Reservoirs typically have elevated fish mercury (Hg) levels compared to natural lakes and rivers. A unique feature of reservoirs is water-level management which can result in sediment exposure to the air. The objective of this study is to identify how reservoir water-level fluctuations impact Hg cycling, particularly the formation of the more toxic and bioaccumulative methylmercury (MeHg). Total-Hg (THg), MeHg, stable isotope methylation rates and several ancillary parameters were measured in reservoir sediments (including some in porewater and overlying water) that are seasonally and permanently inundated. The results showed that sediment and porewater MeHg concentrations were over 3-times higher in areas experiencing water-level fluctuations compared to permanently inundated sediments. Analysis of the data suggest that the enhanced breakdown of organic matter in sediments experiencing water-level fluctuations has a two-fold effect on stimulating Hg methylation: 1) it increases the partitioning of inorganic Hg from the solid phase into the porewater phase (lower log Kd values) where it is more bioavailable for methylation; and 2) it increases dissolved organic carbon (DOC) in the porewater which can stimulate the microbial community that can methylate Hg. Sulfate concentrations and cycling were enhanced in the seasonally inundated sediments and may have also contributed to increased MeHg production. Overall, our results suggest that reservoir management actions can have an impact on the sediment-porewater characteristics that affect MeHg production. Such findings are also relevant to natural water systems that experience wetting and drying cycles, such as floodplains and ombrotrophic wetlands.

Mercury (Hg) concentrations and nitrogen (δ15N) and carbon (δ13C) stable isotopic ratios were measured to assess differences in Hg bioaccumulation in four predatory fish species (Mycteroperca microlepis, Lutjanus campechanus, Caulolatilus microps, and Serioli dumerili) of high commercial and recreational importance in Atlantic waters of the southeastern US. Positive relationships existed between Hg and length, weight, and age, for all species, strongest for M. microlepis and L. campechanus. Intraspecific Hg concentrations also strongly correlated with δ15N for all species, and δ13C for only L. campechanus, and S. dumerili. Comparisons of stable isotopes between species and their impact on mean Hg concentration were inconclusive. This study is the first to report Hg concentrations for C. microps. The current study provides data for an under-sampled region, explores how feeding ecology impacts Hg uptake in commonly co-occurring fishes, and raises questions of the importance of sex and reproduction in Hg accumulation for marine fishes.

A main challenge in ecological risk assessment is to account for the impact of multiple stressors. Nuclear facilities can release both radiological and chemical stressors in the environment. This study is the first to apply species sensitivity distribution (SSD) combined with mixture models (concentration addition (CA) and independent action (IA)) to derive an integrated proxy of the ecological impact of combined radiological and chemical stressors: msPAF (multisubstance potentially affected fraction of species). The approach was tested on the routine liquid effluents from nuclear power plants that contain both radioactive and stable chemicals. The SSD of ionising radiation was significantly flatter than the SSD of 8 stable chemicals (namely Cr, Cu, Ni, Pb, Zn, B, chlorides and sulphates). This difference in shape had strong implications for the selection of the appropriate mixture model: contrarily to the general expectations the IA model gave more conservative (higher msPAF) results than the CA model. The msPAF approach was further used to rank the relative potential impact of radiological versus chemical stressors.

Metals are ubiquitous and normally co-occur as mixtures in soil, but there remains much to do regarding the development of appropriate models which incorporate mixture interactions and bioavailability to estimate their phytotoxicity and phytoaccumulation. Here, we developed a probability-based electrostatic toxicity model (ETM) and a Langmuir-type electrostatic uptake model (EUM) to predict and normalize toxicity and uptake of zinc-copper mixtures in Hordeum vulgare L. in different soils. For model development, the electrical potential (ψ0) and metal ion activities ({M2+}0) at the cell-membrane surface was computed based on plant physiological properties and soil solution chemistry. Single metal toxicity correlated more closely to their corresponding {M2+}0 than to ion activities in soil solution or total soil metal concentrations. The ETM explained up to 89% of the variance in mixture toxicity across different soils. Incorporation of ψ0 into the EUM improved the model's ability for predicting metal uptake. Besides, cell-surface H+ appeared to significantly inhibit copper uptake via competition or other mechanisms, beyond its effect upon ψ0. Our results for the first time demonstrate that electrostatic theory can be used to predict and reconcile mixture toxicity and uptake data in different soils, indicating the potential of electrostatic-based models in risk assessment of multimetal-contaminated soils.

