Sources and transformation pathways for dichlorodiphenyltrichloroethane (DDT) and metabolites in soils from Northwest Fujian, China

Highlights: • DDT and related metabolites in soils were analyzed on a GC-MS/MS. • p,p'-(dicofol + DBP) were majorly originated from the degradation of p,p'-DDT. • Pathways of DDT→DDE→DDMU→DDNU, DDT→DDD→DDMU→DDNU and DDT→ (dicofol + DBP) were verified. • Both p,p'-DDE and p,p'-DDD are significant precursors for p,p'-DDMU in paddy fields. Dicofol (2,2,2-trichloro-1,1-bis-(p-chlorophenyl)ethanol) found in the environment is not only a miticide originated from commercial use, but also a metabolite of dichlorodiphenyltrichloroethane (DDT), which is often overlooked. To verify the sources and transformation pathways of DDT and related metabolites in soils, we measured p,p'-(dicofol + DBP) (sum of p,p'-dicofol and 4,4′-dichlorobenzophenone), DDT and six metabolites in soils from Northwest Fujian, China. The ratios of 1,1,1-trichloro-2-(o-chlorophenyl)-2-(p-chlorophenyl)ethane (o,p'-DDT)/1,1,1-trichloro-2,2-bis-(p-chlorophenyl)ethane (p,p'-DDT) and the mass balance demonstrated that p,p'-(dicofol + DBP) predominantly originated from p,p'-DDT transformation rather than from actual dicofol application. p,p'-(dicofol + DBP) accounted for 45.0% as the primary metabolites of DDT in this study, more than 1,1-dichloro-2,2-bis-(p-chlorophenyl)ethylene (p,p'-DDE) and 1,1-dichloro-2,2-bis-(p-chlorophenyl)ethane (p,p'-DDD), which might lead to large overestimations of the fresh DDT input by using the traditional ratio of (∑₂DDD + ∑₂DDE)/∑₂DDT (with all o,p'- and p,p'- isomers included). In paddy fields where the conditions alternate between aerobic (dry period) and anaerobic (wet period), both p,p'-DDD and p,p'-DDE were likely to degrade to 1-chloro-2,2-bis-(p-chlorophenyl)ethylene (p,p'-DDMU), which further transformed to 2,2-bis(p-chlorophenyl)ethylene (p,p'-DDNU). Degradation of p,p'-DDMU to p,p'-DDNU mainly occurred in waterlogged paddy soils. However, p,p'-DDNU might not transform to other higher-order metabolites in aerobic surface soils. Overall, our study confirmed p,p'-(dicofol + DBP) as metabolites of p,p'-DDT, suggested DDE and DDD were parallel precursors of DDMU, and further verified the transformation pathways of DDT in surface soils.