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Long-term toxicity to aquatic invertebrates

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Description of key information

Based on a reliable OECD Guideline study, NPEO was shown to have a chronic freshwater NOEC of 100 µg (0.1 mg)/L in the 21 day Daphnia reproduction test. A read across study with NPE-1.5 resulted in a lower 28 day NOEC of 7.7 µg/L based on effects on reproduction in Mysidopsis bahia.

Key value for chemical safety assessment

EC10, LC10 or NOEC for freshwater invertebrates:
0.1 mg/L
EC10, LC10 or NOEC for marine water invertebrates:
7.7 µg/L

Additional information

A Daphnia magna reproduction test (semi-static, 21 d) with NPEO was conducted according to OECD 211. For the test, 10 organisms, individually held, were used per concentration level and control. At test start, they were 2 to 24 h old. The study was carried out under semi-static conditions with a three times per week renewal of the test solutions. Test concentrations were 0, 10, 32, 100, 320 and 1,000 µg/L. Doses were verified analytically with samples collected on Days 0, 5 and 16 (fresh media, 0 h) and on Days 2, 7 (old media, 48 h) and 19 (old media, 72 h). The parameters assessed included reproduction capacity and other test substance-related effects such as time of production of first brood, adult mortality, intrinsic rate of natural increase, occurrence of aborted eggs and stillborn juveniles and body length of the parental daphnids. Analytical recovery in fresh (0 h) and old (48 or 72 h) media was determined to be within ± 20% of the nominal values throughout the test at the biologically relevant concentrations of 100 to 1000 µg/L. Therefore, values were expressed based on the nominal test substance concentrations. The average number of juveniles per parent alive at the end of the test in the control group was 122 after 21days.The reproductive output was significantly reduced at 320 µg/L when compared to the control. The EC10 value for the reduction of the reproductive output was calculated by sigmoidal dose-response regression to be 85.3 µg/L. An EC50 for the reproductive output was not determinable because no effects ≥ 50% (reduction or increase of the reproductive output) occurred within the tested concentration range. Due to mortality of all parental daphnids at 1,000 µg/L no reproduction was observed at this concentration. The coefficient of variation of thenumber of living offspringproduced per parent was 7% in controls. At 10.0 and 32.0 µg/L, the calculated coefficient of variation was 5% and comparable to controls. At 100 and 320 µg/L, the coefficients of variation were 17 and 22%. The 21 d reproduction LOEC and NOEC, based on the reduction of reproductive output as the most sensitive effect, were determined to be 320 and 100 µg/L, respectively; the EC50 for reproduction could not be determined. The intrinsic rates of natural increase (IR) of the surviving parent animals accounting for generation time and number of offspring were used for calculation of population growth and maintenance. The mean IR of the surviving daphnids of the treatment groups were compared to the control by Kruskal-Wallis One Way Analysis of Variance on Ranks, Dunnett’s method (p = 0.05), because normality test failed. There was no statistical significance at 10.0 to 32.0 µg/L compared to the controls. For the concentration level of 1,000 µg/L, no IR was calculated due to mortality of all parental daphnids. Nostillborn juvenilesandaborted eggswere produced by the control group. Related to the total number of produced juveniles (dead + alive), the percentage of dead juveniles was in the range of 2 to 3% at 10.0 to 100 µg/L. At 320 µg/L, the percentage of dead juveniles was 14%. According to the report, the validity criteria for the test were met (Noack M, 2010).

A study was conducted to determine the long-term toxicity of the read across substance NPE-1.5 ( (with a composition closely resembling that of the test substance NPEO, except that NPE-1.5 also contains 3.8% of NP), to aquatic invertebrates according to EPA OTS 797.1950 (Mysid Chronic Toxicity Test), in compliance with GLP. Mysisdopsis bahia was exposed to the test substance at concentrations of 0, 2.3, 4.7, 9.4, 19 and 37 µg/L (equivalent to 0, 2.2, 4.0, 7.7, 16 and 32 µg/L (measured concentrations)) for 28 days under flowthrough conditions. Each exposure concentrations were analytically confirmed by HPLC on Days 0, 7, 14, 18, 21 and 28. Mortality (parents and offspring), appearance and behaviour were checked daily. After mating and throughout the rest of the study, the reproductive success was assessed. At study termination, body length and weight were recorded. Water quality measurements (temperature, dissolved O2 concentration, pH and salinity) were also performed. Measurement of the Maximum-Acceptable-Toxicant Concentration (MATC) for determination of significant adverse effect on F0 organisms (survival, growth, and reproduction) was finally calculated. Test substance concentrations were generally consistent (between 91.9 to 106%) and no visible sign of undissolved test substance was observed. After 28 days of exposure, survival of 85% was observed among organisms exposed to the control solution. Survival of 73, 80, 80, 78 and 68% were observed in animals exposed to the mean measured concentrations of 2.2, 4.0, 7.7, 16 and 32 µg/L, respectively. It was not different from the control group. Reproductive success in controls (1.1 offspring per female per day) exceeded minimum standards (i.e., >75% of the paired females produced young and the average number of young produced by the paired females was > 0.30). The reproductive success in the three lower concentrations (2.2 - 7.7 µg/L) was not different from the controls but it became significantly different from the control group for the two highest concentrations, i.e. 16 and 32 µg/L. Reproductive success for organisms exposed to the two highest treatment levels,16 and 32 μg/L, averaged 0.58 and 0.23 offspring per female per reproductive day, respectively, and was significantly different from the reproductive success of the control organisms (1.1 offspring per female per reproductive day). The total body length as well as total body weight in all tested concentrations (for males and females) was not different from the controls, except at the highest concentration tested, i.e. 32 µg/L. Under the study conditions, the 28 d LOEC and NOEC (for reproduction in Mysidopsis bahia) were determined to be 16 and 7.7 µg/L, and the MATC (survival, growth and reproduction) was therefore calculated to be > 7.7 and < 16 µg/L (geom. mean of 11 µg/L) (Sousa, 1999).