Benzenesulfonic acid, mono-C11-13-branched alkyl derivs., sodium salts

Toxicity to terrestrial plants

Description of key information

Studies on terrestrial plants using the analog substance linear alkyl benzene sulfonates (LAS) were used to develop the soil PNEC.  The key study reported a 21-day NOEC for seed emergence in three species of 100 mg/kg a.i.  14-day EC50 values ranged from 90 to 204 mg/kg soil dw.

Key value for chemical safety assessment

Short-term EC50 or LC50 for terrestrial plants:

90 mg/kg soil dw

Additional information

No specific studies on sodium salt brached alkylate derivatives (BABS Na salt) were available. However, a series of studies are available on analogue linear alkyl benzene sulfonates (LAS). The LAS structure is a C10 to C12 linear alkyl chain with a para-substituted benzene sulfonic acid sodium salt group attached at any of the secondary alkyl chain carbon positions. The alkyl chain length averages 11.6. LAS is stucturally similar to BABS Na salt, as both are para C11 -C13 alkylbenzene sulfate sodium salts). The primary difference is whether the alkyl chain is linear or branched.

Based on well accepted principles of modeling (D.W. Roberts, Sci. Total Environ. 109/110: 557-68, 1991), linear structures are more toxic than branched structures of the same carbon chain number. This principle is supported by the results of acute toxicity studies of fish and algae, including five direct comparison of activities while a single daphnia toxicity study is an exception to this pattern. Based on structural similarities, accepted principles of modeling and the weight of evidence from acute toxicity testing, LAS is a good analogue for read-accross for instances where data are available on it but not on BABS Na salt.

In the first study with LAS, the toxicity to three species of plant, sunflower, sorghum, and mung bean, was determined. Seeds of these three species were grown in soil containing concentrations of the test ingredient of 0, 1, 10, 100, 1000 mg/kg active ingredient in dry soil. The emergence and growth of seedlings was monitored for 21 days. There was a decrease in emergence of all three species at the highest concentration, with some shoots barely emerging, and stunted and dying. The NOEC for all three species is 100 mg/kg a.i. The 21 -day EC50 for sunflower was 289 mg/kg a.i, for sorghum it was 167 mg/kg a.i., and for mung bean it was 316 mg/kg a.i. In the second study, three species of crop plant B. rapa, A. sativa, and S. alba, were grown in soil containing concentrations of LAS that varied from 0 -10,000 mg/kg dw soil. The seedlings were grown for 14 days, and then weighed and compared to weights of controls plants. All three species showed a dose-related reduction in growth. The EC10 for B. rapa was 86 mg/kg dw soil, for A. sativa it was 80 mg/kg dw soil, and for S. alba it was 200 mg/kg dw soil.  In a third study, plants from seven different species were exposed to concentrations of 0, 1, 10, 100, and 1000 mg/kg dw of LAS for 14 days, after which their weights were determined. The following EC50s were found: Malva pusilla 204 mg/kg dw, Solanum nigrum 169 mg/kg dw, Chenopodium album 164 mg/kg dw, Amaranthus retroflexus 142 mg/kg dw, Nigella arvensis 133 mg/kg dw, Galinsoga parviflora 90 mg/kg dw, and Brassica rapa 164 mg/kg dw. Also, the following EC10s were found: Malva pusilla 110 mg/kg dw, Solanum nigrum 120 mg/kg dw, Chenopodium album 120 mg/kg dw, Amaranthus retroflexus 110 mg/kg dw, Nigella arvensis 52 mg/kg dw, Galinsoga parviflora 55 mg/kg dw, and Brassica rapa 86 mg/kg dw.