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Sediment toxicity

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Description of key information

Key value for chemical safety assessment

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

Additional information

The information detailed hereafter comes from the european risk assessment report and gathered information available on Dimethyldioctadecylammonium chloride (DODMAC) an

d DHTDMAC. DODMAC as an isolated substance is not produced

or used in a commercial range. But it is one of the active component of the technical product DHTDMAC. DHTDMAC is a mixture of quaternary ammonium compounds, with DODMAC as the main component and therefore information avaialble on DODMAC are considered as relevant for addressing sediment toxicity question of DHTDMAC.

Concerning toxicity of DODMAC (> 96% pure) to sediment organisms there is one test with natural stream sediment (Pittinger et al., 1989). Sediment originated from Rapid Creek, South Dakota, with an organic carbon content of 4.2% prior to testing (71% clay, 19% fine silt, 4% medium and 6% fine sands). 72-h old larvae of Chironomus riparius were exposed for 24 days to prespiked sediment (stirred overnight) in a flow-through system. A single subchronic DODMAC concentration was replenished to the overlying laboratory water in all tests. A significant reduction in midge emergence was observed at 2.7 g/kg sed. dry weight (measured concentration), the NOEC was 876 mg/kg sed. dry weight. The concentration in the overlaying water was 0.29 mg/L and in the interstitial water 0.06 mg/l. In an experiment with water only a 24-day NOEC of 0.45 mg/L was derived related to midge emergence (measured conc.).

In the absence of sediments the effects of DODMAC on egg hatchability of Chironomus riparius were assessed in a static renewal test with laboratory water without sediment (Pittinger et al., 1989). The highest concentration of 21.5 mg/L had no effect on the egg hatching success. The survival of the hatched larvae was more sensitive and the LC50 after 72 hours was 11.3 mg/L (measured concentration).

The toxicity of DODMAC to the oligochaete Lumbriculus variegatus was examined in a 28d test using natural sediment (organic carbon content: 1.73 %). 10 intact worms per vessel were exposed to nominal DODMAC sediment concentrations between 150 and 5,800 mg/kg dw. for 28 days. A mixture of radio-labelled and non-labelled DODMAC was used for the experiment and the analytical determinations were made using the radio-labelled DODMAC. The endpoints of this test were survival, reproduction and growth. Survival and reproduction were treated as single endpoint, that is, the total number of worms per vessel at the end of the test.

At the highest tested concentration no significant decline in worm number or biomass compared to the control was found. Observations throughout the test period showed that the worms did not even avoid the sediment at this concentration. Analytical monitoring showed that the concentration of DODMAC in the sediment did not decline significantly. For the highest tested concentration an average value of 4,830 ± 550 mg/kg was measured after 28 days. Therefore, from this test a NOEC of about 5,000 mg/kg dw can be derived (Conrad et al. 1999).

The toxicity of DODMAC to the oligochaete Tubifex tubifex was assessed using a 28d sediment bioassay (Comber and Conrad, 2000). The same sediment as in the test with Lumbriculus was used. A mixture of radio-labelled and non-labelled DODMAC was used for the experiment and the analytical determinations were made using the radio-labelled DODMAC. 4 adult worms per test vessel (6 vessels per concentration) were exposed to the spiked sediment containing nominal DODMAC concentrations between 0 and 5,000 mg/kg dw. The examined endpoints were survival of the worms, number of juveniles and body weight. At the end of the test samples of overlying water and sediment were taken for analysis. The measured sediment concentrations ranged between 224 mg/kg dw and 3,600 mg/kg dw. All effect values were related to the measured concentrations.

Up to the highest test concentration no effects on the survival of Tubifex were observed. Also in the dry weight of the adult worms no statistically significant difference was found between the control and the worms exposed to DODMAC. However, for the endpoint number of juveniles, a concentration effect was observed. A NOEC of 1,515 mg/kg dw and a LOEC of 2,484 mg/kg dw was found. Using a linear interpolation method, a mean EC10 of 550 mg/kg dw and an EC50 of 3,022 mg/kg dw was calculated.

