Wash-off and sorptive behaviors of two benzothiazolamines(BTs) [i.e., 2-(4-morpholinyl)benzothiazole (24MoBT) and
N-cyclohexyl-2-benzothiazolamine (NCBA)] have beeninvestigated as possible molecular markers for tire debris and/or road dust transported in highway runoff water. Sumof dissolved and particulate 24MoBT and NCBA concentrations in runoff water ranged from 15 to 417ng/L and from22 to 508ng/L, respectively. Proportions of NCBA in particulate(>0.7
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m) phase (<9-79%) were larger than that of24MoBT (<1-14%), which was consistent with theirexperimentally determined octanol/water partition coefficients(
Kow; 10
4.23±0.14 for NCBA; 10
2.42±0.03 for 24MoBT). Theorganic carbon-normalized in-situ partition coefficient(
Koc') observed in runoff events (10
4.69±0.28 for NCBA; 10
3.42±0.23for 24MoBT) were 1 order of magnitude higher thanthose expected from their
Kow, indicating strong affinity ofBTs to suspended particulate matter (SPM) in runoffwater. Furthermore, in desorption experiments lasting 24h, we observed almost the same levels of
Koc' as those inrunoff events, implying that significant fractions of BTsare strongly associated with runoff particles and not easilyavailable to equilibrium partitioning. NCBA was ubiquitousin sediments from the Nogawa River receiving runofffrom the Chuo Highway, whereas many of those sampleshad undetectable levels of 24MoBT. All of above resultsindicate that NCBA would be more suitable than 24MoBTas a molecular marker for runoff particles loading theaquatic environment. By using SPM-weighted meanconcentration of particulate NCBA, at least 3.3 ± 1.6% ofthe mass in the Nogawa sediments is estimated to befrom runoff SPM.