Inter-Annual Concentration Variations and Pollution Assessment of Heavy Metals in the Surface Sediments in the Adjacent Sea Water of Tangshan in Spring

Abstract:

Current study surveyed 70 sampling stations through four cruises in the adjacent seawater near Tangshan between 2006 and 2015. The contents and inter-annual variation characteristics of seven heavy metals: Hg, Cu, Pb, Cd, Cr, Zn and As in the surface sediment were analyzed. The single-factor exceeding rate, geo-accumulation index () and the comprehensive potential ecological risk index (RI) were used to evaluate the pollution degree. The results showed that the overall levels of the heavy metal contents in the surface sediment were low in the survey areas. Specifically, Cu and As contents in several stations exceeded the first class standard value, whereas the contents of other heavy metals accorded with the first class standard. The inter-annual content variations of the surveyed heavy metal were fluctuant slightly between 2006 and 2015. The contents of Cu, Pb, Cd, and Zn were relatively stable throughout the years, but the inter-annual variation of Hg and Cr increased initially followed by decrease. There was no significant change in As contents between the years. The evaluation results showed that the multi-year average of for the seven heavy metals was Hg>Cd>Pb>Cu>As>Cr>Zn, while the potential ecological risk assessment results showed that the multi-year average of the potential ecological risk factor for the seven heavy metals was Hg>Cd>As>Pb>Cu>Cr>Zn. Hg was the main pollution factor in surface sediments in the adjacent sea water of Tangshan based on the consistent results from two pollution evaluation methods, indicating that it has the highest ecological risk level. The inter-annual variations of RI ranged from 44.26 to 153.18 and the inter-annual average value was 89.92, belonging to the low ecological risk level. The trend of the inter-annual variations of RI was increasing and then decreasing, suggesting that the heavy metal pollution in surface sediments has been reduced in recent years.