Pollution characteristics and ecological risk assessment of heavy metals in the sediment of Hengshui Lake

Eleven sampling points were set in Hengshui Lake to analyze the concentration distribution of heavy metals including Cr, Ni, Cu, Zn, As, Cd, Pb, Mn, Co, Sb and Tl in sediment. The degree of heavy metal pollution was evaluated by the method of geo-accumulation index and potential ecological risk assessment index. Pearson correlation analysis was conducted by SPSS. The results showed that the average concentrations of other heavy metals in the sediment of Hengshui Lake were lower than the background value of Layer A soil in Hebei Province except for Cd and Co. The concentrations of Cr, Ni, Cu, Zn, As and Pb at each sampling point were lower than the soil risk screening values of agricultural land in Soil Environmental Quality, Agricultural Land Risk Control Standards for Soil Contamination (Trial) (GB 15618-2018). Sb and Co were lower than the soil risk control values of construction land in Soil Environmental Quality, Construction Land Risk Control Standards for Soil Contamination (Trial) (GB 36600-2018). There were 8 sampling points of Cd whose concentration exceeded the agricultural land risk screening value of GB 15618-2018, and 1 point was higher than the construction land risk control value of GB 36600-2018. The evaluation results of the geo-accumulation index method showed that Cd was generally moderately polluted, Co was generally mildly polluted, and the nine heavy metals of Cr, Ni, Cu, Zn, As, Pb, Mn, Sb and Tl could be regarded as non-polluted. The results of potential ecological risk index evaluation indicated that the impact degree of each pollutant on the ecological risk of Hengshui Lake was Cd>>Co>As>Sb≈Pb>Cu>Ni>Cr>Mn≈Zn. The RI average value was 270.79, which was a medium ecological hazard. However, the contribution rate of Cd to RI was as high as 91%, which was the main pollution factor. Cd pollution was possibly caused by Yellow River water diversion into the lake and other human activities.