Benzenesulfonic acid, 4-C10-13-sec-alkyl derivs.

Endpoint summary

Description of key information

In the key study (Tolls et al 1997), the bioaccumulation potential of a series of LAS homologues and isomers were evaluated in flow-through studies with fathead minnows (Pimephales promelas) according to OECD 305E guidelines. Individual homologues were tested for up to 192 hours for the uptake phase, followed by a depuration phase in which fish were transferred to unspiked water. The resulting BCFs ranged from 2 L/kg (6-phenyl-C₁₀LAS) to almost 1000 L/kg (2-phenyl-C₁₃LAS), with BCFs generally increasing with increasing alkyl chain length for a given isomer.

In addition, Tolls et al. (1997, 2000) demonstrated the closer the p-sulfophenyl moiety is positioned to the terminal carbon of the alkyl chain, the higher the BCF. However, alkyl chain length has a much bigger effect than does the phenyl position. The results show that the bioconcentration potential of LAS is low. Tolls et al. (2000) demonstrated that biotransformation of LAS occurs as a sequence of reactions, with the first step yielding the corresponding alcohol followed by two additional biotransformations to yield p-sulfophenyl-lauric acid and oxidative chain shortening. Dyer et al. (2008) confirmed this with the additional conclusion that biotransformation was mainly due to Phase-I enzymes and that efflux pumps play a critical role in loss from cells. LAS metabolites were eliminated in bile and urine suggesting activities of Phase-II enzymes. Cowan-Ellsberry et al. (2008) developed an effective physiologically constructed BCF model based partly on in vitro biotransformation studies of LAS and showed that the corresponding in vivo BCF estimates were replicated when biotransformation was included.

In a supporting study, the bioconcentration of LAS in the marine shrimp Palaemonetes varians was measured in a radiotracer study. Shrimp in seawater were exposed to radiolabelled [14C]C12-6-LAS at a concentration of 4 µg LAS/L for 7 days. Seawater and radiotracer were renewed daily. At 0.4, 1, 2, 3, 4, and 7 days, 3 shrimp were collected, dried, weighed and ground in methanol. Water was evaporated, and then acidified with 1% formic acid. Ten mL scintillation cocktail was added and radioactivity measured with a liquid scintillation counter. 100% of activity was assumed to be due to the spiked test substance, and corrected for counting efficiency, physical radioactive decay, and quenching effects. Autoradiography was performed on two shrimp after the exposure period. The test animals were embedded in 2.5% carboxymethylcellulose gel, then flash-frozen in dry ice and hexane. Twenty µm sections were cut, freeze-dried, and placed on phosphorus screens for 4 -7 days. The screens were then scanned with a Cyclone Phosphor Imager, and the radioactivity distribution in the tissue was identified. After the exposure period, remaining shrimp were transferred to a new aquarium. Three shrimp were sampled at 1, 2, 3, 4, and 8 days for the depuration phase. Individual BCF values were plotted against specific shrimp weight after 9, 48, and 96 hrs, and 7 days. A first order saturation exponential modeled was used. Sorption of the test substance to the test vessel wall was negligible. Depuration kinetics were described using a one component exponential model. Body residue in shrimp was 0.64 ug/g wet weight. This is at least 40 times below the critical body burden for acute or chronic exposure. The BCF55 for shrimp was calculated to be 159 L/kg. A DT50 of 14 hrs was calculated, and only 1% of the body burden of the test substance remained in the shrimp after 8 days.

Additional information

The bioaccumulation potential of LAB Sulfonic Acid has been evaluated and found to be low based on aquatic data on LAS (read across) in fish. BCF values ranged from between 2 and < 1000 L/kg, with a BCF value of 99 for the 2-phenyl isomer of the C12 homologue. In vitro studies demonstrate that low bioaccumulation is due to rapid biotransformation. BCF values for mixtures can be calculated based on the weight fraction of each homologue. The calculated BCF was 87 L/kg for a standard mixture typical of LAS in European detergent formulations (average alkyl chain length = 11.6). The calculated BCF value was 22 L/kg for a representative environmental sample (filtered Mississippi river water, average alkyl chain length = C10.8), demonstrating that BCF is decreased by environmental processes such as biodegradation and absorption, which reduce aquatic concentrations.