Collaborative evaluation of heavy metal pollution of soil-crop system in the southeast of Yangtze River Delta, China

Abstract

Collaborative quality status of all sample points (a) and spatial distribution of collaborative pollution grade (b). • Collaborative features of heavy metal pollution in soil-crop system were explored. • Soil growing grains was most polluted for single and comprehensive soil pollution. • Grain was the most polluted crop type for single and comprehensive crop pollution. • Collaborative pollution increased from periphery to center and from west to east. • Grain had the strongest abilities of absorbing and accumulating heavy metals. Scientific evaluation of heavy metal pollution is required to understand the status better and formulate policies. However, previous studies primarily focused on a single evaluation of soil pollution or crop pollution, ignoring the collaborative evaluation of soil-crop system pollution from a holistic perspective. In this study, we collected 1815 samples in an industrial city to explore the differences between heavy metal pollution in soil and crops as well as collaborative characteristics of heavy metal pollution in soil-crop system. Our results showed that for the soil where grains and vegetables were grown, approximately half of the study region was comprehensively polluted, concentrated in the downtown. However, grains in most areas were comprehensively polluted, particularly the severe pollution around the downtown (i.e., County C), while the overall crop pollution of vegetables and fruits was much less serious than that of grains. For single soil pollution, the grain was the most polluted crop type in Pb, Hg, Cu, and Zn pollution. In contrast, for single crop pollution, the grain was the most polluted crop type in nearly all heavy metals, especially in Cr, As, and Ni pollution. Therefore, pollution characteristics of the same heavy metal were inconsistent in soil and crops, indicating the demand of an integrated evaluation method for soil-crop system pollution. Our collaborative evaluation results showed that 52.56% of sample points were contaminated and mainly distributed in the middle part. The collaborative pollution grade presented an increasing trend from the periphery to the center, and the west part was more contaminated than the east part. Our study further implies that the grain had the strongest abilities of absorbing and accumulating heavy metals. Cd was the most easily absorbed heavy metal by crops, while Pb was the least easily accumulated heavy metal in soil-crop system.