LINEAR ALKYLBENZENE SULFONATE (LAS) - UNEP Chemicals

OECD SIDS LINEAR ALKYLBENZENE SULFONATE (LAS)
Total discharge to the environment (kg/yr) 1,444,000
Discharge to the air --
Discharge to water 144,000
Discharge to soil 1,296,000
Total input in the region (kg/year) 1,440,000
Total input in the region (kg/hour) 164.4
The authors base these input quantities for the ChemCAN model on a recent
estimate of LAS annual production in North America, western Europe and
Japan as approximately 1.4 million tons and an annual per capita
consumption of LAS in the United States of 1.3 kg/year. LAS is disposed
“down-the-drain” and approximately 98% is removed in sewage treatment.
About 30% of the LAS is removed in treatment by adsorption onto primary
and secondary sewage solids. Over 60% of the sludge was assumed to be
disposed of in landfills or applied to agricultural soils, thus there is the
potential for LAS to reach the soil environment. Therefore, the level III
model assumes a substantial discharge (90%) of LAS to soil following
sewage treatment. Inputs considered the specific nature of nonvolatile
surfactants such as LAS. For example, the use of Kow as a descriptor for
organic phase-water partitioning is inappropriate for LAS and there is no
need for a vapor pressure or air-water partition coefficient. Because LAS is a
mixture, average properties were used as inputs to the models. In the EQC
model, LAS is treated using the equivalence approach as the equilibrium
criterion.
Results: The level I and II models each resulted in LAS partitioning to air, water, soil,
and sediment at percentages of 0%, 25.97%, 56.09%, and 17.76%,
respectively. The overall residence time of LAS is 100 hours and removal is
primarily by biodegradation in water (76%) and partitioning in sediment
(13%). Thus, the impacts of LAS will be restricted to local receiving waters
and their sediments and biota. In level III, when discharges are directly to
water, the residence time is 33 hours and more than 99% remains in the
water, though in shallower receiving waters more partitioning to sediments
might be expected. When the discharge is to soil, as was assumed in the
ChemCAN model, the residence time is 28 days because of the slower
biodegradation rate and little transfers to other media. Based on these
findings, the dominant fate processes are degradation rates in water and soil,
and water-sediment transfer.
Using the ChemCAN 4 model, of the total amount of LAS released to the
environment assuming the discharge rates above, the distribution and
concentrations were predicted to be:
to air: 0% (0 mg/m 3 )
dissolved in water: 0.64% (0.44 µg/m 3 )
in soil: 99.35% (7.06 µg/kg)
in sediment: 0.0036% (0.00347 µg/kg)
Remarks: Based on an estimated total discharge to the environment of 1.44 x 10 6
kg/year (1.44 x 10 5 kg to water and 1.296 x 10 6 kg to soil). It should be
noted that the discharge assumptions used by the authors are highly
conservative and likely overpredict the amount of LAS entering various
compartments, for example, the soil compartment. This study was
conducted by the model developer and acknowledged expert on fugucity to
demonstrate that the approach was appropriate for different types of
chemicals.
UNEP PUBLICATIONS 153