Accumulation and distribution of some heavy metals in water, soil and rice fields along the Pradu and Phi Lok canals, Samut Songkhram province, Thailand

Abstract

This study aims to determine concentrations of heavy metals (Cd, Cu, and Zn) in the water, soil, and rice in paddy fields, and to compare heavy metal concentrations in the water, soil, and four parts of the rice plant (root, shoot, grain, and husk) between organic paddy fields and conventional paddy fields. The study area was the Pradu Canal (sites A and C) and the Phi Lok Canal (site B) in Phraek Nam Daeng Sub-district, Samut Songkhram Province, Thailand. Data was collected from August 2007 to December 2007. The water, soil, and rice samples were prepared for heavy metal analysis using a microwave digestion system and heavy metal concentrations were determine d using an atomic absorption spectrophotometer. Physicochemical parameters of the water and soil were also study.
The results showed the accumulation of heavy metals in the water, paddy soil, and four parts of the rice plant to be as follows (in descending order of frequency): Zn > Cu > Cd. The concentration of heavy metals in samples was also found to be as follows (greatest first): paddy soil > rice root > rice shoot > rice grain > rice husk > water. No significant difference was observed between Cd and Zn in paddy soil before ploughing and after rice harvesting at sites A, B, and C. However, Cu showed a significant difference at the level of 0.05 at site A and no significant difference at sites B and C.
It can be concluded therefore that Cd, Cu, and Zn concentrations in paddy soil and water were lower than the values permitted by the Surface Water Quality Standard and Soil Quality Standard of Thailand. Furthermore, Cd concentrations in rice seeds were lower than the values permitted by international health organizations and thus acceptable for human consumption.