LINEAR ALKYLBENZENE SULFONATE (LAS) - UNEP Chemicals

OECD SIDS LINEAR ALKYLBENZENE SULFONATE (LAS)
Remarks: LAS concentrations in raw sewage ranged from 4.0 to 15.1 mg/L. Only low
concentrations of LAS were discharged to the receiving waters. The range of
mean effluent concentrations was 0.009-0.140 mg/L. The mean
concentration of LAS in river sediments below effluent discharges ranged
from 0.49-5.3 µg/g. Below treatment plants, LAS levels in sediments were
very similar (and sometimes lower) than levels above treatment plants.
Based on these observations, the authors suggest that LAS is bioeliminated in
river sediments. LAS levels in digested sludge from Spain and Italy ranged
from 6.0 to 9.4 g/kg dry weight. Differences in the main operating
characteristics at the five sites (e.g., treatment type, plant size, sludge
retention time, hydraulic retention time, temperature) were not found to
greatly influence the removal of LAS.
Reference: Waters, J. and Feijtel, T.C.J. 1995. AIS/CESIO Environmental Surfactant
monitoring programme: Outcome of five national pilot studies on linear
alkylbenzene sulphonate (LAS). Chemosphere 30:1939-1956.
Reliability: 2 Valid with restrictions
(k)
Type of Measurement: Background [ ]; At contaminated site [ ]; Other [X] Red Beck, a small
Yorkshire stream
Medium: Sewage treatment effluents
Results: The results show an LAS concentration, corrected for dilution, of 0.07
mg/L (uncorrected 0.033 mg/L) at Sunny Bank (the furthest downstream
station, approximately 4.8 km from the out fall) after 6 hours of travel time.
The calculated half-life was in the 2-3 h range, indicating kinetics faster
than that of laboratory biodegradation studies in river waters.
Method: LAS and water quality parameters have been measured at seven sites
downstream of the effluent discharge point of a trickling filter treatment plant
(Shibden Head Sewage Treatment Works, Yorkshire, UK). This study was
carried out specifically to measure in-stream removal kinetics of LAS.
Time of travel was measured by detection of a fluorescent dye (Rhodamine
WT) added to the effluent. Increase in flow as the river proceeds through
the catchment was determined by flow measurements and boron dilution
rate. Nine sampling stations were selected. The study began with the
injection of Rhodamine WT dye to the final effluent. The concentration
profile of the dye pulse was established from plots of fluorescence intensity
versus time, which allowed the measurement of LAS concentration in the
same stream volumes of water as the flow moved downstream. LAS
concentrations were corrected for increased flow of the stream (and dilution
of LAS) by inputs from side streams. Water samples were collected using
automatic samples (time proportional or time proportional centroid
composites) and/or grab samples and analyzed for water quality parameters
and LAS. Boron was used as a reference substance for measuring the
increasing stream flow as boron is highly soluble in water and nondegradable.
LAS was analyzed as per the method of Holt et al. 1995.
Briefly, LAS was extracted from the samples by solid phase extraction on
C18 cartridges, eluted with methanol, evaporated under nitrogen to dryness,
reconstituted in 1 mL methanol, and analyzed by reverse phase HPLC on a
C18 column with fluorescence detection.
Remarks: The study indicates that an LAS removal half-life of 2-3 hours will be
appropriate for small shallow streams, which have an LAS concentration
between 50-250 µg/L, for use in the GREAT-ER model calibration
exercise.
Reference: Fox, K., Holt, M., Daniel, M., Buckland, H., and Guymer, I. 2000. Removal
of linear alkylbenzene sulfonate from a small Yorkshire stream. Contribution
to GREAT-ER project #7. Sci. Total Environ. 251:265-275.
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