Linear alkylbenzenes (LABs) and linear alkylbenzenesulfonates (LAS) were measured in river and coastal (bay) sediments in Tokyo metropolitan area. LABs are widely distributed in the sediments with concentrations of a few µ g/g-dry sediments. LAS contents in sediments are extremely low in Tokyo Bay (~ 0.01µg/g) as compared with those in the rivers (hundreds µg/g). This fact indicates the higher persistency of LABs in the riverine and coastal sediments.

The progressive relative depletion of external isomers (in which the phenyl group is attached near to the end of the alkyl chain) was observed on going from the source (i.e. LABs in commercial LAS-detergents) to Tokyo Bay sediments. An incubation experiment substantiated that the isomeric change of LABs is caused by selective microbial degradation. The I/E ratio (ratio of [6-C12 AB + 5-C12 AB] relative to [4-C12 AB + 3-C12 AB + 2-C12]; n-Cm : n indicates the position of substitution of phenyl group to alkyl chain and m indicates the number of carbons in the alkyl chain) was proposed as an index of LAB degradation. I/E ratio of LABs in Tokyo Bay sediments indicates the degree of degradation of LABs to be 50 % at most.

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