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

Abstract

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. However, the highest test concentration specified in test guideline 301C, 100 mg/L, may cause microbial toxicity and incomplete biodegradation. The authors performed test guideline 301C tests at test concentrations of 30 mg/L for 13 substances that were readily biodegradable in ready biodegradability tests but not in test guideline 301C tests. Of the 5 substances with potential to cause microbial toxicity at 100 mg/L, the percentage of 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 test guideline 301C 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 a 10-d window. Of the 8 substances with a low potential for causing microbial toxicity at 100 mg/L, the percentage of biodegradation of only 2-(diethylamino)ethanol increased in the test guideline 301C test at 30 mg/L. Employing a lower test concentration in the standard test guideline 301C test will contribute to improvement of consistency between results of a test guideline 301C test and other ready biodegradability tests.

Toward the future of OECD/ISO biodegradability testing-new approaches and developments

“…For the latter, an inoculum is used which is pre-cultured with synthetic sewage. The biodegradation potential of this inoculum is much lower than that of the modified MITI (I) test (OECD 301 C, 1992 ), where activated sludge from normal municipal WWTPs is permitted (Kayashima et al 2014 , Nabeoka et al 2016 ).…”

“…A compilation of relevant OECD and ISO guidelines for bacterial toxicity is given in TableS2and the annex II of OECD 301. Examples for the biodegradation of toxic compounds are given byNabeoka et al (2016), who lowered the concentration of several test compounds in OECD 301 C (1992) tests from 100 mg/L to 30 mg/L and could increase the biodegradation of sodium dimethyldithiocarbamate, 4-chloro-3-cresol, thymol and p-tert-butyl-α-methylbenzenepropionaldehyde in this way. A similar problem may arise when biocides are tested which exhibit an intended toxicity.Furthermore, O'Malley (2006) conducted a study, where he tested the lowest possible test concentration of the model substance sodium acetate in the OECD 301 F (…”

Persistence and Bioaccumulation of Persistent Organic Pollutants (POPs) in the Soil and Aquatic Ecosystems: Syrian Frontiers in Ecology and Environment

“…Several authors (Madsen, 2003;Nabeoka et al, 2015;Hayet et al, 2016;Kasthuri & Poornima, 2016) have mentioned disadvantages of field studies such as difficulty and vast amount of analytical work involved, inadequately defined and constantly varying conditions, etc. These considerations, however, can only lead to the conclusion that neither field studies nor laboratory studies alone can give a sufficient basis for legislative measures.…”