Non-discriminating flash pyrolysis and thermochemolysis of heavily contaminated sediments from the Hamilton Harbor (Canada)

Analytical pyrolysis of sediments contaminated with pollutants of medium to high molecular weights (up to approximately 500 Da) is very challenging when using conventional pyrolysis systems due to discrimination of high molecular weight analytes. In the framework of this contribution, non-discriminating pyrolysis and thermochemolysis using rapid heating in a Silcosteel capillary were applied to study organic pollutants in heavily contaminated sediments taken from the Hamilton Harbor. The novel pyrolysis approach, requiring very small amounts of sample, turned out to be very useful as a rapid screening method, e.g. for risk assessment studies, proving superior to commonly used solvent extraction. Main pollutants in the sediments under study included aromatic hydrocarbons, chiefly originating from coal tar and petroleum. Polycyclic aromatic hydrocarbons (PAHs) beyond six-rings, including coronene and truxene, could be detected. Sequential tetramethyl ammonium hydroxide-induced thermochemolysis performed at 500 and 750 degrees C enabled the differentiation between organic pollutants sorbed onto the sediment matrix on the one hand, and structural moieties of the condensed polymeric humic sediment matrix along with bound residues on the other hand. Thermochemolysis at 500 degrees C removed sorbates quantitatively, leaving only bare polymeric humic matrix. Significant PAH source indicators provided evidence that the lipidic fraction sorbed onto the sediments originated from PAHs formed chiefly in coal combustion processes. The polymeric humic organic matter network of the less polluted sediment was mainly of petrogenic origin, whereas black carbon, kerogen, etc. contributed to the organic carbon of the heavily polluted sediment. Thermochemolysis at 500 degrees C was also used to study fatty acid profiles of the sediments. The fatty acid methyl ester patterns obtained for the two sites under study differed significantly, with strong indications that microbial attenuation of the pollutants at the heavily polluted site 2 was strongly suppressed.