Marine oil spill often causes contamination of drinking water sources in coastal areas. As the use of oil dispersants has become one of the main practices in remediation of oil spill, the effect of oil dispersants on the treatment effectiveness remains unexplored. Specifically, little is known on the removal of dispersed oil from contaminated water using conventional adsorbents. This study investigated sorption behavior of three prototype activated charcoals (ACs) of different particle sizes (4–12, 12–20 and 100 mesh) for removal of dispersed oil hydrocarbons, and effects of two model oil dispersants (Corexit EC9500A and Corexit EC9527A). The oil content was measured as n-alkanes, polycyclic aromatic hydrocarbons (PAHs), and total petroleum hydrocarbons (TPHs). Characterization results showed that the smallest AC (PAC100) offered the highest BET surface area of 889 m2/g and pore volume of 0.95 cm3/g (pHPZC = 6.1). Sorption kinetic data revealed that all three ACs can efficiently adsorb Corexit EC9500A and oil dispersed by the two dispersants (DWAO-I and DWAO-II), and the adsorption capacity followed the trend: PAC100 > GAC12 × 20 > GAC4 × 12. Sorption isotherms confirmed PAC100 showed the highest adsorption capacity for dispersed oil in DWAO-I with a Freundlich KF value of 10.90 mg/g∙(L/mg)1/n (n = 1.38). Furthermore, the presence of Corexit EC9500A showed two contrasting effects on the oil sorption, i.e., adsolubilization and solubilization depending on the dispersant concentration. Increasing solution pH from 6.0 to 9.0 and salinity from 2 to 8 wt% showed only modest effect on the sorption. The results are useful for effective treatment of dispersed oil in contaminated water and for understanding roles of oil dispersants.

Accumulation and oral bioavailability of nickel (Ni) were rarely assessed for staple crops grown in high geogenic Ni soils. To assess exposure risk of geogenic Ni, soil, wheat, and rice samples were collected from a naturally high background Ni area and measured for Ni oral relative bioavailability (RBA, relative to NiSO₄) using a newly developed mouse urinary Ni excretion bioassay. Results showed that soils were enriched with Ni (80.5 ± 23.0 mg kg⁻¹, n = 58), while high Ni contents were observed in rice (2.66 ± 1.46 mg kg⁻¹) and wheat (1.32 ± 0.78 mg kg⁻¹) grains, with rice containing ∼2-fold higher Ni content than wheat. Ni-RBA was low in soil (14.8 ± 7.79%, n = 18), but high in wheat and rice with rice Ni-RBA (85.9 ± 19.1%, n = 9) being ∼2-fold higher than wheat (46.1 ± 21.2%, n = 16). A negative correlation (r = 0.61) was observed between Ni-RBA and iron content in rice and wheat, suggesting the low iron status of rice drives its high Ni bioavailability. The higher Ni accumulation and bioavailability for rice highlights that rice consumption was a more important contributor to daily Ni intake compared to wheat, while Ni intake from direct soil ingestion was negligible. This study suggests a potential health risk of staple crops especially rice when grown in high geogenic Ni areas.

We conducted the first comprehensive assessment of the presence, source, and ecotoxicological implication of 13 banned and restricted organochlorine pesticides (OCPs) in the surface water along the Ganga River for two different seasons. Surface water samples were collected along the 2525 km stretch of the Ganga through 43 sites representing five zones of diverse land-use pattern, pesticide consumption rate, and varied flow. The mean concentrations of ΣOCPs were significantly higher (∼2–5 times) in the post-monsoon or wet season [range: 0.126 to 10.402 μg/L (mean: 2.482 μg/L ± 3.589 and median: 1.433)] than in the post-winter or dry season [range: 0.053 to 3.010 μg/L (mean: 0.765 μg/L±1.033 and median: 0.399)]. Lindane (γ-HCH) was the dominant and most frequently detected pesticide at all the sites, indicating possible continued use of this banned pesticide in agricultural practices. The spatial distribution of OCPs revealed non-significant difference amongst different zones and indicate that point source pollution from the open drains along the Ganga could be responsible for observed trend. Ratio diagnostic analysis highlighted the fresh inputs and potential illegal use of lindane and chlordane at all the zones whereas, historical use of DDT was revealed at the majority of sites. Interestingly, fresh inputs of DDT were observed in the relatively pristine high altitude Upper zone (UZ) suggesting long-range atmospheric transfer and its continued use in the zone. Risk quotient (RQ) analysis revealed high ecotoxicological risks (>1), at all the studied sites for p, p’ DDE. The lower zone (LZ) emerged as a high ecological risk zone. The study highlights that though the OCPs analysed in this study are banned/restricted in India, still the implementation of the ban is poor and delayed and the country requires stricter adherence to its National Implementation Plan (NIP) on pesticides.

