and top soils at downstream sites, with their mean contents in these areas arrived to 2950 mg kg^-1, 9.64 mg kg^-1, and 0.98 mg kg^-1, respectively. In addition, the modified ecological risk assessment (NIRI_m) values revealed a substantial ecological risk of As, Cd, Hg, and Sb in both the entire profile soils at the mining, smelting sites and topsoil (0-1.5 m) at the adjacent downstream site. In summary, the pollution characteristics and potential ecological risk of toxic metals in profile soils from the different functional sites at arsenic-containing mine were significantly different and suitable control strategies for available toxic elements should be adopted in the different functional sites of mine.

Environmental monitoring of trace elements and evaluation of environmental impacts to organisms near a former uranium mining site in Nigyo-toge, Japan

This study was conducted to find out characteristics of trace element levels and those impacts to organisms at a former uranium (U) mining site. Concentrations of trace elements (Li, Mg, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, As, Se, Rb, Sr, Mo, Cd, Cs, Ba, Pb, Bi, and U) were determined in sediments, water, and three organism types (insects, frogs, and newts) from three zones in the former U mining site, Ningyo-toge in Japan. Concentrations of As and U in the sediments and water samples were the highest at the mill tailings pond (MP) site, where post-U extraction remnants have been accumulated. Additionally, among the organisms analyzed the highest concentrations of these elements/isotopes were found in newts from MP. Considering data analyses of the whole-body element concentrations, bioaccumulation factors, and δ¹⁵N values for the organisms, it was concluded that newts might be the most vulnerable species in this location. Further monitoring and more accurate evaluation of the ecological impacts are preferred for this former U mining site.

Drivers of biomagnification of Hg, As and Se in aquatic food webs: A review

Biomagnification of trace elements is increasingly evident in aquatic ecosystems. In this review we investigate the drivers of biomagnification of mercury (Hg), arsenic (As) and selenium (Se) in aquatic food webs. Despite Hg, As and Se biomagnify in food webs, the biomagnification potential of Hg is much higher than that of As and Se. The slope of trophic increase of Hg is consistent between temperate (0.20), tropical (0.22) and Arctic (0.22) ecosystems. Se exerts a mitigating role against Hg toxicity but desired maximum and minimum concentrations are unknown. Environmental (e.g. latitude, temperature and physicochemical characteristics) and ecological factors (e.g. trophic structure composition and food zone) can substantially influence the biomagnification process these metal (oids). Besides the level of bioaccumulated concentration, biomagnification depends on the biology, ecology and physiology of the organisms that play a key role in this process. However, it may be necessary to determine strictly biological, physiological and environmental factors that could modulate the concentrations of As and Se in particular. The information presented here should provide clues for research that include under-researched variables. Finally, we suggest that biomagnification be incorporated into environmental management policies, mainly in risk assessment, monitoring and environmental protection methods.

The ZrO2 NPs enhanced the risk of arsenate by promoting its accumulation and reducing its detoxification during food chain transfer from Daphnia magna to zebrafish

Arsenic (As) can co-occur with zirconium dioxide nanoparticles (ZrO₂ NPs) in aquatic environments, but their combined influence along the aquatic food chain is barely explored. This study constructed water flea Daphnia magna - zebrafish Danio rerio to evaluate the impact of ZrO₂ NPs on the accumulation, trophic transfer, transformation, and detoxification of arsenate (As(V)). The zebrafish were fed D. magna exposed to As(V), ZrO₂ NPs, or As(V) + ZrO₂ NPs for 20 d. Results demonstrated that ZrO₂ NPs significantly facilitated total As and As(V) sorption in D. magna and in tissues of zebrafish. ZrO₂ NPs enhanced the transformation of inorganic arsenic (iAs) to monomethylated acid (MMA), while decreased synthesis of arsenobetaine (AsB) in tissues, leading to iAs increased. Co-exposed As(V) and ZrO₂ NPs facilitated upregulation of absorption-related genes (aqp7) and As biotransformation-related genes (gst, gss), and detoxification and oxidative stress-related genes (mt2, cat, sod1 and sod2). Therefore, genetic expression coupling with biotransformation for the first time demonstrated that As(V) combined with ZrO₂ NPs led to increased harm to D. magna and zebrafish and amplified the ecological risks of As(V) along the aquatic food chain. Attention should be paid to the combined toxicity of As(V) and ZrO₂ NPs in aquatic environment.

Pollution characteristics and source identification of soil metal(loid)s at an abandoned arsenic-containing mine, China

Mining activities can result in serious contamination of soil by heavy metal(loid)s. In this study, the sources and spatial distribution of metal(loid)s, and the risks to public health from these metal(loid)s at an abandoned arsenic mine site were explored. The mean concentrations of arsenic (As), cadmium (Cd), mercury (Hg), manganese (Mn), lead (Pb), antimony (Sb), strontium (Sr), and thallium (Tl) in the soil in the mining area were higher than the mean background values. The main pollutants from the mining activities were As, Hg, and Sb. Five pollutant sources were identified using an approach that combined statistical methods, a positive matrix factorization model, and historical information analysis. As, Hg, Sb, and Tl were associated with the mining resources and related activities (37.29%); Mn (15.57%) and Sr (15.96%) were mainly from crustal origin and pedogenesis, respectively; Pb, Sb, and Tl were mainly from industrial sources (17.57%), and Cd was mainly from the production and application of phosphorous fertilizer (13.60%). Using incremental spatial autocorrelation crystallized that As, Hg, and Sb were mainly contained within 500 m of their source. There were formed existing non-carcinogenic hazards and carcinogenic risks from As, and potential carcinogenic risks from Cd, in the soil for those living locally.

The potential of arsenic biomagnification in marine ecosystems: A systematic investigation in Daya Bay in China

In this study, we systematically investigated the bioaccumulation and trophic transfer of arsenic (As) in a typical semi-enclosed gulf, Daya Bay. Ten categories of organisms and environmental samples for As, δ¹³C, and δ¹⁵N analyses were collected from 14 sampling sites in all four seasons. The results demonstrated that As concentrations in the organisms and environmental samples were within the normal range of As levels in other uncontaminated marine ecosystems. Arsenic concentrations were generally lower in the pelagic organisms than in the benthic organisms. Arsenic concentrations in the organisms at higher trophic levels (fish, crabs, shrimp, and cephalopods) were lower in summer and higher in winter, while As in the environments was stable in all seasons. The results of δ¹³C and δ¹⁵N analysis indicated that this ecosystem had a marine-derived food web with approximately 3.5 trophic levels. The positive correlation of As and δ¹⁵N in the organisms demonstrated that As was biomagnified along trophic transfer in the whole gulf food web in winter and spring. Specifically, As was biomagnified in the benthic food chains in all four seasons and in the pelagic food chains in winter and spring. These trends were consistent with the analysis of As transfer among the categories within the empirical food web. The trophic magnification factors (TMFs) of As were generally higher among the benthic categories than the pelagic categories. In addition, As transfer from stomach content to muscle was positively correlated to δ¹³C in fish, suggesting that As transfer was enhanced by a benthic habit. These results demonstrated that As could be biomagnified in marine food webs for specific organism compositions and seasonal variations, and a benthic habit was an important promoter for As biomagnification. Therefore, this study partially explained previous investigations in which As trophic transfers were diverse among marine ecosystems.