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Abstract
Two model compounds, representing the main classes of iso‐branching present in commercial LAS, have been synthesized, namely the sodium salt of the 2‐phenyl, 5‐methyl undecane sulphonic acid (iso‐LAS I) and 6‐phenyl, 6‐methyl undecane sulphonic acid (iso‐LAS II).
The biodegradability of iso‐LAS I and iso‐LAS II was determined in the OECD 301 E screening test and the OECD 303 A continuous activated sludge (CAS) test. Linear C12 LAS was included in these test as a control.
Primary and ultimate biodegradation were measured by applying specific HPLC analyses to the determination of the residual intact material and biodegradation intermediates, the sulphophenyl carboxylates (SPC).
Complete primary biodegradation of iso‐LAS I and iso‐LAS II was observed; in the CAS test their ultimate biodegradation reached 75 to 90% as compared to a value of 99% observed for C12 LAS.
The predominate SPC intermediates, SPC I and SPC II, were derived from the biodegradation of iso‐LAS I and iso‐LAS II, respectively. Their structures were determined by NMR. SPC I is a diastereoisomer mixture at the same 50: 50 ratio as that of iso‐LAS I.
These results demonstrate that the iso‐branching components of commercial LAS should be efficiently removed and extensively mineralized, as LAS itself, in biological sewage treatment plants.
