Fungal-based technologies to face (and solve) soil pollution

Contaminated soil, water and air by persistent toxic chemicals are a major challenge in the modern society. European Union is becoming more and more aware about the risk of soil pollution on the environment and human health. As a non-renewable resource, soil needs to be protected and managed in a sustainable way. Anthropized activities often exacerbate the problem. Soil pollution represents a direct consequence of the industrial activities, improper disposal of waste, with a detrimental effect on the ecosystem services provided by soil. Moreover, the problem can be transferred to other less known ecosystems, then enlarging the impact on the society. For instance, urban agriculture has grown rapidly in the last years, thanks to the possibility of producing fresh foodstuffs at low cost and to reduce socio-economic and environmental issues. However, urban gardens are exposed to continuous pollution caused by the emission from road traffic, domestic heating, previous industrial use of the sites, atmospheric deposition from industrial activities. In all cases, the most abundant pollutants are heavy metals and organic compounds, i.e polycyclic aromatic hydrocarbons (PAH). Since there are still many historical and new contaminated sites where any action is still missing, a focused protection and recovery policy is needed. In particular, in the European Union, 42 potentially contaminated sites and 5.7 contaminated sites per 10,000 inhabitants are present, with about 340,000 sites that require remediation. Several technologies soils have been studied but chemico-physical methods are often cost and energy consuming. The actual challenge is to find innovative technologies with a low environmental, economic and energetic impact. Nature-based solutions (bioremediation) are promising options to mitigate the soil degradation and have received worldwide a particular attention: they usually are simple and cost-effective methods, which have been found capable of reducing the contamination level. The role of fungi and bacteria in bioremediation has been increasingly recognized. Besides the combination of microorganisms and plants may enhance the total organic pollutants removal thanks to a synergic action of different metabolisms. This approach has been here validated in very different polluted sites in Italy, where the major issue was posed by PAH contamination. The LIFE BIOREST project was focused to develop a sustainable bioremediation model for soil decontamination, based on the use of bacteria, fungi and plants. The project focuses on the bioremediation of a portion of the wellcharacterized National Interest Site (SIN) of Fidenza, Italy. An integrated approach was proposed thanks to autochthonous and ecologically adapted bacteria and fungi, the use of local agro-food byproducts and a final revegetation step. The first phase of the project targeted the microbial community of site. Various isolation techniques help to isolate a wide library of bacteria and fungi (more than 500 isolated strains) that were then further tested to evaluate their actual capability to degrade pollutants. Isolated fungi mostly belong to Ascomycetes as Cladosporium, Aspergillus, Penicillium, Fusarium, Scedosporium, Trichoderma and Epicoccum. The bacterial isolates were ascribable to the Gram negative genera Pseudomonas, Sohingobacterium, Pseudoxanthomonas, Rhizobium and Acinetobacter. Several fungal and bacterial strains were very versatile, exploiting pyrene, phenanthrene and alkanes of sole source of carbon confirming their great adaptation skills. The process was scaled up to microcosms and mesocosms, and finally ended up to the setup of a biopile of more than 530 ton of soil. The bioaugmented biopile removed up to 300 mg/kg of hydrocarbons already after 60 days. At the end of the treatment, it was more efficient than the traditional treatment: as regards the total hydrocarbon content, the removal was 38% higher than the control. The toxicity was even halved in comparison with the control. The project REHORTI was instead targeted to polluted urban areas in Turin (Italy) which are devoted to horticulture. The contamination was lower than the above-mentioned SIN but it was still significant to pose serious risks to the society. Once extracted from the soil, many pollutants can indeed migrate up to the fruiting bodies and then enter into the food cycle. The project was primarily focused to isolate the fungi populating this ecological niche. The choice of the microbial consortium considered the shown degradation skills, the capability to produce biosurfactants and to grow on ligninocellulose substrates. The best microbial consortium (made up with 6 fungal strains) was tested at pilot scale with in field trials. The presence of organic soil conditioner to provide additional nutrient to this poor soil was also evaluated. Results indicated that without any treatment, the soil was in a quite static condition. Fungi led to a consistent abatement (30-50% removal) the content of 2-4 rings hydrocarbons already after the first 3 months of treatment. The treatment was also magnified by the addition of the conditioner, which helped to re-activate the ecological services of the soil.