LINEAR ALKYLBENZENE SULFONATE (LAS) - UNEP Chemicals

OECD SIDS LINEAR ALKYLBENZENE SULFONATE (LAS)
3.3 TRANSPORT AND DISTRIBUTION BETWEEN ENVIRONMENTAL
COMPARTMENTS INCLUDING ESTIMATED ENVIRONMENTAL
CONCENTRATIONS AND DISTRIBUTION PATHWAYS
3.3.1 TRANSPORT
(a)
Type: partition coefficient
Media: sludge
Method: Monitoring data were collected in a pilot-scale municipal activated sludge
treatment plant. The plant consisted of a completely mixed aeration tank
(490L) and a secondary settler (280L). The plant was operated at C12 LAS
influent concentrations between 2 and 12 mg/L and at sludge retention times
of 10 and 27 days. At least every other day 24-h samples of 2.5L influent
and 2.5L effluent were collected in PE bottles and total (sum of adsorbed and
dissolved) LAS concentrations were determined using an HPLC method
adapted from Feijtel et al. 1995. At least once a day 200 mL grab samples
were taken from the aeration tank and return sludge and transferred into PE
centrifuge tubes for determination of dissolved and absorbed LAS. The
sludge samples were immediately centrifuged for 15 min at 3500 rpm. The
supernatant was transferred into PE bottles and preserved by 3% formalin
and stored for a maximum of 10 days at 4°C until further analysis.
Representative aliquots of pre-settled influent, final effluent, or supernatant
of the centrifuged sludge samples were passed over 6 mL preconditioned C18
SPE columns at a rate not exceeding 10 mL/min. The SPE columns were
washed with 2 mL methanol/water and eluted with 5 mL of methanol. The
eluate was then passed through strong anion exchange (SAX) columns,
washed, eluted and subsequently evaporated to dryness under a gentle flow
of nitrogen gas. The dry residue was dissolved in 2-5 mL of HPLC mobile
phase. The HPLC was operated according to specifications. Identification of
the different LAS alkyl homologues and quantification were made against a
commercial LAS mixture (Marlon A390). A sorption-isotherm and the
kinetics of adsorption and desorption of LAS to activated sludge were
determined in batch experiments. Three different biodegradation tests were
also carried out (an OECD 301F ready biodegradation test; a batch activated
sludge [BAS] test; and a “by-pass” test developed to mimic condition of the
pilot scale activated sludge plant). Only the sorption results are presented
here.
Results: Kp (C12 LAS): 3210 L/kg (log Kp = 3.5)
Kp (commercial C11.6 LAS mixture): 2,500 L/kg (log Kp = 3.4)
Test Substance: C12 LAS
Remarks: Sorption equilibrium was achieved rapidly, within 5-10 minutes. Desorption
was less pronounced, but still reached rapid equilibration. The sludge-water
partition coefficient Kp of 3210 L/kg volatile suspended solids is reported.
Applying the same QSAR for the commercial C11.6 LAS mixture results in a
value of log Kp = 3.4 (i.e., Kp = 2500 L/kg), consistent with Feijtel et al. 1999
(see section 3.3.1(b)). In the other experiments conducted in this study, only
2-8% was present as dissolved C12 LAS, with the remaining 92-98%
adsorbed to the sludge. Despite this high degree of sorption, more than 99%
of the LAS load was removed by biodegradation, showing that the adsorbed
fraction as well as the soluble fraction of LAS is readily available for
biodegradation.
Reference: Temmink, H. and Klapwijk, B. 2004. Fate of LAS in activated sludge plants.
Water Research 38:903-912.
Reliability: 2 Valid with restrictions
UNEP PUBLICATIONS 148