Long-Chain Alkylbenzenes: Their Analytical Chemistry, Environmental Occurrence and Fate

Abstract

Since ca. 1950 long-chain alkylbenzenes have been produced industrially for the synthesis of alkylbenzenesulfonates, the anionic surfactants most commonly used in commercial detergents. Prior to 1965 the alkylbenzenes were generated by Frieldel-Crafts alkylation of benzene with tetrapropylene. This reaction produces a complex assemblage of phenylalkanes (TABs) having highly branched side chains. Due to their stability, the TABs proved to be environmentally troublesome and were ultimately replaced (during the mid-1960s) by the linear alkylbenzenes (LABs). The LABs consist of a mixture of secondary phenylalkanes with linear alkyl side chains ranging in length from C₁₀ to C₁₄. Because of their unique structures and composition, these compounds are easily identified and measured in complex environmental samples. The linear alkylbenzenes are also found in municipal wastewaters where their presence is thought to result from the use of domestic and industrial detergents. Because they are synthetic and unlikely to occur in other significant inputs to coastal marine waters, long-chain alkylbenzenes have obvious potential as waste-specific molecular tracers. The presence of long-chain alkylbenzenes in sediment trap particulates and marine sediments collected near a major waste outfall system in southern California indicates that these hydrocarbons can survive exposure to an oxygenated water column during sedimentation. Whereas changes in the isomer composition of the LABs with depth in the sediments are suggestive of microbial alteration, the vertical distribution of the TABs and LABs can be used as a geochronological tool to reconstruct waste depositional histories.