Regolith as Baseline to a Future Space Farm

n/

Compost and microbial biostimulant applications improve plant growth and soil biological fertility of a grass-based phytostabilization system

In this work, a grass-based phytoremediation system integrated with an organic amendment and biostimulants was evaluated for remediating contaminated sites. Plant growth and biological fertility were monitored to assess the efficacy of a vegetative cap used as a safety measure to reduce sanitary and environmental risks of industrially contaminated soils and soil-washing sludges. Both matrices were potentially contaminated with Pb and Zn with an ecological risk index from low to moderate. According to potentially toxic elements (PTEs) bioaccessibility tests, the exposure to the released fine particulate matter may cause serious risks to human beings, in particular to children. The grass mixture was well adapted to both the substrates and a low PTEs mobility was detected, thus, reducing the leaching risk to ground water sources. Compost addition augmented significantly nitrogenase reductase (nifH) and ammonia monooxygenase (amoA) gene expression abundance in both substrates. Furthermore, a positive interaction between compost fertilization and a Trichoderma-based biostimulant inoculation was recorded in sludges resulting in a significant stimulation of nitrogen-fixing and ammonia-oxidizing bacteria. The application of compost and biostimulant increased soil fertility and plant growth. Furthermore, there was a slight reduction in PTE bioaccessibility, thus, improving the efficiency of the phytostabilization, limiting the resuspension and dispersion of the health-risk soil particulate

Mobility and phyto-availability of arsenic in soil-plant system and decontamination techniques of arsenic polluted areas

Contamination of terrestrial and aquatic ecosystems by arsenic is a very sensitive environmental issue due to its adverse impact on human health. Urgent action must be taken to reduce this impact by providing access to safe water as a basic human right. In the present work, researches have been carried out on novel arsenic sorbents at low cost, that can be easily synthesized, or even representing by-products from production processes and thus available for free or at very low price. In particular, this work describes the sorption of arsenate on Al-Mg and Fe-Mg layered double hydroxides as affected by pH and varying concentrations of inorganic and organic ligands, the effect of residence time on the arsenate desorption by ligands and the kinetics of arsenate desorption by phosphate. It was also studied the arsenate sorption by Fe- and Al-based drinking-Water Treatment Residual samples (by-products coming from drinking-water treatment plants) as a function of WTRs particles size at different initial As concentrations and solid:solution ratios (SSRs). The Fe-Mg-LDH sorbed nearly twice the amount of arsenate compared to the Al-Mg-LDH, due to its greater surface area and lower degree of crystallinity. Moreover, the Fe-Mg-LDH sorbed more arsenate than phosphate, in contrast to the Al-Mg-LDH, which adsorbed more phosphate than arsenate, probably because of the greater affinity of arsenate than phosphate for Fe sites and, vice versa, the greater affinity of phosphate than arsenate for Al sites. The capacity of ligands to inhibit the fixation of arsenate followed the sequence: nitrate < nitrite < sulphate < selenite < tartrate < oxalate << phosphate on Al-Mg-LDH and nitrate < sulphate ≈ nitrite < tartrate < oxalate < selenite << phosphate on Fe-Mg-LDH. The inhibition of arsenate sorption increased by increasing the initial ligand concentration. The longer the arsenate residence time on the LDH surfaces the less effective the competing ligands were in desorbing arsenate from sorbents. A greater percentage of arsenate was removed by phosphate from Al-Mg-LDH than from Fe-Mg-LDH during kinetics of arsenate desorption. Both WTR samples show a high affinity for arsenate. Anyway, the Al-WTR samples, characterized by a higher surface area, were able to sorb much greater amounts of arsenate than the Fe-WTR. The greater the SSR, the higher the amounts of arsenate sorbed on both WTR samples. The influence of Fe-WTR particles size on the arsenate sorption capacity was greatly pronounced when compared to that of the Al-WTRs. The smallest Fe-WTR particles were able to sorb much more arsenate than the bigger ones, whereas, surprisingly, the biggest Al-WTR particles showed the best arsenate sorption capacity with respect to that of smaller Al-WTR particles. The presence of As in soils and/or groundwaters used for agricultural purposes, causes a strong abiotic stress to the cultivated plants, which results in the reduction of biomasses and yields, and the abundance of non-tradable products. It is therefore desirable to identify and develop production techniques capable of limiting the mobility and phyto-availability of As in soil, through the stabilization of the metalloid on the more recalcitrant soil fractions. In the present work it was carried out an experiment on the bean (Phaseolus vulgaris L.), irrigated with different solutions containing arsenite and grown in a As-uncontaminated soil amended by increasing amounts of stabilized compost. The aims of this experiment were to: i) study the influence of the compost application on the mobility and phyto-availability of As in soil; ii) study the influence of the compost on the growth of the bean plants and their uptake of As from contaminated systems. Bean plants growth was significantly affected by As and compost treatments. The higher the As concentration in the irrigation water, the lower was the plants biomass, as a consequence of the phytotoxic effect of As, whereas a higher application of the compost corresponded to a higher plant biomass, indicating the ability of the compost to alleviate the As phytotoxicity. In all treatments, arsenic concentration in roots was higher than in shoots and bean,. Moreover, the compost application reduced the As concentration in all tissues of the amended plants compared to those non-amended. A low As allocation in bean is definitely desirable, because a high content of As in the edible part of the plant could cause contamination of the human food-chain. The concentration of the free-fraction of As in soil decreased significantly by increasing the level of compost application, whereas the higher the compost application the higher was the concentration of specifically sorbed As by soil colloidal particles

