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Toxicity to fish

Data from acute toxicity testing towards fish can be interpreted in a weight of evidence approach that dicumyl peroxide showed no effects at maximum water solubility. This is in line with a recent study on acute toxicity towards daphnia, where no effects were observed in water accommodated fraction (test solution prepared without solvent, but reaching maximum water solubility).

According to Annex IX of Regulation (EC) No 1907/2006 chronic fish toxicity tests should be proposed if the chemical safety assessment indicates the need to investigate further the effects on fish. However, overall information is sufficient for risk assessment. Therefore, testing of on chronic fish toxicity is not regarded necessary.

Toxicity to aquatic invertebrates

Data from acute toxicity testing towards Daphnia indicate that dicumyl peroxide showed no effects at maximum water solubility.

The 21-day-chronic toxicity of dicumyl peroxide to Daphnia magna was studied under static renewal conditions. The parental 21-day LC50 based on mortality was 0.195 mg/L, the 21-day EC50 for reproduction was 0.231 mg/L. The 21-day NOEC based on average cumulative number of brood was 0.117 mg/L, the 21-day LOEC was 0.247 mg/L. Sublethal effects were observed in the 0.247 mg/L plot (body colour brightening and growth inhibition, besides lethargy, immobility, and activity drop). No symptoms were observed in the other concentration plots. Dead larvae were observed in all the test plots, and the 0.247 mg/L plot had somewhat more than the control plot. Fallen eggs were also observed in all of the test plots, the 0.117 mg/L showed a statistically significant difference. Production of offspring in the treated groups indicated that dicumyl peroxide had an effect on the reproduction at concentrations greater than 0.117 mg/L. The most sensitive end point was reproduction.

Toxicity to algae

In a 72 hour acute toxicity study, the cultures of Pseudokirchneriella subcapitata (reported as Selenastrum capricornutum), strain ATCC 22662, were exposed to dicumyl peroxide. The 72h EbC50 and 72h NOEbC values based on cell density were > 20 mg/L and 3.20 mg/L, respectively (nominal). The 24-48 h ErC50 and the 24-72 h ErC50 were both > 20 mg/L, whereas the 24-48 h NOEC and 24-72 h NOEC values based on growth rate were 8 mg/L, each (nominal).

These results are supported by a second study. Effect concentrations based on growth rate of cultures of Selenastrum capricornutum (new name: Pseudokirchneriella subcapitata) were ErC50 > 1000 mg/L and NOEC (growth rate): 10 mg/L, respectively. The effect concentration based on biomass was EC50 > 1000 mg/L. The NOEC for biomass was not determined in this test, but was < 10 mg/L.

Both studies indicate no effect at maximum water solubility.

Toxicity to micro-organisms

In an activated sludge respiration inhibition test, secondary activated sludge of a predominantly domestic sewage treatment plant was exposed to dicumyl peroxide adsorbed on silica gel at a concentration 1000 mg/L (nominal) under static conditions for 30 min in accordance with OECD guideline 209 (activated sludge, respiration inhibition test). The NOEC based on respiration inhibition was >1000 mg/L.