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Microplastics (MPs) have received an increasing attention because of their ubiquitous presence and aquatic toxicity associated with MPs and MP-bound contaminants in the natural water. This review is to critically examine the chemical additives leached from MPs, the altered contaminant behaviors and the resulting changes in their aquatic ecotoxicity. Available data suggest that heavy metals Zn, Cr, Pb, and Cd regulated and present in plastics at the sub-mg g -1 to mg g -1 level can leach a significant amount depending on MPs size, aging, pH, and salinity conditions. MP-bound organic contaminants are primarily additive-derived (e.g., brominated diphenyl ethers, nonylphenol, and bisphenol A) at the µg g -1 to mg g -1 level, and secondarily pyrogenic and legacy origins (e.g., PAHs and PCBs) in the range of ng g -1 and mg g -1 . MPs tend to have higher but more variable sorption capacities for organic compounds than metals (1.77 ± 2.34 vs. 0.82 ± 0.94 mg g -1 ). MPs alter the behavior of heavy metals through the electrostatic interactions and surface complexation, while the transport of additive derived organic compounds are altered primarily through hydrophobic effect as supported by a positive correlation (R 2 = 0.71) between the logarithmic MPs-adsorbed concentrations and octanol/water partition coefficients (K OW ) of organic compounds. MPs constitute less than 0.01% of the total mass of aquatic particulates in typical waters, but play a discernible role in the local partitioning and long-distance movement of contaminants. MPs alone exert higher toxicity to invertebrates than algae; however, when MPs co-occur with pollutants, both synergistic and antagonistic toxicities are observed depending mainly on the ingestibility of MPs, the extent of sorption, MPs as a transport vector or a sink to scavenge pollutants. We finally suggest several key areas of future research directions and needed data concerning the role of MPs in mitigating pollutant leaching, transport and risk under conditions mimicking natural and polluted waters., (Copyright © 2021 Elsevier B.V. All rights reserved.)

3,3',5,5'-Tetrabromobiphenyl (BB-80) was once used as additive flame retardants. Whether its early exposure and discontinued exposure alter thyroid function remains unknown. We investigate adverse effects after early-life exposure and discontinued exposure to BB-80 and hydroxylated BB-80 (OH-BB-80) on thyroid hormone (TH) levels, thyroid tissue, and transcriptome profiles in zebrafish larvae. BB-80 at 10 μg/L induces pathological changes of thyroid with reduced thyroid follicles in larvae ( P < 0.05), whereas OH-BB-80 significantly increases T4 and T3 contents (1.8 and 2.5 times of the control, P < 0.05) at 14 days postfertilization (dpf) without morphological thyroid alterations. BB-80 and OH-BB-80 cause transcriptome aberrations with key differentially expressed genes involved in the disruption of TH synthesis and signal transduction (BB-80 at 14 dpf) or TH pathway activation (OH-BB-80 at 21 dpf). After 7 days of discontinued exposure, thyroglobulin ( tg ) and thyroid peroxidase ( tpo ) genes are downregulated ( P < 0.05) by 52 and 48% for BB-80 and by 49 and 39% for OH-BB-80, respectively; however, the whole-body TH levels fail to fully recover, and the locomotor activity is impaired more by BB-80. Our results indicate significant adverse impacts of BB-80 and OH-BB-80 on TH homeostasis and thyroid function of zebrafish.

