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Mercury (Hg) is a ubiquitous contaminant in the environment and its methylated form, methylmercury (MeHg), poses a worldwide health concern for humans and wildlife, primarily through fish consumption. Global production of forest fire ash, derived from wildfires and prescribed burns, is rapidly increasing due to a warming climate, but their interactions with aqueous and sedimentary Hg are poorly understood. Herein, we compared the differences of wildfire ash with activated carbon and biochar on the sorption of aqueous inorganic Hg and sedimentary Hg methylation. Sorption of aqueous inorganic Hg was greatest for wildfire ash materials (up to 0.21 μg g-1 or 2.2 μg g-1 C) among all of the solid sorbents evaluated. A similar Hg adsorption mechanism for activated carbon, biochar made of walnut, and wildfire ash was found that involves the formation of complexes between Hg and oxygen-containing functional groups, especially the -COO group. Notably, increasing dissolved organic matter from 2.4 to 70 mg C L-1 remarkably reduced Hg sorption (up to 40% reduction) and increased the time required to reach Hg-sorbent pseudo-equilibrium. Surprisingly, biochar and wildfire ash, but not activated carbon, stimulated MeHg production during anoxic sediment incubation, possibly due to the release of labile organic matter. Overall, our study indicates that while wildfire ash can sequester aqueous Hg, the leaching of its labile organic matter may promote production of toxic MeHg in anoxic sediments, which has an important implication for potential MeHg contamination in downstream aquatic ecosystems after wildfires.

Wildfires are expected to become more frequent and intensive at the global scale due to climate change. Many studies have focused on the loss of mercury (Hg) from burned forests; however, little is known about the origins, concentration, reactivity, and bioavailability of Hg in residual ash materials in postfire landscapes. We examine Hg levels and reactivity in black ash (BA, low burn intensity) and white ash (WA, high burn intensity) generated from two recent northern California wildfires and document that all ash samples contained measurable, but highly variable, Hg levels ranging from 4 to 125 ng/g dry wt. ( n = 28). Stable Hg isotopic compositions measured in select ash samples suggest that most Hg in wildfire ash is derived from vegetation. Ash samples had a highly variable fraction of Hg in recalcitrant forms (0-75%), and this recalcitrant Hg pool appears to be associated with the black carbon fraction in ash. Both BA and WA were found to strongly sequester aqueous inorganic Hg but not gaseous elemental Hg under controlled conditions. During anoxic ash incubation with natural surface water, we find that Hg in most ash samples had a minimal release and low methylation potential. Thus, the formation of wildfire ash can sequester Hg into relatively nonbioavailable forms, attenuating the potentially adverse effects of Hg erosion and transport to aquatic environments along with eroded wildfire ash.

The present study investigates the potential effects and risks of polyethylene microbeads (PEMBs) and PEMBs associated with PCB-153 (PEMB-PCB) on Daphnia magna using a chronic exposure study approach. Daphnia magna were exposed to PEMBs, PCB-153, and PEMB-PCB for 21 days. Accumulation of PEMBs and PCB-153 in D. magna and effects on survival and reproduction of the organisms were measured. Overall, D. magna ingested and accumulated PEMBs and PCB-153. The accumulation of PEMBs increased with exposure time and was higher for PEMB exposure than for PEMB-PCB exposure. However, PCB-153 accumulation did not appear to increase over time. Exposure to PCB-153 in water resulted in higher PCB-153 accumulation than did PEMB-PCB exposure. Polyethylene microbeads and PCB-153 appeared to interact, resulting in a lower accumulation of PEMBs and PCB-153 and causing less effect on reproduction of D. magna. Survival of D. magna was affected by PEMBs, PCB-153, and PEMB-PCB. Results of the present study reveal potential risks of MPs to living organisms and ecosystems, especially when considering long-term exposure, which is relevant for microplastic pollution because of the persistence and continuous increase in MP abundance in the environment. More research should be conducted to understand the interactive effect mechanisms of MP and pollutant mixture exposure on organisms that would help explain the decreased accumulation of pollutants in organisms when MPs are present. [ABSTRACT FROM AUTHOR]

The present study investigates microplastic (MP) accumulation in five small marine fish species living in the nearshore sea of Binh Dinh, Vietnam that are commonly consumed by the local coastal communities. Fish (Oxyurichthys ophthalmonema, Stolephorus commersonnii, Decapterus macrosoma, Upeneus moluccensis, Sardinella gibbosa) were collected from four sites in the nearshore sea of Binh Dinh in rainy and dry seasons. The temporal, spatial, and species variations in MP accumulation were evaluated to understand environmental exposure of MPs to fish and potential human exposure to MPs via fish consumption. Microplastics of different types, sizes, and colors were found in the digestive system of the fish species. Microplastic composition included polyethylene, polyvinyl ether, polymethacrylate, polydichloroethylene, polydivinyl ester, poly ester, polyfluoroethylene, and other additives of plastic materials. Microplastic abundance in the fish was dependent on species, site, and season. Overall, microfiber was the dominant MPs. The average total MP abundance range was 4.70–23.80 particles/fish or 0.29–6.21 particles/g fish. There were statistically significant differences in MP abundances between fish species, sites, and seasons. The presence of MPs in the digestive system of fish suggests that MPs are in the nearshore environment of Binh Dinh. The local communities along the coast of Binh Dinh can ingest MPs from consuming small fish at a weekly rate equivalent to one five-hundredth number of rice grains they consume/week. [ABSTRACT FROM AUTHOR]

Metal mixture toxicity has been studied for decades. However, the results are not consistent, and thus ecological risk assessment and regulation of mixtures has been difficult. The objective of the present study was to use a systematic experimental design to characterize the toxicity of binary-metal mixture of Cu, Zn, and Ni to Pimephales promelas, typically to determine whether the effect of these binary-metal mixtures on P. promelas is more-than-additive. Standard 96-h toxicity tests were conducted with larval P. promelas based on US Environmental and Protection Agency methods to determine metal mixture effects. All experiments were conducted in synthetic moderately hard water with no addition of dissolved organic matter. Three different effect analysis approaches, the MixTox model, the Finney model, and the toxic unit method, were used for comparison. The results indicate that the toxicity of Cu+Zn, Cu+Ni, and Zn+Ni mixtures to P. promelas was more-than-additive. Among the 3 mixtures, the effect of the Cu+Ni mixture was the most profound. The results of the present study are useful for applications to models such as the metal mixture biotic ligand model. More research should be conducted to determine the mechanisms of acute and chronic toxicity of metal mixtures. Environ Toxicol Chem 2016;35:446-457. © 2015 SETAC [ABSTRACT FROM AUTHOR]

Research on the toxicity of arsenic has focused on sublethal effects that do not provide sufficient information for risk estimation. While most studies have focused on organism response to constant arsenic exposures, organisms in nature are exposed to fluctuating As concentrations. Consequently, results obtained from standardized bioassays with constant exposures may not adequately characterize risk to indigenous biota. This research was designed to characterize the response of Daphnia magna to fluctuating arsenic exposures during 21-day experiments. At concentrations ≥3000 µg/L As, 21-day pulsed exposure mortality increased as a function of exposure concentration and duration. In addition, 21-day pulsed exposure mortality increased with increasing recovery time. Pulsed As exposure did not affect the growth of D. magna over 21 days. Twenty-one day accumulative reproduction of D. magna was only affected by pulsed exposures of high As concentration and long durations. [ABSTRACT FROM AUTHOR]