Treatability studies were designed in order to investigate both the fate and impact of canola oil in aquatic environments. As any other edible oil, canola is composed of triacylglycerols (TAGs), namely, esters formed from glycerol by reacting all three of its hydroxy groups with long chain fatty acids (LCFAs). These esterified moieties are mainly palmitic acid (P), 16 full-saturated carbons; stearic acid (S), 18 full-saturated carbons; oleic acid (O), 18 carbons with one unsaturation; linoleic acid (L), 18 carbons with two unsaturations; and linolenic acid (Ln), 18 carbons with three unsaturations. Hence, individual respirometry experiments were conducted with five TAGs, tripalmitin (PPP), tristearin (SSS), triolein (OOO), triolenin (LLL), and trilinolein (LnLnLn). The metabolism of these lipids was monitored with time by measuring oxygen uptake and evolved CO2 as a consequence of the microbial respiration. Additionally, in order to close the carbon mass balance, chemical analysis of the both the aqueous phase and insoluble matter (e.g. suspended solids and colloids) allowed to determine the substrate depletion and identify potential byproducts.The non-polar nature of the saturated TAGs (PPP and SSS) limited their bioavailability by forming solid aggregates that impeded the lipase activity; consequently, no mineralization was observed. On the other hand, bacteria readily degraded the unsaturated acylglycerols (OOO, LLL, and LnLnLn) because these substrates formed well-disperse emulsion that facilitated the enzymatic hydrolysis of the ester bonds. Nevertheless, owing to the unsaturations, fractions of these TAGs experimented autoxidation and subsequent polymerization. This abiotic reaction competed with the biomass for the substrate and restrained the lipid mineralization since the polymers withstood microbial activity. In a second set of experiments, commercially available canola oil along with two synthetic oils (i.e. one prepared with monoacid TAGs and the other composed of free fatty acids and glycerol) were tested. The complete mineralization of the commercial oil was achieved since abiotic processes did not interfere. On the other hand, the synthetic mixtures showed partial removal due to low solubility of the saturated LCFAs and autoxidation of the unsatured ones.
Finally, in all the experiments, toxicity was not detected in aqueous phase whereas EC50 values were measured in the extracts obtained from the insoluble components present in the test media. Such results can be explained on the grounds of both the TAGs hydrophobicity and low polarity, which dramatically minimized the concentration of these compounds within solution.