Organic micropollutants in the Yangtze River: Seasonal occurrence and annual loads

Abstract

Twenty percent of the water run-off from China’s land surface drains into the Yangtze River and carries the sewage of approximately 400million people out to sea. The lower stretch of the Yangtze therefore offers the opportunity to assess the pollutant discharge of a huge population. To establish a comprehensive assessment of micropollutants, river water samples were collected monthly from May 2009 to June 2010 along a cross-section at the lowermost hydrological station of the Yangtze River not influenced by the tide (Datong Station, Anhui province). Following a prescreening of 268 target compounds, we examined the occurrence, seasonal variation, and annual loads of 117 organic micropollutants, including 51 pesticides, 43 pharmaceuticals, 7 household and industrial chemicals, and 16 polycyclic aromatic hydrocarbons (PAHs). During the 14-month study, the maximum concentrations of particulate PAHs (1–5μg/g), pesticides (11–284ng/L), pharmaceuticals (5–224ng/L), and household and industrial chemicals (4–430ng/L) were generally lower than in other Chinese rivers due to the dilution caused of the Yangtze River’s average water discharge of approximately 30,000m3/s. The loads of most pesticides, anti-infectives, and PAHs were higher in the wet season compared to the dry season, which was attributed to the increased agricultural application of chemicals in the summer, an elevated water discharge through the sewer systems and wastewater treatment plants (WWTP) as a result of high hydraulic loads and the related lower treatment efficiency, and seasonally increased deposition from the atmosphere and runoff from the catchment. The estimated annual load of PAHs in the river accounted for some 4% of the total emission of PAHs in the whole Yangtze Basin. Furthermore, by using sucralose as a tracer for domestic wastewater, we estimate a daily disposal of approximately 47million m3 of sewage into the river, corresponding to 1.8% of its average hydraulic load. In summary, the annual amounts flushed by the Yangtze River into the East China Sea were 2.9×106tons of dissolved and particulate organic carbon (DOC and POC), 369tons of PAHs, 98tons of pesticides, 152tons of pharmaceuticals, and 273tons of household and industrial chemicals. While the concentrations seem comparably moderate, the pollutant loads are considerable and pose an increasing burden to the health of the marine coastal ecosystem.