Inorganic arsenic (iAs) in its dominant dissolved phase in the environment is known to pose major threats to ecological and human health. While the biological effects in many arsenic-bearing freshwaters have been extensively studied, the behavior and bioaccumulation of dissolved iAS in the presence of extracellular polymeric substances (EPS) still remains to be a critical knowledge gap. In this study, the uptakes and kinetic characteristics of iAs were studied using Chlorella pyrenoidosa (a typical freshwater green algae) by addressing the different effects of EPS on arsenite (As Ш ) and arsenate (As V ). The arsenic uptake capacity increased as the exposure concentration increased from 0 to 300 µmol L -1 , and the uptake rate constants (K u ) in the Bio-dynamic model were greater for As V than As Ш (0.63-11.57 L g -1  h -1 vs. 0.44-5.43 L g -1  h -1 ). The toxic effects as mitigated by EPS were observed through the morphological changes of algal cells by TEM and SEM. When compared with the EPS-free algal cells (EPS-F), EPS-covered cells (EPS-C) had a higher arsenic adsorption capacity through EPS-enhanced surface adsorption and reduced intracellular uptake. The overall decrease (35% and 23.3% for As Ш and As V , respectively) in the maximum uptake capacity in intact algae cells favors cell's tolerance to the toxic effects of iAs. These observed discrepancies between As Ш and As V and between EPS-C and EPS-F were further elucidated through morphological images (TEM and SEM) and molecular/atomic spectroscopic data that combine three-dimensional excitation-emission matrix fluorescence spectroscopy (3D-EEM), Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS). Altogether, the spectroscopic evidence revealed the interactions of iAs with C-O-C, C-O-H and -NH 2 functional groups in EPS' tyrosine- and tryptophan-like proteins as the binding sites. Overall, this study for the first time provides comprehensive evidence on the iAs-EPS interactions. Such insights will benefit our understanding of the biogeochemical processes of iAs and the strategic development of bioremediation techniques involving microalgae in the natural and engineered systems., (Copyright © 2019 Zhejiang University. Published by Elsevier B.V. All rights reserved.)

The tert-butylphenols (TBPs) are one group of alkylated phenolic compounds with wide applications in UV absorbers and antioxidants. They are becoming contaminants of emerging concern with residues frequently detected in natural surface water or drinking water. The direct sunlight may photolyze TBPs in waters and affect their aquatic toxicities; however, such data are very limited. In the present study, we investigate the photodegradation of 2,6-DTBP by direct sunlight in water and compare the aquatic toxicities of 2,6-DTBP with that of its product toward Photobacterium phosphoreum. 2,6-DTBP is photodegraded by 71.31 ± 2.64% under simulated sunlight following a pseudo-first-order kinetics with rate constant (k) of 0.061 h -1 . Density functional theory simulations at M06-2X/def2-SVP level reveal that the photodegradation occurred sequentially through oxidation, photo-isomerization and hydrogenation. The degradation product 2,5-DTBP is toxic to P. phosphoreum (EC 50 3.389 × 10 -5  mol/L) whereas 2,6-DTBP is not harmful (EC 50 3.917 × 10 -3  mol/L) as designated by the European Union Standard, indicating the enhanced toxicities driven by the direct sunlight photodegradation. We demonstrate the enhanced toxicities of 2,6-DTBP by natural sunlight, suggesting that negligence of photodegradation of TBPs-related contaminants will underestimate the comprehensive risk of these emerging contaminant in natural waters., (Copyright © 2019 Elsevier Ltd. All rights reserved.)

In the past two decades, neonicotinoid insecticides have been widely used in agricultural activities in China. Many previous studies have investigated the neonicotinoid pollution in aquatic ecosystems, but the status of water safety of neonicotinoid uses in China is very scarce. The present study aims to reveal the spatial and temporal distribution of neonicotinoids in rivers, and then evaluate the ecological risks to aquatic animals. Water samples were collected from all sixteen rivers along the east coast of China during the dry and wet seasons in 2016, and nine individual commercialized neonicotinoids were quantified. Higher concentrations were found during the dry season (343 ± 210 ng/L) compared to those during the wet season (174 ± 162 ng/L). The concentration of neonicotinoid insecticides in river water is mainly affected by the intensity of agricultural activities. The spatial and temporal pollution patterns we discovered suggested the use of neonicotinoids has shifted from old types (i.e., imidacloprid and acetamiprid) to new types (i.e., dinotefuran and nitenpyram) in some areas. The estimated annual quantity of neonicotinoids released into the adjacent seas totaled 1256 ± 780 tons, most of which (95%) ran into the East China Sea due to heavy agricultural use in the Yangtze River Basin. Using the species sensitive distribution (SSD) method, the thresholds for aquatic animals were determined (acute: 362 ng/L; chronic: 58 ng/L). Under current agricultural practices, 27% and 84% of the river water samples exceeded the thresholds for acute and chronic ecological risks, suggesting intervention programs are in urgent need to ensure river water safety for aquatic life in China., (Copyright © 2019 The Authors. Published by Elsevier Ltd.. All rights reserved.)

