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Environmental fate & pathways

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For chemical structures please refer to CSR chapter 4.1.5 Figure 2: The chemical structures of TEA-Esterquat diester (Compound I); DODMAC, TEA-Esterquat monoester (Compound II).

DODMAC has a chemical structure similar to the TEA-Esterquat Diester Compound I. TEA-Esterquats are UVBC substances. The main component is the dialkylester compound, besides smaller amounts of the monoalkyl- and trialkylester.

The molecular diester moiety of the registration substance for which the highest adsorption potential is expected is the diester with saturated ester groups, chain length C18 (Compound I) and differs from DODMAC by the ester linking groups between the alkyl chains (of C18chain length) and the head group (effectively the quarternary ammonium group). Minor components are the TEA-Esterquat monoester and triester.

Regarding lipophilic properties of the registration substance, the registration substance sorption is expected to be lower than that for DODMAC: The chemical structure of the registration substance includes, in contrast to DODMAC, one, two or three polar ester moieties and one or two ethanol moieties that lower hydrophobic character. The monoester is considerably less lipophilic than the main component, TEA-Esterquat diester. The minor component, TEA-Esterquat triester with alkyl chain length C18 should be more lipophilic than the TEA-Esterquat diester. All TEA-Esterquats are biodegradable/hydrolysable (see 4.1.2) which also will result in lower environmental concentrations for the registration substance. DODMAC is poorly biodegradable and much more stable than the registration substance. For DODMAC, no abiotic degradation is expected. The degradation rate is very low for biotic degradation in water (1.4·10-4day-1) (EU RAR, 2009).As outlined in the EU RAR (2009), DODMAC is adsorbed by both the mineral and the organic fraction of soil and sediments. Furthermore, the adsorption coefficient is more dependent on the nature of the mineral phase than on the organic carbon content.

Measured sorption coefficients for soils and sediments are available from the structurally very similar substance DODMAC (EU RAR 2009):

„DODMAC adsorbs onto both the mineral and the organic fraction of soil and sediments.

In a test with14C-DODMAC and 3 different sediments, sediment-water partitioning coefficients from 3,833 to 12,489 l/kg dw were analytically determined. The results indicate that the coefficient is more dependent on the nature of the mineral phase than on the organic carbon content. Kinetic studies indicated that adsorption was rapid, reaching equilibrium values within a few hours (Larson & Vashon, 1983).

During a test on toxic effects on sediment organisms, the14C-DODMAC concentrations were measured in sediment (organic carbon 4.2%) and in interstitial water. From these results, a distribution coefficient can be calculated. The Ksed-water values are in the range of 2,150 to 15,000 (related to dry weight and dimensionless). The Ksed-water values are increasing with rising DODMAC concentrations (Pittinger et al., 1989)

The partitioning of 14C-DODMAC between porewater and the whole sediment (collected from a gravel pit) was studied by Conrad et al. (1999). The equilibrium was reached before the first sampling time (2 days). Sediment and porewater concentrations were measured applying different DODMAC amounts, and from the regression slope the partitioning coefficient was determined to 3018 l/kg….

Kappeler (1982) found that on average 27% of the DHTDMAC in river water is adsorbed onto suspended matter (mean 22 mg/l suspended solids). ….

McAvoy et al. (1994) examined the mobility of DHTDMAC in an aquifer containing 78% sand, 5.8% clay, 16.1% silt, and 0.26% organic carbon. The estimated sorption coefficients were relatively low, varying from 25 to 62 l/kg.

These investigations demonstrate that DODMAC can be bound very strongly by some minerals, while in others relatively small distribution constants were estimated. Under environmental conditions, the sorption properties of DODMAC … probably vary in a wide range depending on the nature of the adsorbant.  

In the EU Risk Assessment Report of DODMAC, a value of 10,000 l/kg dw was chosen for both Kpsed and Kpsoil.

No data are available on volitalisation. Considering the molecular structure, extremely low vapour pressures for the ionic substances are expected. Therefore volatilisation of the TEA-Esterquats is negligible.

This is supported by the findings for partially unsaturated TEA-Esterquat.Based on experimentally derived results and using the Antoine equation the vapour pressure at 20 and 25 °C was calculated to be 4.4 x 10E-6 hPa/ 4.4 x 10E-4 Pa (at 20 °C) and 6.7 x 10E-6 hPa/6.7 x 10E-4 Pa (at 25 °C).

The calculation of the Mackay Level I failed as the log Kow, which is needed as input parameter, cannot be determined due to the surface-active properties of TEA-Esterquats. Based on the available data, it can be assumed that TEA-Esterquats will not volatilise from aqueous solution. According to the results of adsorption/desorption experiments, TEA-Esterquats will mainly be adsorbed by soil and sediments. The distribution to biota is negligible.