Ecological Risk Assessment for Heavy Metals Occurrence in Rice Cultivation Areas in An Giang Province, Vietnam

Abstract

The study was conducted to assess the occurrence and ecological risk of heavy metal concentrations (Cu, Zn, Pb, Cd and As) in the soil of paddy fields in An Giang province in 2020. Soil samples were collected at 112 locations in seven paddy fields. Cluster analysis (CA) was used to present the spatial distribution of heavy metals. Ecological potential risk index (RI) was used to determine risk levels caused by heavy metals. The results showed that Cu, Zn, Pb and As in all soil samples ranging from 1.83-124.04, 4.87-114.18, 7.87-39.22 and 4.66-16.32 mg/kg, respectively. Cd was not detected in the soil samples. All heavy metal values were within the allowable limits of Vietnamese technical regulation on heavy metals in the soils. However, Cu concentration at the rice area in An Hoa hamlet, Khanh An commune, An Phu district (D10) and As concentration at D11 (An Hoa hamlet, Khanh An commune), D33 & D36 (Hoa Ha hamlet, Kien An commune, Cho Moi district) and D38 (Phu Thuong 2 hamlet, Kien Thanh commune, Cho Moi district) exceeded the allowable limits. The CA results revealed that soil quality at 112 study sites was classified into 12 soil quality groups, possibly reducing the soil monitoring cost by 72.32%. As is the most significant contributor to potential ecological risks in soils, although RI values still showed that heavy metals pose a low risk in rice cultivation areas. However, heavy metals in soils could degrade soil quality, accumulate in agricultural commodities, and eventually humans through the food chain. Therefore, the frequency of the monitoring can be considered to increase to two or three times per year to evaluate the seasonal variation of the heavy metals.