Occurrence, spatial distribution, and seasonal variation of emerging trace organic pollutants in source water for Shanghai, China

The long-term low concentrations of trace "contaminants of emerging concern" (CECs) can have potential toxic effects on human health and serious risks to the ecological environment. This study investigated the occurrence, spatial distributions, and seasonal variations of 65 target CECs, including 35 pesticides, 17 antibiotics, 7 microcystins, 5 estrogens, and 1 plasticizers in Shanghai's source water. The detected pesticides and antibiotics of sulfonamides and macrolides were relatively ubiquitous in source water of Shanghai, with levels decreasing in the following order: pesticides (average (avg.) 0.0003-1.67 μg/L) > antibiotics (avg. 0.1-14.1 ng/L). While microcystins, estrogens, and plasticizers (ng/L) were non-ubiquitous, with detected species of below 50%, and detection frequencies of mostly below 50%. Pesticide concentrations did not show obvious variations in the water from the inlets of the two rivers. Compare to all other water sources of Shanghai, the much higher concentrations of antibiotics found in the Y3, H2 reservoir and H3 were mainly from roxithromycin and sulfapyridine, roxithromycin and sulfadiazine, and sulfamethazine and roxithromycin, which accounted for 69.5%, 88.1% and 70.8% of the total concentration in corresponding water source, respectively. Pesticide concentrations in the Huangpu River were higher in the wet season than in the flat season, while the concentration decreased in the Yangtze River during the wet season. In Y1, Y3 and Y4, there were relatively large differences in pesticide levels in the wet season, and flat season when the maximal contribution of the pesticide concentration was from acephate, which accounted for about 67% of the total pesticide concentration. The levels of antibiotics in the flat season were higher than those in the wet season in both water sources. Overall, improvement of raw water quality was observed after entering the reservoir except for microcystin.