Enzymatic Degradation of Phthalic Acid Esters

Abstract

Endocrine disrupting compounds (EDCs) are environmental pollutants which interfere with the hormone system even at low concentrations resulting in adverse health effects on both human and wildlife. In this study, we aimed to investigate enzymatic degradation of diethylhexyl phthalate (DEHP) and diethyl phthalate (DEP) using both commercial porcine pancreas lipase and lipase from recombinant E.Coli strains that contain lipase genes from thermophilic Bacillus sp. isolated from Balçova Geotermal region in İzmir. Incubation of 20 mg/L DEHP with 20,000 U/L PPL enzyme for 7 days resulted in formation of monoethyl phthalate (MEHP), phthalic acid (PA), and dimethyl phthalate (DMP) which are the possible metabolites of DEHP. The percent decrease in DEHP (20 mg/L) was found to be 92% compared to positive control samples. In the case of DEP, about 53% decrease was obtained after incubation with 20.000 U/L for 7 days. Hydrolysis constants for DEHP ranged between 0.13 and 0.22 d-1, whereas those for DEP ranged 0.43 and 0.54 d-1. As a result of enzymatic hydrolysis of DEHP (1-20 mg/L) with 4000 U PPL enzyme, DEP was produced as hydrolysis product of DEHP after 44 h. In the case of DEP (1-20 mg/L) incubated with 4000 U crude lipase solution for 140 h, DMP was obtained as a possible product of transesterification reaction. The maximum rate (Vmax) of enzymatic hydrolysis reaction for DEHP and DEP was calculated as 0.79 mg/L.h and 1.83 mg/L.h, respectively. The Michealis-Menten constants (Km) for enzymatic hydrolysis of DEHP and DEP were calculated as 2.45 and 2.12 mg/L, respectively.