Speciation and toxicity of arsenic in mining-affected lake sediments in the Quinsam watershed, British Columbia

Occurrence and mobility of thiolated arsenic in legacy mine tailings

We studied the occurrence of dissolved thiolated Arsenic (As) in legacy tailings systems in Ontario and Nova Scotia, Canada, and used aqueous and mineralogical speciation analyses to assess its governing geochemical controls. Surface-accessible and inundated tailings in Cobalt, Ontario, contained ∼1 wt-% As mainly hosted in secondary arsenate minerals (erythrite, yukonite, and others) and traces of primary sulfide minerals (cobaltite, gersdorffite and others). Significant fractions of thiolated As (up to 5.9 % of total dissolved As) were detected in aqueous porewater and surface water samples from these sites, comprising mostly monothioarsenate, and smaller amounts of di- and tri-thioarsenates as well as methylated thioarsenates. Tailings at the Goldenville and Montague sites in Nova Scotia contained less (<0.5 wt-%) As, hosted mostly in arsenopyrite and As-bearing pyrite, than the Cobalt sites, but exhibited higher proportions of dissolved thiolated As (up to 17.3 % of total dissolved As, mostly mono- and di-thioarsenate and traces of tri-thioarsenate). Dissolved thiolated As was most abundant in sub-oxic porewaters and inundated tailings samples across the studied sites, and its concentrations were strongly related to the prevailing redox conditions and porewater hydrochemistry, and to a lesser extent, the As-bearing mineralogy. Our novel results demonstrate that thiolated As species play an important role in the cycling of As in mine waste systems and surrounding environments, and should be considered in mine waste management strategies for high-As sites.

Assessment of heavy metal contamination in street dust: concentrations, bioaccessibility, and human health risks in coal mine and thermal power plant complex

Coal mining has also been associated with adverse environmental and health impacts including cancer and respiratory disorders, with the presence of thermal power plants exacerbating the problem of heavy metal pollution. Minimal studies have been conducted on the environmental impacts, health risks, and bioaccessibility of heavy metals in coal mine areas. Consequently, samples of street dust were collected from different locations in the Singrauli mine complex and analysed. Heavy metals (Cu, Ni, Zn, Cr, Co, As, and Mo) were found to be higher than the background concentration, with the maximum concentration was found in areas close to the Thermal Power Plants, like Near Vindyachal TPP, Near Shakti Nagar TPP, and Anpara. The highest geo-accumulation index value was found for Co, Mo, Zn, and As, indicating moderate to strong pollution levels. Health risk assessment (for both adults and children) revealed that Cr and Fe posed significantly higher Hazard Quotient and Hazard Index (HI) values, indicating significant non-carcinogenic threats. Moreover, Carcinogenic Risk (CR) values for Cd, Cr, and Ni indicated a risk of carcinogenicity to the public exposed to road dust. The study also examined the bioaccessibility of the metals, which showed that the gastric phase accumulated a higher percentage of Ni (42.52%), Pb (34.79%), Co (22.22%), As (20%) and Cu (15%) than the intestinal phase. Strong positive correlation was observed between metal concentration (Cu, Pb, Cr, Fe, Zn, and Mn), HI, and CR of adult and child, while bioaccessibility of intestinal phase was positively correlated with gastric phase of metals (Cu, Ni, Co, As, and Mn).

Trends and environmental factors of arsenic in sediments from the five lake ecoregions, China

The behavior and risk of arsenic (As) closely relate to its geochemical fractionation and environmental factors in sediments. The soluble (F1), reducible (F2), oxidizable (F3), and residual fraction (F4) of As were extracted in the sediments from Lake Hulun, Wuliangsuhai, and Dalinor of Inner Mongolia Plateau. Coupled with lakes from Eastern and Northeast Plain, Yunnan-Guizhou and Qinghai-Tibetan Plateau, the responses of As fractions to environmental conditions were investigated according to the spatial distribution of As fractionations in five lake ecoregions at a national scale of China. Generally, F1 was more sensitive to environmental changes, and the pH presented significantly negative effects on the amount of soluble As, while water depth played an important role in regulating the distribution of the fraction F2 and F4. The As pools in surface lake sediments presented a latitudinal zonation due to the gradient effects of climate and anthropogenic activities on nutrient decomposition, and their influence on the capacity of sediments holding As. This work indicated that nutrients played a coordinating role in regulating the impacts of climate and environmental factors on As fractionation in aquatic environments.

