Environmental Toxicology and Chemistry最新文献

Current standard test methods for assessing biodegradation of chemicals are laborious and not suited for high-throughput screening of chemicals because of both the required volume of the test medium and the limited possibility for automation of measurements of biodegradation. A high-throughput method (HTM) should be miniaturized, suitable for automation, and based on generic parameters that can indicate biodegradation of any chemical. The aim of this study was to develop an HTM based on bacterial proliferation (i.e., growth) as an indicator of biodegradation, measured by flow cytometry. Natural bacterial communities were exposed to reference chemicals in 96-well plates for up to 14 days at 19 °C and the results compared with parallel standard biodegradation screening tests for freshwater (Organisation for Economic Co-operation and Development [OECD] 301F) and seawater (OECD 306). Increased bacterial growth, compared with nonexposed inocula, was used as an indication of biodegradation. Sodium benzoate induced a significant growth response that corresponded to the biodegradation experiments in both freshwater and marine water. Aniline induced a lower frequency of significant growth compared with the frequency of positive biodegradation results, whereas caffeine induced a higher frequency and more rapid growth response compared with biodegradation results. This shows the potential for an HTM for biodegradation testing using bacterial growth.

Pharmaceuticals and personal care products (PPCPs) are widely detected in aquatic environments. However, recent studies on the environmental occurrence of currently used PPCPs in Japan are limited. In this study, a nationwide monitoring initiative focusing on PPCPs was undertaken to investigate the occurrence and fate of PPCPs in aquatic environments in Japan. A total of 700 samples were collected and analyzed from 2018 to 2022. Ninety-one PPCPs were detected in the analyzed samples. Three PPCPs (N, N-diethyl-meta-toluamide [DEET], salicylic acid, and crotamiton) were detected at particularly high frequencies, with a prevalence exceeding 99% of analyzed samples. Seasonal variations were observed for several PPCPs across multiple rivers, with concentrations generally increasing during fall/winter and decreasing during spring/summer (except DEET) throughout the sampling period. The detection frequencies and concentrations were higher in PPCPs with higher domestic prescription amounts. Some PPCPs, such as acetylsalicylic acid, exhibited low frequencies and concentrations despite high domestic prescription amounts, suggesting transformation into metabolites or degradates in the aquatic environment. The contribution of sewage treatment plant effluent to the PPCP concentrations in the environment was estimated by examining the correlation between each PPCP and sucralose concentration. Sewage effluents appeared to be a significant contributor to the majority of target PPCPs; however, DEET and certain other PPCPs may originate from alternate sources. This study is the first to provide a comprehensive assessment of the occurrence and fate of PPCPs in Japan's aquatic environment. Future research should assess the environmental and human health risks of these PPCPs and identify the occurrence of their metabolites or degradates in the aquatic environment.

Per- and polyfluoroalkyl substances (PFAS) are thousands of toxic synthetic chemicals that bioaccumulate and persist in the environment. They are known to cause immunotoxicity, organ damage, endocrine disruption, and reproductive impairments in wildlife such as sea otters (Enhydra lutris). However, there is limited information on the distribution of these chemicals across the northeastern Pacific, and baseline data are missing to assess their potential impacts on sea otters in regions such as British Columbia (BC), Canada. We analyzed liver (n = 11) and skeletal muscle samples (n = 5) from 11 deceased sea otters from coastal BC using the U.S. Environmental Protection Agency method 1633 with ultrahigh performance liquid chromatography coupled to a triple quadrupole mass spectrometer. We found 8 of the 40 tested PFAS were present in all sampled sea otters, although concentrations of each PFAS varied between individuals. Sea otter livers contained more PFAS compounds at higher total average concentrations than skeletal muscle (i.e., 8 PFAS totaling 10.38 ng/g wet wt vs. 1 PFAS totaling 0.38 ng/g wet wt). Only perfluorooctanesulfonamide (PFOSA) was identified in both liver and muscle tissues, whereas the remaining 7 PFAS were unique to the liver. The three PFAS that dominated the liver PFAS composition (perfluorononanoic acid, PFOSA, and perfluorooctanesulfonic acid) accounted for 84% of the contaminant load in the livers. Geographically, PFAS concentrations were more than three times higher on average in sea otters recovered near major cities and shipping routes. Identifying the contaminants accumulating in sea otters provides insights into the health threats confronted by recovering sea otter populations. Our study also establishes baseline PFAS contamination levels in BC sea otters, which can be used to monitor and regulate the presence of PFAS on marine environments in western Canada.

