Biodegradation of plasticizers by rhodotorula rubra

The degradation of plasticizers by the yeast Rhodotorula rubra J-96-1 (ATCC 9449) was studied in the presence of a water-soluble substrate (glucose). The plasticizers studied included bis 2-ethylhexyl adipate (B(EH)A), dioctyl phthalate (DOP) and terephthalate (DOTP), which are in widespread use. In addition, the degradation of two less common plasticizers, di-propylene glycol dibenzoate (D(PG)DB) and di-ethylene glycol dibenzoate (D(EG)DB), were studied. It has been proposed that the latter plasticizers be used as alternatives to the commonly used plasticizers, which have been associated with negative environmental impacts.The degradation of D(PG)DB or D(EG)DB led to a significant increase in solution toxicity. This increase in toxicity was associated with the production of metabolites resulting from the incomplete breakdown of the original plasticizers. The metabolites responsible for the acute toxicity in the D(PG)DB system were identified as isomers of di-propylene glycol monobenzoate. A mechanism for the formation of this metabolite was proposed. Although the metabolite observed when D(EG)DB was being degraded was not isolated, it was tentatively identified as di-ethylene glycol monobenzoate by analogy to the D(PG)DB system. This same metabolite was observed when D(EG)DB was degraded by the fungus, Aspergillus niger ATCC 9642-U.In contrast, there were no observable metabolites nor increases in toxicity in the media during the degradation of B(EH)A, DOP, or DOTP by R. rubra. These observations also differ from those of earlier work in which it was reported that the degradation of all three of these plasticizers by bacteria resulted in the production of toxic metabolites.Collectively, these results do not support the use of D(PG)DB and D(EG)DB as environmentally safe alternatives to B(EH)A, DOP or DOTP