A mixture of branched and linear C7-C9 alkyl 3-[3-(2H-benzotriazol-2-yl)-5-(1,1-dimethylethyl)-4-hydroxyphenyl]propionates

Toxicity to terrestrial plants

Additional information

According to Annex XI of Regulation (EC) 1907/2006 substances whose physicochemical, toxicological and ecotoxicological properties are likely to be similar or follow a regular pattern as a result of structural similarity may be considered as a group, or “category” of substances. Application of the group concept requires that physicochemical properties, human health effects and environmental effects or environmental fate may be predicted from data for reference substance(s) within the group by interpolation to other substances in the group (read-across approach). The similarities may be based on (1) a common functional group, (2) the common precursors and/or the likelihood of common breakdown products via physical and biological processes, which result in structurally similar chemicals or (3) a constant pattern in the changing of the potency of the properties across the category.

The read-across substance (EC 400-830-7) consists of two major components: (1) a monoester component present at 51 w/w% and (2) a diester component present at 35.4 w/w%. Both the read-across compound and EC 407-000-3 share the same phenolic benzotriazole core structure with a hydroxyl group at position 2 and a tertiary butyl group at position 3 of the phenyl group. At position 5 of the phenyl ring a CH₂-CH₂-COO group is connected to a (C₂H₄O)n group (n is typically in the range of 2 to 10). Both the monoester and the diester are highly similar to EC 407-000-3, especially the phenolic benzotriazole core structure which is identical in the respective compounds. The only structural difference is the side chain connected to the carboxylic moiety. Due to the carboxylic moiety and the ester linkage to the side chain the compounds are susceptive to hydrolysis and further degradation processes. The primary degradant of both the diester and the monoester are therefore highly similar/identical to the degradant of EC 407-000-3.

Although the water solubility of the monoester (monoester: 1.74 mg/L; diester: <0.2 mg/L) differ from the solubility of EC 407-000-3 (0.018 mg/L) it can be stated that both substances have low solubilities. However, more important for the assessment of terrestrial toxicity is the ability to adsorb to soil. Both the components of the read-across substance and EC 407-000-3 strongly adsorb to the solid soil phase indicated by high logKoc (monoester: 4.1; diester: 4.2; EC 407-000-3: 5.9) and logKow (monoester: 5.9; diester: 4.6; EC 407-000-3: 9.2) values. Therefore a similar distribution pattern in the environment is expected for both substances and the uptake is expected to take place mainly via the solid soil phase and not the soil pore water.

In summary, taking into account the common functional core structure as well as the common breakdown product via physical and biological processes a read-across from EC 400-830-7 to EC 407-000-3 is regarded as suitable. Furthermore, due to the physico-chemical properties a similar distribution pattern in the environment is expected.

The toxicity of the substance to plants was investigated by a study following OECD guideline 208. The study focused on the seedling emergence and seedling growth of the three plant species Triticum aestivum, Brassica rapa and Vicia sativa in presence of the test substance. The toxicity of the substance to the plants was tested at three different substance concentrations (1, 10, 100 mg/kg). Seeds of the three plant species were sown separately in artificial soil mixed with the test substance. Based on seedling emergence the LC50 was > 100 mg/kg soil dw for all three plant species. Furthermore an EC50 > 100 mg/kg soil dw was determined for plant growth of all three species (Ciba-Geigy Ltd., 1987).