Benzenesulfonic acid, 4-mono-C20-24 (even numbered)-alkyl derivs., magnesium salts

Endpoint summary

Description of key information

Adsorption / desorption

Benzenesulfonic acid, mono-C20-24-alkyl derivs., magnesium salts could not be investigated experimentally for its adsorption potential towards soil particles based on its chemical structure. The procedure according to OECD 121 / EU Method C.19 is technically not feasible. A prediction with KOCWINv2.00 (EPIWIN software) revealed a logKoc of 13.3. Higher alkyl chains (> 20 carbons) would result in an even higher value.

Henry´s Law Constant

The Henry´s Law Constant of the magnesium sulfonate target substance (CAS 231297-75-9) was predicted with HENRYWIN v3.20 (EPIWIN software) by US-EPA (Chemservice S.A., 2012a).The term describes the ration of the equilibrium concentration of a dissolved substance in air and water.Using the Bond Method of the computer program HENRYWIN from US-EPA a Henry´s Law Constant of 6.13 E-2 Pa*m³/mol was calculated for the test substance at 25 °C.

Distribution modelling

Distribution modelling forthe magnesium sulfonate target substance (CAS 231297-75-9)is performed with EPIWIN by US-EPA (Chemservice S.A., 2012b). The executable file for this Mackay Level III fugacity model is called LEVEL3NT.EXE.The software is no stand-alone version and it contains a direct adaption of the Level III fugacity model developed by Dr. Donald Mackay et al. (Mackay, 1991; Mackay et al., 1996).The partitioning of an organic compound in an evaluative environment is predicted by fugacity models, in generalLevel III modelling assumes a steady-state, but no common equilibrium conditions between the different environmental compartments. 4 main compartments are concerned: air, water, sediment and soil. Between these compartments, mass transport is modelled via volatilization, diffusion, deposition and runoff. A fixed temperature of 25 °C is assumed.No substance properties are entered manually, thus default values are used.

In general, disappearance of a chemical occurs via two processes: reaction and advection. The abiotic or biotic degradation belongs to reaction, whereas the removal from a compartment through losses other than degradation is called advection. The rate of advection is determined by a specific flow rate, which may be specified by the user. Furthermore, the user can specify emission rates; otherwise the default emission rate is equal amounts to air, water and soil. For the sediment compartment, no direct emissions are considered.If half-lives in the different compartments are known, the values should be entered manually. Otherwise, EPIWIN software BIOWIN (Biowin 3 – Ultimate Biodegradation Timeframe) and AOPWIN are used to make these estimations by default. If a chemical is susceptible to abiotic hydrolysis, HYDROWIN may be able to provide the half-life.If a combination of hydrolysis, photolysis and biodegradation is likely for the compound, the half-lives shall be converted to rate constants and added together. The resulting overall half-life should be entered into the modelling.The output of Biowin 3 cannot be used directly by the Level III mass balance model. The mean value is converted to a half-life using a set of conversion factors, which consider that 6 half-lives constitute complete degradation with first-order kinetics.

Ultimate biodegradation is generally slower under anaerobic conditions than under aerobic conditions. The program concerns aerobic conditions; only for sediment an anaerobic environment is assumed. The rate of ultimate degradation in sediment is on average one-ninth (1/9) of that in the water column.A further adjustment is taken into account: In general, the biodegradation rate in soil is, on average, one-half (1/2) that in water. Therefore, a half-life in soil twice that estimated for water is assigned.The default environmental emission rates are 1000 kg/h to air, water and soil (sediment: 0 kg/h), which may be altered manually.The advection lifetimes of the substance in air, water and sediment compartments are set to the default values of 100, 1000 and 50000 hours, respectively. These lifetimes are used to determine the advective flow rate (m³/h). If no advection to any compartment is expected, the lifetime should be set to some arbitrarily large value (such as 1E20); this effectively changes the advective flow rate to zero.A soil Koc value is also required for the fugacity model. By default, the connectivity-based adsorption coefficient is used (MCI result by KOCWIN).

For the four compartments, i.e. air, water, soil and sediment, the following mass amounts are predicted: 0.0031 %, 0.629 %, 99.4 % and 3.04E-10 %, respectively. The half-life of the test substance in air will be 4.42 h and 100,000 h in the water, sediment and soil compartment. The overall persistence time gives a measure of how long the chemical remains in the model environment and is estimated as 54,300 h (ca. 6.2 years) for the test substance.