Relationship between biodegradation and sorption of phthalate esters and their metabolites in natural sediments

Abstract

Regulatory evaluations of commercial chemicals in Canada, the United States, the European Union, and other countries aim to identify biodegradation rates of chemicals in natural soils and sediments. However, commonly used biodegradation testing methods are limited in their capacity to determine biodegradation rates under natural environmental conditions. As a result, widely varying biodegradation rates have been reported for many very hydrophobic substances. This variability causes difficulties in regulatory evaluations, potentially leading to chemical misclassification. In the present study, the authors developed a model of the relationship between biodegradation, sorption, and hydrophobicity, and tested the model in experiments that measured the biodegradation rates of a range of di-phthalate esters (DPEs) and mono-phthalate esters (MPEs) in natural sediments. The results indicate that DPEs and MPEs have the inherent capacity to be quickly degraded by microbes in sediments at a common rate, but that DPE biodegradation rates in natural sediments decrease with increasing phthalate ester sorption to sediments. The results show that inherently biodegradable substances that are subject to a high degree of sorption can be expected to exhibit long half-lives in natural sediments. The model provides a potential methodology for assessing biodegradation rates in natural sediments from inherent biodegradation rates measured in screening tests by accounting for chemical sorption. The present study indicates that a reduced rate of biodegradation is due to a reduced fraction of freely dissolved chemical concentration in the interstitial water, and that the environmental significance of sorption-reduced biodegradation rates needs to be viewed in the context of risk in chemical evaluations.

Carbamazepine as a Possible Anthropogenic Marker in Water: Occurrences, Toxicological Effects, Regulations and Removal by Wastewater Treatment Technologies

“…However, in this case, concentration of these pollutants is not significantly reduced by the in-stream biotic and abiotic attenuation processes [81,84,89]. In a study by Riml et al [90], concentration of two PhACs, namely bezafibrate and metoprolol, was observed to be mainly reduced by sorption onto sediments, while the role of biotransformation and photolysis was insignificant.…”

Occurrence and in-stream attenuation of wastewater-derived pharmaceuticals in Iberian rivers

“…In this way, those compounds become less exposed to other biotic (biotransformation) and abiotic (photolysis, volatilization) transformation processes and therefore become the least affected by the variation of environmental conditions between river segments. In this regard, a study using phthalate esters and their metabolites as test compounds showed that hydrophobic substances with high capacity to sorb to particulate organic matter were the least exposed to biodegradation, and were expected to have a low rate of biodegradation in natural sediments despite their inherent biodegradability (Kickham et al 2012). Similarly, another study on in-stream attenuation of pharmaceuticals identified sorption as the predominant attenuation mechanism for 3 compounds with relatively high K ow (bezafibrate, metropolol and naproxen) (Riml et al 2013), which were among the identified compounds with the lowest variability among river segments in our study.…”

Anaerobic biotransformation of N‐methyl perfluorobutanesulfonamido ethanol and N‐ethyl perfluorooctanesulfonamido ethanol

“…Although the biotransformation reactions for MeFBSE and EtFOSE appear to be identical and are likely catalyzed by the same enzymes, and likewise between 6:2 FTOH and 8:2 FTOH, the decreased half-lives for the short-chain replacement chemistries may be more attributed to their increased bioavailability as a result of lowered sorption to sludge solids, as indicated by their lower log K OW values. The sorption of hydrophobic substances to solids can be a significant rate-limiting process which dictates biodegradation rates for substances catalyzed by the same enzymes [45].…”