Leachability characteristic of heavy metals and associated health risk study in typical copper mining-impacted sediments

A total of 100 samples were collected from the sediments of a typical copper mining area, south China. Leaching concentrations of selected heavy metals (Ni, Cd, Cu, Pb, Zn, Ba, As, and Hg) were measured to evaluate their distribution patterns and associated health risk. Leaching concentrations of Cu (3.58 ± 1.49 mg/L), Pb (1.50 ± 1.06 mg/L), and Zn (4.04 ± 1.68 mg/L) were significantly higher than the other metals in the samples. By evaluating the spatial heterogeneity, it was found that leaching metal concentrations did not decrease with environmental gradients, mostly caused by diverse distribution in pollution sources. The hazard index and carcinogenic risk indices showed significant risks of human exposure. For public safety, priority governance should be given to the main pollutants (Cd, Cu, Pb, Zn, and As) in sediments. In future studies, the integrated data will be urgently required for local stakeholders to conduct environmental monitoring and remediation scenarios.

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.

Controls governing the spatial distribution of sediment arsenic concentrations and solid-phase speciation in a lake impacted by legacy mining pollution

Forty-seven sediment cores were collected as part of a spatial survey of Long Lake, Yellowknife, NWT, Canada to elucidate the physical and geochemical controls on the distribution of arsenic (As) in sediments impacted by the aerial deposition of arsenic trioxide (As₂O₃) from ore roasting at legacy gold mines. High-resolution profiles of dissolved As in bottom water and porewater were also collected to determine As remobilization and diffusion rates across the sediment-water interface. Arsenic concentrations in Long Lake sediments ranged from 2.2 to 3420 mg kg^-1 (dry weight). Two distinct types of sediment As concentration profiles were identified and are interpreted to represent erosional and depositional areas. Water depth is the best predictor of As concentration in the top 5 cm of sediments due to the inferred focusing of fine-grained As₂O₃ into deeper water. At greater sediment depths, iron (Fe) concentration, as a likely indicator of As, Fe, and sulphur (S) co-diagenesis, was the best predictor of As concentration. The sediments are a source of dissolved As to surface waters through diffusion-controlled release to bottom water. Arsenic concentrations, solid-phase speciation, and diffusive efflux varied laterally across the lake bottom and with sediment depth due to the interplay between sediment-focusing processes and redox reactions, which has implications for human health and ecological risk assessments.

In situ arsenic speciation and the release kinetics in coastal sediments: A case study in Daya Bay, South China Sea

In-situ study on arsenic speciation and the release kinetics in marine sediments was scarce. In this study, the distributions of labile As and their speciation in coastal sediments of Daya Bay were obtained by separate diffusive gradients in thin films (DGT) probes. Results showed that the DGT-labile As(V) was the main speciation in surface sediments (from -20 to 0 mm) with a concentration range of 0.07-3.05 μg·L^-1, while the labile As(III) was the main speciation in deep layers of sediments (from -100 to -20 mm). In coastal areas, mariculture farms was the most dominated contributor to As(V) contamination in surface sediments. Both the apparent diffusion flux estimation and the DGT induced flux in sediments (DIFS) simulation indicated that As(V) contamination in surface sediments of mariculture, harbor and petrochemical areas suffered the potential risk of As(V) release into the overlying water from sediments. DIFS modeling also found that the sediments of mariculture farms were the main sediment As pools. Linear regression analysis indicated that the mobility of As mainly attributed to the As(V) in sediments.

