Biodegradation of plasticizers : characterization and toxicity of their metabolites

More than one billion pounds of plasticizers are produced each year to supply the plastics industry. Some of these plasticizers, particularly phthalates, are suspected endocrine disruptors. However, few studies have been conducted to determine if they are susceptible to biodegradation by naturally occurring bacteria once they are released into the environment.Six organisms were tested for their ability to grow in the presence of six different industrial plasticizers. Two bacteria, Rhodococcus rhodochrous and Arthrobacter paraffineus, grew well in media containing n-hexadecane and one of the plasticizers.Fermentations in a 2-liter reactor were performed with Rhodococcus rhodochrous and three plasticizers: bis 2-ethylhexyl adipate, dioctyl phthalate and dioctyl terephthalate. The organism degraded all of the adipate, half of the terephthalate was degraded and the phthalate was degraded slightly.In these growth studies, the toxicity of the media increased as the organism grew. This trend was linked to the accumulation of metabolites from the partial degradation of the plasticizer. The two major metabolites were identified as 2-ethyl hexanol and 2-ethyl hexanoic acid. The alcohol was only observed part way through the growth in the presence of the adipate. Its concentration decreased as it was oxidized to the acid and it was not present at the end of the fermentation.The acid was observed for all three types of plasticizers and it was present in high concentrations at the end of every experiment. The nature and pattern of production of the metabolites were consistent with a pathway for the degradation of all three plasticizers by hydrolysis of the ester bonds.The accumulation of toxic metabolites indicates that biodegradation may not be a solution to reducing environmental impacts associated with plasticizers that have leached into the environment