Residues and source identification of persistent organic pollutants in farmland soils irrigated by effluents from biological treatment plants

Also in this case study, low levels of the OCPs were observed and were not of significant concern in this wastewater irrigation area. Among the different OCPs analyzed, DDTs (mean 8.41 ng/g) and HCHs (mean 2.91 ng/g) were the major components. From the ratios of DDT/DDTs and β-HCH/HCHs, it indicated that OCPs residues should be from historical usage.