Ecological risk assessment of boreal sediments affected by metal mining: Metal geochemistry, seasonality, and comparison of several risk assessment methods

The mining industry is a common source of environmental metal emissions, which cause long-lasting effects in aquatic ecosystems. Metal risk assessment is challenging due to variations in metal distribution, speciation, and bioavailability. Therefore, seasonal effects must be better understood, especially in boreal regions in which seasonal changes are large. We sampled 4 Finnish lakes and sediments affected by mining for metals and geochemical characteristics in autumn and late winter, to evaluate seasonal changes in metal behavior, the importance of seasonality in risk assessment, and the sensitivity and suitability of different risk assessment methods. We compared metal concentrations in sediment, overlying water, and porewater against environmental quality guidelines (EQGs). We also evaluated the toxicity of metal mixtures using simultaneously extracted metals and an acid volatile sulfides (SEM-AVS) approach together with water quality criteria (US Environmental Protection Agency equilibrium partitioning benchmarks). Finally, site-specific risks for 3 metals (Cu, Ni, Zn) were assessed using 2 biotic ligand models (BLMs). The metal concentrations in the impacted lakes were elevated. During winter stratification, the hypolimnetic O2 saturation levels were low (<6%) and the pH was acidic (3.5-6.5); however, abundant O2 (>89%) and neutral pH (6.1-7.5) were found after the autumnal water overturn. Guidelines were the most conservative benchmark for showing an increased risk of toxicity in the all of the lakes. The situation remained stable between seasons. On the other hand, SEM-AVS, equilibrium partition sediment benchmarks (ESBs), and BLMs provided a clearer distinction between lakes and revealed a seasonal variation in risk among some of the lakes, which evidenced a higher risk during late winter. If a sediment risk assessment is based on the situation in the autumn, the overall risk may be underestimated. It is advisable to carry out sampling and risk assessment during periods in which metals are assumed to be the most environmentally harmful. Integr Environ Assess Manag 2016;12:759-771. © 2015 SETAC.

In-situ characterization and assessment of arsenic mobility in lake sediments

In-situ characterization and assessment of arsenic (As) mobility in sediments was scarce. In this study, the distributions of labile As at a vertical resolution of 2 mm were obtained in the sediments of a large Lake Taihu through in-situ measurements using a Zr-oxide diffusive gradients in thin films (Zr-oxide DGT) technique. The DGT-labile As, interpreted as DGT flux (FDGT), exhibited three different patterns in the lake, with all the patterns generally showing an increasing mobility followed by a decreasing mobility with sediment depth. The mobility of As could be characterized by the average FDGT (0.06-1.27 pg cm(-2) s(-1)) in the top 10 mm surface sediments, the maximal FDGT (FDGT-M, 0.14-2.44 pg cm(-2) s(-1)) in the end of the initial increasing phase of FDGT, and the diffusion length (ΔL, 28-66 mm) from the depth showing the FDGT-M to the sediment-water interface. The upward mobilization of labile As from the deep sediments to the surface sediments and overlying water became evident when FDGT-M > 1.7 pg cm(-2) s(-1) or ΔL < 41 mm. The results, for the first time, showed a prospect in in-situ risk assessment of the pollution of sediment As. It was suggested that the increasing mobility of As in the upper sediments was controlled by the reduction of As(V) and the reductive dissolution of Fe(III) (hydr)oxides, while the decreasing mobility in the deep sediments was attributed to immobilization of As(III) by secondary Fe(II)-bearing minerals.

