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Sediment toxicity

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Description of key information

The NOEC of 1000 mg/kg dw obtained from the frog study will be used for PNEC sediment derivation.

Key value for chemical safety assessment

EC10, LC10 or NOEC for freshwater sediment:
1 000 mg/kg sediment dw

Additional information

The RAR, 2008, reports all available data except the study by Park and Choi (2007). Today no new data are available. The reliable studies have been re-evaluated for the purpose of REACH regulation and chemical safety assessment and have highlighted two key studies and six supportive studies.

- The key study on frogs exposed via sediment (Solyom et al., 2001) explored some of the methodological differences between the two supportive studies I and II (Larsson and Thuren (1987) and Wennberg et al. (1997) respectively). Solyom et al. (2001) exposed moor frog eggs to DEHP at two temperatures (5 and 10°C) using two different types of sediment, a fine sediment with mostly degraded material and a coarse sediment containing undegraded material. The sediments were spiked with DEHP using essentially the same method as in Study II with acetone as a solvent. The nominal exposure concentrations were 100, 300 and 1,000 mg/ kg dwt. No statistically significant differences between controls and DEHP exposed groups were seen in any of the 4 test series.

DEHP recovery in sediment was not well maintained in all concentrations tested, in particular in fine sediment (origin of the variation unidentified). However in coarse sediment, concentrations seemed to be better maintained during experiment. As these data are more representative of tadpole habitat and no adverse effect on hatching, survival or growth of tadpoles was observed whatever the sediment or the temperature, the results are considered reliable with restrictions.

Therefore for both sediments and for both temperatures, a NOEC of 1000 mg/kg dw was identified.

Although using the same temperature (5°C) as in study I, in the key study no effects on egg hatching or tadpole survival were seen as was the case in study I (Larsson P and Thurén A, 1987). The reasons for this differences are not clear. The oxygen depletion caused by simultaneous degradation of ethanol and DEHP may be the cause of the dose dependent effects seen in study I even though this is not supported by the results from the “ethanol” control used in study II. Alternatively the extremely high DEHP concentrations in the water in study I may have caused the effects toxicologically or physically.

In study II, Wennberg et al. (1997) studied at 10°C embryo hatching (determined on day 14) and tadpole survival and growth exposed to DEHP in natural sediments spiked at 15, 30, 50, 100, 150, 300, and 600 mg/kg dwt. Like in key study, no significant effect on hatching (at 14 days) or survival of tadpoles (after 29 days) was observed in any of the test concentrations. Neither was any effects observed in sediments with differing organic contents (and about 300 mg/kg (dwt) of DEHP).

Despite the fact that the findings in Study I cannot be adequately explained the conclusion drawn based on the key study from Solyom et al. (2001) and supported by Wennberg et al. (1997) (study II) is, that the hatchability of eggs and survival of tadpoles does not seem to be affected when exposed to DEHP spiked sediments up to 1000 mg/kg dwt.

In a reliable (reliability category 1) supporting study on the midge Chironomus riparius Brown et al., (1996) performed a long-term sediment toxicity test according to GLP and ASTM guidelines. DEHP in acetone (4 ml) was added to a dried sediment portion and the solvent was evaporated before the spiked portion was blended into wet sediment. No effect was observed on hatching and survival of the midges at the highest tested concentration, 10 000 mg/kg dwt (unbounded NOEC, 28 d.

A reliable (with restrictions, RL category 2) supporting long-term study on a third organism group is available. Woin and Larsson, (1987) studied predatory dragonfly larvae (Aeshna). Organisms were kept in aquaria for 60 days. One control and one treatment group with 2 replicate exposures were examined. For the treatment replicates, DEHP solubilized in ethanol was directly added to wet sediment. After 3 d equilibration time with DEHP, 5 L, each were given into two 60 L glass aquaria and after 2 days, overlayed with 40 L of water. The control was prepared in analogous manner using the same amount of ethanol. After 3 weeks of acclimatization, the predation efficiency of Aeshna larvae was recorded 8-10 times within 40 days observation period. At the nominal exposure concentration of 500 mg/kg (mean measured concentration: 600 mg/kg) the predation efficiency was 'significantly affected' by 18.4 -22.5% compared to solvent control (containing 0.4 mg DEHP/kg (wet weight, measured): LOEC = 600 mg/kg sed wet weight (mean measured concentration). According to REACH guidance R.10 a NOEC can be calculated as LOEC/2 when the effect percentage is 10-20%, resulting in a NOEC of about 300 mg/kg (wet weight).

Applying the factor of 2.6 for sediment and 4.6 for suspended matter according to REACH guidance R.16 for converting sediment concentration from wet weight to dry weight results in a NOEC between 780 (sediment) and 1380 (suspended matter) mg/kg dw. No details on sediment composition are given but origin from eutrophic pond.

High ethanol concentration initially applied to sediment (1% by volume, treatments and control) should be without consequences as further dilution by 40 L of overlaying water occurred and experiment was started only after an acclimatization period of 21 days and ethanol is quickly biodegraded.

These results are supported by four other studies where species from various genera Chironomus, Hyallela, Aeshna were not affected when exposed to 40.6 mg/L for 24 hours (LC10, Chironomus tetans; Park and Choi, 2007; original data: 104 µmol/L) or 48 and 59 µg/L for 10 days (NOECs, Hyalella azteca and Chironomus tentans, Staples et al, 1997) via water and 2950 mg/kg sed. dw for 10 days (NOECs, Hyalella azteca and Chironomus tentans; Call et al., 2001) or 780 mg/kg sed. dw. for 60 days (NOEC, Aeshna, Woin and Larsson, 1987) via sediment.

Considering studies testing toxicity to organisms living on or inside the sediment, all concentrations tested whether via water or via sediment exposure were high and not consistent with natural environmental conditions. However, none of these studies have shown adverse effect to these organisms at environmentally relevant concentrations. Therefore we can assume that in realistic environmental conditions sediment organisms will not be adversely affected by DEHP.

From the reliable chronic studies (Solyom et al., 2001, key study; Brown et al., 1996, supporting study; Woin and Larsson et al, 1987, supporting study) the lowest NOEC values were reported for frog (Solyom et al., 2001) and Aeshna (Woin and Larsson, 1987). As for Aeshna larvae only one concentration had been tested and due to the uncertainty associated with approximation of NOEC from LOEC and conversion from wet weight to dry weight, this result is taken as confirmation of the NOEC determined for frog eggs of 1000 mg/kg sed. dw.in accordance with EU RAR (2008). Thus, the NOEC of 1000 mg/kg dw obtained from the frog study will be used for PNEC sediment derivation.