Distribution and sources of DDTs in urban soils with six types of land use in Beijing, China.

The concentrations of dichlorodiphenyltrichloroethanes (DDTs) were investigated for urban soil samples collected from business area (BU), classical garden (CL), culture and educational area (CU), large public green space (LA), residential area (RE), and roadside area (RO) in Beijing. The DDTs concentrations ranged from 0.03 to 1282.58 ng/g, with an average of 68.14+/-189.46 ng/g. The DDTs concentration in CL was much higher than that in the other five types of land use, which was due to the usage of DDTs to protect vegetation in CL, and the DDTs concentration was affected by both the usage history of DDTs and the age of the CL. Only 22% of the samples, mainly located in RO, manifested the application of technical DDTs recently. DDTs concentration showed a decreasing trend from the city center to the suburb, and it increased with the age of the urban area. DDTs were positively correlated with total organic carbon and black carbon in soils. About 81.7% of the samples met the grade I standard (50 ng/g soil) of the Chinese Environmental Quality Standard for Soils, and only 1.5% of the samples exceeded the grade III standard (1000 ng/g soil).