Zeolite composites from fly ashes mixed with leonardite as a useful addition to fertilizer for accelerating the PAHs degradation in soil

Extensive soil degradation caused by polycyclic aromatic hydrocarbons (PAHs) leads to serious agriculture problems around the world. One of the most effective ways to restore soil functionality and fertility, limiting the possibility of PAHs uptaken by plants, is soil remediation. The remediation of PAHs in soils can be enhanced by adding mineral-organic additives rich in carbon. The aim of the work was the evaluate the effectiveness of the mineral-organic mixtures consisting of the zeolite-carbon (NaX-C) or zeolite-vermiculite (NaX-Ver) composites mixed with leonardite and mineral salts (NPK) in terms of their effect on the remediation of PAHs contaminated soils. The accumulation and translocation of PAHs in maize tissues, the fatty acids profile in grains and the BaP equivalent concentration (B(a)Peq) based on the n-ary sumation 4 PAHs with the highest carcinogenic to humans were also investigated. The application of zeolite composites with leonardite increased the losses of PAHs content in soils with simultaneous reduction of their content in plants without a negative impact on the mass of maize grains. In soils, a significant correlation was found between 4, 5, and 6-rings PAHs and total organic carbon (TOC) content and between dehydrogenases activity and TOC content. The highest reduction of PAHs in plant tissues and the lowest B(a)Peq was observed after application of zeolite-carbon composites with the lover dose. The addition of the proposed amendments positively affected the unsaturated fatty acids/saturated fatty acids (UFA/SFA) ratio.