Molecular and isotopic characterization of polycyclic aromatic hydrocarbon distribution and sources at the international segment of the St. Lawrence River

This paper documents the molecular and compound-specific carbon isotope composition of polycyclic aromatic hydrocarbons (PAH) in St. Lawrence River sediments from the outflow of Lake Ontario (Kingston, ON) to the Massena area (NY). The sediment inventory of PAH is characterized by the dominance of 4 to 6 ring parent compounds, with the PAH ranging from 0.8 to 6700 μg/g. The high abundance of high molecular weight parent compounds, high parent/alkylated PAH ratios and ¹³C-enriched values recorded for individual PAH are consistent with a dominant combustion PAH source for the sediments upstream of the Massena area, but areas receiving higher petroleum contributions were also identified (e.g., Prescott-Ogdensburg, Cornwall). PAH contribution from aluminum smelting operations in the Massena area is pronounced in the southern bank of the St. Lawrence River, where sediment samples display the highest ΣPAH and higher ¹³C values for three ring PAH than for sediments immediately upstream. Thus, sediments at the international segment of the St. Lawrence River show localized enrichments in petroleum-related and aluminum smelter contributions against the regional backdrop of combustion-dominated PAH sources in sediments.