Microbial degradation of dibenzoate plasticizers

Earlier work with the dibenzoate plasticizers, di(propylene-glycol) dibenzoate (D(PG)DB) and di(ethylene-glycol) dibenzoate (D(EG)DB), had shown that one yeast could hydrolyze one of the ester bonds of these compounds resulting in an accumulation of the monoesters, di(propylene-glycol) monobenzoate or di(ethylene-glycol) monobenzoate, respectively. These monoesters exhibited an acute toxicity greater than that of the parent compounds and greater than the metabolites of the widely used phthalate and adipate plasticizers.In the present study, it was shown that the degradation of dibenzoate plasticizers is a common phenomenon among soil microorganisms. In most examples, the degradation was incomplete leading to the accumulation of the expected monoesters. However, the biodegradation of these monoesters was shown to be possible even if the rates of biodegradation were much slower than the rates of hydrolysis of the parent compounds. In addition, it was found that di(ethylene-glycol) monobenzoate was easier to biodegrade than di(propylene-glycol) monobenzoate. This difference was attributed to the methyl substituents on the di(propylene-glycol) monobenzoate. The very fast rates of degradation of simpler benzoate esters such as methyl and ethyl benzoate confirmed that steric effects could be important.The rate of biodegradation of 1,6-hexanediol dibenzoate was much faster than that of either of the dibenzoate plasticizers. From this, it was hypothesized that the stability of the monoesters of the plasticizers was due to the presence of an ether function. It was also shown that the presence of the monoester of D(PG)DB was shown to increase the rate of hydrolysis of the parent di-ester. This was attributed to the ability of the monoester to enhance the bioavailability di-ester.Collectively, these results do not support the use of dibenzoate plasticizers as environmentally friendly alternatives to phthalate and adipate plasticizers