Altered transfer of heavy metals from soil to Chinese cabbage with film mulching.

The influence of film mulching on the migration of metals from soil to cabbage was investigated. Following a 50-day growth in field plots mulched or unmulched, root-zone soils and Chinese cabbage (Brassica chinensis L.) were sampled for metal analysis. Mulching slightly decreased the soil mobile (acid-extractable) Cd, but increased its transfer from root to the cabbage parts. As an essential element, Cu was readily transferred to the cabbage parts. While mulching decreased the soil mobile Zn, reduced soil pH resulted in its enhanced soil-to-root migration. This, however, did not increase the transfer of Zn within cabbage. Although mulching increased the soil mobile Pb by 200%, an increase in Pb in cabbage leaves but a decrease in stem result presumably from the enhanced foliar uptake of atmospheric Pb. This study suggests that mulching may promote the accumulation of toxic metals such as Cd and Pb in cabbage and therefore increase crop risks to human health.