Pesticides in three rural rivers in Guangzhou, China: spatiotemporal distribution and ecological risk.

Frequent and widespread pesticide use is a major concern for both human and environmental health. The aim of this study was to screen for 19 pesticides in rural rivers in Guangzhou, China, evaluating the potential impact of detected pesticides on the local ecosystem. Sampling was performed in rural rivers in three environment types: agricultural, industrial, and unpolluted, with sampling of water and sediments in both wet and dry seasons. A total of 11 pesticides were detected overall and their spatiotemporal distribution in water and ecological risk were assessed. Five pesticides were detected at concentrations above 100 ng L-1, with the highest concentration pesticides being dimethoate (1318 ng L-1) in surface water and quinalphos (328 ng g-1 dry weight (dw)) in sediments. The most commonly detected pesticides were chlorpyrifos, acetochlor, and butachlor with detection frequencies of 50-57% and 29-43%, in water and sediments, respectively. Samples from the agricultural rural river contained the most pesticides and at higher concentrations, as compared to industrial and unpolluted areas, especially during the wet season. Ecotoxicological risk assessment through Risk Quotients (RQs) showed that chlorpyrifos and fenvalerate pose high ecological risks in water and therefore, reduction of the source input of these pesticides is essential.

Removal of chlorpyrifos in recirculating vertical flow constructed wetlands with five wetland plant species.

The removal efficiency of the pesticide chlorpyrifos (50 and 500 µg L-1) by five wetland plant species (Cyperus alternifolius, Canna indica, Iris pseudacorus, Juncus effusus and Typha orientalis) was studied in recirculating vertical flow constructed wetland systems (RVFCWs). Results reveal that for chlorpyrifos at different concentrations, good removal efficiencies (94-98%) were observed using the same plant systems, while no significant differences in removal efficiencies were seen between the different plant systems. In addition, the chlorpyrifos removal efficiency of the planted systems increased significantly compared with the unplanted controls. The chlorpyrifos removal efficiency for wetland systems over time fit to the first-order kinetic model, with the first-order kinetic constant (k) ranging from 0.045 to 0.065 h-1. The half-life of chlorpyrifos in the systems ranged from 10.66-15.43 h. The shortest chlorpyrifos half-life was detected in the wetland system containing C. indica, followed by that with C. alternifolius and I. pseudacorus. The main pathways to remove chlorpyrifos in these wetland systems were sorption (accounting for 64.6-86.4% of the total removal efficiency) and biodegradation (8.1-33.7%). Plants can enhance chlorpyrifos removal through enhanced biodegradation in the system. Plants with high biomass and transpiration were able to accelerate the removal of chlorpyrifos and conventional pollutants. Hence, C. indica, C. alternifolius and I. pseudacorus could be used as optimal plants for pesticide removal in wetland systems.

Factors Affecting Behavior of Phenolic Endocrine Disruptors, Estrone and Estradiol, in Constructed Wetlands for Domestic Sewage Treatment.

This study investigated the efficiency of 12 pilot-scale constructed wetlands (CWs) with different configurations on the removal of estrone and estradiol from raw domestic sewage. An orthogonal design was employed to evaluate the impact of four principal design parameters of CWs, including four wetland types, three substrates, three plant conditions, and three hydraulic loading rates, in summer and winter. A bench-scale anoxic simulation test was performed in the laboratory to clarify the photolysis, sorption, and degradation of estrogens. Estrogens were more effectively removed by the 12 CWs during summer. The experiment showed that target estrogens were efficiently removed by wetland substrate under anoxic conditions through exothermic sorption and degradation even in winter. This suggests that the inefficient removal in CWs in winter likely resulted from subsequent cleavage of a considerable amount of estrogen conjugates in influent due to insufficient decomposition at low temperatures. The transformation from estradiol to estrone could be driven by residual microbial activities not inhibited by azide, and the reversible process was then driven by active microorganisms but not solely abiotic redox reactions. Among the four design parameters, wetland-type was the most important and downward-vertical flow CWs performed best.

Removal and factors influencing removal of sulfonamides and trimethoprim from domestic sewage in constructed wetlands.

Twelve pilot-scale constructed wetlands with different configurations were set up in the field to evaluate the removal and factors that influence removal of sulfonamides (sulfadiazine, sulfapyridine, sulfacetamide, sulfamethazine and sulfamethoxazole) and trimethoprim from domestic sewage. The treatments included four flow types, three substrates, two plants and three hydraulic loading rates across two seasons (summer and winter). Most target antibiotics were efficiently removed by specific constructed wetlands; in particular, all types of constructed wetlands performed well for the degradation of sulfapyridine. Flow types were the most important influencing factor in this study, and the best removal of sulfonamides was achieved in vertical subsurface-flow constructed wetlands; however, the opposite phenomenon was found with trimethoprim. Significant relationships were observed between antibiotic degradation and higher temperature and redox potential, which indicated that microbiological pathways were the most probable degradation route for sulfonamides and trimethoprim in constructed wetlands.