Bioaccumulation studies with Eisenia fetida using an established degradation test system

Autor: Claudia Norr, Frank Riepert
Rok vydání: 2007
Předmět:
Zdroj: Journal of Soils and Sediments. 7:393-397
ISSN: 1614-7480
1439-0108
Popis: Earthworms are considered as an appropriate test system to assess the bioaccumulation potential of substances in the terrestrial environment. For regulatory purposes test methods were developed and incorporated in the validation process. A test design that is particularly suited for testing 14C-labelled substances will be described here. This design was adapted from an established degradation test system for bioaccumulation tests with earthworms in soil. The antibiotic sulfadiazine was used as test substance in this study. Due to the biological activity and the widespread entering into soil by manure application, veterinary medicines have become the target of ecotoxicological risk assessment. A German research group provided the soil samples mixed with liquid pig manure, which contained the 14C-labelled test substance after having passed through the gut of animals. This exposure pathway reflects the real environmental conditions. Therefore, sulfadiazine was tested even though a significant bioaccumulation potential was not expected to be detected owing to its chemical properties. Two adult earthworms of the species Eisenia fetida were inserted in a 500 ml glass container filled with 100 g soil. The test substrate consisted of soil mixed with liquid manure containing 14C-sulfadiazine. The glass containers were fitted with a soda-lime trap, which is permeable for oxygen but absorbs produced CO2 and other volatile metabolites. As food source for the earthworms, 5 g of mashed potato powder was applied per test container at the beginning of the test. The levels of radioactivity in soil samples and earthworms were determined by combustion in an oxidizer over a four-week exposure phase. The test design follows the instructions described by the OECD draft guideline for testing the bioaccumulation behaviour of chemicals with oligochaetes in soil. The earthworms nearly doubled their biomass during the four-week exposure phase. The mortality of the earthworms was less than 10%. The test substance was characterized by a high persistence in the soil. An uptake of 14C-sulfadiazine was detected in the earthworms. However, the accumulation of 14C-sulfadiazine in the earthworms was negligible compared to the test substance concentration in soil. A bioaccumulation factor around 1 was calculated at the end of the exposure phase. In accordance with the chemical properties, an accumulation of sulfadiazine in the earthworms was not determined. But the uptake of 14C-sulfadiazine in the earthworms was clearly detected. These results obtained with a non-bioaccumulative substance like sulfadiazine demonstrate the sensitivity of the test system and its suitability for assessing the bioaccumulation potential of substances in earthworms. An established degradation test system was modified, such that it is now well suited for testing the bioaccumulation of substances in earthworms enabling the determination of both the biodegradability and the bioaccumulation behaviour of a substance in a single test system. The test design described here is a meaningful methodical addition to the new OECD draft guideline for testing the bioaccumulation behaviour of chemicals with terrestrial oligochaetes in soil. In order to comprehensively assess the bioaccumulation potential of veterinary medicines in soil, further studies with other compounds and aged soils are required. These investigations could be conducted optimally using the test design described here.
Databáze: OpenAIRE
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