Comparison of biodegradation rates in laboratory screening studies with rates in natural waters

Abstract

Microbial degradation (biodegradation) of organic chemicals is generally recognized as an important removal mechanism in natural systems. For chemicals which reach the aquatic environment in significant quantities, estimates of biodegradability are key in assessing the overall hazard associated with the use of a particular chemical (Larson 1980). Estimates of biodegradability are often generated in the laboratory via biodegradability screening studies (Larson 1979). In screening studies, compounds are tested as sole carbon and energy sources at relatively high (mg/L) concentrations with a dilute synthetic salts solution as the test medium. Degradation is measured nonspecifically by following the amount of carbon dioxide produced or oxygen consumed during microbial metabolism, and soil or sewage are typically used as the source of degradative microorganisms. These experimental conditions do not accurately simulate natural aquatic environments, where chemical concentrations are low (μg/L) and a variety of nutrient conditions and microbial species exist. As a result, legitimate questions have been raised about the reliability of biodegradability screening tests, and the ability of such tests to predict fate of compounds in the “real world” (Alexander 1981).