Efficient high molecular weight polycyclic aromatic hydrocarbons removal by microalgal extracts containing degrading...

Polycyclic aromatic hydrocarbons (PAHs) degradative capacity by intra- and extracellular extracts (IE and EE) from Selenastrum capricornutum cultures exposed to benzo(a)pyrene (BaP) was evaluated. These IE and EE (containing BaP-degrading enzymes) were exposed to BaP, benzo(a)anthracene (BaA), benzo(k)fluoranthene (BkF), and benzo(b)fluoranthene (BbF): each PAH at 266 µg/L. Then, PAH and their metabolites were extracted by solid-phase extraction and analyzed by HPLC with ultraviolet and fluorescence detection; these analytical methodologies were validated over concentration ranges (µg/L) of 63-1000 (PAHs) and 10-100 (metabolites); obtained good linearity (R² ≥ 0.985), global recoveries average between 81 %-90 %, and limits of detection between 0.21-62.6 µg/L. Individually, the extracts efficiently degrade PAHs (Removal percentages (%R): BkF, 60 % and 45 %; BbF, 40 % and 24 %; and BaA, 52 % and 16 %), as confirmed through metabolite formation: 4,5-dBaP, 8,9-dBkF, 9,10-dBbF, and 5,6-dBaA. In PAH mixtures, the EE and IE showed degrading capacity, but slightly lower compared to individual PAHs, and with significant differences (p < 0.05) between extracts; BkF has the highest %R (45.3 %) while BaA presents the lowest %R (16.5 %-21.1 %). These results indicate that the BaP-degrading enzymes act efficiently on 4- to 5-ring PAH, which is confirmed by the simultaneous formation of PAH metabolites; 9,10-dBbF and 5,6-dBaA amounts were higher in IE than in EE, while the 8,9-dBkF amounts are highest in EE. These findings: i) suggest a common metabolic pathway of PAHs biodegradation by S. capricornutum; and ii) contribute to the development of ecological PAH-bioremediation methods.