Polyhalogenated Carbazoles in Sediments of Lower Laurentian Great Lakes and Regional Perspectives

This work continued investigations of polyhalo-genated carbazoles (PHCZs) in sediments of the Laurentian Great Lakes. A total of 77 Ponar grab samples plus approximately 300 segments from 12 sediment cores from Lakes Erie and Ontario were analyzed for carbazole (CZ) and 26 PHCZs. CZ is widespread in sediments of all five Great Lakes, particularly in Lake Erie where it has accumulated >100 tonnes, which is similar to that of total polychlorinated biphenyls. Among the 26 PHCZs, 3-bromo-(3-BCZ) and 3-chloro-(3-CCZ) carbazoles exhibited the greatest mass loads in Lakes Ontario and Erie, although their stratigraphic sediment records suggest peaking of input occurred before 1980 and are now decreasing. Of emerging concern are several dibromocarbazoles, which exhibit rapid increases in net fluxes to sediment since the 1980s. Accumulation of PHCZs that are considered to be of natural origin decreases in an eastward and southward transect across the region, opposite to the trend for those that are predominantly of human activity related origin. The dependences on water depth and sediment organic matter content differ among PHCZs and their categories. Results presented here demonstrate the inter-related influences of natural processes and human activities on occurrences, fates, and dispositions of PHCZs and likely other organohalogens in the Great Lakes.

Automated summary

This study investigated polyhalogenated carbazoles (PHCZs) in sediments of the Laurentian Great Lakes. The results showed that CZs were widely present in the sediments, with 3-bromo-carbazoles and 3-chloro-carbazoles being the most abundant. Since the 1980s, the concentrations of some dibromocarbazoles have rapidly increased, while PHCZs of natural origin have decreased in the eastern and southern regions.