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Sediment toxicity

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Description of key information

There are no SCCPs studies available on sediment-dwelling organisms (information is available on the midge Chironomus tentans, but exposure was via water only). In view of the similarities in structure and physiochemical properties [between SCCPs and MCCPs], it can reasonably be predicted that SCCPs would have similar effects to MCCPs. In GLP studies based on OECD guideline 218, 28-day NOECs of 130 mg/kg dry wt (of sediment) have been determined for Cereclor S52 (a C14-17 chlorinated paraffin; 52% chlorination) based on the reduced growth seen in female amphipods (Hyalella azteca) and effects on mortality/reproduction of worms (this is equivalent to about 50 mg/kg wet weight). 

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Additional information

There are no studies currently available on the effects of exposure to SCCPs on sediment-dwelling organisms (information is available on the midge Chironomus tentans, but exposure was via water only). In view of the similarities in structure and physiochemical properties [between SCCPs and MCCPs], it can reasonably be predicted that SCCPs would have similar effects to MCCPs on sediment-dwelling organisms. Indeed aquatic invertebrates (Daphnia) have been shown to be the most sensitive species following exposure to both SCCPs and MCCPs, therefore further testing of sediment-dwelling organisms is not considered necessary.

In a GLP study based on OECD Guideline 218, the long-term effects of Cereclor S52 (a C14-17 chlorinated paraffin; 52% chlorinated), on survival, growth and sexual development of the freshwater amphipod, Hyalella azteca, was investigated using a semi-static system with spiked artificial sediment. The test substance was mixed with 8-14C-labelled chlorinated pentadecane (51% chlorinated) to facilitate measurement of test concentrations. Nominal concentrations of the test substance in the artificial sediment ranged from 38 to 600 mg/kg dry wt, achieving mean measured concentrations of 32, 61, 130, 270 and 470 mg/kg dry wt. Untreated and solvent controls were included. Exposure of amphipods to the test substance in the sediment at measured concentrations up to 270 mg/kg dry wt for 28 days had no significant adverse effect on survival compared to the controls, whereas at 470 mg/kg dry wt survival was significantly reduced to 50%. Growth of male amphipods was not significantly different to controls at concentrations up to 470 mg/kg dry wt, whereas growth of females was significantly reduced at the two highest concentrations (270 and 470 mg/kg dry wt). The proportion of gravid females was significantly reduced compared to controls at the highest concentration only (470 mg/kg dry wt), although as the initial proportion of males to females in the replicates varied with the treatments, and was affected by the mortalities seen, the significance of this latter finding is uncertain. Overall, the lowest NOEC determined in this study was 130 mg/kg dry weight of sediment (equivalent to about 50 mg/kg wet wt), based on the reduced growth of females over 28 days (this NOEC will be used for the derivation of the PNEC). 28-Day NOECs of 270 mg/kg dry wt of sediment were determined for both sexual development and survival in the females (Thompson et al. 2002).

 

A prolonged toxicity and reproduction test was performed with Cereclor S52 on the oligochaete worm, Lumbriculus variegatus, using a static freshwater system spiked with artificial sediment, based on OECD Guideline 218 (Thompson et al. 2001a). The test substance was mixed with 8-14C-labelled chlorinated pentadecane (51% chlorinated) to facilitate measurement of test concentrations. Nominal concentrations of test substance in the artificial sediment ranged from 44 to 14000 mg/kg dry wt, achieving measured concentrations of 39, 130, 410, 1300, 4000 and 13,000 mg/kg dry wt. Exposure of the worms to spiked sediment for 28 days resulted in a statistically significant decrease in mean number of worms per replicate and in the mean total dry weight of worms per replicate at a measured concentration of 410 mg/kg dry wt sediment and above. A slight, but not statistically significant, decrease on the mean dry weight per worm at concentrations up to 13,000 mg/kg dry wt was also reported. The 28-day NOEC for mortality/reproduction, and therefore the overall NOEC in this study, is 130 mg/kg dry wt of sediment (equivalent to about 50 mg/kg wet weight; this NOEC will be used for the derivation of the PNEC).

 

The toxic effects of Cereclor S52 on larval development and emergence of the fresh water midge, Chironomus riparius, was investigated in a static system using spiked artificial sediment, based on OECD Guideline 218 (Thompson et al. 2001b). The test substance was mixed with 8-14C-labelled chlorinated n-pentadecane (51% chlorinated) to facilitate measurement of test concentrations. Nominal concentrations of the test substance in the artificial sediment ranged from 44 to 14000 mg/kg dry wt, achieving mean measured concentrations of 36, 110, 370, 1200, 3800 and 13000 mg/kg dry wt. Controls and solvent controls were included. Exposure of midge larvae to the spiked sediment at up to a mean measured concentration of 13000 mg/kg dry weight had no significant effect on time to first emergence of adults, mean emergence time or sex ratio, when compared to the controls. However, at the highest concentration, the mean number of emerged adults after 28 days was significantly reduced (with a mean percentage emergence of 64%) compared with the controls (greater than 80% emergence). The lowest overall NOEC for the test material in this study, based on a reduction in the number of emerged adult midges, was 3800 mg/kg dry wt.