Microplastic-derived dissolved organic matter (MP-DOM) has attracted widespread attention due to its adverse effects on ecological health. However, the dynamic formation of MP-DOM at the molecular level is not yet fully understood. Herein, the molecular level formation characteristics and mechanism of polyamide-MP-derived DOM (MPPA-DOM) during irradiation were explored using fluorescence spectroscopy. Fourier transform-ion cyclotron resonance mass spectrometry, and parallel factor analysis. The results showed that the time-dependent fluorescence signatures revealed a dominant tyrosine-like component, whose relative abundance increased from 49.63% to 89.62% during irradiation, suggesting a gradual accumulation of protein-related substances. Molecular element analyses of MPPA-DOM revealed the predominance of CHON molecules (78.82%-89.30%), which was attributed to the degradation of the C-N backbone structure. In contrast, CHO molecules exhibited a lower proportion (9.45%) under prolonged irradiation. Aliphatic/peptide-like compounds in MPPA-DOM remained the dominant component with a percentage range of 66.4% to 68.7%, whereas lignin-like compounds slightly increased with the increase of irradiation time. The reduced molecules were dominated in MPPA-DOM with a percentage range of 96.4% to 99.1%. As irradiation increased, the saturated compounds decreased from 91.53% to 82.45% and the unsaturated compounds increased from 7.6% to 14.1%. This study proposed a molecular-level formation mechanism of MPPA-DOM under irradiation. Nitrogen-rich molecules were persistent and highly stable during irradiation, indicating that they could play a more important role in the migration and transformation of MPPA-DOM. The findings in this study will provide support for assessing the potential ecological risks of MP-DOM in water systems.

Amphibians serve a central role in food webs and provide a link between aquatic and terrestrial habitats. Because of their dependence on water, amphibians are susceptible to legacy and emerging contaminants. We investigated mercury (Hg) and per- and polyfluoroalkyl substances (PFAS) concentrations in wild populations of two amphibian species-the green frog (Lithobates clamitans) and the American toad (Anaxyrus americanus)-which exhibit different life histories. We evaluated whether proximity to PFAS point source (State Superfund site) affected PFAS exposures in amphibians and assessed length, mass, sex, diet, and trophic position as predictors of contaminant concentrations. We found higher Hg concentrations in the more aquatic species (i.e., green frog) but higher PFAS concentrations (summed PFAS, perfluorodecanoic acid [PFDA], perfluoroundecanoic acid [PFUnA], perfluorododecanoic acid [PFDoA], perfluorotridecanoic acid [PFTrDA], and perfluorotetradecanoic acid [PFTeDA]) in the more terrestrial species (i.e., American toad). Proximity to the PFAS State Superfund site did not strongly affect PFAS exposures in amphibians. Of the biological predictors tested, diet best explained PFAS concentrations, but other factors (e.g., physiological differences) are likely contributing to the difference in PFAS bioaccumulation between aquatic and terrestrial species. Only three reports on PFAS concentrations in wild amphibians exist, all from contaminated sites in China, reporting much higher concentrations than found here. Additionally, experimental exposure studies have only investigated the effects of exposure to a few PFAS compounds, of which long-chain perfluoroalkyl carboxylic acids detected here (PFDA, PDUnA, PFDoA, PFTrDA, and PFTeDA) are not represented in the literature. To truly understand the effects that detectable PFAS impose on wild amphibians, research is needed on the effects of more PFAS compounds, bioaccumulation in larval and terrestrial amphibians, and the elimination of PFAS via their skin to different media.

