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Long-term toxicity to aquatic invertebrates

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Description of key information

Read-across, OECD Guideline 211, GLP, key study, validity 2:

21d-EC10 (reproduction) = 1.02 mg/L (95% CL: <0.0432 - 3.11 mg/L).

Key value for chemical safety assessment

Fresh water invertebrates

Fresh water invertebrates
Effect concentration:
1.02 mg/L

Additional information

γ-decalactone is a linear saturated 4-hydroxycarboxylic acid derived-lactones with 10 carbons. γ-nonalactone and γ-undecalactone are structurally similar compounds of aliphatic lactones with 9 and 11 carbons, respectively. According to acute data available on these lactones, γ-undecalactone is considered as the most toxic substance.

To assess long-term toxicity of γ-decalactone to aquatic invertebrates, the experimental study performed on γ-undecalactone was used and was considered as a worst case read-across approach. This study was performed according to OECD Guideline 211 with GLP statement.

Daphnia magna were exposed to five test substance concentrations: 0.205, 0.512, 1.28, 3.2 and 8.0 mg/L, plus one control, during 21 days under semi-static conditions (renewal of the test solutions 3 times per week) in order to assess effects on the reproduction capacity and other test item-related effects or parameters (such as intrinsic rate of natural increase, number of broods with living juveniles, first appearance of living juveniles, occurrence of aborted eggs and stillborn juveniles, adult mortality and body length of the parental daphnids).

All test substance concentrations (and the control) were analytically verified by SPME-GC-MS at the start of the exposure intervals on days 0, 7, 9, 14, 19 and at the end of the exposure intervals on days 2, 9, 12, 16, 21. The measured concentrations of the test substance at the start of the exposure intervals (0 hours) were in the range of 81 to 106 % of the nominal values. At the end of the exposure intervals (after 48 and 72 hours), the measured concentrations of the test substance were in the range of < LOQ to 88 % of the nominal values. The geometric mean measured concentrations of the test substance, calculated at 0.0432, 0.0693, 0.138, 1.83 and 6.91 mg/L, were used for estimation of the effect levels, because the test substance concentrations at the end of the exposure intervals did not remain stable within the recommended range of ± 20 % of the nominal or initially measured concentrations. According to the results of this study, the test substance induced signficant adult mortality of the concentration levels of 1.83 mg/L (70%) and 6.91 mg/L (100%) during the test period of 21 days. In the control and in the concentration level of 0.0693 mg/L, all parental daphnids survived until the end of the test after 21 days. In the concentration levels of 0.0432 and 0.138 mg/L, an adult mortality of 10% was observed, which is not biologically significant. The reproduction output, determined by the average number of living juveniles per surviving parental daphnid at the end of the test after 21 days, was statistically significant reduced at the concentration level of 1.83 mg/L (21.3%) in comparison to the reproductive output in the control. In the concentration levels of 0.0432 to 0.138 mg/L, the reproduction output was comparable to the reproduction output in the control. In the concentration level of 6.91 mg/L, all daphnids died before producing juveniles and therefore the reduction of the reproductive output was set to 100%.

In conclusion, based on the significant reduction of the reproduction output at the concentration level of 1.83 mg/L, the 21d-NOEC and 21d-LOEC were assessed at 0.138 mg/L and 1.83 mg/L, respectively. The 21d-EC10 for the reduction of the reproductive output was calculated by sigmoidal dose-response regression to be 1.02 mg/L (95% CL: <0.0432 - 3.11 mg/L).

NOECs are increasingly contested in ecotoxicology. Indeed, the NOEC is determined as the concentration directly below the LOEC and depend upon the choice made by the Study Director and not a statistically interpolated value. So, NOEC may occur at concentrations considerably lower than the point at which no biological effect occurs. The choice of the concentrations tested is therefore a limiting factor for the NOEC determination. To use a less selective method, ECx approach was taken into account. EC10 values are accepted for risk assessment purposes and CLP allows the use of both NOEC/ECx (e.g. EC10) for classification to determine long-term effects, and are considered as the best endpoint for long-term data. For this reason, the 21d-EC10 value at 1.02 mg/L was considered as the key worst case value that was suitable for use as a read-across value for the long-term toxicity of γ-decalactone to aquatic invertebrates.