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Environmental fate & pathways

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One ready biodegradation study according to OECD 301 A is available for Reaction mass of 2-(3,4-dimethyl-1H-pyrazol-1-yl)succinic acid and 2-(4,5-dimethyl-1H-pyrazol-1-yl)succinic acid. No biodegradation was observed during the 28-day test period (<0% based on DOC removal). Based on this result, the mineralisation of the test substance in surface waters is expected to be very slow, and for the purpose of the risk assessment no degradation is assumed in surface waters, as a worst case assumption. However, due to its sole use as fertiliser on agricultural crops, the target compartment of the test substance is soil.

Biodegradation of Reaction mass of 2-(3,4-dimethyl-1H-pyrazol-1-yl)succinic acid and 2-(4,5-dimethyl-1H-pyrazol-1-yl)succinic acid and its metabolite 3,4-dimethylpyrazole (DMP) in soil was investigated in two independent soil degradation studies, conducted following the OECD Guideline 307 (Wissemeier, 2012). A rapid transformation of the test substance to DMP was observed during both studies. In a separate kinetics evaluation conducted with data from the two studies, normalised half-lives of 1.5 - 3.3 days and formation fractions of 0.32 - 0.45 were determined for the transformation of the test substance

to DMP. The degradation of DMP, tested in parallel, was also rapid with normalised half-lives of 3.8 - 8.9 days (Kahl, 2012).

The formation of additional metabolites in soil cannot be excluded, but they are assumed to be covered by the risk assessment of the parent compound, based on a total residue approach.

The total residue approach is used in the case of Reaction mass of 2-(3,4-dimethyl-1H-pyrazol-1-yl)succinic acid and 2-(4,5-dimethyl-1H-pyrazol-1-yl)succinic acid to show that the risk assessment of the parent compound also covers any potential degradation products. The low toxicity of the test substance and its metabolites was demonstrated in the long-term studies with terrestrial organisms. In the study with Eisenia fetida, the toxicity of the test substance was shown to be low (NOEC 500 mg/kg soil dw). Since the half-live of the test substance in soil is < 4 days, it is very likely that the test organism was exposed to all potential metabolites during the 56-day test period. The observed low toxicity, thus would apply to the metabolites as well. The same applies to the carbon transformation study with soil microorganisms, which runs for 28 days and showed no effects of the test substance or its metabolites on carbon transformation.

Low toxicity and rapid metabolism of degradation products is also likely, based on the potential molecular structures. Due to the small size and low complexity of the parent molecule, any potential further metabolites are expected to have a simple structure and to be rapidly degraded to ubiquitous, short-chained molecules and finally be mineralised.

In conclusion, Reaction mass of 2-(3,4-dimethyl-1H-pyrazol-1-yl)succinic acid and 2-(4,5-dimethyl-1H-pyrazol-1-yl)succinic acid is not readily biodegradable. Nevertheless, it is degraded in soil with a half-life < 4 days and is thus not persistent in the environment. Since the quantitative risk assessment performed for the substance shows no risk for any of the environmental compartments, no further testing on biodegradation is considered necessary.