Residual characteristics of HCHs and DDTs in surface soils from the western zone of Bohai Bay

Three hundreds and two surface soil samples were collected from the western watershed of Bohai Bay and measured for residual HCHs and DDTs.The analytical results indicated that,the arithmetic average concentrations and standard deviations of HCHs and DDTs were(3.88±25.92)ng·g-1 and(63.60±255.83)ng·g-1,respectively;and the geometric mean values and standard deviations of HCHs and DDTs were(0.44±3.97)ng·g-1 and 8.68(5.51 ng·g-1,respectively.The distribution of the raw data showed right-skew characteristics.The logarithm transformed concentrations of HCHs had significant correlation with angular transformed soil TOC contents,while this correlation was not found for the case of DDTs.There were apparent differences between different types of land use,and vegetable plot,woodland and barren had relatively higher concentrations of HCHs,while elevated residues of DDTs occurred at vegetable plot,woodland,cultivated land and cotton field.In some areas,new inputs of HCHs and DDTs may exist.Based on the current national soil quality standards,the percentage of the number of the sites with DDTs concentrations over the III or higher quality grades was 2.6%,and 11.9% for the sites with DDT residual levels in the II grade;in the case of HCHs,the proportion of the sites with concentrations above the II grade was only 2%.Accordingly,the resulted sites with higher potential ecological risk of HCHs were mainly located in Shijiazhuang of Hebei Province,Beijing and Tianjin,while the corresponding sites with higher potential ecological risk of DDTs were mostly situated in Shijianzhuang and Handan of Hebei Province,Jinan of Shandong Provinve,Beijing and Tianjin.