Establishing a ready biodegradability test system using OxiTop^® to evaluate chemical fate in a realistic environment

Abstract

The purpose of this study is to propose the use of OxiTop ® for measuring biochemical oxygen demand (BOD) under the Japanese Chemical Substances Control Law in order to properly evaluate chemical fate in a real environment. In our previous study, the biodegradation of test chemicals was accelerated by both adsorbing the chemical to silica gel with chloroform and increasing the medium volume from 300 to 3900 mL in the OECD 301F test using a coulometer. However, the biodegradability of these chemicals could not be evaluated based on BOD due to chloroform residue in the silica gel, or the medium volume could not be increased further due to the oven size of the coulometer. In this study, we established an evaluation system using OxiTop ® based on BOD by increasing the medium volume to 9000 mL. Based on triplicate testing, increasing the medium volume accelerated biodegradation and decreased variation in BOD.

Metagenomic analysis of ready biodegradability tests to ascertain the relationship between microbiota and the biodegradability of test chemicals

“…By increasing the medium volume from 300 or 3900 mL to 9000 mL with tris(2-ethylhexyl) trimellitate, Takekoshi et al found that initiation of rapid biodegradation in all of the three replicates for 9000 mL nearly coincided with the earliest one for 300 or 3900 mL. 28) In this study, the earliest initiation of rapid biodegradation observed at rep. 1 for 3900 mL did not coincide with the earliest one at rep. 1 for 300 mL or at rep. 1 for 900 mL. It appeared that a test medium volume of 300, 900 or 3900 mL was not sufficient to reduce the variability in this study, suggesting that the initiation of rapid biodegradation would converge to a specific time (e.g., a time observed at rep. 1 for 3900 mL) only if the medium volume was increased further.…”

“…Only the tests with Bis for volumes of 900 and 3900 mL were performed using a coulometer and the other tests were conducted using OxiTop ® because there was little difference between the coulometer and OxiTop ® in terms of BOD values. 28) In order to investigate differences in the local environment within the test bottle, the distribution of oxidation-reduction potential (ORP) in the test bottle was checked near the surface (2 cm below the medium surface), in the middle (at the midpoint between the medium surface and the test bottom), and at the bottom (2 cm above the test bottom), based on the autoxidation of sodium sulfite by pH/ORP meter F72L (HORIBA Advanced Techno, Kyoto, Japan) without adding any activated sludge. This measurement was conducted from addition of the sodium sulfite to the test medium until a stable ORP was obtained by sufficient oxidation of the sodium sulfite for each medium volume.…”