Cadmium contamination in Tianjin agricultural soils and sediments: relative importance of atmospheric deposition from coal combustion

Cadmium (Cd) in coal, fly ash, slag, atmospheric deposition, soils and sediments collected from Tianjin, northern China, were measured to provide baseline information and determine possible Cd sources and potential risk. The concentrations of Cd in coal, fly ash and atmospheric deposition were much higher than the soil background values. Fallout from coal-fired thermal power plants, heating boilers and industrial furnaces has increased the Cd concentration in soils and sediments in Tianjin. The concentrations of Cd in soils of suburban areas were significantly higher than in rural areas, suggesting that coal burning in Tianjin may have an important impact on the local physical environment. Cd from coal combustion is readily mobilized in soils. It is soluble and can form aqueous complexes and permeate river sediments. The high proportion of mobile Cd affects the migration of Cd in soils and sediments, which may pose an environmental threat in Tianjin due to the exposure to Cd and Cd compounds via the food chain. This study may provide a window for understanding and tracing sources of Cd in the local environment and the risk associated with Cd bioaccessibility.