A comparative study of the sorption of O-PAHs and PAHs onto soils to understand their transport in soils and groundwater

Polycyclic aromatic hydrocarbons (PAHs) and their oxygenated derivates (O-PAHs) are identified in soils and groundwater of industrialized sites and contribute to the risk for Humans and the Environment. Nevertheless, data are scarce in literature concerning their retention and transfer in soils and no soil - water partition coefficients are available for these compounds. Sorption of two PAHs, fluorene and acenaphthene and two O-PAHs, 9H-fluorenone and dibenzofuran onto two soils with different organic carbon contents was evaluated and compared by determining their sorption isotherms. Effect of ionic strength and liquid to solid ratio, on fluorene and fluorenone sorption was also evaluated. Sorption equilibrium is achieved within less than 24 hr of mixing and linear sorption models best fit the isotherm data. Acenaphthene and dibenzofuran are similarly sorbed onto the soil. K_D of fluorene is higher than the one of fluorenone, showing a smaller affinity of fluorenone towards the solid phase. This means that O-PAH could form larger contamination plumes in groundwater than PAHs. Decreasing the L/S ratio from 100 to 50 and 30, increases the sorption of fluorenone onto the soil by 56% and 67% respectively, while the sorption of fluorene is slightly increased. Increasing the ionic strength of the aqueous phase also modifies the sorption of fluorenone, contrary to the sorption of fluorene which is slightly affected.

The antioxidant defense responses of Hordeum vulgare L. to polycyclic aromatic hydrocarbons and their derivatives in biochar-amended soil

The recent studies indicated that the biochar (BC) may be a source of polycyclic aromatic hydrocarbons (PAHs) as well as their oxygen, nitrogen, or sulfur-containing derivatives that are considered as more toxic pollutants than their parent compounds. Here, the assessment of the impact of various biochars addition (1% wt.) to soil on barley Hordeum vulgare L. growth was presented. The concentrations of bioavailable PAHs and their derivatives in biochar were determined. PAHs increased reactive oxygen species generation resulting in oxidative stress in organisms. In this study, the response of soil-grown plants was examined in terms of the activity of the antioxidative enzymes (superoxide dismutase, catalase, peroxidase), lipid peroxidation, and the expression of genes related to oxidative stress. The results indicate that despite low content of a bioavailable fraction of parent compounds and their derivatives (up to 4.45 ± 0.24 ng g_biochar^-1 and 0.83 ± 0.03 ng L^-1, respectively) the biochemical response of plant was present, the activity of superoxide dismutase increased up to 2 times, but the activity of the other enzymes was lowered. The transcript level values support the studies on enzymatic activity. The presence of PAHs and their derivatives induced oxidative stress slightly but the plant was able to mitigate it.

Occurrence and toxicity of polycyclic aromatic hydrocarbons derivatives in environmental matrices

In the last years, there is great attention paid to the determination of polycyclic aromatic hydrocarbons (PAHs) in different environmental matrices. Extensive reviews on PAHs presence and toxicity were published recently. However, PAHs formation and transformation in the environment lead to the production of PAHs derivatives containing oxygen (O-PAHs), nitrogen (N-PAHs and aazarenes AZA) or sulfur (PASHs) in the aromatic ring. The development of new analytical methods enabled the determination of these novel contaminants. The presence of oxygen, nitrogen, or sulfur in PAHs aromatic rings increased their toxicity. The most common primary sources of PAHs derivatives are biological processes such as microbial activity (in soil, water, and wastewater treatment plants (O-PAHs)) and all processes involving combustion of fuel, coal, and biomass (O-PAHs, N-PAHs, AZA, PASHs). The secondary resources involved i) photochemical (UV light), ii) radical-mediated (OH, NO₃), and iii) reactions with oxidants (O₃, NO_x) (O-PAHs, N-PAHs, AZA). Furthermore, N-PAHs were able to transform to their corresponding O-PAHs, while other derivatives were not. It indicated that N-PAHs are more vulnerable to photooxidation in the environment. 85% of O- and N-PAHs were detected with particle matter below 2.5 μm suggesting their easier bioaccessibility. More than 90% of compounds with four and more aromatic cycles were present in the particle phase in the air. Although the concentrations of N-PAHs or O-PAHs may be similar to PAHs concentration or even 1000 times lower than parent PAHs, PAHs derivatives accounted for a significant portion of the total mutagenicity. The present review is describing the results of the studies on the determination of PAHs derivatives in different environmental matrices including airborne particles, sediments, soil, and organisms. The mechanisms of their formation and toxicity were assessed.