Chemical and toxicological characterization of sediments along a Colombian shoreline impacted by coal export terminals

Extraction, transport and utilization of coal spread out coal dust. Nowadays, Colombia is an important producer of this mineral in South America, being the Santa Marta area one of the largest coal exporting ports in the country. The aim of this work was to assess the pollutants levels and toxicity of shoreline sediments from this place. 16 PAHs and 46 elements were measured in nine locations during dry and rainy seasons. HepG2 cells were exposed to 1% sediment extracts and mRNA expression evaluated for selected genes. PAHs levels were greater during the rainy season. The highest ∑PAHs (89.9 ng g(-1)) appeared at a site located around 300 m far from the coast line at close proximity to the area where coal is loaded into cargo vessels for international shipments, being naphthalene the most abundant PAH. At Santa Marta Bay port, ∑PAHs were 62.8 ng g(-1) and 72.8 ng g(-1) for dry and rainy seasons, respectively, with greatest levels for fluoranthene. Based on sediment standards, most stations have poor condition regarding Cr, but moderate contamination on Cu, Pb and Zn. Sediments from the port and coal transport sites, the most polluted by PAHs and metals, induced CYP1A1 and NQO1 during the dry season. Data showed the sediments from this shoreline have bioactive chemicals that determine their toxicological profile.

Arsenic toxicity effects on microbial communities and nutrient cycling in indoor experimental channels mimicking a fluvial system

The toxicity of chemicals in the environment is influenced by many factors, such as the adsorption to mineral particles, active biological surfaces, biotransformation and/or nutrient concentration. In the present study, a simplified fluvial system including fish, periphyton and sediment was used to investigate the fate and effects of environmentally realistic concentration of arsenic (As) on biofilm growth and nutrient cycling. Total dissolved arsenic concentration decreased exponentially from 120μg/L to 28.0±1.5μg/L during the experiment (60 days), mostly sinking to the sediment and a smaller percentage accumulated in the periphytic biofilm. Most P and N, which was provided by fish, was also retained in the epipsammic biofilm (growing on sediment grains). We conclude that exposure to this concentration of arsenic under oligotrophic conditions is changing the quality and quantity of the base of the aquatic food chain and its respective contribution to nutrient cycling, and normal functioning of the ecosystem. The effects include lowering the total biomass of biofilm and its potential ability to use organic P (i.e., phosphatase activity), inhibiting algal growth, especially that of diatoms, decreasing nitrogen content, and making the epipsammic biofilm more heterotrophic, thus reducing its ability to oxygenate the aquatic environment.

Individual and cumulative effects of agriculture, forestry and metal mining activities on the metal and phosphorus content of fluvial fine-grained sediment; Quesnel River Basin, British Columbia, Canada

The impact of agriculture, forestry and metal mining on the quality of fine-grained sediment (<63 μm) was investigated in the Quesnel River Basin (QRB) (~11,500 km(2)) in British Columbia, Canada. Samples of fine-grained sediment were collected monthly during the snow-free season in 2008 using time-integrated samplers at replicate sites representative of agriculture, forestry and mining activities in the basin (i.e. "impacted" sites). Samples were also collected from replicate reference sites and also from the main stem of the Quesnel River at the downstream confluence with the Fraser River. Generally, metal(loid) and phosphorus (P) concentrations for "impacted" sites were greater than for reference sites. Furthermore, concentrations of copper (forestry and mining sites), manganese (agriculture and forestry sites) and selenium (agriculture, forestry and mining sites) exceeded upper sediment quality guideline (SQG) thresholds. These results suggest that agriculture, forestry and metal mining activities are having an influence on the concentrations of sediment-associated metal(loid)s and P in the Quesnel basin. Metal(loid) and P concentrations of sediment collected from the downstream site were not significantly greater than values for the reference sites, and were typically lower than the values for the impacted sites. This suggests that the cumulative effects of agriculture, forestry and mining activities in the QRB are presently not having a measureable effect at the river basin-scale. The lack of a cumulative effect at the basin-scale is thought to reflect: (i) the relatively recent occurrence of land use disturbances in this basin; (ii) the dominance of sediment contributions from natural forest and agriculture; and (iii) the potential for storage of contaminants on floodplains and other storage elements between the locations of disturbance activities and the downstream sampling site, which may be attenuating the disturbance signal.