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Biodegradation in water: screening tests

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Description of key information

Ready biodegradability assessed in OECD 301D and 301F studies.

Key value for chemical safety assessment

Biodegradation in water:
inherently biodegradable, not fulfilling specific criteria

Additional information

Two ready biodegradation studies have been conducted. In these two studies, N-isopropylhydroxylamine did not meet the requirements for readily biodegradable. The available data indicate that the compound meets the criteria of primary, inherently biodegradable.

The Biodegradability of Chainguard I-15, aqueous N-isopropylhydroxylamine solution, was examined in the Closed-Bottle Test/OECD 301D. Test concentrations of 50 and 30 mg/L were used. The Discharge from the secondary settler of the domestic water-treatment plant in the city of Bruhl was used. The test was conducted at 19+2 °C over a 28 day period.

The test substance, Chainguard I-15, showed a biodegradability of 40% BOD of the COD after 28 days under the conditions of the method.

Under the conditions of this test, some biodegradation of N-isopropylhydroxylamine occurred but it did not meet the requirements for readily biodegradable.

The ready biodegradability of XU-18770.00 (isopropyl hydroxylamine [IPHA]) was evaluated using the OECD Guideline No. 301F: Manometric Respirometry Test. This test employed a series of biodegradation reaction mixtures containing a non-adapted

activated sludge inoculum, which was suspended in a defined mineral medium at a concentration of ~30 mg/L (dry solids). Biodegradation of IPHA was evaluated at a concentration of 18.1 mg/L, which was equivalent to 30.8 mg/L theoretical oxygen

demand (ThOD). Cumulative oxygen demand in duplicate Test Mixtures containing the test substance did not exceed that in unamended Inoculum Blanks; thus indicating that no biodegradation of IPHA had occurred over the duration of this test.

However, since cumulative oxygen consumption in the Test Mixtures was less than that in Inoculum Blanks, the results suggest that the test substance was at least partially inhibitory to the sludge inoculum under the conditions of the test.

The test also showed no formation of CO2in the Test Mixtures which indicates that little mineralization of the test substance had occurred. Dissolved organic carbon (DOC) analyses indicated that the test substance was completely dissolved in the reaction mixtures, and 26% of this initial DOC was removed from the Test Mixtures over 28 days. Concomitantly, the DOC concentrations in the abiotic control decreased by 14%, suggesting that much of the loss of DOC in the Test Mixtures was due to abiotic processes (e.g. volatilization).

These DOC analyses confirmed that minimal biodegradation of the test substance occurred in this study. Therefore, the results of this test indicate that IPHA does not meet OECD criteria for “ready biodegradability” in the Manometric Respirometry test.