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The Loess Plateau has been a focus of public discussion and environmental concerns over the past three decades. In this study, in order to investigate the effect of OCP pollution in water of the Beiluo River, concentrations of 25 OCPs at 17 locations in the water were examined. The results showed that the concentration of ∑OCPs in the water ranged from 1.76 to 32.57 ng L-1, with an average concentration of 7.23 ng L-1. Compared with other basins in China and abroad, the OCP content in the Beiluo River was at a medium level. Hexachlorocyclohexane (HCH) pollution in the Beiluo River was mainly from the mixed input of lindane and technical HCHs. Dichlorodiphenyltrichloroethane (DDT) pollution was mainly from the mixed input of technical DDTs and dicofol. Most of the OCP pollution came from historical residues. The risk assessment results showed that hexachlorobenzene (HCB) and endosulfan had high ecological risks in the middle and lower reaches of the Beiluo River. Most residual OCPs were not sufficient to pose carcinogenic and non-carcinogenic health risks to humans. The results of this study can provide a reference for OCP prevention and control and watershed environmental management.

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The distribution and source of polychlorinated biphenyls (PCBs) pollution in the Beiluo River, the secondary tributary of the Yellow River, still remain unclear. With the purpose of determining the distribution, origins, and pollution levels of PCBs and their consequences on ecological risks, the concentrations of 27 PCBs at 17 locations in the sediments of the Beiluo River were examined in this study. The results showed that the mass concentrations of ∑PCBs in the sediment ranged from 0.12 to 1.25 ng∙g-1 (DW), with the highest point at sampling site B13 downstream of the river. Compared to most river sediments, both domestically and internationally, the concentration of PCBs in the sediment of the Beiluo River was at a low level, with 10-PCB and 6-PCB as the main components, indicating that the PCBs that are difficult to volatilise and degrade are more likely to remain in the sediment. The origins of PCBs in the sediments of the Beiluo River were examined by using positive matrix factorisation (PMF). The results revealed that the contamination of PCBs in the sediments of the Beiluo River mainly resulted from industrial emissions, technical PCB mixtures, and coal and wood combustion. The results of the ecological risk assessment indicated that PCBs in the sediments of the study area rarely contribute to adverse biological effects and the potential low risk to the environment.

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The occurrence of hormesis in the algal growth inhibition test is a major challenge in the dose-response characterization, whereas the molecular mechanism remains unraveled. The aim of this study is therefore to investigate the changes in the molecular pathways in a model green alga Raphidocelis subcapitata treated with erythromycin (ERY; 4, 80, 120 µg L-1) by transcriptomic analysis. After 7 day exposure, ERY at 4 µg L-1 caused hormetic effects (21.9 %) on cell density, whereas 52.0 % and 65.4 % were inhibited in two higher exposures. By using adj p < 0.05 and absolute log2 fold change> 1 as a cutoff, we identified 218, 950, and 2896 differentially expressed genes in 4, 80, 120 µg L-1 treatment groups, respectively. In two higher ERY treated groups, genes involved in phases I, II & III metabolism processes and porphyrin and chlorophyll metabolism pathway were consistently suppressed. Interestingly, genes (e.g., pri2, mcm2, and mcm6) enriched in DNA replication process were up-regulated in 4 µg L-1 group, whereas these genes were all repressed in 120 µg L-1 group. Alteration trend in gene expression was consistent with algal growth. Taken together, our results unveiled the molecular mechanism of action in ERY- stimulated/ inhibited growth in green alga.

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Algal species Raphidocelis subcapitata and Chlorella vulgaris are commonly used to test the chemicals with an antibacterial mode of action during marketing authorization process. However, significant differences in the sensitivity toward antibiotic exposure have been reported. The selection of an inappropriate test species would thus underestimate the environmental hazard of target chemicals and pose a potential threat to the ecosystem. Since oxidative stress is a crucial factor determining the inhibition of algal growth, an investigation on oxidative stress and antioxidant defense mechanisms in these two species was performed to explore its roles in species sensitivity. Here, roxithromycin (ROX), a macrolide antibiotic extensively used to treat respiratory, urinary and soft tissue infections, was used for testing. After 7 days exposure to ROX at the low (0.01 mg L-1) and high (0.09 mg L-1) concentrations, R. subcapitata was inhibited while the growth of C. vulgaris was stimulated. We investigated the roles of oxidative stress in algae by measuring the oxidative stress biomarkers (MDA), non-enzymatic antioxidants (GSH), and antioxidant enzymes (SOD, CAT, GP, GST). The results suggested that when the growth of algae is inhibited, MDA content as well as activities of oxidative stress enzymes would increase, and thus, activating the antioxidant system. On the contrary, it was inferred that when the growth is stimulated, MDA content and oxidative stress enzymes activities would decrease.

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RESUMEN

Clarithromycin (CLA), a macrolide antibiotic, has been frequently detected in the global surface waters. Concerns have been raised over the potential impacts of CLA on the non-target aquatic species, particularly algae acting as the primary producers in the ecosystem. This study therefore evaluated the toxicological effects of CLA at a range of concentration levels (0, 5, 20, 40, 80 µg L-1) on two green algae, Raphidocelis subcapitata (R. subcapitata) and Chlorella vulgaris (C. vulgaris). The algal growth, photosynthetic pigment contents, lipid peroxidation biomarker malondialdehyde (MDA), responses of antioxidants including superoxide dismutase (SOD), catalase (CAT), glutathione (GSH), glutathione peroxidase (GP), and glutathione S-transferase (GST) were measured. After 7 d exposure, the growth of R. subcapitata was inhibited with the CLA exposure levels higher than 20 µg L-1, whereas the inhibition in C. vulgaris was detected at the concentration level of 80 µg L-1. The MDA contents in both species were elevated. To cope with the increased levels of ROS, the activities of enzymatic antioxidants (SOD, CAT, GP, and GST) and the content of non-enzymatic antioxidant (GSH) in R. subcapitata were all enhanced. However, in C. vulgaris, enhancement was detected only in the activities of antioxidant enzymes (SOD, CAT, and GP). In addition, chlorophyll a, b, and carotenoid contents were all significantly increased in R. subcapitata but decreased in C. vulgaris. The results suggested that R. subcapitata is more sensitive to CLA exposure than C. vulgaris. This study provides insights into the CLA - oxidative stress process in two algae.

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