Characteristics of Mercury Transformation in Soil and Accumulation in Rice Plants in an Acidic Purple Paddy Soil Area

Abstract

A pot experiment was conducted to analyze the characteristics of mercury (Hg) accumulation during the rice growth period in acidic purple paddy soil. Results showed that the soil total Hg concentration was stable with time during the rice growth period, while methylmercury (MeHg) increased greatly. Therefore, the ratio of MeHg/THg was mainly affected by MeHg concentration. THg concentration in rice plant parts followed the trend:root > grain > stalk > leaf > husk at the mature grain stage, while MeHg concentration followed grain > root > stalk > leaf > husk. The average of MeHg/THg in rice (24.03%) far exceeded that in soil (3.05%), suggesting that rice plants have a strong affinity for MeHg accumulation. This conclusion was supported also by the great difference in average of bio-concentration factors between MeHg (8.16) and THg (2.31) or the transfer factor in the grain, which was more than 1. Moreover, the bio-concentration factor for grain was higher than that for roots, stalks, and leaves, suggesting MeHg was prone to accumulation in grain compared with other part of rice plants.