Dissolved organic matter (DOM) affects arsenite [As(III)] toxicity by altering its sorption equilibrium at the cell wall interface. A better understanding of such mechanism is of great importance to assess As(III) ecotoxicity in aquatic systems. Batch experiments were conducted to study the effects of DOM on the regulation of As(III) sorption and toxicity in the diatom Navicula sp. The influence of humic acid (HA) on As(III) toxicity was assessed by measuring algal growth, chlorophyll a, and reactive oxygen species (ROS), whereas As(III) mobility across the cell wall was estimated by determining the concentration of intracellular, cell-wall-bound, and free As(III) ions in cell media. Results showed that the effects of HA on arsenite toxicity varied depending on various combinations of As(III)-HA concentrations. EC50 had an approximate threefold increase from 8.32 (HA-free control) to 22.39 μM (at 20 mg L(-1) HA) when Navicula sp. was exposed to 1.0-100.0 μM of As(III), compared to an overall low complexation ratio of HA-As(III) in a range of 0.91-6.00 %. The cell wall-bound and intracellular arsenic content decreased by 19.8 and 20.3 %, respectively, despite the lower arsenite complexation (2.10 ± 0.16 % of the total As). Meanwhile, intracellular ROS was decreased by 12.6 % in response to 10.0 μM As(III) and 10 mg L(-1) HA vs. the HA-free control. The significant contrast indicated that complexation alone could not explain the HA-induced reduction in arsenite toxicity and other factors including HA-cell surface interactions may come into play. Isotherms describing adsorption of HA to the Navicula sp. cells combined with morphological data by scanning electron microscopy revealed a protective HA floccule coating on the cell walls. Additional Fourier transform infrared spectroscopic data suggested the involvement of carboxylic groups during the adsorption of both HA and As(III) on the Navicula sp. cell surface. Collective data from this study suggest that cell wall-bound HA can moderate As(III) toxicity through the formation of a protective floccule coating occupying As(III) sorption sites and decreased effective functional groups capable of binding As(III). Our findings imply that As(III) toxicity can be alleviated due to the increased hindrance to cellular internalization of As(III) in the presence of naturally abundant DOM in water.

Toxicity and biosorption responses to arsenite (As[III]) were examined in a 96-h exposure study using Scenedesmus quadricauda, one of the most popular green algae distributed in freshwaters in China. Results indicated that the pH-dependent distribution of two arsenite species (H2AsO3(-) and H3AsO3) played an important role in biosorption and toxicity. The undissociated H3AsO3 was more toxic than its monoanionic H2AsO3(-) through comparison of algal cell numbers, chlorophyll-a contents, and algal ultrastructural changes observed with transmission electron microscopy. An effective biosorption of 89.0mgg(-1) at 100mgL(-1) As[III] was found in the treatments with an initial pH of 9.3 and 25.2μgg(-1) at 0.03mgL(-1) As[III] at an initial pH of 8.2 as a result of the predominant species of H2AsO3(-) under the ambient pH and Eh conditions. Our results imply that S. quadricauda may provide a new means for the removal of toxic arsenite species present in contaminated surface water., (Copyright © 2013 Elsevier Ltd. All rights reserved.)

A large portion of polychlorinated biphenyls (PCBs) from e-waste released into the coastal areas may be the potential source of PCBs to the global oceans. The paper presents data of PCBs concentrations in fifty surface sediment samples and a dated sediment core in Yangtze River Delta (YRE) and adjacent East China Sea (ECS). The total PCBs levels varied from 5.08 to 19.64 ng/g dry weight, with the highest concentrations situate within the river-sea boundary zone which is so-called "marginal filter". Concurrent with the operation of e-waste recycling over the last two decades, PCB fluxes started to rise again after 1980s and reached a maximum in this century. The full data set was used to estimate the burden of PCBs in YRE and adjacent ECS. A total sediment burdens were 192.8 tons, with the spatial density of 364 ng/cm(2) which accounts for 1.9% of all the PCBs in China., (Copyright © 2012 Elsevier Ltd. All rights reserved.)

