Effect of air drying on speciation of heavy metals in flooded rice paddies

Flooded soil samples were collected in the typical area of the Yangtze Delta Region; fractions of heavy metals in flooded and air dried samples were measured with BCR sequential extraction method and atomic absorption spectrometry. In flooded soils, fractions of heavy metals increased in the order of acid soluble < oxidizable < reducible < residual. The acid soluble and reducible fractions significantly decreased but residual fraction significantly increased when the samples were air dried. The data obtained from air dried soil samples could not accurately represent the speciation of heavy metals in flooded field conditions.