Source and health risk assessment of heavy metals in non-certified organic rice farming at Nakhon Nayok Province, Thailand

Abstract

Heavy metals contamination is a problem in some non-certified organic rice farms that do not have buffer zones. Soil monitoring is therefore required to estimate the potential risk of such organic products. The objectives of the present study are to determine the extent of heavy metal contamination, sources of contamination and assessment of non-carcinogenic health risks to local consumers. Concentrations of toxic heavy metals were determined in soil and rice grain to assess the bioaccumulation factor. The health risk assessment was analyzed following Target Hazard Quotients (THQ) and the Hazard Index (HI). Sources of heavy metal contamination were determined by a correlation study of heavy metal contents, THQ and HI with some physical properties of these non-certificated organic rice fields. The occurrence of heavy metals in agricultural soils and rice grain were ranked in the following order: Pb > Mn > Zn > Cu > Ni and Zn > Mn > Cu > Ni. However, Pb and Zn contamination exceeded maximum permissible levels in rice grain. Non-certified organic rice from these locations might therefore present a health risk for consumers; the high HI values of rice consumption for adult males (5.10-35.09) and 6.12-42.08) indicated a serious adverse health risk for consumers. Individual correlation analysis and principal component analysis indicated that the THQ of Zn was positively correlated with its content in soil and in the grain. Main roads and community activities were found to be the main source of contamination for Zn and Mn, while Pb and Cu contamination mainly derived from paddy field activities such as fertilizer application. This finding will contribute to raising public awareness of the health risks of non-certified organic rice farming. © 2019, Chulalongkorn University - Environmental Research Institute. All rights reserved.