Assessment of heavy metals contamination and ecological risk of roadside agricultural soil, used for sunflower (Helianthus annuus L.) cultivation

Abstract

The present study is an attempt for comprehensive assessment of the pollution intensity and corresponding ecological risk of heavy metals including Cd, Co, Cr, Cu, Fe, Ni, Pb, Zn and Sb for agricultural soil, located alongside the national road II-81 in Bulgaria, used for the sunflower (Helianthus annuus L.) cultivation, by various factors and indices calculation. In total, 18 surface soil samples (0 - 20 cm depth) were collected at distances 11 m, 36 m and 61 m from the road edge at two sunflower plants’ growth stages: vegetative (V-3) and maturity (R9). The total concentrations of heavy metals of soil samples, collected at two different sunflower growth stages were used for assessment of the potential ecological risk. Based on the results for the potential ecological risk index, pollution load index, enrichment factor, contamination factor and the degree of contamination, calculated from the average total concentrations, considerable pollution of the tested agricultural soil was observed, mainly with Sb. The values of enrichment factor show that with the exception of Fe, Cr and Ni the rest of the tested heavy metals are mostly from anthropogenic sources. There are strong, not statistically significant correlations between the enrichment factors, ecological risk index, pollution load index and contamination degree and the distance from the road edge and strong correlations between enrichment factors of heavy metals related to the road traffic emissions and the distance from the road edge. The values of the factors and indices above mentioned are lower at the growth stage R9 than at the growth stage V-3 that shows the sunflower capacity of accumulation of the tested heavy metals.