Over 97% of the Earth's water is high salinity water in the form of gulfs, oceans, and salt lakes. There is an increasing concern for the quality of water in bays, gulfs, oceans, and other natural waters. These waters are affected by many different sources of contamination. The sources are, but not limited to, groundwater run-off of nitrogen containing fertilizer, pesticides, cleaning agents, solid wastes, industrial waters, and many more. The final destinations of these contaminants are rivers, lakes, and bayous that eventually will lead to bays, gulfs, and oceans. Many industries depend on the quality of these waters, such as the fishing industry. In addition to wild marine life, there are large aquariums and fish and shrimp farms that are required to know the quality of the water. However, the ability of these industries to monitor their processes is limited. Most analytical methods do not apply to the analysis of high salinity waters. They are dependent on wet chemistry techniques, spectrophotometers, and flow analyzers. These methods do not have the accuracy, precision, and sensitivity when compared to ion chromatography (IC). Since the inception of IC, it has become a standard practice for determining the content of many different water samples. Many IC methods are limited in the range of analytes that can be detected, as well as the numerous sample sources of which the methods are applicable. The main focus of current IC methods does not include high salinity waters. This research demonstrates an ion chromatographic method that has the ability to determine low level concentrations of inorganic nitrogen and related anions (nitrite-N, nitrate-N, phosphorous-P, sulfate, bromide, chloride, sulfide, fluoride, ammonia, calcium, and magnesium) in a single run using a combination of UV and conductivity detectors. This method is applicable to various waters, and uses both freshwater and high salinity water samples.

Effluents from sewage treatment plants (STPs) are known to contain residual micro-contaminants including endocrine disrupting chemicals (EDCs) despite the utilization of various removal processes. Temperature alters the efficacy of removal processes; however, experimental measurements of EDC removal at various temperatures are limited. Extrapolation of EDC behavior over a wide temperature range is possible using available physicochemical property data followed by the correction of temperature dependency. A level II fugacity-based STP model was employed by inputting parameters obtained from the literature and estimated by the US EPA's Estimations Programs Interface (EPI) including EPI's BIOWIN for temperature-dependent biodegradation half-lives. EDC removals in a three-stage activated sludge system were modeled under various temperatures and hydraulic retention times (HRTs) for representative compounds of various properties. Sensitivity analysis indicates that temperature plays a significant role in the model outcomes. Increasing temperature considerably enhances the removal of β-estradiol, ethinyestradiol, bisphenol, phenol, and tetrachloroethylene, but not testosterone with the highest biodegradation rate. The shortcomings of BIOWIN were mitigated by the correction of highly temperature-dependent biodegradation rates using the Arrhenius equation. The model predicts well the effects of operating temperature and HRTs on the removal via volatilization, adsorption, and biodegradation. The model also reveals that an impractically long HRT is needed to achieve a high EDC removal. The STP model along with temperature corrections is able to provide some useful insight into the different patterns of STP performance, and useful operational considerations relevant to EDC removal at winter low temperatures., (Copyright © 2011 Elsevier Ltd. All rights reserved.)

