Arsenic (V) bioconcentration kinetics in freshwater macroinvertebrates and periphyton is influenced by pH

Arsenic bioaccumulation and biotransformation in aquatic organisms

Arsenic exists universally in freshwater and marine environments, threatening the survival of aquatic organisms and human health. To elucidate arsenic bioaccumulation and biotransformation processes in aquatic organisms, this review evaluates the dissolved uptake, dietary assimilation, biotransformation, and elimination of arsenic in aquatic organisms and discusses the major factors influencing these processes. Environmental factors such as phosphorus concentration, pH, salinity, and dissolved organic matter influence arsenic absorption from aquatic systems, whereas ingestion rate, gut passage time, and gut environment affect the assimilation of arsenic from foodstuffs. Arsenic bioaccumulation and biotransformation mechanisms differ depending on specific arsenic species and the involved aquatic organism. Although some enzymes engaged in arsenic biotransformation are known, deciphering the complicated synthesis and degradation pathway of arsenobetaine remains a challenge. The elimination of arsenic involves many processes, such as fecal excretion, renal elimination, molting, and reproductive processes. This review facilitates our understanding of the environmental behavior and biological fate of arsenic and contributes to regulation of the environmental risk posed by arsenic pollution.

Mediation of arsenic mobility by organic matter in mining-impacted sediment from sub-Arctic lakes: implications for environmental monitoring in a warming climate

Arsenic (As) is commonly sequestered at the sediment-water interface (SWI) in mining-impacted lakes through adsorption and/or co-precipitation with authigenic iron (Fe)-(oxy)hydroxides or sulfides. The results of this study demonstrate that the accumulation of organic matter (OM) in near-surface sediments also influences the mobility and fate of As in sub-Arctic lakes. Sediment gravity cores, sediment grab samples, and porewaters were collected from three lakes downstream of the former Tundra gold mine, Northwest Territories, Canada. Analysis of sediment using combined micro-X-ray fluorescence/diffraction, K-edge X-ray Absorption Near-Edge Structure (XANES), and organic petrography shows that As is associated with both aquatic (benthic and planktonic alginate) and terrestrially derived OM (e.g., cutinite, funginite). Most As is hosted by fine-grained Fe-(oxy)hydroxides or sulfide minerals (e.g., goethite, orpiment, lepidocrocite, and mackinawite); however, grain-scale synchrotron-based analysis shows that As is also associated with amorphous OM. Mixed As oxidation states in porewater (median = 62% As (V), 18% As (III); n = 20) and sediment (median = 80% As (-I) and (III), 20% As (V); n = 9) indicate the presence of variable redox conditions in the near-surface sediment and suggest that post-depositional remobilization of As has occurred. Detailed characterization of As-bearing OM at and below the SWI suggests that OM plays an important role in stabilizing redox-sensitive authigenic minerals and associated As. Based on these findings, it is expected that increased concentrations of labile OM will drive post-depositional surface enrichment of As in mining-impacted lakes and may increase or decrease As flux from sediments to overlying surface waters.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s12665-022-10213-2.

Exploring the role of water chemistry on metal accumulation in biofilms from streams in mining areas

Biofilms play a key role in aquatic ecosystems. They are ubiquitous, even in the most contaminated ecosystems, and have great potential as biomonitors of exposure to contaminants such as metals. Freshwater biofilms and surface waters were sampled in two active mining areas of Canada: in the northern part of Nunavik (Quebec) and in the Greater Sudbury area (Ontario). Significant linear relationships were found between both total dissolved and free metal ion concentrations with biofilm metal contents for Cu and Ni, but not for Cd. When pH was below 6, biofilms accumulated less metals than at higher pHs. These results confirm that protons have a protective effect, leading to lower internalized metal concentrations. When considering only the sites where pH was above 6, the linear relationships between metal concentrations in water and in biofilms were improved for all three studied metals. The presence of metal ions could also modify the internalization of a given metal. To further study the role of cations as competitors to Cu, Ni and Cd uptake, relationships between the ratio of biofilm metal contents (Cu, Ni and Cd) on the ambient free metal ion concentrations were built as a function of potential cation competitors, such as major cations and metals. Surprisingly, our data suggest that calcium plays a minor role in preventing metal accumulation as compared to magnesium and possibly other metals. At a global scale, metal accumulation remained highly consistent between the two studied regions and over the sampling period, despite differences in ambient physicochemical water characteristics, climate or types of ecosystems. Metal bioaccumulation is thus a promising biomarker to assess metal bioavailability in a mining context. Nevertheless, more data are still required to further highlight the contribution of each competitor in metal accumulation by biofilms and to be able to build a unifying predictive model.

