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Contaminated soils can only be efficiently managed if proper procedures are adopted for evaluating the risks due to contamination as well as the actual volume of contaminated soil [...]

One of the main drawbacks of using biomass as pyrolysis feedstock consists of the huge variability of the different biomass resources which undermines the viability of downstream processes. Inherent inorganic elements greatly contribute to enhance the compositional variability issues due to their catalytic effect (especially alkali and alkaline earth metals (AAEMs)) and the technical problems arising due to their presence. Due to the different pretreatments adopted in the experimental investigations as well as the different reactor configurations and experimental conditions, some mechanisms involving interactions between these elements and the biomass organic fraction during pyrolysis are still debated. This is the reason why predicting the results of these interactions by adapting the existing kinetic models of pyrolysis is still challenging. In this work, the most prominent experimental works of the last 10 years dealing with the catalytic effects of biomass inherent metals on the pyrolysis process are reviewed. Reaction pathways, products distributions and characteristics, and impacts on the products utilization are discussed with a focus on AAEMs and on potential toxic metallic elements in hyperaccumulator plants. The literature findings are discussed in relation to the applied laboratory procedures controlling the concentration of inherent inorganic elements, their capability of preserving the chemical integrity of the main organic components, and the ability of resembling the inherent inorganic elements in the raw biomass. The goal is to reveal possible experimental inconsistencies and to provide a clear scheme of the reaction pathways altered by the presence of inherent inorganics. This analysis paves the way for the examination of the proposed modifications of the existing models aiming at capturing the effect of inorganics on pyrolysis kinetics. Finally, the most relevant shortcomings and bottlenecks in existing experimental and modeling approaches are analyzed and directions for further studies are suggested.

This work aimed to study the effects of compost (applied at two rates) and two commercial microbial biostimulants on the mobility and bioavailability of potentially toxic elements (PTEs) in an industrial soil phytostabilized by Dactylis glomerata L. or a mixed stand of grasses (Lolium perenne L., Poa pratensis L. and Festuca arundinacea Shreb.). The soil showed very high pseudototal and bioavailable concentrations of cadmium (Cd) and lead (Pb), due to improper lead-acid batteries storage. Compost amendment in combination with the two biostimulants produced the best outcomes in terms of plant growth and nutrient uptake. The same mix of beneficial microbes improved soil biological fertility enhancing soil nitrogen fixing and ammonia oxidizing bacteria, while reduced the pore water and NH4NO3 extractable concentrations of Cd and at lower extent of Pb in soil. Accordingly, the lower mobility and bioavailability of Cd in soil determined a lower uptake and accumulation of Cd in shoots of different grass species. Our results suggest that a green cap with turfgrass assisted by biostimulants and compost amendment in PTE-contaminated industrial sites could be a reliable and effective practice to protect and restore soil biological fertility and to reduce the risk of PTE dispersion in the surrounding environment.

Phytoextraction of potentially toxic elements (PTEs) is eco-friendly and cost-effective for remediating agricultural contaminated soils, but plants can only take up bioavailable forms of PTEs, thus meaning that bioavailability is the key for the feasibility of this technique. With the aims to assess the phytoextraction efficiency on an agricultural soil contaminated by Cr, Zn, Cd, and Pb and the changes induced by plants in PTE bioavailability and in human health risk due to dietary exposure, in this work we carried out a mesocosm experiment with three successive croppings of Brassica juncea, each followed by Rocket salad as bioindicator. Brassica juncea extracted more Zn and Cd than Cr and Pb, significantly reducing, after three repeated croppings, the bioavailable element concentrations in soil as a result of plant uptake and soil pH changes. For Cd, this reduction did not bring the bioavailable amounts obtained by soil extraction with NH4NO3 below the trigger value of 0.1 mg kg&minus, 1 set by some European countries. Nevertheless, the Hazard Quotient for Cd in Rocket salad decreased across three repeated croppings of Brassica juncea. This indicated the beginning of a re-equilibration process between soil PTE forms of different bioavailability, that are in a dynamic equilibrium, thus stressing the need to monitor the possible regeneration of the most readily bioavailable pool.

In agricultural soils, thallium (Tl) of geogenic origin may represent a potential risk for human health, mainly via ingestion of food crops. In this work, a pot experiment was carried out to evaluate (1) the bioavailability of Tl and other potentially toxic elements (PTEs) in an agricultural soil with naturally occurring Tl, (2) the uptake and accumulation of PTEs in Lactuca sativa L. var. acephala, Diplotaxis tenuifolia L. DC and Silene latifolia Poir, (3) the health risks arising from plant and soil ingestion by different subpopulations and dermal contact of soil by farmers. In soil, only Tl and Pb pseudototal contents were above Italian screening values. Nevertheless, the promptly bioavailable contents of all PTEs were always below internationally recognized trigger values. Plants affected PTE bioavailability in soil by their rhizodepositions and accumulated PTEs in their shoots. Acceptable risks (hazard index &lt, 1) arose from dietary intake of both L. sativa L., D. tenuifolia L. and dermal contact of soil by farmers. Significant health risks can derive from the intake of S. latifolia Poir. (accumulating high Tl concentrations), in particular by children (HI = 74). In conclusion, an adequate management and crop selection are needed to profitably exploit soils with geogenic Tl for agricultural purposes.