Goethite is a common iron hydroxide, which can be substituted by manganese (Mn) in the goethite structure. It is important to investigate the immobilization of uranium(VI) on Mn-substituted goethite (Mn-Goe) to understand the fate and migration of uranium in soils and sediments. In this study, the sorption of uranium(VI) by Mn-Goe was investigated as a function of pH, adsorbent dosage, contact time, and initial uranium concentration in batch experiments. Several material analysis techniques were used to characterize manganese substituted materials. Results indicated that Mn was successfully introduced into the goethite structure, the length of particles increased gradually, the surface clearly exhibited higher roughness with increasing Mn content, and that uranium(VI) sorption of synthetic Mn-Goe appeared to be higher than that of goethite. The sorption kinetics supported the results presented by the pseudo-second-order model. The sorption capacity of uranium on Mn-Goe was circa 77 mg g⁻¹ at pH = 4.0 and 25 °C. Fourier transform-infrared spectroscopy (FT-IR) analyses revealed that uranium ions were adsorbed through functional groups containing oxygen on the Mn-Goe structure. The enhancement of Mn-substitution for the uranium(VI) sorption capacity of goethite was revealed. This study suggests that goethite and Mn-Goe can both play a significant role in controlling the mobility and transport of uranium(VI) in the subsurface environment, which is helpful for material development in environmental remediation.

Hypoxia off the Changjiang Estuary (CE) and its adjacent waters is purported to be the most severe in China, attracting considerable concern from both the scientific community and the general public. Currently, continuous observations of dissolved oxygen (DO) levels covering hypoxia from its appearance to disappearance are lacking. In this study, twelve consecutive monthly cruises (from February 2015 to January 2016) were conducted. The consecutive spatiotemporal variations in hypoxia throughout the annual cycle were elucidated in detail, and the responses of annual variations in hypoxia to the different influential factors were explored. Overall, hypoxia experienced a consecutive process of expanding from south to north, then disappearing from north to south. The annual variations in hypoxia were mainly contingent on stratification variations. Among different stages, there was significant heterogeneity in the dominant factors. Specifically, low-DO waters initially appeared from the intrusion of nearshore Kuroshio branch current (NKBC), as NKBC intrusion provided a low-DO background and triggered stratification. Thereafter, stratification was enhanced and gradually expanded northward, which promoted the extension of low-DO areas. The formation of hypoxia was regionally selective, and more intense organic matter decomposition at local regions facilitated the occurrence and discontinuous distribution of hypoxia. Hypoxic zones were observed at the Changjiang bank and Zhejiang coastal region from August (most extensively at 14,800 km²) to October. Thereafter, increased vertical mixing facilitated the dissipation of hypoxia from north to south.

Oxadiazon-Butachlor (OB) is a widely used herbicide for controlling most annual weeds in rice fields. However, its potential toxicity in aquatic organisms has not been evaluated so far. We used the zebrafish embryo model to assess the toxicity of OB, and found that it affected early cardiac development and caused extensive cardiac damage. Mechanistically, OB significantly increased oxidative stress in the embryos by inhibiting antioxidant enzymes that resulted in excessive production of reactive oxygen species (ROS), eventually leading to cardiomyocyte apoptosis. In addition, OB also inhibited the WNT signaling pathway and downregulated its target genes includinglef1, axin2 and β-catenin. Reactivation of this pathway by the Wnt activator BML-284 and the antioxidant astaxanthin rescued the embryos form the cardiotoxic effects of OB, indicating that oxidative stress, and inhibition of WNT target genes are the mechanistic basis of OB-induced damage in zebrafish. Our study shows that OB exposure causes cardiotoxicity in zebrafish embryos and may be potentially toxic to other aquatic life and even humans.

Perfluorooctanoic acid (PFOA) is an emerging persistent organic pollutant which has been identified at significant levels in soils. Existed ecotoxicological studies have mainly employed earthworms to evaluate the toxicity of PFOA. However, little information do we know about the toxicity of PFOA regarding soil microorganisms. Accordingly, the adverse effects of PFOA on microbial activity in a wheat soil under four fertilization treatments were investigated in this study. The microcalorimetric results revealed that the toxicity of PFOA on soil microbial activity in four treatments followed a descending sequence: Control (no fertilization), NK (no P fertilizer, but N and K fertilizers were used), PK (no N fertilizer, but P and K fertilizers were used), and NPK (N, P and K fertilizers were used). The soil sample with higher available P content had higher resistant to PFOA. There were significant differences in urease activity and alkaline phosphatase activity among the four fertilization treated soils. Molecular modeling studies clearly demonstrated that the binding of PFOA with alkaline phosphatase was more stable than with urease through electrostatic interaction, van der Waals force, and hydrogen bonds. These results are expected to provide more comprehensive information in toxicity of PFOA in soil environment.

