Relations of arsenic concentrations among groundwater, soil and paddy from an alluvial plain of Korea

摘要

Serious groundwater arsenic (As) contaminations are frequently associated with alluvial plains, and which are mostly used for rice cultivation in Asian countries. Because rice cultivation requires large quantities of irrigation, the long-term use of Ascontaminated groundwater for irrigation may cause As contamination in the soil with a consequent impact on rice grains. In this study, we investigated As concentrations in groundwater, soil and rice and the soil properties from an alluvial plain of the Mankyeong River, Korea, to understand their relations from the viewpoint of As contamination in rice. Arsenic in the rice varied from 0.03 mg/kg to 0.22 mg/kg, with a mean of 0.13 mg/kg, which is much lower than the World Health Organization's maximum permissible limit of As in rice (1.0 mg/kg). Some groundwater samples showed As concentrations much higher than the drinking water standard (10 ug/L). Despite the rice As is independent of groundwater As it showed a good relation with soil As and Fe-oxide fractions. Because As is mainly occurred in Fe-oxide fractions and the soil is mostly silty, it is speculated that under flooding conditions arsenic can easily mobilize to the soil solution and potentially be available for plants. However, this availability can be controlled by As uptake mechanisms and/or incomplete reduction of Fe-oxides. It is observed that rice As is significantly correlated with soil exchangeable-PO_4 (r = -0.41, p < 0.05), indicating that PO_4 competition in the soil-rhizosphere may be one of the factors controlling rice As.