Impact of humic substances on the bioremediation of polycyclic aromatic hydrocarbons in contaminated soils and sediments: A review

Polycyclic aromatic hydrocarbons (PAHs) are present in the environment due to both natural sources and human activities. They are abundant and resistant to decomposition. Humic substances, depicted as a significant component of soil organic matter, can influence the effectiveness of PAHs bioremediation in contaminated environments. We review bioremediation studies on soil contamination with PAHs in the presence of humic substances in reports published from 2000 to 2023. Around 36% of the studies indicated that the presence of humic substances enhances the bioavailability and biodegradation rate of PAHs in soils and sediments. This enhancement is attributed to the surfactant properties of humic substances, particularly humic acids, which display a micellar microstructure. In contrast, approximately 19% of the studies suggested that humic substances could diminish the bioavailability and biodegradation rate of PAHs due to the sequestration of PAHs within humic substances. Moreover, the impact of humic substances on the bioavailability of PAHs seems to be concentration-dependent. Humic acidx can function as a carrier for PAHs, aiding in their transfer to bacterial cells. In contrast, humin, a substantial component of soil organic matter, has the ability to adsorb more PAHs, potentially resulting in their long-term aging.