A further sediment test with Caenorhabditis elegans, a bacterivorous nematode that is primary found in terrestrial soils but also in aquatic sediments, was recently performed with DHTDMAC (BSB (2000). Toxicity of sodium tetrapropylen benzene sulfonate, cocos dimethylamine, di hardened tallow dimethyl ammonium chloride and tallow alkylamine on the nematode Caenorhabditis elegans in artificial sediment.). An artificial sediment with an organic content of 2 % was used. Test endpoints were growth, egg production and fertility. Before the start of the test, 0.25 ml of a bacterial suspension (E. coli in M9-medium) was added to each test vessel as food for the nematodes. Afterwards, 10 juvenile nematodes of the first stage were added to the vessels, containing 0.5 g sediment, 0.5 ml test solution and 0.25 ml bacterial suspension. The vessels were incubated for 72 h at 20 °C on a shaker. At the end of the test, the nematodes were heat killed and stained with “Rose Bengal”. After extracting the nematodes from the sediment, body length and number of eggs inside the body were determined. A NOEC of 1,350 mg/kg dw and a LOEC of 2,030 mg/kg dw related to nominal concentrations was found.

DHTDMAC (77% active ingredient, 1.7% MTTMAC) was applied in a partial life cycle test with Chironomus riparius in natural lake water (Roghair et al. 1992). The water of the Lake Veluwe (Netherlands) contained 1-4 mg/L suspended solids and 7.1 - 9.3 mg/L DOC (pH = 8.5, 320 mg/l CaCO3). Eggs not older than 24 hours were exposed in a static renewal system for 28 days. In one experiment larval weight, mortality, behaviour and appearance were affected with similar sensitivity and the NOEC for all was 0.8 mg/L (nominal concentration of active ingredient). In a second experiment the most sensitive endpoint was retardation in development with a NOEC of 1.4 mg/L. Besides a 96h LC50 of 7.1 mg/L was given by the authors for the second instar larvae.

The effects of natural sediment and river water containing DHTDMAC on Paratanytarsus parthenogenica were assessed in a static test system over 20 days (Lewis & Wee, 1983). Samples collected from different points along the Rapid Creek, South Dakota, contained 2 to 67 mg/kg DHTDMAC in the sediment and 0.008 to 0.092 mg/L in the water. Midge eggs exposed to these concentrations showed no significant difference in larval survival and adult emergence relative to the control with laboratory water.

Roghair et al. (1992) determined the acute effect of the technical product (77 % DHTDMAC, 1.7 % MTTMAC) on the pond snail Lymnea stagnalis in pond water without sediment. A 96h-LC50 of 18 mg/L and a 96h-EC50 of 7.5 mg/L (reduced movements and withdrawal into the shell) was found. In 2 additional tests over a period of several weeks (29 resp. 26 days) the authors studied the effect of the test substance on snail mortality and reproduction. At the lowest nonlethal concentration of 1 mg/L the following sublethal effects were observed: retracted and curled antennae, depressed locomotory activity, withdrawal into the shell and decreased food intake. A NOEC of 320 μg/L was obtained. For the derivation of the PNECsed only such tests can be used in which the test organisms were exposed to whole sediment spiked with the test substance.

Among the above cited tests with sediment organisms four tests are appropriate for the effects assessment of sediment: the studies by Pittinger et al., Conrad et al., Comber/Conrad and BSB. For Chironomus riparius a NOEC of 876 mg/kg dw was found. Lumbriculus variegatus was less sensitive to adsorbed DODMAC. A NOEC of about 5,000 mg/kg dw was found for this sediment ingesting worm. For the nematode Caenorhabditis elegans a NOEC of 1,350 mg/kg dw was derived. The NOEC found for the oligochaete Tubifex tubifex was with 1,515 mg/kg dw in the same range with the NOECs from the other tests. However, a EC10-value of 550 mg/kg dw could be calculated that is used a basic value for the PNEC derivation.

Based on RAR information it can be concluded that DHTDMAC is not highly toxic to sediment organisms depending on operational conditions of exposure. The same conclusion is therefore applied to N-benzyl-N-C16-18 (even numbered) -alkyl-N-methyl-C16-18 (even numbered) -alkyl-1-aminium chloride.

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