Octamethylcyclotetrasiloxane (D4) is a cyclic volatile methylsiloxane compound associated with the production of polydimethylsiloxanes (PDMS). Depending on processing conditions, silicone fluids made by equilibration polymerization can contain residual D4 at parts-per-million to parts-per-hundred levels. When silicone fluids enter the environment through use or disposal, aquatic organisms may be exposed to residual D4. To accurately assess the contribution of D4 to the aquatic hazard of silicone fluids, knowledge of the partitioning behavior of D4 is needed. In this study, PDMS-to-air partition coefficients (KPDMS-air) for D4 were directly measured at 21 °C using a static equilibration method. The influence of various factors on KPDMS-air was explored, including the PDMS fluid viscosity (molecular weight), the D4 concentration in the polymer, addition of hydrophobized fumed silica to PDMS, and the presence of amine functional groups within the PDMS structure. For permethylated PDMS, log KPDMS-air values varied between 4.39 and 4.53. Incorporation of treated silica filler at up to 25%w/w had no impact on KPDMS-air, while introduction of (aminopropyl)methyl-dimethylsiloxy units to the polymer (3.7 wt% nitrogen) produced modestly lower log KPDMS-air, 4.19. The KPDMS-air values were combined with reported air-water partition coefficients (Kair-water) for D4 to calculate values of KPDMS-water based on the thermodynamic cycle. The resulting log KPDMS-water values ranged from 6.88 to 7.22, which were used to estimate the maximum attainable aqueous D4 concentrations for different polymer/water phase ratios. For a D4 content of 0.025% w/w in the polymer, the current threshold for classification of the polymer as hazardous to the aquatic environment, the maximum aqueous D4 concentration was ≤ 0.032 μg/L. These concentrations were at least 100-fold less than chronic aquatic toxicity thresholds derived from studies with D4, suggesting that the 0.025% w/w threshold is overly stringent in assigning aquatic hazard classifications to PDMS materials like those tested here.

Natural complex substances (NCSs) are botanical extracts of unknown or variable composition. Such NCS contain long chain substances that are very difficult or impossible to identify, representing a challenge to characterization and toxicity assessment. This study aims to provide an innovative and relevant method to identify the constituents of galbanum resinoid, experimentally assess, and accurately predict its ecotoxicity. A fractionation technique was used to separate the NCS into three phases: "volatile," "nonvolatile but potentially bioavailable," and potentially "inert." The whole substance (WS) and each fraction were tested as water accommodated fractions (WAFs) for acute and chronic ecotoxicity to algae and daphnids. The toxicity of fractions and the WS was predicted using (a) an in silico method adapted for mixture toxicity testing and (b) the additivity Classification Labelling and Packaging/Global Harmonised System (CLP/GHS) method, based on analytically determined composition. The volatile fraction was more toxic than the nonvolatile fraction, and the inert fraction was not chronically toxic to algae or daphnids. The experimental daphnid chronic toxicity was higher than the acute for the WS because of larger molecules not toxic to their solubility limit in acute studies. The results from the experiments validated the in silico predictions, which accurately predicted toxicity of the fractions and the WS even if rather conservative for chronic daphnids. Also, the in silico method mechanistically explained the WAF test results and attributed the observed toxicity to specific constituents. However, CLP/GHS overpredicted toxicity in all cases and failed to account for observed toxicity. Experimental and in silico approaches appear to be highly complementary to deal with NCSs. Moreover, the in silico method provides a rapid and cost-effective option to obtaining data for difficult-to-test substances.

