Microbes alter estrogenic power of surfactant breakdown products
10.1021/es801976u
as low as 50-100 parts per billion. The isomers all share a phenol ring but differ in the structure and position of the alkyl chain attached to the ring, says HansPeter Kohler, a coauthor of the study and an environmental biochemist at the Swiss Federal JUPITERIMAGES
The challenge of tracking a common detergent breakdown product in the environment may have just gotten a lot more complicated. New research published in ES&T (DOI 10.1021/es800577a) indicates a substantial risk that bacteria can selectively degrade the hundreds of isomers in nonylphenol into a more estrogenic brew. Current regulations do not take this complexity into account, according to many scientists. “This study clarifies the structure-activity relationship for the estrogenic potency of nonylphenol isomers on the one hand and gives a full picture of the importance of isomeric-specific analysis for environmental monitoring and risk assessment on the other hand,” says Thomas Preuss, an ecotoxicologist at RWTH Aachen University (Germany). Researchers have been studying technical nonylphenol, a complex mixture of more than 100 isomers. Previous work has shown that the isomers vary in estrogenic potency and that bacteria degrade some isomers more easily than others. “But this is the first study combining both findings and giving the potential impact for the environment,” Preuss says. Technical nonylphenol is used to synthesize nonylphenol polyethoxylates, an important family of nonionic surfactants applied as emulsifying, wetting, or stabilizing agents in products such as industrial detergents, pesticides, and plastics. Worldwide production is estimated at 650,000 metric tons per year, says Klaus Guenther, a coauthor of the study and an environmental chemist at Ju ¨ lich Research Centre (Germany). When exposed to microbes such as bacteria, nonylphenol polyethoxylates degrade to technical nonylphenol. Numerous studies have shown it to be toxic, endocrine-disrupting, and capable of feminizing male fish at levels
Microbes in sludge at sewage plants such as this one alter the distribution of hundreds of isomers of a common surfactant.
Institute of Aquatic Science and Technology (Eawag). The new Ju ¨lich Nomenclature, which numbers nonylphenol isomers on the basis of their IUPAC names, helped the researchers identify 211 isomers. The researchers fed nonylphenol to a species of bacteria isolated from sewage sludge and, every 9 days for a month, analyzed the degradation products by using mass spectrometry. The experiments showed that bacteria likely degrade nonylphenol isomers via ipso-substitution, which clips off the alkyl chain, Kohler says. After culturing for 9 days, the bacteria had consumed up to 100% of some isomers but only 31% of others. The different deg-
2008 American Chemical Society
Published on Web 07/23/2008
radation rates of the isomers are probably caused by differences in the ipso-hydroxylation rates of the various isomers, Kohler explains. The degradation rate was strongly correlated to structure. Isomers with bulky side chains attached to the alpha carbon atom were more recalcitrant to degradation than isomers with less bulk surrounding this atom. In addition, isomers that resist degradation are predicted to have a higher estrogenic potency. The most potent individual isomers were twice as estrogenic as the technical mixture of isomers, but still 1690 times less potent than 17β-estradiol, Kohler says. Nevertheless, selective degradation of the less potent isomers might produce a mixture of isomers more potent than the original technical mixture. Bacterial action will produce a distinct isomer fingerprint of nonylphenol isomers in sewage sludge or water bodies that depends on the composition of the microbial community or how bioavailable the nonylphenol is, Kohler says. For instance, the distribution of nonylphenol isomers from river water samples around Tokyo Bay matches what would be expected from microbial degradation by ipso-hydroxylation, he says. “But the EU risk assessment for nonylphenol and also important toxicological studies for this substance were established without consideration of isomer-specific effects,” Guenther says. Nonylphenol is listed in the EU Water Framework Priority List and therefore must be monitored, Preuss adds. “This study clearly shows that an assessment of nonylphenol is not possible as a single compound; therefore, monitoring of nonylphenol is only meaningful by measuring individual isomers,” he says. —JANET PELLEY
September 1, 2008 / ENVIRONMENTAL SCIENCE & TECHNOLOGY 9 6309
