Novel stressors introduced by human activities increasingly threaten freshwater ecosystems. The annual application of more than 2.3 billion kg of pesticide active ingredient and 22 billion kg of road salt has led to the contamination of temperate waterways. While pesticides and road salt are known to cause direct and indirect effects in aquatic communities, their possible interactive effects remain widely unknown. Using outdoor mesocosms, we created wetland communities consisting of zooplankton, phytoplankton, periphyton, and leopard frog (Rana pipiens) tadpoles. We evaluated the toxic effects of six broad-spectrum insecticides from three families (neonicotinoids: thiamethoxam, imidacloprid; organophosphates: chlorpyrifos, malathion; pyrethroids: cypermethrin, permethrin), as well as the potentially interactive effects of four of these insecticides with three concentrations of road salt (NaCl; 44, 160, 1600 Cl⁻ mg/L). Organophosphate exposure decreased zooplankton abundance, elevated phytoplankton biomass, and reduced tadpole mass whereas exposure to neonicotinoids and pyrethroids decreased zooplankton abundance but had no significant effect on phytoplankton abundance or tadpole mass. While organophosphates decreased zooplankton abundance at all salt concentrations, effects on phytoplankton abundance and tadpole mass were dependent upon salt concentration. In contrast, while pyrethroids had no effects in the absence of salt, they decreased zooplankton and phytoplankton density under increased salt concentrations. Our results highlight the importance of multiple-stressor research under natural conditions. As human activities continue to imperil freshwater systems, it is vital to move beyond single-stressor experiments that exclude potentially interactive effects of chemical contaminants.

Simulation model is very essential for predicting the environmental fate and the potential environmental consequences of chemical pollutants including those from accidental chemical spills. However very few of such simulation model is seen related to Chinese costal water body. As the first step toward our final goal to develop a simulation model for the prediction and the risk assessment of chemical pollutants in Chinese coastal water, this study developed a three-dimensional (3D) hydrodynamic model of Xiamen Bay (XMB). This hydrodynamic model was externally derived by meteorological data, river discharge and boundary conditions of XMB. We used the model to calculate the physical factors, especially water temperature, salinity and flow field, from June to September 2016 in XMB. The results demonstrated a good match between observations and simulations, which underscores the feasibility of this model in predicting the spatial-temporal concentration of chemical pollutants in the coastal water of XMB. Longitudinal salinity distributions and the mixing profile of river-sea interactions are discussed, including the obvious gradation of salinity from the river towards sea sites shown by the model. We further assumed that 1000 kg and 1000 mg/L of a virtual chemical pollutant leaked out from Jiulong River (JR) estuary (point source) and whole XMB (non-point source), respectively. The model illustrates that it takes three months for XMB to become purified when point source pollution occurs in the estuary, while half a year to be required in the case of non-point source pollution across the entire bay. Moreover, the model indicated that pollutants can easily accumulate in the western coastal zone and narrow waters like Maluan Bay, which can guide environmental protection strategies.

In this study, the distribution profiles, emission characteristics, and health risks associated with 43 volatile and semi-volatile organic compounds, including 15 phenols, 18 polycyclic aromatic hydrocarbons (PAHs), 6 BTEX, and 4 other compounds, were determined in the wastewater treatment plant (WWTP) of a coking factory (plant C) and the succeeding final WWTP (central WWTP). Total phenols with a concentration of 361,000 μg L⁻¹ were the predominant compounds in the influent wastewater of plant C, whereas PAHs were the major compounds in the final effluents of both coking WWTPs (84.4 μg L⁻¹ and 30.7 μg L⁻¹, respectively). The biological treatment process in plant C removed the majority of volatile organic pollutants (94.1%–99.9%). A mass balance analysis for plant C showed that biodegradation was the main removal pathway for all the target compounds (56.6%–99.9%) except BTEX, chlorinated phenols, and high molecular weight (MW) PAHs. Chlorinated phenols and high MW PAHs were mainly removed via sorption to activated sludge (51.8%–73.2% and 60.2%–75.9%, respectively). Air stripping and volatilization were the dominant mechanisms for removing the BTEX compounds (59.8%–73.8%). The total emission rates of the detected volatile pollutants from plant C and the central WWTP were 1,640 g d⁻¹ and 784 g d⁻¹, respectively. Benzene from the equalization basins of plant C and the central WWTP corresponded to the highest inhalation carcinogenic risks (1.4 × 10⁻³ and 3.2 × 10⁻⁴, respectively), which exceeded the acceptable level for human health (1 × 10⁻⁶) recommended by the United States Environmental Protection Agency. The results showed that BaP exhibited the highest inhalation non-cancer risk, with a hazard index ratio of 70 and 30 for plant C and the central WWTP, respectively. Moreover, the excess sludge generated during wastewater treatment should also be carefully handled because it adsorbed abundant PAHs and chlorinated phenols at coking plant C (58,000 μg g⁻¹ and 3,500 μg g⁻¹) and the central WWTP (622 μg g⁻¹ and 54 μg g⁻¹).

