Fate of Linear alkylbenzenes released to the coastal environment near Boston Harbor

Linear alkylbenzenes (LABs) were used to assess the fates of hydrophobic or ganic compounds (HOCs) released to a large urban harbor and the adjoining o ffshore waters. We found that particulate concentrations of the individual C-12 LAB isomers in 1996 summertime surface waters decreased from 1 pM in B oston Harbor to 20-200 fM in coastal Massachusetts and Cape Cod Bays. Level s fell to only a,few fM in offshore Gulf of Maine locations. These observat ions were consistent with municipal wastewater in Boston Harbor as the pred ominant input followed by dispersal via known circulation patterns in this region. Phase-dependent removal rate coefficients for flushing, verticals s cavenging, volatilization, photodegradation, and biodegradation of individu al LAB isomers were constrained from literature,field observations, and lab oratory experiments and combined with estimates of wastewater release rates into a predictive 3-box model. Vertical scavenging, biodegradation, 'and f lushing were predicted to be the most important fate processes for C12 LABs in the Boston Harbor-MA Bay-Cape Cod Bay flow system with about 1% of the harbor releases "surviving" passage. For HOCs such as the relatively bio-re calcitrant LAB, 6-phenyldodecane, it appears that we are at present able to predict the coastal fate of harbor-introduced HOCs in this system within a factor of 2. Contrary to expectations from biodegradation experiments, the ratio of internal-to-external (I/E) LAB isomers decreased offshore in both water and sediment samples, suggesting we are "missing" an important proce ss affecting LAB fates.