Accumulation of trace metals in freshwater macroinvertebrates across metal contamination gradients

Historical mining activities cause widespread, long-term trace metal contamination of freshwater ecosystems. However, measuring trace metal bioavailability has proven difficult, because it depends on many factors, not least concentrations in water, sediment and habitat. Simple tools are needed to assess bioavailabilities. The use of biomonitors has been widely advocated to provide a realistic measure. To date there have been few attempts to identify ubiquitous patterns of trace metal accumulation within and between freshwater biomonitors at geographical scales relevant to trace metal contamination. Here we address this through a nationwide collection of freshwater biomonitors (species of Gammarus, Leuctra, Baetis, Rhyacophila, Hydropsyche) from 99 English and Welsh stream sites spanning a gradient of high to low trace metal loading. The study tested for inter-biomonitor variation in trace metal body burden, and for congruence amongst accumulations of trace metals within taxa and between taxa across the gradient. In general, significant differences in trace metal body burden occurred between taxa: Gammarus sp. was the most different compared with insect biomonitors. Bivariate relationships between trace metals within biomonitors reflected trace metal profiles in the environment. Strong correlations between some trace metals suggested accumulation was also influenced by physiological pathways. Bivariate relationships between insect biomonitors for body burdens of As, Cu, Mn and Pb were highly consistent. Our data show that irrespective of taxonomic or ecological differences, there is a commonality of response amongst insect taxa, indicating one or more could provide consistent measures of trace metal bioavailability.

Testing the response of benthic diatom assemblages to common riverine contaminants

Benthic diatoms constitute keystone assemblages in riverine ecosystems, and their structure is used to support regulatory water quality assessment. However, no standard ecotoxicological tests exist using integrated responses of the benthic diatom assemblages. This work aimed to assess whether benthic diatom assemblages are responsive to different riverine contaminants through a previously developed rapid toxicity test, supporting future attempts towards its standardization and integration in both prospective and retrospective Environmental Risk Assessment (ERA) schemes. We selected two benthic diatoms assemblages likely responding similarly to pollution (similar IPS diatom index score), collected from two rivers in Northern-Central Portugal (sites: Palhal and Cabreia). Fresh whole diatom assemblages were exposed for 48 h to five model contaminants (glyphosate, imidacloprid, SDS, CuSO₄, and Pb). At the end of the test, changes induced by the exposures in overall yield and in the yield of each diatom genus were assessed. The assemblage collected at Palhal was invariably more responsive and sensitive than that collected at Cabreia, both considering overall and genus-specific yields, regardless of the tested contaminant. Achnanthes, Fragilaria and Navicula were the most responsive genus, regardless of the tested contaminant or assemblage. The distinct response profiles observed for the two assemblages to the same contaminants at the same concentration ranges suggest that using this test method to support prospective ERA is inadequate. However, the method can be an asset supporting retrospective ERA, as the responses seem to be shaped by the interplay of resilience drivers promoted by the local conditions, e.g. adaptive changes in assemblage structure.

Proton Competition and Free Ion Activities Drive Cadmium, Copper, and Nickel Accumulation in River Biofilms in a Nordic Ecosystem

Biofilms can be used as a biomonitoring tool to determine metal bioavailability in streams affected by mining and other anthropogenic activities. Surface water and biofilm were sampled over two years from rivers located in the vicinity of a mine located in a Nordic ecosystem (Nunavik, Quebec). Biofilm metal content (Cd, Cu, and Ni) as well as a variety of physicochemical properties were determined to examine relationships between metal accumulation and water quality. Among the three metals of interest, copper and nickel had the highest levels of accumulation and cadmium had the lowest. When considering the exposure levels, nickel was the most abundant metal in our sampling sites. Both exposure and accumulation levels were consistent over time. Biofilm metal content was highly correlated to the ambient free metal ion concentration for sites of circumneutral pHs for all three metals. When the surface water pH was below 6, biofilm metal content was much lower than at other sites with similar aqueous metal concentrations of exposure. This apparent protective effect of decreasing pH can be explained by proton competition with dissolved metals for uptake binding sites at the surface of the organisms within the biofilm as described by the Biotic Ligand Model principles. The relationships obtained for Cd and Cu were overlapping those observed in previous publications, indicating strong similarities in metal accumulation processes in biofilms over very large geographical areas. Although more data are needed for Ni, our results show that biofilms represent a promising metal biomonitoring tool.

Sorption and transformation of arsenic by extracellular polymeric substances extracted from Synechocystis sp. PCC6803

Cyanobacteria widely distribute in the aqueous ecosystem and produce abundant extracellular polymeric substances (EPS), yet little is known about how the quantity and composition of cyanobacterial EPS change upon As exposure, and what are functions of these complex biopolymers in the As sorption and transformation processes. Here we extracted the EPS from Synechocystis sp. PCC6803, characterized their properties, quantified their components upon exposure to arsenite (As^(III))/arsenate (As^(V)) treatments, and investigated As binding and speciation as affected by the levels of EPS and solution pH. The total binding sites, zeta potential and reducing power of EPS were 17.47 mmol g^-1, -19.72 mV and 1.71. The amounts of EPS increased by 22-65.3% and 13.8-39% when the cells were treated with 10-500 μM As^(III) and As^(V) respectively. The As removal was influenced by the EPS doses and solution pH, with 52.8% at pH 8.5 for As^(III) and 49.5% at pH 4.5 for As^(V) at 300 mg L^-1 EPS. In addition, As speciation was transformed with the addition of EPS. As^(V) and As^(III) respectively accounted for 4.9-20.3% and 6.5-26.7% of the total dissolved As after the EPS were added (100-300 mg L^-1) to the As^(III) and As^(V) solutions. Fourier transform infrared spectroscopy (FTIR) and three-dimensional excitation-emission fluorescence spectra (3D-EEM) revealed that As was bound to functional groups such as C═O, ─NH, and ─OH in the EPS via surface complexation/hydrophobic interactions. Taken together, this study demonstrated that the EPS extracted from Synechocystis were capable to bind and transform As and could be potentially applied to remove or detoxify As in solutions.

