Biodegradation of plasticizers by Rhodococcus rhodochrous.

Rhodococcus rhodochrous was grown in the presence of one of three plasticizers: bis 2-ethylhexyl adipate (BEHA), dioctyl phthalate (DOP) or dioctyl terephthalate (DOTP). None of the plasticizers were degraded unless another carbon source, such as hexadecane, was also present. When R. rhodochrous was grown with hexadecane as a co-substrate, BEHA was completely degraded and the DOP was degraded slightly. About half of the DOTP was degraded, if hexadecane were present. In all of these growth studies, the toxicity of the media, which was assessed using the Microtox assay, increased as the organism degraded the plasticizer. In each case, there was an accumulation of one or two intermediates in the growth medium as the toxicity increased. One of these was identified as 2-ethylhexanoic acid and it was observed for all three plasticizers. Its concentration increased until degradation of the plasticizers had stopped and it was always present at the end of the fermentation. The other intermediate was identified as 2-ethylhexanol and this was only observed for growth in the presence of BEHA. The alcohol was observed early in the growth studies with BEHA and had disappeared by the end of the experiment. Both the 2-ethylhexanol and 2-ethylhexanoic acid were shown to be toxic and their presence explained the increase of toxicity as the fermentations proceeded. The appearance of these intermediates was consistent with similar degradation mechanisms for all three plasticizers involving hydrolysis of the ester bonds followed by oxidation of the released alcohol.