Salinity and Persistent Toxic Substances in Soils from Shanghai, China

Some farmland soils in Shanghai had high salinity levels, suggesting secondary salinization of the soils. The soil problems in Shanghai were studied, including the salinity and nitrate nitrogen (NO^-₃-N) concentrations, heavy metal pollution characteristics, and organochlorine pesticide (OCP) residual levels and polycyclic aromatic hydrocarbon (PAH) contents. Accumulation of NO^-₃-N in vegetable soils was the most significant among different functional soils. Heavy metal pollution was significant in the samples collected from the sewage-irrigated land and roadside. The identification of the metal sources through multivariate statistical analysis indicated that Pb, Zn, Cu and Cr in urban soils were from the traffic pollutants; excessive application of fertilizer and irrigation were the main reasons for the metal pollution in agricultural soils; Ni in the observed soils was controlled by parent soils. OCPs could still be detected in farmland soils but degraded greatly in last 20 years after prohibition of their usage. PAHs with 2-3 rings were the main components in industrial soils. The concentrated PAHs in the investigated soils were likely from petroleum and coal combustion.