Digestive solubilization of particle-associated arsenate by deposit-feeders: The roles of proteinaceous and surfactant materials

Solubilization of arsenate in guts of deposit-feeders is a key process for their dietary uptake of arsenate from contaminated sediments. The present study explored this digestive solubilization with in vitro extraction experiments that quantified arsenic (As) release from substrates (natural sediment and As-enriched iron oxides) in the presence of various digestive agents (proteins, amino acids and surfactants collected from gut fluid of a sipunculan worm). To investigate potential mechanisms for the influence of digestive agents, analyses determined correlations between As and Fe concentrations, the size distribution of the As bound to the digestive agents, and the adsorption of the digestive agents on the substrates. Both the digestive surfactants and proteinaceous materials increased arsenate mobilization, with the surfactants enhancing the effects of the proteinaceous materials. Arsenate reduction and reductive dissolution of iron oxides were not observed and correlations between the concentrations of released As and Fe were weak. These findings indicate that dissolution release of Fe did not appear to be the main route by which the digestive agents mobilized particle-associated As. Most of the released As (>70%) was distributed in the <10 kDa fraction of the digestive agents, showing that the As mobilization was also not caused by complexation with proteins in the digestive agents. In contrast, adsorption of the digestive agents occurred along with the release of arsenate from the arsenate-rich substrates, suggesting that competitive adsorption was the mechanism by which the digestive agents mobilized sedimentary arsenate. Our work demonstrated that the presence of digestive surfactants significantly enhances arsenate availability during deposit feeding.

Biological toxicity response of Asian Clam (Corbicula fluminea) to pollutants in surface water and sediment

As a typical test species, Asian Clam (Corbicula fluminea) is widely used in the identification and evaluation of freshwater toxicity. This study provides a summary of the research published from 1979 to 2018. The focus was on the bioaccumulation, morphological and behavioral changes, and biochemical index alterations of Corbicula fluminea to target pollutants (i.e., ammonia, metal(loid)s, and organic chemicals) in surface water and sediment. The applications on the evaluation of actual aquatic pollution, determination of toxicological mechanisms, prediction of toxicity, and bioremediation are also specifically discussed. The primary purpose is to facilitate the comprehensive understanding and accurate application of Corbicula fluminea in freshwater ecotoxicological studies.

Periphyton and abiotic factors influencing arsenic speciation in aquatic environments

Benthic periphytic biofilms are important food sources at the base of aquatic ecosystems. These biofilms also sit at the interface of oxic waters and hypoxic sediments, and can be influenced by or influence trace element speciation. In the present study, we compared arsenic (As) enrichment in periphyton exposed to arsenate (As[V]) or arsenite (As[III]) (20 μg/L, static renewal, 7 d), and we found similar accumulation patterns of total As (101 ± 27 and 88 ± 22 mg kg^-1 dry wt, respectively). Periphyton As was 6281- and 6684-fold higher than their aqueous exposures and occurred primarily as As(V). When these biofilms were fed to larval mayflies, similar total As tissue concentrations (13.9 and 14.6 mg kg^-1 dry wt, respectively) were observed, revealing significant biodilution (∼ 10% of their dietary concentrations). Finally, we investigated the influence of aeration and periphyton presence on As speciation in solutions and solid phases treated with As(III). Predominantly As(III) solutions were slowly oxidized over a 7-d time period, in the absence of periphyton, and aeration did not strongly affect oxidation rates. However, in the presence of periphyton, solution and solid-phase analyses (by microscale x-ray absorption spectroscopy) showed rapid As(III) oxidation to As(V) and an increasing proportion of organo-As forming over time. Thus periphyton plays several roles in As environmental behavior: 1) decreasing total dissolved As concentrations via abiotic and biotic accumulation, 2) rapidly oxidizing As(III) to As(V), 3) effluxing organo-As forms into solution, and 4) limiting trophic transfer to aquatic grazers. Environ Toxicol Chem 2018;37:903-913. © 2017 SETAC.

Periphyton uptake and trophic transfer of coal fly-ash-derived trace elements

To determine whether the bioavailability of trace elements derived from coal ash leachates varies with the geochemical conditions associated with their formation, we quantified periphyton bioaccumulation and subsequent trophic transfer to the mayfly Neocloeon triangulifer. Oxic ash incubations favored periphyton uptake of arsenic, selenium, strontium, and manganese, whereas anoxic incubations favored periphyton uptake of uranium. Mayfly enrichment was strongest for selenium, whereas biodilution was observed for strontium, uranium, and arsenic. Environ Toxicol Chem 2017;36:2991-2996. © 2017 SETAC.