Iman Tahmasbian

Chelating Agents and Heavy Metal Phytoextraction

Phytoremediation is a naturally slow process limited by low availability of target metals in soils. Adsorption−desorption at the particle–solution interface are the most responsible reactions controlling heavy metal bioavailability in soil. Simply put, metal bioavailability and transport are mainly affected by iron and manganese oxides, clay minerals, carbonates, organic matters, and soil microorganisms. In the soils with higher clay content, cation exchange capacity (CEC), organic carbon (OC), biological activity, and amorphous and crystalline Fe and Al, a metal, e.g., Pb, is mostly observed in residual form followed by organic matter-associated and Mn–Fe-associated forms, respectively, whereas in the soils with higher sand content, pH, and equivalent carbonate calcium (EEC), the higher amount of this metal is reported to be in carbonate-associated form. It is worth noting that the existence and absence of soil microorganisms can alter the above distributions by different mechanisms. In order to increase the bioavailability of heavy metals in soil, application of chelating agents in soil is recommended. What chelating agents do is increasing the metal bioavailability and also increasing soil productivity through enhancing soil available nutrients; both result in a more efficient phytoremediation. Chelating agents are mainly categorized into synthetic (e.g., polycarboxylates, hydroxy carboxylates, etc.) and natural (e.g., organic acids, manures, siderophores, etc.) groups. Among all the other chelating agents, EDTA, which is a synthetic chelate, is frequently reported as the most efficient chelant to increase availability of metals in soil and enhance the translocation of them to aerial (harvestable) parts of plant. In terms of biomass production which is important for an efficient phytoremediation, EDTA cannot play its role as successfully as when it is used to enhance metal concentration. Toxicity of EDTA itself on the one hand and the toxicity of increased amount of heavy metals caused by EDTA on the other hand prevent plant from producing much biomass. It may be applied in soil during plant growth with lower concentration and different times. Natural chelating agents, nevertheless, noticeably enhance biomass production, although they are not so effective to improve metal concentration as EDTA is. On the other hand, electrokinetic is another technique used to increase available forms of heavy metals and their movement in soil toward plant roots. The most recent researches, interestingly, were designed based on the combination of electrokinetic and chelating agents, which significantly increases the uptake of metals by plants. Giving the negative charge to plant can lead to more cation taken up by plant roots because the electric field makes biomembranes more permeable, providing a transient exchange of metals across the perturbed membrane structure. More interesting results would be obtained when chelating agents provided more bioavailable metals for plant roots simultaneously. As a result, application of chelating agents along with electric fields amazingly raises the phytoremediation efficiency.

A non-destructive determination of peroxide values, total nitrogen and mineral nutrients in an edible tree nut using hyperspectral imaging

Nuts are nutritionally valuable for a healthy diet but can be prone to rancidity due to their high unsaturated fat content. Nutrient content of nuts is an important component of their health benefits but measuring both rancidity and nutrient content of nuts is laborious, tedious and expensive. Hyperspectral imaging has been used to predict chemical composition of plant parts. This technique has the potential to rapidly predict chemical composition of nuts, including rancidity. Hence, this study explored to what extent hyperspectral imaging (400–1000 nm) could predict chemical components of Canarium indicum nuts. Partial least squares regression (PLSR) models were developed to predict kernel rancidity using peroxide value (PV) for two different batches of kernels, and macro- and micronutrients of kernels using the spectra of the samples obtained from hyperspectral images. The models provided acceptable prediction abilities with strong coefficients of determination (R2) and ratios of prediction to deviation (RPD) of the test set for PV, first batch (R2 = 0.72; RPD = 1.66), PV, second batch (R2 = 0.81; RPD = 2.30), total nitrogen (R2 = 0.80; RPD = 1.58), iron (R2 = 0.75; RPD = 1.46), potassium (R2 = 0.51; RPD = 0.94), magnesium (R2 = 0.81; RPD = 2.04), manganese (R2 = 0.71; RPD = 1.84), sulphur (R2 = 0.76; RPD = 1.84) and zinc (R2 = 0.62; RPD = 1.37) using selected wavelengths. This study indicated that visible-near infrared (VNIR) hyperspectral imaging has the potential to be used for prediction of chemical components of C. indicum nuts without the need for destructive analysis. This technique has potential to be used to predict chemical components in other nuts.

The effects of short term, long term and reapplication of biochar on soil bacteria

Biochar has been shown to affect soil microbial diversity and abundance. Soil microbes play a key role in soil nutrient cycling, but there is still a dearth of knowledge on the responses of soil microbes to biochar amendments, particularly for longer-term or repeated applications. We sampled soil from a field trial to determine the individual and combined effects of newly applied (1 year ago), re-applied (1 year ago into aged biochar) and aged (9 years ago) biochar amendments on soil bacterial communities, with the aim of identifying the potential underlying mechanisms or consequences of these effects. Soil bacterial diversity and community composition were analysed by sequencing of 16S rRNA using a Miseq platform. This investigation showed that biochar in soil after 1 year significantly increased bacterial diversity and the relative abundance of nitrifiers and bacteria consuming pyrogenic carbon (C). We also found that the reapplication of biochar had no significant effects on soil bacterial communities. Mantel correlation between bacterial diversity and soil chemical properties for four treatments showed that the changes in soil microbial community composition were well explained by soil pH, electrical conductivity (EC), extractable organic C and total extractable nitrogen (N). These results suggested that the effects of biochar amendment on soil bacterial communities were highly time-dependent. Our study highlighted the acclimation of soil bacteria on receiving repeated biochar amendment, leading to similar bacterial diversity and community structure among 9-years old applied biochar, repeated biochar treatments and control.