Department of Biological Sciences, Simon Fraser University, Burnaby, British Columbia, Canada.
Environ Toxicol Chem. 2012 Aug;31(8):1730-7. doi: 10.1002/etc.1903. Epub 2012 Jul 3.
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.
在加拿大、美国、欧盟和其他国家，对商业化学品的监管评估旨在确定化学品在自然土壤和沉积物中的生物降解速率。然而，常用的生物降解测试方法在确定自然环境条件下的生物降解速率方面能力有限。因此，许多非常疏水的物质的生物降解速率报告差异很大。这种可变性给监管评估带来了困难，可能导致化学品分类错误。在本研究中，作者开发了一个生物降解、吸附和疏水性之间关系的模型，并在实验中测试了该模型，该实验测量了一系列邻苯二甲酸二酯 (DPE) 和邻苯二甲酸单酯 (MPE) 在自然沉积物中的生物降解速率。结果表明，DPE 和 MPE 具有在沉积物中的微生物以常见速率快速降解的固有能力，但 DPE 在自然沉积物中的生物降解速率随着邻苯二甲酸酯向沉积物的吸附增加而降低。结果表明，高度吸附的固有可生物降解物质预计在自然沉积物中具有较长的半衰期。该模型通过考虑化学吸附，为从筛选测试中测量的固有生物降解速率评估自然沉积物中的生物降解速率提供了一种潜在的方法。本研究表明，生物降解速率降低是由于间隙水中自由溶解化学浓度的分数降低所致，并且需要在化学评估的风险背景下看待吸附降低生物降解速率的环境意义。
