Hexahydro-4-methylphthalic anhydride

Endpoint summary

Additional information

Acute immobilisation to Daphnia magna, algal growth inhibition to unicellular freshwater green alga and acute toxicity to fish have been investigated. In Daphnia and fish no effects were observed at a concentration of 100 mg/L. In algae,.4 –MHHPA was found to inhibit the growth after 72 hours exposure, EC50-values with 95 % confidence intervals for inhibition of specific growth rate (ErC50) and yield (EyC50) being 135 (127 – 143) mg/L and 81.3 (72.7 – 89.8) mg/L, respectively. In accordance with ECHA guidance on information requirements and chemical safety assessment, Chapter R.7b: Endpoint specific guidance, the ErC50 endpoint is used in DNEL derivation. This is because use of values based on biomass cannot be applied to an analysis of results from a system in exponential growth without logarithmic transformation.

Toxicity to microorganisms has been investigated in an activated sludge respiration inhibition test according to OECD test methods. 4 –MHHPA caused a concentration related inhibition ranging from 14% at 58 mg/L to 99% at 1000 mg/L. The EC50 was 219 (189 – 248) mg/L with concentrations of 95.3 mg/L and below causing less that 20% inhibition and regarded as not toxic to microorganisms of a municipal sewage treatment plant. EC10, estimated from reported EC20, EC50 and EC80 values, was approximately 70 mg/L. Effects or pH on inhibition were examined and found to be the major factor in determining effects, a concentration of 1000 mg/L causing <20% inhibition when pH was adjusted back to neutral.

No effects data following long-term exposure are available on the registered substance itself. Reliable data on fish are available for two structural analogues of the substance - MTHPA and phthalic anhydride, with the best quality data being that from an early life stage study with phthalic anhydride. The lower NOEC value of 10 mg/L determined for phthalic anhydride was used as suitable read-across value for 4-MHHPA considering a worst case approach.  When the NOEC of 10 mg/Lfrom this study is corrected for differences in molecular weight, a calculated NOEC of 11 mg/L for 4–MHHPA is obtained. Data from long-term studies on aquatic invertebrates are available on three structural analogues of the substance, which after considering differences in molecular weight, lead to comparable NOEC values. The best quality data are that from a recent study with methyl-tetrahydrophthalic anhydride (MTHPA). The NOEC from this study was 20 mg/L which, when corrected for differences in molecular weight, results in a calculated NOEC of 20 mg/L for 4-MHHPA. For a more detailed read-across justification please refer to section 13.