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Environmental fate & pathways

Biodegradation in water: screening tests

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Description of key information

readily biodegradable (according to OECD criteria)

Key value for chemical safety assessment

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A test on ready biodegradability was performed, which followed a modified procedure based on OECD guideline 301B [BASF MicroCheck 1999]. 14C-labelled bronopol was used and in deviation from the guideline, the methods were modified with respect to the test substance concentration, incubation vessels and method of determining the test substance mineralisation. In fact, the test substance concentration of 0.1 mg/L was chosen to avoid bacteria toxicity; the yield of CO2 derived from the test substance was measured as mineralisation to 14CO2 by liquid scintillation counting (LSC) and 14C-material present in the cells was determined by means of combustion analysis using a biological oxidiser. Two experiments were undertaken.

In experiment 1, around 10 % of mineralisation was reported for day 1 wehereas 55 % mineralisation was achieved within the 10 day window and ca. 89 % after a period of 29 days. In experiment 2, around 10 % degradation appeared within the first two days, followed by 45 % degradation during the 10 -day window. After 29 days, 67 % mineralization was achieved. For the radioactivity related to cell biomass, a mean value of 12 % was found to be associated with cell biomass by material alance measurements at day 29, bringing the total biodegradation in experiment 1 to 100 % at day 29 and to about 80 % for experiment 2. Considering the results of both experiments, a mean degradation rate of about 90 % of the initial 14C derived from the test substance bronopol (0.1 mg/L) was shown to be biotransformed by day 29, and consisted of about 78 % 14 CO2 and about 12 % 14C incorporated into microbial biomass.

In both experiments, the 10 -day widow acceptance criterion for "ready biodegradability" was not achieved. However, considering the additional 12 % recovery of radioactivity in the microbial cell biomass and assuming that this percentage was converted to cell biomass by day 10 (as reported in Boots MicroCheck, ELL/834), the degree of biodegradation achieved within the 10 day window would be >= 60 % (i.e. 67 %) for experiment 1 and about 57 % for experiment 2. Therefore, bronopol can be regarded as readily biodegradable in the test system.

Supportingly, an inherent biodegradability test was conducted according to modified procedures based on OECD guidelines 304 A and 302 B [Boots MicroCheck 1994]. During this test, bronopol was completely biodegraded by microorganisms within 3 days. A major metabolite (similar to 2 -nitropropane-1,3 -diol) appeared around day 3 which was again subjected to rapid and complete biodegradation on day 17. At the end of the test (on day 64), biodegradation was quantified as 68 and 23 % related to the CO2 and biomass production, respectively.

Additionally to the screening studies, there is one simulation test available which assesses the biodegradability of bronopol discharged in wastewater. The test was conducted under GLP and according to OECD guideline 314B [BASF SE 2012]. The outcomes of this study showed that 0.5 mg/L [14C]bronopol is degraded to 99% within 1 hour in municipal activated sludge which provides further confirmation of the ready biodegradability of bronopol.