Mobility and distribution of lead, cadmium, copper and zinc in soil profiles in the peri-urban market garden of Kunming, Yunnan Province, China

Five profiles located in the peri-urban market garden of Yunnan Province, China were investigated for the distribution and sequential extraction fractions (SEF) of Pb, Cd, Cu and Zn, and mobility in relation to soil properties. SEF heavy metals included acetic acid extractable (A-fraction), hydroxylamine hydrochloride extractable (B-fraction) and hydrogen peroxide and ammonium acetate extractable fractions (C+D-fraction). The results showed that: (1) Total Pb and Zn contents decreased with soil depth. The accumulation of different fractions of Pb and Zn was due to accumulation of organic carbon and Fe-Mn oxides. (2) Total Cd content increased with soil depth with the ratio of A to C horizons (RAC)<1.0. Cd was relatively mobile within the A horizon. C+D-Cd contents were consistent with organic carbon accumulation. (3) Total Cu content in profiles 2 and 3 decreased with depth, while in other profiles it increased. A-Cu contents in the B horizon in profiles 1, 2 and 3 were higher than in the A and C horizons, and decreased with depth in profiles 4 and 5 in the transition unit. B-Cu content increased with depth, whereas C+D-Cu contents decreased. The mobility and redistribution of heavy metals in soil profiles were influenced by clay content, organic carbon and Fe-Mn oxides.