Ingestion of microplastics by marine organisms has been well documented, but their interaction with chemical pollutants has not been sufficiently addressed. The aim of this study was to determine the individual and combined effects of chlorpyrifos (CPF) and polyethylene microplastics (MP) on the survival, fecundity, feeding and egg viability of Acartia tonsa, a calanoid copepod widely distributed in planktonic communities. The median lethal concentration obtained for CPF was higher (LC₅₀ = 1.34 μg/L) than for the combination with MP (LC₅₀ = 0.37 μg/L), or CPF-loaded MP (LC₅₀ = 0.26 μg/L). Significant effects were also observed for feeding and egg production (EC₅₀ = 0.77 and 1.07 μg/L for CPF, 0.03 and 0.05 μg/L for CPF combined with MP, 0.18 and 0.20 μg/L for CPF-loaded MP). No significant effects were observed in the exposure to ‘virgin’ MP. This study confirms the role of MP as vectors of pollutants to marine organisms and supports the increased availability of certain toxicants carried out by MP. The effects observed in fitness-related responses suggest potential damage to A. tonsa populations. The comparison of the results obtained here with environmental concentrations indicates that the combined exposure to CPF and MP could constitute a risk to A. tonsa in the natural environment.

Organic chemical pollutants associated with microplastic (MP) may represent an alternative exposure route for these chemicals to marine biota. However, the bioavailability of MP-sorbed organic pollutants under conditions where co-exposure occurs from the same compounds dissolved in the water phase has rarely been studied experimentally, especially where pollutant concentrations in the two phases are well characterized. Importantly, higher concentrations of organic pollutants on ingested MP may be less bioavailable to aquatic organisms than the same chemicals present in dissolved form in the surrounding water. In the current study, the sorption kinetics of two model polycyclic aromatic hydrocarbons (PAHs; fluoranthene and phenanthrene) to MP particles in natural seawater at 10 and 20 °C were studied and the bioavailability of MP-sorbed PAHs to marine copepods investigated. Polyethylene (PE) and polystyrene (PS) microbeads with mean diameters ranging from 10 to 200 μm were used to identify the role of MP polymer type and size on sorption mechanisms. Additionally, temperature dependence of sorption was investigated. Results indicated that adsorption dominated at lower temperatures and for smaller MP (10 μm), while absorption was the prevailing process for larger MP (100 μm). Monolayer sorption dominated at lower PAH concentrations, while multilayer sorption dominated at higher concentrations. PE particles representing ingestible (10 μm) and non-ingestible (100 μm) MP for the marine copepod species Acartia tonsa and Calanus finmarchicus were used to investigate the availability and toxicity of MP-sorbed PAHs. Studies were conducted under co-exposure conditions where the PAHs were also present in the dissolved phase (Cfᵣₑₑ), thereby representing more environmentally relevant exposure scenarios. Cfᵣₑₑ reduction through MP sorption was reflected in a corresponding reduction of lethality and bioaccumulation, with no difference observed between ingestible and non-ingestible MP. This indicates that only free dissolved PAHs are significantly bioavailable to copepods under co-exposure conditions with MP-sorbed PAHs.

The quality of freshwater undoubtedly reflects the health of our surrounding environment, society, and economy, as these are supported by various freshwater ecosystems. Monitoring efforts have therefore been considered a vital means of ensuring the ecological health of freshwater environments. Nevertheless, most aquatic environmental monitoring strategies largely focus on bulk water sampling for analysis of physicochemical and key biological indicators, which for the most part do not consider pollution events that occur at any time between sampling events. Because benthic biofilms are ubiquitous in aquatic environments, pollution released during sporadic events may be absorbed by these biofilms, which can act as repositories of pollutants. The aim of this study was to assess whether benthic biofilm monitoring could provide an efficient way of properly characterizing the extent of pollution in aquatic environments. Here, bulk water and benthic biofilms were sampled from three Hong Kong streams having various pollution profiles, and subsequently compared via high-resolution microscopy, metagenomic analysis, and analytical chemistry. The results indicated that biofilms were, indeed, reservoirs of environmental pollutants, having different profiles compared with that of the corresponding bulk water samples. Moreover, the results also suggested that biofilms sampled in polluted areas were characterized by a higher species richness. While the analytical testing of benthic biofilms still needs further development, the integration of chemical-pollutant profiles and biofilm sequencing data in future studies may provide unique perspectives for understanding and identifying pollution-related biofilm biomarkers.

