Biocide partitioning

The degree of partitioning is dependant upon the solubility of the biocide in each of the phases and is effected by the type of fuel, extent of mixing, contact time and the fuel to water ratio (Williams et al., 1992). The partition coefficient (K) of a substance is a measure of the relative solubility of a substance between two immiscible liquid phases. It can describe the affinity of the biocide for one phase over the other. For a fuel/water system  

A biocide with a high partition coefficient favors the fuel phase over the water phase. Under these circumstances, higher biocide concentrations would be required to treat a system with a high fuel to water ratio of 1,000 1, to insure that adequate active ingredient levels reach the water phase to effectively kill the microorganisms (Dorris and Pitcher, 1988). With a low partition coefficient, the biocide would favor the water phase over the fuel phase. This biocide would be effective at low doses in treating a system with a high fuel to water ratio, because so much of the biocide partitions into the water phase (Dorris and Pitcher, 1988). 

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The extent of ecotoxicity data requirements is, to some extent, covered by the exposure and fate and behaviour of the active substance and/or substance of concern. This can be seen in the data requirements table, where extensive data are required for biocidal products that have widespread environmental exposure. Fate and behaviour studies will identify the environmental compartment of concern, e.g. if a substance partitions strongly into sediment from the water column. 

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