Bromide is ubiquitously found in drinking water. It is introduced into source water primarily by contact with bromide-containing soils or seawater having high bromide content. Bromide is converted into carcinogenic bromate during ozonation processes employed in some drinking water and wastewater treatment plants. Therefore, monitoring of bromate in drinking water and its precursor bromide in source water is required. The purpose of this study was to survey bromide and bromate concentrations in randomly selected bottle waters of various brands and several tap water samples in the coastal Houston area using a direct-injection ion chromatography (IC) and a suppressed conductivity system. The method employs a simple isocratic IC with loop injection with calculated detection limit of 0.009 microg/L for bromate and 0.028 microg/L for bromide (250-microL sample volume). Allowing the detection of both species at the microg/L level in drinking water, this method does not require specialized instrumentation such as two-dimensional IC, expensive sample preparation, or post-column reactions. The results show that, whereas bromate remains undetected in all five tap water samples, there are significant high concentrations of bromide in the coastal Houston area (294.79 +/- 56.97 microg/L). Its link to potential seawater intrusion need to be further investigated. For bottle water samples randomly collected, 18.2% (2 out of 11) showed detectable amount of both bromide and bromate. The detection of bromate coincides with those bottle water samples that underwent ozonation treatment. Further sample campaign with exclusively ozonated bottle water samples (n = 19) showed 100% detection rate for both bromide and bromate. The 99% confidence intervals were 14.45-37.97 microg/L and 0.32-2.58 microg/L for bromide and bromate, respectively. The highest level of bromate among all ozonated bottle water samples was 7.57 microg/L, a concentration close to the U.S. EPA prescribed limit for drinking water standard. Regression analysis indicated that although a positive correlation exists between bromide and bromate concentrations, such a correlation is not statistically significant. This finding is not unexpected since a variety of other parameters in the ozonation process (such as water quality, ozone dose, and time in addition to bromide concentration) affect the formation of bromate. Our results strongly suggest that cautions should be exercised to examine the potential formation of bromate when source water from coastal zone undergoes ozonation treatment. Another strong proof of our findings is that all the tap waters collected were treated in jurisdictions that do not use ozonation for disinfection. The fact that none of these tap water samples contained bromate (despite an abundance in bromide) proves our hypothesis even further.

Two UV-based advanced oxidation processes (AOPs), UV/H2O2 and UV/TiO2, were tested in batch reactor systems to evaluate the removal efficiencies and optimal conditions for the photodegradation of methyl tert-butyl ether (MTBE). The optimal conditions at an initial MTBE concentration of 1 mM ([MTBE]0=1 mM) were acidic and 15 mM H2O2 in UV/H2O2 system, and pH 3.0 and 2.0 g/l TiO2 in UV/TiO2 suspended slurries system under 254-nm UV irradiation. Under the optimal conditions, MTBE photodegradation during the initial period of 60 min in UV/H2O2 and UV/TiO2 systems reached 98 and 80%, respectively. In both systems, MTBE photodegradation decreased with increasing [MTBE]0. While MTBE photodegradation rates increased with increasing dosage of H2O2 (5-15 mM) and TiO2 (0.5-3 g/l), further increase in the dosage of H2O2 (20 mM) or TiO2 (4 g/l) adversely reduced the MTBE photodegradation. Pseudo first-order kinetics with regard to [MTBE] can be used to describe the MTBE photodegradation in both systems. The pseudo first-order rate constants linearly increased with the increase in the molar ratio of [H2O2]0 to [MTBE]0 in UV/H2O2 system and linearly increased with the decrease in [MTBE]0 in UV/TiO2 system.

A stoichiometric equation and kinetic model were developed and validated using experimental data from batch respirometer studies on the biodegradation of 2,4-dinitrotoluene (DNT). The stoichiometric equation integrates bacterial energetics and is revised from that in a previous study by including the mass balance of phosphorus (P) in the biomass. Stoichiometric results on O2 consumption, CO2 evolution, and nitrite evolution are in good agreement with respirometer data. However, the optimal P requirement is significantly higher than the stoichiometrically derived P, implying potentially limited bioavailability of P and the need for buffering capacity in the media to mitigate the adverse pH effect for optimal growth of DNT-degrading bacteria. An array of models was evaluated to fit the O2/CO2 data acquired experimentally and the DNT depletion data calculated from derived stoichiometric coefficients and cell yield. The deterministic, integrated Monod model provides the goodness of fit to the test data on DNT depletion, and the Monod model parameters (Ks, X0, mumax, and Y) were estimated by nonlinear regression. Further analyses with an equilibrium model (MINTEQ) indicate the interrelated nature of medium chemical compositions in controlling the rate and extent of DNT biodegradation. Results from the present batch respirometer study help to unravel some key factors in controlling DNT biodegradation in complex remediation systems, in particular the interactions between acidogenic DNT bacteria and various parameters, including pH and P, the latter of which could serve as a nutrient, a buffer, and a controlling factor on the bioavailable fractions of minerals (Ca, Fe, Zn, and Mo) in the medium.