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Biodegradation in water: screening tests

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Description of key information

Within 28 days, a degradation rate of 4 %  was determined for tetrasodium hydrogen 2-phosphonatobutane-1,2,4-tricarboxylate. Therefore tetrasodium hydrogen 2-phosphonatobutane-1,2,4-tricarboxylate is considered to be "Not Readily Biodegradable". Assessing inherent biodegradability yields a degradation rate of 17%  within 28 days. Based on this result tetrasodium hydrogen 2-phosphonatobutane-1,2,4-tricarboxylate is considered to be not inherently biodegradable. Under anaerobic conditions no biodegradation was observed within 56 days, therefore tetrasodium hydrogen 2-phosphonatobutane-1,2,4-tricarboxylate is also considered as not anaerobic biodegradable.

Key value for chemical safety assessment

Biodegradation in water:
under test conditions no biodegradation observed

Additional information

To test for its biodegradation potential, 41 % solution of tetrasodium hydrogen 2-phosphonatobutane-1,2,4-tricarboxylate ("PBTCNa4") in water was incubated for 28 days in continuously stirred 250 mL closed flask (in duplicate) in the dark with an inoculum originally collected from a local, predominantly municipal wastewater treatment plant. In this assay, conducted according to the EU Method C.4-B (Determination of the "Ready" Biodegradability - Modified OECD Screening Test), biodegradation was determined by dissolved oxygen carbon (DOC) over time. DOC was measured with a carbon analyzer. The incubation temperature was 22 ± 2 ° C. The concentration of inoculum and one concentration of PBTCNa4 was 19.9 mg/L DOC. The 28 day degradation was 4 % and for the positive control (with reference substance) the biodegradation was 99 %. In conclusion PBTCNa4 is not readily biodegradable.

Inherent biodegradability of PBTCNa4 was assessed according to the OECD TG 203 B (Inherent biodegradability: Zahn-Wellens Test) under aerobic conditions at a defined temperature. As test suspension, a measured volume of mineral medium containing a known concentration of PBTCNa4 of 100 mg DOC/l as the nominal sole source of organic carbon is inoculated. Degradation is followed by DOC determinations at 0 h, 3 h, 7 d, 14 d, 21 d, 27 d and 28 d. The degree of biodegradation is calculated by expressing the concentration of DOC removed (corrected for that in the blank inoculum control) as a percentage of the concentration initially present. PBTCNa4 showed 17% degradation after 28 days. Based on this result PBTCNa4 is considered to be not inherently biodegradable.

Anaerobic biodegradation was determined with a method equivalent or similar to EPA OTS 796.3140 (Anaerobic Biodegradability of Organic Chemicals) at a defined temperature. A mineral medium containing digested sludge and a known concentration of PBTCNa4 (20 mg C/l) as the sole source of organic carbon was inoculated. Degradation was measured by CH4 and CO2 evolution, and verified by DIC, TOC and TIC analysis. As no degradation was observed within 56 days PBTCNa4 is considered as not biodegradable under anaerobic conditions.

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