John Wiley & Sons, Ltd.

Effect of test concentration in ready biodegradability test for chemical substances: Improvement of OECD test guideline 301C

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In Japan, understanding the environmental persistence of chemicals is very important for risk assessment, and ready biodegradability tests are mainly conducted according to the Organisation for Economic Co‐operation and Development Test Guideline 301C (TG301C). However, the highest test concentration specified in TG301C, 100 mg/L, may cause microbial toxicity and incomplete biodegradation. We performed TG301C tests at test concentrations of 30 mg/L for 13 substances that were readily biodegradable in ready biodegradability tests but not in TG301C tests. Of the five substances with potential to cause microbial toxicity at 100 mg/L, the percentage biodegradation of sodium dimethyldithiocarbamate, 4‐chloro‐3‐cresol (CC), thymol (THY), and p‐tert‐butyl‐α‐methylbenzenepropionaldehyde measured by biochemical oxygen demand (BOD) increased in the TG301C test at 30 mg/L, suggesting a reduction in toxicity effects. Furthermore, CC and THY met the criteria for ready biodegradability, which are more than 60% of biodegradation by BOD and 10‐d window. Of the eight substances with low potential of causing microbial toxicity at 100 mg/L, the percentage biodegradation of only 2‐(diethylamino)ethanol increased in the TG301C test at 30 mg/L. Employing a lower test concentration in the standard TG301C test will contribute to improvement of consistency between results of a TG301C test and other ready biodegradability tests. This article is protected by copyright. All rights reserved

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