Properly increasing mobility of heavy metals could promote phytoremediation of contaminated soil. Fe₁₋ₓS/biochar was successfully prepared from sawdust with loading pyrrhotite (Fe₁₋ₓS) at a pyrolysis temperature of 550 °C. Thiobacillus were successfully adsorbed and enriched on the surface of Fe₁₋ₓS/biochar. Microbial growth for 36 d supported by bio-oxidization of Fe₁₋ₓS decreased the system pH from 4.32 to 3.50, increased the ORP from 298 to 487 mV, and the Fe³⁺ release reached 25.48 mg/g, enhancing the oxidation and leaching of soil Pb. Finally, Fe₁₋ₓS/biochar and Thiobacillus were simultaneously applied into Pb-contaminated soil for 60 d, the soil pH decreased from 7.83 to 6.72, and the exchangeable fraction of soil Pb increased from 22.86% to 37.19%. Ryegrass planting for 60 d in Pb-contaminated soil with Fe₁₋ₓS/biochar and Thiobacillus showed that the Pb content in shoot and root of ryegrass increased by 55.65% and 73.43%, respectively, confirming an obvious increase of phytoavailability of soil Pb. The relative abundance of Thiobacillus in remediated soil significantly increased from 0.06% to 34.55% due to the addition of Fe₁₋ₓS/biochar and Thiobacillus. This study provides a novel approach for regulating the Pb phytoavailability for phytoremediation of Pb-contaminated soil.

Long-term trends (2004–2017) in the chemical composition and sources of PM₂.₅ (particulate matter smaller than 2.5 μm in diameter) in a metropolitan area were investigated using daily integrated PM₂.₅ chemical speciation data and continuous air pollution measurements. Eleven source factors were identified: coal combustion characterized by secondary sulphate, secondary nitrate, summertime organic carbon (OC), regional elemental carbon (EC), biomass burning, oil combustion, primary tailpipe emissions, non-tailpipe emissions related to road dust, non-tailpipe emissions related to brake wear, metal production, and road salt. Overall, coal combustion, secondary nitrate, regional EC, and oil combustion underwent marked decreases in concentrations with large reduction rates ranging from −8% yr⁻¹ to −18% yr⁻¹, contributing to an overall 34% decrease in annual PM₂.₅ over the past 14 years. Decreases in local tailpipe emissions (−3% yr⁻¹) were consistent with the reduction of traffic-related air pollutants. In contrast, non-tailpipe emissions remained constant until 2010–2011 and then increased with a range of rates of 21% yr⁻¹ to 27% yr⁻¹ from 2011 to 2016. The contribution of summertime OC increased to approximately 27% in the summer of 2013–2016, rising to become the largest PM₂.₅ source driven by the reduction of regional sources. The chemical composition of PM₂.₅ in the urban area drastically changed from inorganic-rich to organic- and metal-rich particles during 2013–2016. The depletion of ascorbic acid was measured using filter samples collected over one year to identify PM₂.₅ components and sources contributing to the oxidative potential (OP) of PM₂.₅. The OP was clearly associated with trace elements (e.g., Ba, Cu, Fe). Non-tailpipe emissions related to road dust and brake wear presented high redox activity per mass of PM₂.₅. This work suggests that summertime OC and non-tailpipe emissions in recent years have become increasingly important. As such, policies targeting traffic-related PM₂.₅ should focus on these sources for maximum impact.

Arsenic (As) contamination of water poses severe threats to human health and thus requires effective remediation methods. In this study, Synechocystis PCC6803, a model cyanobacterium common in aquatic environments, was used to investigate the role of extracellular polymeric substances (EPS) in As toxicity, accumulation, and transformation processes. We monitored the growth of Synechocystis with As exposure, measured the zeta potential and binding sites on the cell surface, and analysed As accumulation and speciation in Synechocystis cells with and without EPS. After EPS removal, the binding sites and zeta potential of the cell surface decreased by 44.43% and 31.9%, respectively. The growth of Synechocystis decreased 49.4% and 43.7% with As⁽ᴵᴵᴵ⁾ and As⁽ⱽ⁾ exposure, and As accumulation in the cells decreased by 12.8–44.5% and 14–42.7%, respectively. As absorption was enhanced in cells with EPS removed. The oxidation of As⁽ᴵᴵᴵ⁾ and reduction of As⁽ⱽ⁾ were significantly greater in cells with intact EPS compared to those with EPS removed. Fourier transform infrared spectroscopy (FTIR) showed that functional groups of EPS and Synechocystis cells, including –NH, –OH, CO, and CC, interacted with As species. Together the results of this work demonstrate that EPS have significant impacts on cell surface properties, thereby affecting As accumulation and transformation in Synechocystis PCC6803. This work provides a basis for using EPS to remedy As pollution in aquatic environments.