In order to investigate the effects of dissolved humic acid (DHA) and tourmaline on uptake of 2, 2′, 4, 4′, 5, 5′- hexabrominated diphenyl ether (BDE-153) by Lactuca sativa, different fractions of DHA, including DHA1 and DHA4, as well as different doses of tourmaline were introduced into BDE-153 contaminated solutions for plant growth. The levels of BDE-153 in L. sativa tissues were positively correlated with the Fe levels (R² = 0.9264) in seedings of the treatments with different doses of tourmaline. However, when adding DHA1 and DHA4 into the system, the correlation coefficients (R²) decreased to 0.6976 and 0.5451 from 0.9264, respectively. In contrast with the Fe contents, the presence of DHAs didn't affect the R² between the levels of BDE-153 and the lipid contents in plant tissues. Our results indicated that both DHA1 and DHA4 could severely alter the BDE-153 uptake by L. sativa through reducing the Fe uptake instead of the lipid contents. Additionally, DHA4 exhibited much stronger abilities to alter the BDE-153 accumulation than DHA1. Transmission electron microscopy (TEM) observations indicated that either DHA1 or tourmaline or co-treatment with DHA and tourmaline had no negative impact on L. sativa at the cellular level. The present study provides important information for the impacts of different fractions of DHA extracted from soil on the BDE-153 migration in plant systems. Moreover, we elucidated the importance of the iron in tourmaline for migration of the polybrominated diphenyl ethers (PBDEs) in plant systems.

The antagonistic effect of selenium (Se) on mercury (Hg) toxicity has been known for decades. Earlier studies mainly focused on Hg-Se interaction based on biokinetics and bioaccumulation, but the influences of Se on in vivo biotransformation of methylmercury (MeHg) have not been well understood. We conducted a 42-day exposure study to investigate the dynamic changes of MeHg and its primary degradation product - inorganic mercury (IHg) - in different organs of black seabream (Acanthopagrus schlegeli) exposed to different dietary Se levels. A physiologically based pharmacokinetic (PBPK) model was then developed to describe the biotransformation and disposition of MeHg under the influence of Se. Our results demonstrated that Se significantly increased the transformation from MeHg into IHg, thereby decreasing the accumulation of MeHg. The simulation further showed that the intestine was the major site for demethylation, with an estimated rate 1.5-fold higher in high Se treatment than in low Se treatment. However, the hepatic demethylation rate was extremely low and comparable between the two treatments (0.012–0.015 d−1). These results strongly suggested that the intestine instead of the commonly assumed liver was the major site for Hg-Se interaction. Furthermore, Se did not show significant influences on the distribution and elimination of MeHg, but promoted the uptake and elimination of the generated IHg from demethylation. Therefore, Se-induced demethylation especially in the intestine played an important role in mitigating the MeHg accumulation. This study provided new sight to elucidate the Hg-Se interaction in fish.

Per- and polyfluoroalkyl substances (PFASs) are a family of compounds that includes numerous compound classes. To date, only a subset of these PFASs have been studied thoroughly in the general population. In this study, pooled serum samples from Australia collected in 2002–2013 were analyzed for PFASs according to gender and age (age categories of 0–4 years, 5–15 years, 16–30 years, 31–45 years, 46–60 years, and >60 years), in total 54 pooled samples and 4920 individuals. Compound classes included were perfluorocarboxylic acids (PFCAs), perfluorosulfonic acids (PFSAs), and two groups of PFCA precursor compounds; polyfluoroalkyl phosphate diesters (diPAPs), and fluorotelomer sulfonic acids (FTSAs). Several PFASs that were not reported in previous studies of Australian serum samples were found in this sample set including; diPAPs, FTSAs, perfluoropentane sulfonic acid (PFPeS), perfluoroheptane sulfonic acid (PFHpS), perfluoroheptane carboxylic acid (PFHpA), perfluoroundecanoic acid (PFUnDA), perfluorododecanoic acid (PFDoDA), and perfluorotridecanoic acid (PFTrDA). Various temporal trends were observed with a significant reduction (p < 0.05) between 2002 and 2013 for 8:2 FTSA, perflurohexane sulfonic acid (PFHxS), PFHpS, PFOS, and perflurooctanoic acid (PFOA). Levels of longer-chained PFDA and PFUnDA started to decrease more recently, between 2006 and 2013, while PFDoDA increased during the same time period. Higher levels in younger age groups (0–4 and 5–15 years) compared to adults (>15 years) were found for 8:2 FTSA and PFHpA, while levels of PFHpS, PFOS, PFUnDA, PFDoDA and PFTrDA were higher in adult age groups compared to younger age groups. Gender-specific patterns were seen for PFOA, PFHxS, PFHpS and PFOS, where levels were lower in women. Changes in manufacturing processes were reflected in the temporal time trends, and differences in bioaccumulation potential between homologues could be associated with age trends. Our results emphasize the importance of including emerging classes of PFASs in biomonitoring studies.

