Biodegradation Potential of 1,1,1-Trichloro-2,2-Bis( p -Chlorophenyl) Ethane (4,4′-DDT) on a Sandy-Loam Soil Using Aerobic Bacterium Alcaligenes eutrophus A5

Abstract

Abstract

Although banned by industrialized countries in the early 1980s, experimental bioremediation data on 1,1,1-trichloro-2,2-bis(p-chlorophenyl) ethane (4,4′-DDT) is scarce. This study investigated the biodegradation potential of DDT in a spiked sandy-loam soil using aerobic bacterium Alcaligenes eutrophus A5 over a year; tracking both the aqueous and soil phase. Specific research objectives of different initial DDT concentrations, soil contact times (soil age), and sorption/desorption on bioremediation were evaluated while fixing factors that may impact assessment (i.e., soil particle size, temperature, inoculation periods, and nutrient composition). Two separate ∼25 mg/kg concentration soil samples were aged for 60 and 200 days while 136 and 630 mg/kg were aged only for 60 days. Biodegradation experiments and controls were sampled at 7 days, 14 days, 28 days, 3 months, 6 months, 9 months, and 1 year. DDT degradation was found to be 13%, 11%, 7%, and 2.5% for 24 mg/kg (60 day aged), 33 mg/kg (200 day aged), 136 mg/kg (60 day aged), and 630 mg/kg (60 day aged), respectively. This corresponds to 0.25–1.34 mg/year partial DDT degradation with the main metabolites observed being DDE [1,1-dichloro-2,2-bis(p-chlorophenyl)ethylene] and DDD [1,1-dichloro-2,2-bis(p-chlorophenyl) ethane]. However, metabolite formation was only 0.25–0.45 mg/year for DDE and 0.04–0.421 mg/year for DDD. DDT was seen to mostly remain in the soil while the metabolites were mainly measured in the aqueous phase. This work generated a transient dissipation data set for the aerobic metabolism of DDT and formation of DDE and DDD from which kinetic pathways can be explored and rate constants quantified.