Bioconcentration and Metabolism of Linear Alkylbenzene Sulfonate by Daphnids and Fathead Minnows

Abstract

The bioconcentration potential of the anionic surfactant linear alkylbenzene sulfonate (LAS) was studied using daphnids (Daphnia magna) and fathead minnows (Pimephales promelas) in studies extending up to 50 days. Uptake in the test organisms, as measured by 14C activity, was a function of chain length and exposure concentration. In whole organisms, the dry weight bioconcentration factors (BCF) were 500 to 4000 for daphnids and 200 to 2000 for fathead minnows. In fish tissues, the greatest 14C activity occurred in the gall bladder, the BCFs ranging from 20 000 to 70 000, while the least occurred in the muscle, the BCFs remaining in the range of 100 to 400. In depuration studies, greater than 85 percent of the 14C content was cleared from all tissues within three to four days, with nearly 100 percent clearance within ten days. The results of desulfonation/gas chromatography analyses of tissues suggested that the fathead minnows metabolised LAS, and the daphnids did not. Substantial portions of the 14C content in the tissues of fathead minnows were not present as LAS, but presumably were present as metabolites (30 to 50 percent in muscle tissue, and 97 percent or more in the case of the gall bladder). A comparison of the uptake of 14C from tagged LAS with that from tagged taurocholic acid (TCA), a naturally occurring bile surfactant, gave somewhat contrasting uptake patterns in fathead minnows. The 14C-LAS activity reached a steady state in tissues within three days, while the 14C-TCA activity continued to accumulate in tissues throughout the exposure period. It can be concluded from these LAS and TCA bioconcentration studies that surfactant materials may, in general, show similar patterns of uptake, site of deposition, metabolism, and depuration. From the present studies and from previously reported toxicity and microbial biodegradation studies, it can be further concluded that under environmental conditions there is little likelihood that LAS bioconcentration creates a hazard to aquatic ecosystems.