Chlorine isotope evidence for the anthropogenic origin of tris-(4-chlorophenyl)methane

Compound-specific Cl-isotope analysis was performed on the persistent and bioaccumulating compound tris-(4-chlorophenyl)methane (4,4′,4″-TCPMe, referred to as TCPMe in this study) to elucidate whether its main source is natural or anthropogenic. Blubber from the Baltic grey seal (Halichoerus grypus) was extracted by continuous acetonitrile partitioning, and the TCPMe was isolated from the extract by preparative-capillary gas chromatography. Chlorine isotope analysis was subsequently performed by sealed-tube combustion in conjunction with thermal-ionization mass spectrometry (TIMS). The δ37Cl of TCPMe was −3.5 ± 0.5‰, similar to the previously reported δ37Cl of technical grade p,p′-DDT (referred to as DDT in this study). The data is not consistent with a putative marine natural source of TCPMe, as enzymatic (biotic) production is reported to give values of δ37Cl < −10‰. The δ37Cl–TCPMe data thus supports the hypothesis that TCPMe is produced as a byproduct during DDT synthesis and is released to the environment through the same pathways as DDT. It is also consistent with tris-(4-chlorophenyl)methanol as the primary biotransformation product of TCPMe.

Research highlights
► TCPMe is a bioaccumulating organochlorine found at significant levels in organisms at high trophic levels, e.g. birds and mammals.
► Previous investigations have suggested TCPMe being co-released as a trace byproduct in pesticides such as DDT.
► The results from compound-specific chlorine isotope analysis of TCPMe supports the hypothesis that the source of TCPMe is indeed the extensive historical use of DDT.