Microbial degradation of Di-ester plasticizers in the presence of surfactants

Abstract

The degradation of common di-ester plasticizers, including di-2-ethylhexyl phthalate, di-2-ethylhexyl adipate and di-(propylene glycol) dibenzoate, by several strains of soil bacteria has been previously shown to lead to an accumulation of metabolites that are more toxic than the parent compounds. This research has shown that the pattern of degradation of these plasticizers can be significantly different in the presence of biosurfactants or synthetic surfactants. In particular, the additions of surfactin, sophorolipid or Pluronic L122 to cultures of Bacillus subtilis each resulted in increases in the quantities of the first metabolites in the plasticizer degradation pathway. One of these was 2-ethylhexanol, which had been previously shown to be the most toxic intermediate released during plasticizer degradation. The other was mono-2-ethylhexyl adipate, the mono-ester released from the hydrolysis of di-2-ethylhexyl adipate. This compound was isolated in this work and found to have a toxicity comparable to that of 2-ethylhexanol.The cause of the significant accumulation of the first and most toxic plasticizer metabolites in the presence of surfactants was investigated. Results were obtained that suggested that the action of the surfactants was to sequester these initial metabolites. The effect of this would be to reduce the observed rates of subsequent degradation of these two intermediates to less toxic compounds