Polybrominated diphenyl ethers have emerged as a major environmental pollutant, being used as an additive flame retardant in various kinds of products including electronic devices (computers and television sets), upholstery, carpets, plastics, textiles, and building materials. They can undergo the degradation process to form less brominated or low brominated diphenyl ethers in the environment. In the current study, genotoxic, biochemical, histopathological, and ultrastructural scanning electron microscopy (SEM) changes in liver tissue of zebrafish were studied after acute and subchronic exposure of diphenyl ether (DE). The zebrafish were exposed to 2.13 mg/L DE (¼ median lethal concentration [LC50]) and 4.25 mg/L DE (½ LC50) for the acute toxicity assessment and to 425 μg/L DE (1/20th LC50) and 850 μg/L DE (1/10th LC50) for the subchronic toxicity study. After acute and subchronic exposure of DE, % tail intensity in liver tissue was found to be significantly increased in a concentration and duration-dependent manner. The malondialdehyde content, glutathione-S-transferase, and acetylcholinesterase activity in liver tissue were found to be significantly elevated after acute and subchronic exposure of DE, whereas the activity of superoxide dismutase enzyme was found to be depleted in the liver tissue of zebrafish. The histological observations revealed various types of alterations including aggregation of hepatocytic nuclei, necrosis, vacuolization, sinusoidal dilation, disintegrated hepatocytes, and erythrocytic infiltration in liver tissue of zebrafish after DE exposure. The SEM analysis showed changes in the surface of liver tissue such as multiple pore formation, swelling in hepatocytes, necrosis, and degeneration of hepatocytes after acute and subchronic exposure of DE.

Fish are exposed to countless chemicals over their lifetime, with the totality of internal exposure termed the eco-exposome. In vitro bioassays can be used to complement targeted chemical analysis to quantify the mixture effects of chemicals in fish and relate them to the effects measured in extracts of water and sediment. Fathead minnows (Pimephales promelas) were exposed in cages for 48 hr and 21 days at four field sites with diverse chemical profiles. Fish, water, and sediment were collected, extracted, and analyzed with four cell-based reporter gene assays. Water from all sites activated xenobiotic metabolism in vitro, whereas only water from a site near a wastewater treatment plant activated the estrogen receptor. Only 5% of water samples were above their effect-based trigger values (EBTs) for surface water, suggesting a low overall chemical burden. In contrast, 77% of bioactive sediment samples exceeded tentative sediment EBTs, suggesting the mixture effects of chemicals in the sediment are likely to be more problematic. Whole fish extracts activated the arylhydrocarbon receptor and oxidative stress response, with the greatest effect observed at a site affected by both legacy and more recent contamination. Interpretation of mixture effects in extracts from caged fish versus laboratory controls was confounded by background contamination of fish food, as well as endogenous chemicals. Comparison of measured mixture effects with mixture effects predicted from detected chemical concentrations and their relative effect potencies indicated that mixture effects in fish extracts were mainly dominated by chemicals detected in sediment. Sediment and water did not reliably serve as a proxy for the eco-exposome. Bioanalytical investigation of whole fish extracts provides a novel approach to comprehensively characterize the fish exposome.

With global lithium (Li) production rising from 6,000 to 100,000 metric tons annually over the past three decades, environmental concerns about elevated anthropogenic Li releases have grown. Whereas marine waters show relatively stable Li concentrations (∼ 180 µg/L Li), freshwater levels vary substantially due to local geological and climatic factors. Using the sensitive freshwater crustacean Daphnia magna, we conducted three independent Daphnia magna reproduction tests according to Organisation for Economic Co-operation and Development 211 guidelines and Good Laboratory Practices on Li compounds, minimizing experimental variability. Reproduction consistently exhibited a steep concentration-response curve, with no observed effect concentration values ranging from 661 to 1,700 µg/L Li. In contrast, recent chronic studies on D. magna reported lower toxicity values by one or two orders of magnitude under apparently similar protocols. We identified four potential confounders, the exact influence of which needs to be disentangled in future studies: Li acclimation prior to exposure, water hardness and alkalinity, body size in controls, and light intensity. We argue that the current dataset on chronic Li toxicity in freshwaters is not robust enough to support the derivation of environmental exposure limits that are both protective and representative of the wide local variability in natural background levels and bioavailability conditions.