A Surfactant Biodegradability

Surfactants are performance chemicals that is, they are used to perform a particular function in some process or product, in contrast to other organic chemicals that may be used to produce another chemical or product. Since they are used in products or processes that impact on the environment, there are concerns regarding their effect, particularly their biodegradability in the environment and their toxicity to marine organisms. 

In isomeric alkylbenzene and alkylphenol derivatives, degradation decreases as the phenyl group is moved from a position near the terminal end of a linear alkyl group to a more central position. 

In POE nonionics, biodegradation is retarded by an increase in the number of oxyethylene groups. The inclusion of oxypropylene or oxybutylene groups in the molecule tends to retard biodegradation. Secondary ethoxylates degrade more slowly than primary ethoxylates even when both have linear hydrophobic groups. 

The toxicity of surfactants to marine organisms and their concentration in them depends upon their tendency to adsorb onto them and their ability to penetrate their cell membranes (Rosen, 1999). The parameter AG0ad/a, where AG°a(j is the standard free energy of adsorption of the surfactant at the aqueous solution-air interface (Chapter 2, Section IIIF) and am is the minimum cross-sectional area of the surfactant at that interface (Chapter 2, Section IIIB), was found to correlate well for several anionic and nonionic surfactants with rotifer toxicity. The same parameter was found to correlate well for a series of cationic surfactants with rotifer and green algae toxicity and, for a series of linear alkylbenzenesulfonates, with bioconcentration in fish (Rosen, 2001). 

toxicity increases with an increase in the length of the hydrophobic group and, for isomeric materials, decreases with branching or movement of the phenyl group to a more central position in the linear alkyl chain in linear POE alcohols, toxicity increases with decrease in the number of oxyethylene units in the molecule, all due to the expected changes in the values of both AG°a(j and of am. 

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