Benzothiazolamines as tire-derived molecular markers: Sorptive behavior in street runoff and application to source apportioning

Wash-off and sorptive behaviors of two benzothiazolamines (BTs) [i.e., 2-(4-morpholinyl)benzothiazole (24MoBT) and N- cyclohexyl-2-benzothiazolamine (NCBA)] have been investigated as possible molecular markers for tire debris and/ or road dust transported in highway runoff water. Sum of dissolved and particulate 24MoBT and NCBA concentrations in runoff water ranged from 15 to 417ng/L and from 22 to 508ng/L, respectively. Proportions of NCBA in particulate (>0.7 mum) phase (<9-79%) were larger than that of 24MoBT (<1-14%), which was consistent with their experimentally determined octanol/water partition coefficients (K-ow; 10(4.23) (+/- 0.14) for NCBA; 10(2.42+/-0.03) for 24MoBT). The organic carbon-normalized in-situ partition coefficient (K-oc') observed in runoff events (10(4.69) (+/- 0.28) for NCBA; 10(3.42 +/-0.23) for 24MoBT) were 1 order of magnitude higher than those expected from their K-ow, indicating strong affinity of BTs to suspended particulate matter (SPM) in runoff water. Furthermore, in desorption experiments lasting 24 h, we observed almost the same levels of K-oc' as those in runoff events, implying that significant fractions of BTs are strongly associated with runoff particles and not easily available to equilibrium partitioning. NCBA was ubiquitous in sediments from the Nogawa River receiving runoff from the Chuo Highway, whereas many of those samples had undetectable levels of 24MoBT. All of above results indicate that NCBA would be more suitable than 24MoBT as a molecular marker for runoff particles loading the aquatic environment. By using SPM-weighted mean concentration of particulate NCBA, at least 3.3 +/- 1.6% of the mass in the Nogawa sediments is estimated to be from runoff SPM.