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Sediment toxicity

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Description of key information

A 28 d study conducted with NP and the sediment-dwelling species Chironomus riparius, with an EC10 of 231 µg/g (mg/kg) sediment dw was selected as representative for NPEO toxicity to sediment organisms. Evidence from a large body of testing indicates that aquatic toxicity decreases as NP ethoxylation grade increases, so that the value of NP can be considered protective for NPEO.

Key value for chemical safety assessment

EC10, LC10 or NOEC for freshwater sediment:
231 mg/kg sediment dw

Additional information

A study was conducted to evaluate the toxicity of NP (a mixture of ring and chain isomers) to Chironomus riparius in a 28 day spiked sediment test. Chironomus riparius (10 first-instar larvae per dose) were exposed at a concentration range of 270-580 and 290-1100 µg/g sediment dw, respectively, in two non-simultaneous tests. NP was directly added to the wet sediment, avoiding any solvent. Five replicates were used for each concentration, including the control. The total number of fully emerged male and female midges was recorded daily for the maximum test duration of 28 d. Egg depositions during the bioassays were also noted. Analytical dose verification was not conducted. The emergence of midges significantly decreased with increasing NP concentrations (p < 0.05). The average 28 day EC10 and EC50 for emergence were 230.9 and 383 µg/g (231 and 383 mg/kg) sediment dw, respectively. No significant differences were noted in the sex ratio of the emerged chironomids when exposed to NP compared to the controls, but the emerged chironomids did not lay eggs at concentrations higher than the EC10 (Bettinetti R and Provini A, 2002).

In another study by the same authors, the toxicity of NP (a mixture of ring and chain isomers) to Tubifex tubifex in a 28 day spiked sediment test was evaluated.Foursexually mature worms per dose were exposed at concentrations in the range of 180-650 and 90-610 µg/g sediment dw, respectively, in two non simultaneous tests. NP was directly added to the wet sediment, avoiding any solvent. Five replicate were used for each concentration, including the control. At the end of the test, the total number of surviving adults, cocoons and young worms was counted. Qualitative observations on the reworking activity of worms in sediments were also recorded. At the end of the second test some adult worms taken from the control, 190 and 610 µg/g sediment dw groups were histologically analyzed to identify malformations in gonadal development. In both bioassays breeding adults started to die at 600 µg/g sediment dw. Results indicate that the number of cocoons and young worms decreased significantly (P < 0.0001) with increasing concentrations of NP in sediments. With increasing concentrations of NP in sediments, a reduced reworking activity in sediments of adult worms was observed based on decreased number of galleries. At concentration of 610 µg/g sediment dw, an interference in the development of the gonads of adult worms was noted upon histological examination but it was impossible to determine whether this effect was due to NP toxicity or to its hormone mimicking properties. Based on the results, the average 28 day EC50 values in the Tubifex tubifex bioassays for the deposition of cocoons and the development of young worms were 428 and 420 µg/g (mg/kg) sediment dw and respective EC10 values were 360 and 359 µg/g (mg/kg) sediment dw (Bettinetti R and Provini A, 2002).