The chemical composition of PM2.5 and cellular effects from exposure to fine aerosol extracts were studied for samples collected in Beijing, Tianjin, Shijiazhuang, and Hengshui, China in winter 2015. Effects of priority polycyclic aromatic hydrocarbons (PAHs) and their oxygenated derivatives (OPAHs) in PM2.5 on cell cultures were a major focus of the study. Total quantified PAHs and OPAHs at Shijiazhuang and Hengshui were higher than at Beijing and Tianjin, and benz(a)anthracene, chrysene and 1,8-naphthalic anhydride were the most abundant species. Exposure to PM2.5 extracts caused a concentration-dependent decline in cell viability and a dose-dependent increase in nitric oxide production. Two cytokines, tumor necrosis factor α (TNF-α) and interleukin 6 (IL-6), also increased when A549 test cells were exposed to PM2.5 extracts. PAHs and OPAHs in PM2.5 can potentially cause cell damage and induce cytotoxicity and pro-inflammatory responses: benzo(a)anthracene-7,12-dione was highly correlated with NO production, dibenz(a,h)anthracene and 1,4-chrysenequinone were correlated with TNF-α production, and 1-naphthaldehyde was significantly correlated with IL-6 production. The study provides a new approach for evaluating relationships between air-quality and cell toxicity with respect to specific chemicals.

Like many urban catchments, the River Thames in London is contaminated with plastics. This pollutant is recorded on the river banks, in the benthic environment and in the water column. The present study was conducted to assess the extent of microplastic ingestion in two River Thames fish species, the European flounder (Platichthys flesus) and European smelt (Osmerus eperlanus). Samples were collected from two sites in Kent, England; Erith and Isle of Grain/Sheppey, near Sheerness, with the latter being more estuarine. The results revealed that up to 75% of sampled European flounder had plastic fibres in the gut compared with only 20% of smelt. This difference may be related to their diverse feeding behaviours: European flounder are benthic feeders whilst European smelt are pelagic predators. The fibres were predominantly red or black polyamides and other fibres included acrylic, nylon, polyethylene and polyethylene terephthalate and there was no difference in occurrence between the sites sampled.

Polybrominated dibenzo-p-dioxins (PBDDs) and hydroxylated polybrominated diphenyl ethers (OH-PBDEs) can be formed from bromophenols (BPs) by thermal degradation, biosynthesis or phototransformation. However, it is unknown whether PBDDs and OH-PBDEs can be formed during the chemical production processes that utilize BPs as raw materials. 2,4,6-tribromophenol (2,4,6-TBP) is an important raw material for the synthesis of 1,2-bis(2,4,6-tribromophenoxy)ethane (BTBPE), a novel brominated flame retardant. In this study, PBDDs, polybrominated dibenzofurans (PBDFs) and OH-PBDEs have been identified and quantified in commercially available BTBPE and 2,4,6-TBP. Furthermore, their formation as unintentional by-products during the laboratory synthesis of BTBPE from 2,4,6-TBP and 1,2-dibromoethane in the presence of sodium carbonate has also been investigated. 2,3,7,8-substituted PBDDs and PBDFs (2,3,7,8-PBDD/Fs) were undetectable in commercial samples of BTBPE and present in low levels (nanogram per gram) in 2,4,6-TBP. Two tetrabrominated dibenzo-p-dioxins (TeBDDs), namely 1,3,6,8- and 1,3,7,9-TeBDD, and three hydroxylated pentabrominated diphenyl ethers (OH-pentaBDEs), namely 4′-OH-BDE121, 2′-OH-BDE121, and 6′-OH-BDE100, were identified or tentatively identified, and quantitatively estimated to be at concentrations in the range of undetectable to several thousands of nanograms per gram in commercial BTBPE and 2,4,6-TBP. TeBDDs and OH-pentaBDEs were formed as by-products from 2,4,6-TBP during BTBPE synthesis. Further studies need to be conducted in order to determine whether PBDD/Fs and OH-PBDEs are also formed during the industrial synthesis of other chemical compounds that utilize BPs as raw materials or intermediates.