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Sediment toxicity

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Description of key information

Three sediment toxicity studies are available using LAS (read across). The first study (Comberet al. 2006) determined the toxicity to sediment dwelling worms. Samples of natural sediment were spiked with test substance at concentrations of 50, 75, 100, 150, 300, and 600 mg/kg/dry weight. Ten test organisms of species Lumbriculus variegatus were then added. Exposure lasted 28 days, at which time the organisms were observed for survival and biomass. The test substance half-life in aerobic sediment was approximately 20 days. The EC50 was ≥ 105 mg/kg sediment dry weight. The NOEC was 81 mg/kg sediment dry weight.

The second study (Comberet al. 2006) consisted of samples of natural sediment spiked with concentrations of 10, 50, 100, 200, 300, 400, 500, 750 and 1000 mg/kg dw and controls. Ten test organisms of the nematode species Caenorhabditis elegans were then added. Exposure lasted 3 days, at which time the organisms were observed for survival and reproduction. The NOEC for egg production was 100 mg/kg sediment dw, the NOEC for fertility was 200 mg/kg sediment dw and the EC10 for growth was 275 mg/kg sediment dw.

In the final toxicity study (Pittinger et al. 1989; The Procter & Gamble Company 1986; van de Plassche et al 1999), which was conducted following the OECD 218 guideline, the midge Chironomus riparius, was exposed to C11.9LAS for 24 days. This actually consisted of a series of separate tests. In an egg hatchability semi-static assay (acute test), midge eggs were exposed to a range of LAS concentrations in water and were monitored for hatching success and posthatch survival. No significant reduction in egg hatching was observed at the highest concentration tested (18.9 mg/L). However, significant reduction in the survival of the newly hatched larvae occurred at 4.7 mg/L. The 72 hour LC50was between 1.0 and 4.7 mg/L, based on survival of newly hatched larvae. In the partial life cycle bioassay in a flow-through sediment/water test system (chronic test), percentages of winged adults emerging after continuous exposure of larvae and pupae to a range of LAS concentrations were determined. Exposure concentrations in sediment, interstitial water and overlying water were monitored by14C liquid scintillation counting. The effect of LAS level in the water column was determined in a total of six chronic toxicity tests. The NOECs from these tests ranged from 2.4 to 3.0 (without sediment), and 3.0 to 6.0 (with sediment). The effect of LAS on Chironomus was also evaluated in an experiment using sediment spiked with LAS. In this test, the NOEC of sediment-spiked LAS was 319 mg/kg sediment (dry weight basis). The normalized NOEC is 2.87 mg/L for C11.6LAS.

Key value for chemical safety assessment

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

Additional information

LAS provides suitable read across for LAB Sulfonic Acids as both form the identical chemical species in aqueous solutions at neutral (physiological) pH. Three toxicity studies are available for sediment organisms. Test materials are considered to represent the materials in the category. As summarized in the Table below, the average alkyl chain lengths of tested materials ranged from C11.4 to C11.8, similar to C11.6 for the LAB Sulfonic Acids/LAS typically used in European detergent formulations. The C14 homologue content of tested materials was not reported for the C11.4 LAS (and likely to be <=1%) while the C14 content for the C11.8 LAS was 8.7%, compared to <1% for the LAB Sulfonic Acids/LAS used in European detergent formulations.  The lowest sediment data point is a 28 day NOEC = 81 mg/kg sediment dw for the earthworm Lumbriculus variegates using C11.4 LAS.

 

Table: Alkyl Chain Lengths and C14 Content of LAS Used in Sediment Toxicity Tests*

Test

Average Alkyl Chain Length

C14 Homologue Content

Results

.001 Earthworm (Lumbriculus variegates)

C11.4

N/A

28 day NOEC = 81 mg/kg sediment dw

.002 Nematode (Caenorhabditis elegans)

C11.4

N/A

72 hour NOEC (egg production) = 100 mg/kg sediment dw

.003 (midge,Chironomus riparius), water only test

C11.8

8.7%

24 day NOEC = 319 mg/kg sediment dw

* N/A = not available, dw = dry weight.

 

Based on the availability of toxicity data on three sediment organisms, the assessment factor (AF) method was used to determine the PNECsediment in accordance with R.10.5.2.2. Based on the lowest NOEC value from the three studies (81 mg/kg sediment dw) and an AF = 10 (in accordance with Table R.10-7), the final calculated PNECsediment-freshwater value is 8.1 mg/kg sediment dw. Applying an additional assessment factor of 10 for marine systems results in the final calculated PNECsediment-marine value of 0.81 mg/kg sediment dw.