The Organisation for Economic Co-operatoin and development (OECD) Guidelines for the Testing of Chemicals list 7 types of tests for determining the ready biodegradability of chemical compounds (301A-F and 310). The present study compares the biodegradation performance of test guideline 301C, which is applied in Japan's Chemical Substances Control Law, with the performance of the other 6 ready biodegradability tests (RBTs) listed in the guidelines. Test guideline 301C specifies use of activated sludge precultured with synthetic sewage containing glucose and peptone (301C sludge) as a test inoculum; in the other RBTs, however, activated sludge from wastewater treatment plants (WWTP sludge) is frequently employed. Analysis based on percentage of biodegradation and pass levels revealed that the biodegradation intensity of test guideline 301C is relatively weak compared with the intensities of RBTs using WWTP sludge, and the following chemical compounds are probably not biodegraded under test guideline 301C conditions: phosphorus compounds; secondary, tertiary, and quaternary amines; and branched quaternary carbon compounds. The relatively weak biodegradation intensity of test guideline 301C may be related to the markedly different activities of the 301C and WWTP sludges. These findings will be valuable for evaluating RBT data in relation to Japan's Chemical Substances Control Law.

Reducing the environmental burden and assessing the safety of plastics are huge global challenges. However, standard test data on the ready biodegradability of plastics are limited. We evaluated the ready biodegradability of 8 biodegradable plastics using Organisation for Economic Co‐operation and Development (OECD) test guideline 301F with nonspecific bacteria and examined the effects of prolonging the test duration to a maximum of 90 d. Cellulose used as a potential reference material for plastics was not comparable to the reference material of OECD test guideline 301, but it may be improved by using a test concentration lower than the typical test concentration (100 mg/L). Of the 8 plastics examined, polyamide 4, poly(3‐hydroxybutyrate‐co‐3‐hydroxyhexanoate), polycaprolactone, and poly(butylene succinate adipate; PBSA) were biodegraded by >60% by day 28 and considered to show ready biodegradability. Poly(3‐hydroxybutyrate; PHB), poly(3‐hydroxybutyric acid‐co‐3‐hydroxyvaleric acid; PHBV), and poly(butylene succinate; PBS) were biodegraded but did not fulfill the ready biodegradability criteria. Because the typical test concentration is considered to have negative effects on biodegradation and calculation of biodegradation percentage, using a lower concentration may result in PHB, PHBV, and PBS fulfilling the ready biodegradability criteria. Poly(d,l‐lactide; PLA) was not biodegraded. The biodegradation of PBS and PBSA was noted to vary depending on the used inoculum and/or particle size. For the 7 plastics except PLA, the percentage biodegradation on day 60 was larger than that on day 28, indicating that a longer test period could be useful for evaluating the environmental persistence of plastics. In tests in which the plastics were not biodegraded by day 60, no marked biodegradation was observed by day 90. Environ Toxicol Chem 2021;40:2443–2449. © 2021 SETAC

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.

No abstract

The removal of chemical substances during wastewater treatment plays a key role in environmental risk assessments. In this study, the usefulness of the activated sludge die-away test (OECD Test Guideline [TG] 314B) was evaluated in terms of its accuracy for predicting the removal of cationic surfactants in wastewater treatment using an ester-amide-type dialkylamine salt (EA). The results show that the estimated removal rate through aerobic biological treatment (37.1%) in activated sludge, calculated from a first-order elimination rate constant, was lower than measured removal rates in actual water treatment systems (wastewater treatment plant [WWTP]: ≥ 99.9%; on-site domestic wastewater treatment plant: ≥ 99.7%). The lower estimation was probably caused by the tendency that chemical substances with high K oc values were transferred from the aqueous fraction to the suspended solid (SS) fraction to activated sludge. Thus, the EA concentration in effluent from the WWTP was calculated from the EA concentration of the SS fraction and the SS concentration in effluent; the estimated removal rate (99.7-99.9%) was equivalent to the measured removal rate. Therefore, when using OECD TG 314B to estimate the removal of chemical substances with a high K oc value, removal via adsorption to activated sludge should be considered.