Tracing sewage pollution using linear alkylbenzenes (LABs) in surface sediments at the south end of the Southern California Bight.

Distribution and isomeric composition of LABs in surface marine sediments were evaluated at the southern end of the southern California Bight. LABs are used as tracers of wastewater discharges. The area studied extends from the Mexico-USA border to the Todos Santos Bay, Baja California in the south. The area was partitioned into a northern, central and a southern stratum. GC-MS was used for the analysis of LABs concentration. The average value of total LABs concentration was 17.4, 32.0 and 24.9 ng/g for the north, central and southern strata, respectively. LABs were not correlated with either sediments grain size (%<63 microm) or sediment organic carbon contents. The highest concentrations values of LABs were found in the northern and central strata near the 200 m isobath. Based on the I/E index, the estimated average percentage degradation was 21.3, 15.9, and 8.4% for the northern, central and southern strata respectively. Based on the isomeric composition of LABs, the largest degradation value was found in the northern stations. Internal isomers did not show significant enrichment, however, short-chained isomers (LAB(10), LAB(11)) showed enrichment. It was found that 67 out of the 68 stations measured had concentrations above detection limits. This suggests extensive contact of wastewater discharges with marine sediments in the area. An estimate of the amount of LABs per year based on detergent consumption per capita is provided.