Divergent patterns of heavy metal accumulation in paddy fields affect the dietary safety of rice: a case study in Maoming City, China.

Abstract

The objective of this work was to study the impact of large petrochemical plants and mining operations on the accumulation of heavy metals in farmland and rice, as well as assess their potential risks on human health. The contents of seven heavy metals, Cd, Pb, Cr, Ni, Co, Cu, and Mn, were monitored in a typical polluted paddy soil-rice system near a petrochemical plant and mining area in Maoming, China. The results showed that the content of Cd in the soil exceeds the standard rate by 100%, and the single factor pollution index of Cd was 5.12, which is considered heavy pollution. Excessive heavy metals can inhibit and poison the growth of rice plants. Rice plants can maintain a certain level of heavy metal content by reducing the absorption or interception in the root cells, leading to great differences in the distribution of different heavy metals in plant tissues. Cadmium, Cu, Co, and Mn are easily absorbed from the soil by rice roots, while other heavy metals are relatively difficult to absorb by rice roots. Cuprum, Cd, Co, Pb, and Cr were mainly accumulated in the root of rice, but Mn and Ni migrate to the above ground plant tissues quickly. The brown rice produced in the paddy fields in the study area was seriously polluted. The concentration of Cd, Pb, and Ni in brown rice exceeded the standard by 100%, and Cr in brown rice also exceeded the standard by 80%. If residents consume rice from the study area, their daily intake of Cr and Cd will be 1.02 and 3.24 times higher, respectively, than the standard limit recommended by the FAO/WHO. The irrigation streams were polluted due to the discharge of petrochemical plants and mining wastewater, causing the serious pollution of heavy metals in the surrounding paddy fields. The rice produced in this area poses a serious risk to consumers, and so this problem of pollution should be addressed.