Heavy Metals Pollution Characteristic And Human Health Risk Assessment In Roadside Soils And Plants Grow Wild Along Highways In Hunan Province, China

With the rapid develepment of highway in China, soil pollution with heavy metal along highways have become increasingly serious in the environmental system. This study was performed to analyze the distribution, contamination degree, translation of traffic-related heavy metals(HMs) in soil-plant system, human health risks of HMs in roadside soils along G4 highway and G60 highway in Hunan province, China. A total of 45 composite soil samples from three sampling sites(LC, CT, and TS)with different distance(5 m、10 m、15 m、40 m and 80 m) were analyzed for HMs concentrations of Zn, Pb, Cd, Cr and Cu.The results showed that the concentrations of those HMs in r oadside soils decreased with increasing distance from highways. The results showed that the concentrations of those HMs in roadside soils decreased with increasing distance from highways. A pollution assessment by Geo-accumulation Index(Igeo) showed that the pollution level for the HMs is in the following order: Cd >Pb>Cr>Zn>Cu. The Cd levels can be considered “heavily contaminated” status in the distance of 5 m. And Cd also presented high risk based on potential ecological risk indexes(RI). The other detected heavy metals are practically uncontaminated or uncontaminated to moderately contaminated. The health risk of HMs in highway roadside soils was evaluated by hazard index(HI) and cancer risk(CR). The results showed high HI for Cd, Cr and Pb, which indicating a potential human health risk for both adult and children in these areas. But cancer risk of all those HMs for both adult and children was acceptable. Cr in three studied sections showed a slight cancer risk(carcinogenic risk in the acceptable range) in the distance of 80 m, which indicated the residents around highways should be living outside the distance of 80 m.The fractionation(relative percent) of these heavy metals in soils did not vary significantly with depth. And different heavy metal had different changing situation with the increasing of distance from highways. Owing to the previously mentioned difference in soil physicochemical properties and traffic volume, there were some discrepancies apparent on the fractions of heavy metal among LC, CT and TS, especially in TS. And the results of the modified BCR sequential extraction procedure showed that the mobile fraction of these HMs was in order of Cd> Pb> Zn >Cu >Cr. The high percent of the mobile fraction, indicating Cd, Pb and Zn were labile and available for uptake by wild plants. According to the value of RAC, Cd was the major risk factors, which was in the range high to very high risk.The mean concentrations, biological accumulation factor(BAF) and the metal accumulation index(MAI) of those traffic-related HMs in selected wild plants indicating all of them have good capacity of accumulate HMs. In general, the accumulation capacity for most HMs in selected wild plant tissues were bark> leaf. The bark of Cinnamomum camphora(L) Presl and Pinus massoniana Lamb showed high accumulation ability to Cd, Zn and Pb, indicating thei r potential for bio-monitoring. And these two plants should be used more frequently as barriers between polluted and vulnerable areas, especially highways.