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Environmental fate & pathways

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Fugacity modelling:

Two models have been used:

The 1997 Level I model implemented as the EQC program.

The 1999 Level III model, available on the Canadian government web site.

Both models use key property data as inputs (molecular weight; melting point, vapour pressure, water solubility, log Kow) and also use degradation half-lives. The purpose of this modelling is to gain an overview of relative exposure, not any absolute values of predicted concentration. In modelling the long chain aliphatic alcohols, some degradation has been allowed for in both the Level I and Level III models. The half-life for degradation in air is estimated using the SRC AOPWIN v1.91 model, which predicts the rate of reaction with hydroxyl radicals in the atmosphere. This is converted into a half-life using the standard EU atmospheric concentration of hydroxyl radicals. The half-lives in soil, sediment and in water are set to 720 hours, i.e. 30 days, for all of the alcohols, to reflect that they are all aerobically biodegradable. Whilst some of the alcohols demonstrably degrade very much faster than this, for the purpose of a comparative study the input value is not critical.

The Level I model results for (Z)-octadec-9 -enol show that upon equal release to the air, water and soil compartments, the majority of substance will partition to soil (98%) with low levels in sediment (2.2%), water (<0.1%) and air (<0.1%).

The Level III model results for (Z)-octadec-9 -enol show that releases originally passing to air will tend to deposit to soil (83%) with some remaining airborne (14%); releases via water will largely be deposited (80%) with some remaining in solution (20%); releases via soil will remain in soil (>99%). Therefore, degradability in each separate compartment is important.

Distribution in wastewater treatment plant

The distribution in a sewage treatment plant has been estimated using the SimpleTreat model (implemented in EUSES v2.1.2), using Koc 354000, Henry's Law constant 6.1 Pa.m3/mol at environmental temperature, and biodegradation rate 100 /h. The outputs are 20% degraded; 76% passing to sludge; <0.1% to air and 3.6% to water.

This may substantially underestimate the degree of biodegradation, which was shown to be >98% for linear alcohols of chain length C12 -18 (Wind et al., 2006).

References:

Wind, T., R.J. Stephenson, C.V. Eadsforth, A. Sherren, R. Toy. (2006) Determination of the fate of alcohol ethoxylate homologues in a laboratory continuous activated sludge unit. Ecotox and Environ Safety, 64: 42-60.

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