Bioaccumulation and maternal transfer of two understudied DDT metabolites in wild fish species

While the secondary metabolites of DDT such as 2,2-bis(chlorophenyl)-1-chloroethylene (DDMU) and 2,2-bis(chlorophenyl)methane (DDM) have been detected in the environment for several decades, knowledge is extremely limited on their bioaccumulation characteristics. Here, we reported the bioaccumulation and maternal transfer of p,p'-DDMU and p,p'-DDM in two wild fishes, i.e., the northern snakehead (Channa argus) and crucian carp (Carassius auratus), from a DDT contaminated site in South China. The hepatic concentrations of p,p'-DDMU and p,p'-DDM in the fish were up to 549 and 893 ng/g lipid weight, contributing 5.3% and 3.2% in average to ΣDDXs (the sum concentrations of DDT and its 6 metabolites), respectively. The residues of p,p'-DDMU and p,p'-DDM in the fish exhibited interspecific and intraspecific variations, resulting from the differences in lipid content, sex, and body sizes (length and mass) between or within species. Both p,p'-DDMU and p,p'-DDM were consistently detected in the fish eggs, demonstrating their maternal transfer in female fish. The mean eggs to liver lipid-normalized concentration (E/L) ratios of p,p'-DDMU and p,p'-DDM were 0.98 and 1.77 in the northern snakehead, 0.35 and 0.01 in crucian carp, respectively; which were comparable to or even exceeded those of DDT and its major metabolites calculated in the same individual. Statistical analyses of the data showed that the E/L ratios were positively correlated with body sizes of the fish, but negatively correlated with the hepatic concentrations of p,p'-DDMU and p,p'-DDM in females; suggesting the influences of fish sizes and the mother body residues on their maternal transfer efficiencies.