Affinity of endosulfan and HCB with human serum albumin affects serum concentrations in a general population

Endosulfan and hexachlorobenzene (HCB) were previously widely used organochlorine pesticides. Much attention has been paid to trends in human exposure to endosulfan and HCB and to the transport and distribution of endosulfan and HCB within the body. We determined endosulfan I, endosulfan II, and HCB concentrations in serum samples collected from the general population of Wuxi in Jiangsu Province (China) between 2012 and 2016. The endosulfan concentrations varied little throughout the study period, but the HCB concentrations increased. The HCB concentrations were significantly higher in serum from overweight people and smokers than in serum from normal weight people (p = 0.028) and non-smokers (p = 0.011), respectively. HCB binds to human serum albumin (HSA) and can form halogen bonds to CYS-461 and ARG-484 at site II (subdomain IIIA). Fatty acids and nicotine increase the affinity between HCB and HSA, explaining the higher HCB concentrations in serum from overweight people and smokers than normal weight people and non-smokers, respectively.