Assessments of heavy metal pollution of a farmland in an urban area based on the Environmental Geochemical Baselines

Abstract

To study the possible adverse impacts of urbanization on the accumulation of heavy metals in cultivated soils. Five hundred thirty-one topsoil samples in the farmland of the peripheral areas of western Ningbo City, Zhejiang Province, Southeast China, were collected. The contents of heavy metal elements, As, Cd, Cr, Cu, Hg, Ni, Pb, Zn, and crustal stable trace elements, Li, Eu, Sc, Sm, in the samples were determined. The stable trace elements, best correlated with the heavy metals, were chosen as the reference elements to calculate the Environmental Geochemical Baselines (EGBs) of As, Cd, Cr, Cu, Hg, Ni, Pb, and Zn in the soils. Based on the established EGBs, the Enrichment Factors (EF) and Hankson Potential Ecological Risk (HRER) of the heavy metals in the soils were calculated to assess their potential ecological hazard risks. As a result, more than 30% of the sampling points of the study area were in moderate, considerable, or high risk of Cd, and 42% in moderate or considerable risk of Hg. The other heavy metals in the soils were mostly in low ecological risk. The BAF (Bio-accumulation Factor) and RAC (Risk Assessment Code) of Cd in the Cd high-risk soils were 12.43% and 45.14% on average, respectively, suggesting its high bio-availability. About 80% of the rice grain growing on the Cd high-risk soils of the study area exceeded the threshold of Cd for food safety, indicating high edible risk. It implies that the farmland of the study area has been significantly adversely impacted by industrial, vehicular, or other anthropogenic activities.