Biogeochemical processes at soil-root interface

Rhizosphere is a microsite where interactions among roots, microorganisms, soil constituents (minerals and organic matter), and soil solution take place. Biomolecules produced by plants and microorganisms and soil organic substances are involved in many biogeochemical processes at soil-root interface such as: a) weathering of clay minerals and release of Al and Fe, b) formation of nanoprecipitates and organo-mineral complexes, c) sorption/desorption of cations and anions on/from soil colloids and d) bioavailability of nutrients and pollutants. Many exudates form strong complexes with Fe and Al ions, retard or inhibit their hydrolytic reactions and promote the formation of noncrystalline or short-range ordered Al and Fe nanoprecipitates. The so-called iron plaques, present on many wetland plant roots, are Fe(III)-oxyhydroxides (mainly ferrihydrite). These precipitates may interact with biopolymers (proteins, polysaccharides, DNA, RNA and so on), phyllosilicates, soil organic substances as well as microorganisms forming organo-mineral complexes. Root exudates play a vital role on the sorption/desorption of nutrients and pollutants at soil-root interface. The processes, which affect the sorption of cations and anions on sorbents present in the rhizosphere are particularly complex, being sorption of cations quite different from that of anions. Root exudates usually inhibit the sorption of anions, but may promote or inhibit the sorption of cations. They may desorb, at least partially, nutrients and pollutants previously sorbed on soil components, promoting their bioavailability for plants and microorganisms. Finally, some plants release chelating organic ligands able to complex metals (e.g. Al) which become less toxic. Many factors control these processes, for example; pH, nature and concentration of the biomolecules present in the rhizosphere, nature of sorbent and sorbate, reaction time

Chemical Processes Affecting the Mobility of Heavy Metals and Metalloids in Soil Environments

The mobility, bioavailability, and toxicity of metal(- loid)s are influenced by their interactions with phyllosilicates, organic matter, variable charge minerals, and microorganisms. Physicochemical processes influencing the chemistry of metal(- loid)s in soil environments include sorption/desorption, solution complexation, oxidation-reduction, and precipitationdissolution reactions. In particular, the sorption/desorption reactions of metal(loid)s on/from soil sorbents are influenced by pH, nature of soil components, and presence and concentrations of cations and inorganic anions. In recent years, many extraction tests have been used for assessing trace elements mobility and phytoavailability. Chemical speciation of toxic elements may be achieved by spectroscopic analyses (XAS), which provide information about oxidation state, symmetry, and identity of the coordinating ligand environment, and possible solid phases

A Comparison among Synthetic Layered Double Hydroxides (LDHs) as Effective Adsorbents of Inorganic Arsenic from Contaminated Soil–Water Systems

The need for cost-effective adsorbents of inorganic arsenic (As(III) and As(V)) stimulates the academia to synthesize and test novel materials that can be profitably applied at large-scale in most affected areas worldwide. In this study, four different layered double hydroxides (Cu-Al-, Mg-Al-, Mg-Fe- and Zn-Al-LDH), previously synthesized and studied for As(III) removal capacity, were evaluated as potential adsorbents of As(V) from contaminated systems, in absence or presence of common inorganic anions (Cl&minus;, F&minus;, SO42&minus;, HCO3&minus; and H2PO4&minus;). The As(V) desorption by H2PO4&minus; was also assessed. Lastly, the As(V) adsorption capacities of the four layered double hydroxides (LDHs) were compared with those observed with As(III) in a complementary paper. All the LDHs adsorbed higher amounts of As(V) than As(III). Fe-Mg-LDH and Cu-Al-LDH showed higher adsorption capacities in comparison to Mg-Al-LDH and Zn-Al-LDH. The presence of competing anions inhibited the adsorption of two toxic anions according to the sequence: Cl&minus; &lt; F&minus; &lt; SO42&minus; &lt; HCO3&minus; &lt; &lt; H2PO4&minus;, in particular on Mg-Al-LDH and Zn-Al-LDH. The kinetics of As(V) desorption by H2PO4&minus; indicated a higher occurrence of more easily desorbable As(V) on Zn-Al-LDH vs. Cu-Al-LDH. In conclusion, synthetic Cu- and Fe-based LDHs can be good candidates for an efficient removal of inorganic As, however, further studies are necessary to prove their real feasibility and safety