Coexistence of antibiotics/heavy metals and the overexpression of resistance genes in the vermicompost has become an emerging environmental issue. Little is known about the interaction and correlation between chemical pollutants and biological macromolecular compounds. In this study, three typical vermicompost samples were selected from the Yangtze River Delta region in China to investigate the antibiotic, heavy metal and corresponding antibiotic resistance genes (ARGs) and heavy metal resistance genes (HRGs). The results indicated the prevalence of tetracycline (TC), copper (Cu), zinc (Zn), cadmium (Cd), corresponding TC-resistance genes (tetA, tetC, tetW, tetM, tetO, and tetS) and HRGs (copA, pcoA, cusA, czcA, czcB, and czcR) in the three vermicompost samples. In addition, the ARG level was positively associated with the water-soluble TC fraction in the vermicompost, and it was same between the HRG abundance and exchangeable heavy metal content (p < 0.05). Moreover, a positive correlation was found between ARG and HRG abundance in the vermicompost samples, suggesting a close regulation mechanism involving the expression of both genes. The result obtained here could provide new insight into the controlling risk of heavy metals, TC, and relevant resistance genes mixed contamination in the vermicompost.

Microplastics can adsorb chemical pollutants such as metals or pharmaceuticals, and transferred them along the food chain. In this work, an investigation of the adsorption of Cd, Co, Cr, Cu, Ni, Pb and Zn by five different types of microplastics was performed in Milli-Q water and natural waters (seawater, urban wastewater and irrigation water) via a series of batch adsorption experiments. The effects of concentration of metals and physicochemical characteristics of polymers were particularly studied. Results revealed a significant adsorption of lead, chromium and zinc on microplastics, especially on polyethylene and polyvinyl chloride. In the case of polyethylene terephthalate, it showed little adsorption capacity. Specific surface, porosity and morphology are characteristics that affect the molecular interactions. The adsorption isotherms were better described by Langmuir model, which indicates that the main adsorption mechanism might be chemical adsorption. Finally, results obtained in natural waters indicated that dissolved organic matter may play a major role on metal adsorption on microplastics. Results showed an enhancement of metal adsorption in waters with high chemical and biological oxygen demands as urban wastewater and irrigation water.

There is an increasing awareness of the threats posed by the worldwide presence of microplastics (MPs) in the environment. Due to their high persistence, MPs will accumulate in the environment and their quantities tend to increase with time. MPs end up in environments where often also chemical contaminants are present. Since the early 2000s, the number of studies on the sorption of chemicals to plastic particles has exponentially increased. The objective of this study was to critically review the literature to identify the most important factors affecting the sorption of chemical contaminants to MPs. These factors include the physicochemical properties of both the MPs and the chemical contaminants as well as environmental characteristics. A limited number of studies on soil together with an increased notion of the importance of this compartment as a final sink for MPs was observed. Therefore, we assessed the distribution of model chemicals (two PCBs and phenanthrene) in the soil compartment in the presence of MPs using a mass balance model. The results showed a high variation among chemicals and microplastic types. Overall, a higher partitioning to MPs of chemical contaminants in soil is expected in comparison to aquatic environments. As sorption to a large extent determines bioavailability, the effects of combined exposure to chemicals and MPs on the toxicity and bioaccumulation in biota are discussed. Finally, some considerations regarding sorption and toxicity studies using MPs are given.

Gut microbial communities constitute a compartment of crucial importance in regulation of homeostasis of multiple host physiological functions as well as in resistance towards environmental pollutants. Many chemical contaminants were shown to constitute a major threat for gut bacteria. Changes in gut microbiome could lead to alteration of host health. The access to high-throughput sequencing platforms permitted a great expansion of this discipline in human health while data from ecotoxicological studies are scarce and particularly those related to aquatic pollution. The main purpose of this review is to summarize recent body of literature providing data obtained from microbial community surveys using high-throughput 16S rRNA sequencing technology applied to aquatic ecotoxicity. Effects of pesticides, PCBs, PBDEs, heavy metals, nanoparticles, PPCPs, microplastics and endocrine disruptors on gut microbial communities are presented and discussed. We pointed out difficulties and limits provided by actual methodologies. We also proposed ways to improve understanding of links between changes in gut bacterial communities and host fitness loss, along with further applications for this emerging discipline.