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Sediment toxicity

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Description of key information

For DMA category member C12-14 DMA and supporting substances reliable chronic studies assessing sediment toxicity on representatives of two different sediment organism groups (Nematoda, Oligochaeta) are available. The NOEC (28 d; reproduction & body weight) obtained for C20/22 ATQ in the sediment test with Lumbriculus variegatus of 62.5 mg/kg sed. dw may be regarded as a worst case estimate for sediment toxicity of DMA category members. 

Key value for chemical safety assessment

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

Additional information

Overview of the available Key Freshwater sediment test

 Test Guideline  Endpoint   Value (mg/kg sediment dw)  Test substance
 Chronic C. elegans  ISO 10872  NOEC repro (72h) 1620   C12 -14 DMA
 Chronic L. variegatus  OECD 225  NOEC repro (28d)  62.5  C20/22 ATQ

For the DMA category member C12-14 DMAa reliable (RL 2) key study on Caenorhabditis elegansassessing chronic sediment toxicity is available. The study was performed similar toISO 10872 (pre-guideline test). Over an exposure period of 72 hours growth (length of worms) and fertility (number of gravid worms, number of eggs per worm) were assessed. ANOEC (72 h; growth & fertility) of 1620 mg/kg sed. dw. and a LOEC (72 h; growth & fertility) of 2030 mg/kg sed. dw. were determined. Because at the LOEC about 80% size reduction and zero % gravid worms were observed, fertility seems not to be significantly more sensitive than growth. Rather, the severely impaired growth at the LOEC most probably reflects an overall poor constitution of the worms such that failure of pregnancy is rather a secondary effect.

Two further supporting studiesare available assessing chronic sediment toxicity on Caenorhabditis elegans:

The first supporting study was performed with the supporting substance tallow alkyl amines (C16-18-(even numbered, C18-unsaturated)-alkylamines) which is very similar to DMA category member C16-18-(even numbered, C18 unsaturated) DMA (for details on similarity see Category Document, chapter 1). The study was performed similar toISO 10872 (pre-guideline test; RL 2). Over an exposure period of 72 hours growth (length of worms) and fertility (number of gravid worms, number of eggs per worm) were assessed. An unboundedNOEC (72h, growth rate & reproduction) of 2030 mg/kg sed. dw was determined.

The second supporting study – areliable Caenorhabditis elegans reproduction test performed according to ISO/DIS 10872 (2008) and compliant to GLP (reliability category 1) -was performed with the supporting C20/22 ATQ.C22 ATQ may be regarded as worst case for DMA category members due to its longer alkyl chain. A further difference is that it has - in addition to the two methyl substituents at the amino group inherent to all DMA category members - an additional methyl substituent at the amino group, rendering it a quaternary amine being permanently positively charged. Indeed, compared to the afore mentioned results obtained with C12-14 DMA andtallow alkyl aminesa considerably lower NOEC (Mortality, Fertility, Reproduction, Growth) and LOEC of 250 and 500 mg/kg sed. dw., respectively, was determined for C20/22 ATQ. However, in line with the results obtained with C12-14 DMA at the LOEC no specific reproductive toxicity had been found, rather growth and reproduction were affected at the same time. Thus, compared with DMA and primary alkyl amines (tallow alkyl amine), C20/22 ATQ can be regarded to be of higher sediment toxicity, possibly due to its stronger adsorptive behaviour caused by the longer alkyl chain (hydrophobic interaction) and the permanent positive charge (ionic interaction).

In this regard,the second key studyfor sediment toxicity of DMA category members performed with supporting substance C20/22 ATQ may be taken as conservative worst case estimate of DMA sediment toxicity. Lumbriculus variegatus as representative of a second sediment organism group was used as test organism in a reliable reproduction test performed in a water-sediment system according to OECD 225 and compliant to GLP (RL 1). Test duration was 28 days after insertion of the test organisms. The study was performed by spiking the test item into the sediment with five concentrations of 62.5 - 125 - 250 - 500 and 750 mg/kg sediment dry weight. Six replicates per control as well as solvent control and four replicates per test item concentration were set up for the biological investigation. Analytical verification of test item concentrations at 0 d, 14 d and 28 d demonstrated that the nominal range of the test item concentrations was met. TheNOEC (28 d) determined for all endpoints assessed was 62.5 mg/kg sed. dw. In line with the results from the studies on C. elegans outlined above no specific reproductive toxicity was found: At the LOEC of 125 mg/kg sed. dw. a mean reduction in body mass of 34% and concurrently an inhibition of reproduction by 24% was observed. An EC50 (28 d) for reproduction and biomass of 169 and 221 mg/kg, respectively, was estimated.

In conclusion, the results of the C. elegans studies performed with C12-14 DMA, tallow alkyl amine (primary fatty alkyl amine, PFA) and C20/22 ATQ strongly suggest a higher sediment toxicity of C20/22 ATQ compared to DMA and PFA, probably caused by its stronger adsorptive properties.Thus the NOEC obtained for C20/22 ATQ in the sediment test with Lumbriculus variegatus of 62.5 mg/kg sed. dw may be regarded as a worst case estimate for sediment toxicity of DMA category members. This value will be used for derivation of a PNEC for sediment organisms.