With a view to conserving or improving soil ecosystem services, environment-friendly techniques, such as bio- and phytoremediation, can effectively be used for the characterization, risk assessment, and remediation of contaminated agricultural sites. Polyannual vegetation (meadows, poplar, and cane stands) is widely considered the most efficient tool for remediation (extraction of bioavailable fraction of contaminants), for undertaking safety measures (reducing the mobility of contaminants towards other environmental compartments), and for restoring the ecosystem services of contaminated agricultural sites (biomass production, groundwater protection, C storage, landscape quality improvement, and cultural and educational services). The roles of agronomic approaches will be reviewed by focusing on the various steps in the whole remediation process: (i) detailed environmental characterization; (ii) phytoremediation for reducing risks for the environment and human health; (iii) agronomic management for improving efficiency of phytoremediation; and (iv) biomass recycling in the win-win perspective of the circular economy.

The risks for human health and the ecosystem due to potentially toxic elements (PTEs) were investigated in a farmland classified as potentially contaminated by Cr and Zn by analysing native vegetation and relative rhizo-soils. Rhizo-soils of different plant species were found to be enriched by Cr and Zn as well as by elements omitted from official environmental characterization, namely Cd, As and Pb. The ecological risk index (ERI) had a mean value of 510, indicating high to “very high” risk in different habitats. ERI above the very high risk threshold characterized the rhizo-soils of Lolium perenne , Erigeron sumatrensis , Oloptum thomasii and Amaranthus retroflexus . Two of these plant species ( E. sumatrensis and A. retroflexus ) are exotic in Italy and accumulated Cd in the shoots above the EU threshold for forage, suggesting a potential risk of Cd transfer to the food chain. Hence, this element was found to contribute most to the ERI. Cynodon dactylon was recognized as the most suitable plant species for the phytostabilization of the contaminated site, as it showed the highest bioavailable Cd accumulation in roots coupled with the highest frequency and soil-cover capacity during spring-summer, when the risk of soil resuspension is generally more intense.

The urgency to reduce resource depletion and waste production is expected to lead to an economy based on renewable resources. Biofuels, for instance, are a great green alternative to fossil fuel, but they are currently derived from edible vegetable oils such as soybean, palm, and sunflower. Concerns have been raised about the social–economic implication and ecological impacts of biodiesel production. Cultivating new lands as biodiesel feedstock rather than food supply, with the consequent increase in food prices, leads to so-called indirect land-use change (ILUC). Establishing bioenergy crops with phytoremediation ability on contaminated soils offers multiple benefits such as improving soil properties and ecosystem services, decreasing soil erosion, and diminishing the dispersion of potentially toxic elements (PTEs) into the environment. Castor bean is an unpalatable, high-biomass plant, and it has been widely demonstrated to possess phytoremediation capability for several PTEs. Castor bean can grow on marginal lands not suitable for food crops, has multiple uses as a raw material, and is already used in biodiesel production. These characteristics make it perfect for sustainable biodiesel production. Linking biofuel production with environmental remediation can be considered a win–win strategy.

The long-term use of Cu-based fungicides at doses of several kilograms per hectare stimulated a wide debate about the human health and environmental risks of the progressive accumulation of Cu in agricultural soils. Here, the health risks due to copper accumulation in agricultural soils were evaluated with a survey in intensive agricultural land of the Campania region (Italy), aiming to evaluate Cu accumulation in food crops. The health risk due to dietary exposure was estimated by using the Hazard Quotient (HQ), calculated as the ratio between the average daily dose and the reference dose of copper, suggesting that when HQ > 1 there is a potential risk for consumers. According to a survey of soils with a Cu content up to 217 mg kg−1, no foodstuffs showed dietary risks. Nevertheless, the contribution of Cu contained in these foodstuffs to the overall intake of Cu by consumers could increase health risks since such risks must be evaluated on the basis of the whole standard diet by quantifying the Cu content not only in vegetables and fruits but also in other sources, such as cereals, not cultivated in the study area and thus not considered in this paper. The environmental risks due to copper accumulation in agricultural soils were then evaluated with a field experiment in a soil characterized by a very high Cu concentration (up to 1700 mg kg−1), aiming to study the impacts of Cu on native soil microorganisms. The study of the microbiota highlighted that the presence of Cu in soil did not reduce the total richness and diversity of microorganisms, which were not related to increasing concentrations of Cu in the soil. Nevertheless, Cu contamination was found to exert significant selection pressure on the soil microbiota, as shown by beta diversity and correlation analysis between taxa and Cu content.

The risk for human health and environment due to the presence in agricultural soils of organic and inorganic contaminants derived from illegal waste disposal, posed the need to develop a sustainable strategy for the restoration of soils with high agricultural potential. In this study an eco-compatible method as soil tillage and compost amendment was applied in two sites of a National Interest Priority Site of Campania Region (Italy) known as “Terra dei Fuochi”. After one year, the concentration of heavy hydrocarbons (C > 12) significantly reduced in a range from 84 to 95%, probably due to the aeration causing photo-oxidation processes and an improvement of microbial activity able to degrade organic pollutants. Although a reduction trend was observed, the potentially toxic elements (PTEs) concentration in soils was unmodified indicating a potential risk of plant uptake. The high-throughput sequencing approach used to explore the response of native microbial populations following in situ treatments showed that microbiota dynamic was differently affected in the two sites. Therefore, the characteristics of the sites could differently interact with compost determining a different microbial response. Alphaproteobacteria (incidence range of 14–18%), Actinobacteria (incidence range of 10–22%) and Sordariomycetes (incidence range of 23–57%) were the dominant autochthonous populations in all soils indicating their high adaptability to different environments and high resistance to environmental stress as well as their high potential in degradation of organic xenobiotic compounds. The remediation practices based on soil tillage and compost amendment promoted the restoration of the microbial biofertility of soils affected by spotted multi-contamination, to bring them back to agricultural use.