Formation, properties and reactivity of coprecipitates and organomineral complexes in soil environments

In soil environments the formation of simple coprecipitates formed by the interaction of two or more cations and/or anions are the rule and not the exception. In this review we describe the formation, the nature and the reactivity of coprecipitates formed by the interaction between cations (Fe, Al, Mg, Mn, Zn) with the formation of mixed oxides or layered double hydroxides (LDHs) and of coprecipitates formed by the interactions of inorganic and low molecular mass organic (LMMOLs) ligands with OH-Al and/or OH-Fe species both in the absence or presence of phyllosilicates. The presence of anions within these samples strongly affect the sorption of other ligands on the surfaces of the coprecipitates. Furthermore, the anions coprecipitated with Al and/or Fe hydrolytic products are only partially replaced even by ligands with strong affinity for the surfaces of the final samples, clearly because they are also incorporated into the network of the precipitates. We also describe the formation, surface properties and reactivity of binary complexes obtained by the interaction of hydrolytic products of Al and Fe with clay minerals and of ternary OH-Al(-Fe)-organics-phyllosilicates (organics included also large anions as tannate or proteins). The effect of the sequence of addition of the components of the final organomineral complexes influenced the physicochemical and mineralogical properties of the samples. Attention was also devoted to the stabilization of organic substances in organo-mineral coprecipitates and soils

Higher sorption of arsenate versus arsenite on amorphous Al-oxide, effect of ligands

Arsenic pollution is currently a major health issue because As is toxic for human beings, animals, and plants. Knowledge of As mobility is therefore important to assess health risk. The sorption of arsenite and arsenate on metal oxides in the presence of various anionic ligands is closely linked to the mobility, bioavailability, and risk. It was reported that the sorption mechanisms and characteristics of arsenite and arsenate on Al-oxides were different from that on Fe-oxides. Previous work reports the sorption of arsenite and arsenate on Fe-oxides in the presence of ligands. Whereas there is few knowledge on the sorption of arsenite and arsenate by Al-oxides in the presence of ligands. Here, we studied the sorption of arsenite and arsenate on amorphous Al-oxide by batch experiments. We tested the effect of organic ligands: oxalate, malate, tartrate, citrate; and inorganic ligands: sulfate, phosphate, selenate, selenite. Results show that amorphous Al-oxide has more sorption affinity for arsenate than arsenite. The inhibition of As sorption by ligands at pH 6 is higher for arsenite than arsenate. For arsenite, the As sorption inhibition decreases in the order phosphate, citrate, malate, selenite, oxalate, tartrate, sulfate, and selenate. For arsenate, the As sorption inhibition decreases in the order phosphate, malate, citrate, selenite, tartrate, oxalate, sulfate, and selenate

Sorption of arsenite and arsenate on ferrihydrite: Effect of organic and inorganic ligands

We studied the sorption of As(III) and As(V) onto ferrihydrite as affected by pH, nature and concentration of organic [oxalic (OX), malic (MAL), tartaric (TAR), and citric (CIT) acid] and inorganic [phosphate (PO4), sulphate (SO4), selenate (SeO4) and selenite (SeO3)] ligands, and the sequence of anion addition. The sorption capacity of As(III) was greater than that of As(V) in the range of pH 4.0-11.0. The capability of organic and inorganic ligands in preventing As sorption follows the sequence: SeO4≈SO4<OX<MAL≈TAR<CIT<SeO3≪PO4. The efficiency of most of the competing ligands in preventing As(III) and As(V) sorption increased by decreasing pH, but PO4 whose efficiency increased by increasing pH. In acidic systems all the competing ligands inhibited the sorption of As(III) more than As(V), but in alkaline environments As(III) and As(V) seem to be retained with the same strength on the Fe-oxide. Finally, the competing anions prevented As(III) and As(V) sorption more when added before than together or after As(III) or As(V)