Determination of OCPs, OPPs, and 21 SVOCs in water and sediment samples in five rivers of Shenzhen, China, during the period of 2017 and 2018.

One hundred two semivolatile organic compounds (SVOCs), including 20 organochlorine pesticides (OCPs) and 12 organophosphorus pesticides (OPPs), were determined in the main rivers of Shenzhen, China. As a result, p,p'-dichlorodiphenyldichloroethane (DDD), aldrin, and benzoepin sulfate were the main OCPs detected in surface water, and p,p'-DDD, heptachlor, and endrin aldehyde were the main compounds in sediment. In addition, diazinon was the most frequent OPP detected in both water and sediment. At most sites, SVOCs were at similar concentration levels in 2017 and 2018. Compared with other areas, diazinon and malathion had comparative high concentrations in Maozhou River in this study. Analyzed from the SVOCs concentrations in water and sediment, p,p'-DDD was from the quick degradation of p,p'-dichlorodiphenyltrichloroethane (DDT), and no recent DDT was input around the investigated area. Besides, the interrelationships among these pollutants were calculated, revealing that OPPs were mainly from the chronically cumulative content, rather than the directly transferring from surface water to sediment. According to the risk assessment, the occurrence of p,p'-DDD and p,p'-DDT affected the aquatic community. All in all, further investigations on the occurrence and source of these pollutants are still needed to avoid the potential risk for human beings living around the contaminated environment.

Qualitative and quantitative analysis of source for organic carbon and nitrogen in sediments of rivers and lakes based on stable isotopes.

Sediment is the most dominant reservoir of organic pollutants in the aquatic environment. Understanding carbon and nitrogen sources in sediments and factors that controls distribution enhances our understanding of biogeochemical cycles of carbon and nitrogen. Different end-members and surface sediments of rivers and sediments profiles of lakes were collected. The concentrations of TOC and TON and their δ13C and δ15N were studied for qualitative and quantitative analysis of natural and anthropogenic sources. The results show that TOC and TON concentrations of the sediments from rivers range from 0.63% to 10.83% and 0.06%-0.86%, respectively, indicating substantial great environmental risks in these rivers. The concentrations of TOC and TON for the four sediment profiles below the 5 cm, increase in the order of Miyun < Chuidiao < Qunming < Houhai, as influenced by their respective environment condition. Moreover, water quality was quite good and there was no risk of eutrophication in Miyun reservoir. δ13Corg and δ15Norg in surface sediments of the studied 18 rivers range from -27.2‰ to -24.9‰ and -2.2‰ to +10.9‰, respectively. Based on a simple δ13C-based end-member mixing and a C/N ratio model, organic matter in the surface sediments of these rivers were mainly derived from sewage and C3 plant. In addition, the sources of organic matter differed in each layer of the four sediment profiles. This study provides a reliable method for qualitative and quantitative identification of the source of organic matter in sediments, and offers theoretical basis for better management of rivers and lakes.