LINEAR ALKYLBENZENE SULFONATE (LAS) - UNEP Chemicals

OECD SIDS LINEAR ALKYLBENZENE SULFONATE (LAS)
Toxicity to Microorganisms
Three LAS mixtures (average chain lengths of C11, C11.6 and C13) and five pure homologues
were used to evaluate inhibition to activated sludge using OECD Guideline 209 (Verge and Moreno
1996b, dossier section 4.4a,b). Results showed EC50 values of 760, 550 and 650 mg/L for the C11,
C11.6, and C13 commercial materials, respectively, and 1042-1200, 740-782, 500-723, 700-795,
and 900-1045 mg/L for the C10, C11, C12, C13, and C14 pure homologues, respectively. In all of
these studies, an extended contact time of 3 hours (instead of the standard 15 minutes) was used to
better simulate the normal residence time in wastewater treatment plants. An older study using the
standard 15-minute exposure reported EC50 values of 107-152 mg/L for a commercial LAS sample
(dossier 4.4c; reliability not assignable). Studies with C11.6/C11.8 LAS and the bacterium
Pseudomonas putida reported EC50 values of 350 mg/L (30-min. exposure, dossier 4.4e), 150 mg/L
(16-hr exposure, dossier 4.4f) and 60.9-63.5 mg/L (18-hr. exposure, dossier 4.4d) and
EC0/EC10/NOEC values of 64 and 250 mg/L (30 min. exposures, dossier 4.4e,g), 30 and 50 mg/L
(16-hr. exposure, dossier 4.4f,h) and 52.7-56.6 (18-hr. exposure, dossier 4.4d). While there is
variability in the values, the data are consistent in showing LAS toxicity to activated sludge or a
bacterium only at LAS concentrations considerably above those observed in the aquatic
environment.
Normal operation of an activated sludge digester was observed even in the presence of high and
atypical concentrations of LAS (30 g/kg dry matter) in anaerobic sludge indicating that the
microbial population present was not inhibited (Berna et al., 1989, dossier 4.4i). The treatment
plant operational records were not directly available for review, so these conclusions are based on
the evaluation of Berna et al. (1989). Sanz et al. (1999, dossier 3.5p) determined that
concentrations of LAS usually found in anaerobic digesters are an order of magnitude lower than
concentrations that may be inhibitory to anaerobic microbial populations (40-150 mg C11.54
LAS/L). Based on the sludge partition coefficient for C11.6 LAS (dossier 3.3.1a) of 2500 L/kg,
aqueous phase concentrations inhibitory to anaerobic microbial populations (40-150 mg/L) would
require LAS levels in sludge of 100-375 g/kg, fully supportive of the results of Berna et al (1989)
above showing no inhibition of anaerobic microbial populations in activated sludge digesters at
LAS concentrations of 30 g/kg dw sludge.
Sediment Toxicity Test Results
Several studies have investigated the toxicity to organisms exposed to LAS in the sediment, as
summarized in Table 14. Midge larvae (Chironomus riparius) were exposed for 24 days to natural
stream sediment spiked with commercial LAS with an average alkyl chain length C11.8 (Pittinger et
al. 1989). The resultant LOEC was 993 mg/kg and the NOEC 319 mg/kg, based on emergence
success. A fresh water bivalve mollusk, Anodonta cygnea, was exposed to commercial LAS sorbed
to natural pond sediment by repeated additions for 80 days (Bressan et al. 1989). All animals
survived and were actively filter-feeding at sediment concentrations measured to be 750 mg/kg at
the beginning of the test and 200 mg/kg at the end of the test. Similarly, a tubificid, Branchiura
sowerbyi, was exposed for 220 days to sediment spiked with an undefined LAS (Casellato et al.
1992). No effects were observed at mean measured concentrations that were initially 26 mg/kg and
decreased to 7.18 mg/kg by the end of the study. While the absence of reported toxicity is
reassuring, it appears that the range of exposure concentrations was too low to derive a useful
NOEC value. In addition, the reliability of the study could not be assessed so it is not included in
Table 14. According to Marin et al. (1994), no effects were observed in the marine mussel, M.
galloprovinciallis, at 132 mg/kg (initial measured concentration) of C11.6 LAS. The LAS
concentration decreased by 90% by the end of the exposure to 7.85 mg/kg, which is the value
reported as the NOEC in Table 14. Most recently, GLP studies have been conducted with
Lumbriculus variegates (an oligochaete worm) and Caenorhabditis elegans (a nematode worm) to
finalize the effects assessment of sediment associated C11.4 LAS (Comber et al. 2004). After 28
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