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Chemical Reaction: Down the Drain
By: Steve Herman
Posted: August 26, 2008, from the October 2007 issue of GCI Magazine.
page 3 of 4
The most widely recognized aspect of environmental fate is biodegradability, and a widely recognized set of biodegradation standards comes from the Organisation for Economic Co-operation and Development (OECD). Biodegradation results are not appropriate for complex mixtures, so each component must be evaluated separately.
Ready biodegradability is defined by EPA2 as “an expression used to describe those substances which, in certain biodegradation test procedures, produce positive results that are unequivocal and which lead to the reasonable assumption that the substance will undergo rapid and ultimate biodegradation in aerobic aquatic environments.” Inherent biodegradability requires 60–70% biodegradation with OECD 302, with the test determined by the properties of the target material such as solubility or volatility.
Boethling3 has proposed methods for designing biodegradability into molecules.
An example of a historic triumph from our industry was the development of linear alkylbenzene sulfonate (LAS). In the 1940s, soap was replaced by alkylbenzene sulfonate surfactants (ABS). Problems were soon noted because of limited biodegradation and foaming problems in treatment plants. The underlying problem was identified as extensive branching in the alkyl chains. Molecular sieves were used to separate linear alkanes from petroleum, and the LAS, with greater than 98% biodegradability, became the standard detergent by the early 1960s.
The first rule of green chemistry is to make safe products at the beginning of development. Some basic generalizations for designing biodegradable chemicals are to incorporate ester linkages and hydroxyl groups and to avoid halogens, quaternary carbons and nitro groups. Boethling also explains the possibilities of using various computer models.