BACKGROUND The distribution, migration and biological effects of lead in the red soil region of Southern China are still not clear.
BAOBJECTIVES To study the soil and rice in Longhai city, Fujian Province, and systematically analyze the distribution characteristics, morphological composition, bioaccumulation ability and influencing mechanism of soil lead, and summarize the enrichment and distribution of lead in the parent rock-soil-rice migration process.
METHODS The content of Pb in parent material and its speciation in top soil, as well as the content of Pb in rice was analyzed complying with a systemic sampling code for agro-ecology research.
RESULTS The top soil in the central area of Longhai city has high lead content, and the remaining areas are relatively low. The 92.5% sample values range from 10 to 90 mg/kg, corresponding to a pH of 4.0 to 7.5, and the lead content in strongly acidic and alkaline soils is slightly lower. 4.1% of the rice lead (0.018-0.398 mg/kg) exceeded the standard, indicating that the rice has a weak soil lead enrichment capacity (enrichment coefficient 0.23%±0.16%). Therefore, rice in the study area may not necessarily exceed the standard when lead exceeds the standard. The main factors influencing soil lead are soil-forming parent rocks and soil types. The rules of soil lead content in different parent-rock areas are Quaternary marine sediments > Quaternary residual sediments > Granite and acid volcanic rocks > Fotan Formation basic basalt. The rules of lead content in different soil types were fluvo-aquic > coastal saline soil > paddy soil > red soil > red soil > coastal aeolian sandy soil.
CONCLUSIONS The soil lead availability status (ion-exchange state, water-soluble state) accounted for only 4.95% of the total lead, and the strong organic state and residual state accounted for 94.99% of the total, indicating that soil lead exists mainly in a stable state and is difficult to be absorbed by plants. This provides investigation basis for reasonable interpretation of the phenomenon that the soil exceeds the standard lead and the rice does not exceed the standard. The study also showed that there is no significant correlation between rice lead and surface soil lead, and maintaining soil pH in the weakly acidic to weakly alkaline range can reduce soil lead activity.