The impacts of exogenous phosphorus on Cd absorption in perennial ryegrass root cell: Kinetic and mechanism study.

Phosphorus (P) is critical to plants in metal-contaminated soils because it participates in various biochemical reactions during plant growth. However, the mechanisms of P in mitigating the toxicity of heavy metals to ryegrass root is still veiled. In this study, the physiological and biochemical dynamics of the ryegrass root under various cadmium (Cd) and P conditions were investigated in a hydroponic system. Cd stress decreased the length of the ryegrass root, but P application enhanced the root elongation to reduce the Cd concentration in the root. Both Cd and P dosages were positively correlated with hemicellulose 1 content, pectin content, and PME activity, while having a negative effect on cellulose content. Moreover, the addition of 80 mg L-1 P increased the contents of pectin and hemicellulose 1 by 2.5 and 5.8% even with 4 mg L-1 Cd. In addition, P supply increased pectin methylesterbase activity under Cd stress, which further changed the extra-cytoplasmic structures and cell wall composition. Thus, exogenous P promoted the immobilization of Cd onto the cell wall and protected protoplast primarily through indirectly regulating the binding capacity of the root cell wall for Cd.

Bioremediation of hexavalent-chromium contaminated groundwater: Microcosm, column, and microbial diversity studies.

Sulfate reducing bacteria (SRB) have the capability of bioreducing hexavalent chromium [Cr(VI)] to trivalent chromium [Cr(III)] under sulfate-reducing conditions for toxicity reduction. However, a high amount of sulfate addition would cause elevated sulfide production, which could inhibit the growth of SRB and result in reduced Cr(VI) bioreduction efficiency. A slow release reagent, viscous carbon and sulfate-releasing colloidal substrates (VCSRCS), was prepared for a long-lasting carbon and sulfate supplement. In the column study, VCSRCS was injected into the column system to form a VCSRCS biobarrier for Cr(VI) containment and bioreduction. A complete Cr(VI) removal was observed via the adsorption and bioreduction mechanisms in the column with VCSRCS addition. Results from X-ray diffractometer analyses indicate that Cr(OH)3(s) and Cr2O3(s) were detected in precipitates, indicating the occurrence of Cr(VI) reduction followed by Cr(III) precipitation. Results from the Fourier-transform infrared spectroscopy analyses show that cell deposits carried functional groups, which could adsorb Cr. Addition of VCSRCS caused increased populations of total bacteria and dsrA, which also enhanced Cr(VI) reduction. Microbial diversity results indicate that VCSRCS addition resulted in the growth of Cr(VI)-reducing bacteria including Exiguobacterium, Citrobacter, Aerococcus, and SRB. Results of this study will be helpful in developing an effective and green VCSRCS biobarrier for the bioremediation of Cr(VI)-polluted groundwater.

Synergistic construction of green tea biochar supported nZVI for immobilization of lead in soil: A mechanistic investigation.

Biochar-based nanocomposites with functional materials provide an excellent prospect in reactivity and stability. Most biochar reported have no reusability upon aging and offer the risk of release of immobilized components after short-term immobilization. To overcome this, we developed nano zero-valent iron (nZVI) impregnated magnetic green tea biochar (nZVI@GTBC) and studied its performance in immobilizing Pb and long-term effectiveness in the soil. The reactive nZVI units were obtained from iron oxide solution by reducing with polyphenol solution (green tea extract) and were successively stabilized by impregnation onto the remaining green tea waste matrix through co-precipitation technique. Finally, the magnetic biochar was developed from the above nZVI impregnated green tea waste through oven drying and slow pyrolysis technique in different temperature range (150-650 °C). The synthesized nZVI@GTBC biochar was characterized and studied by XRD, FTIR, Raman, UV-Vis, TG/DSC, XPS, SEM, and TEM. The nZVI@GTBC obtained with a particle size of 130 nm and surface charge of +2.8 C/m2 at 450 °C. Moreover, colloidal stability and mobility experiments were considered to explain the transport behavior and stability of bare nZVI and magnetic nZVI@GTBC in the soil. The immobilization of Pb by pristine nZVI, GTBC, and nZVI@GTBC was compared and explained under different soil pH conditions. The bioavailability of Pb content before and after immobilization was investigated through leaching experiments. Further, thirty days of soil incubation were carried out to examine different species of Pb according to the Tessier sequential extraction scheme. The study suggested that nZVI@GTBC enhanced the immobilization efficiency by 19.38% in comparison with pristine nZVI and 57.14% in comparison with bare GTBC biochar.

Exogenous phosphorus treatment facilitates chelation-mediated cadmium detoxification in perennial ryegrass (Lolium perenne L.).

Cadmium (Cd) is an on-going environmental pollutant associated with hindered plant growth. In response, plants possess various strategies to alleviate Cd stress, including reactive oxygen species (ROS) scavenging and chelation-mediated Cd detoxification. The present study examined the Cd defense mechanism of perennial ryegrass (Lolium perenne L.), taking into account the effect of exogenous phosphorus (P) input. It was found that despite triggering antioxidant enzyme activity, Cd stress heightened lipid peroxidation levels. Exogenous P input partially mitigated the lipid peroxidation impact and decreased the levels of superoxide dismutase (SOD), catalase (CAT), and peroxidase (POD) antioxidant enzymes, revealing reduced ROS-scavenging activity. Importantly, notable relationships were determined between the amount of Cd uptake in the root and the amount of non-protein thiols (R2 = 0.914), glutathione (R2 = 0.805) and phytochelatins (R2 = 0.904) in proportion to the amount of exogenous P applied. The levels of amino acids proline and cysteine were also enhanced by exogenous P input showing their influence in alleviating Cd stress. Overall, it is reported that Cd detoxification in ryegrass plants can be stimulated by exogenous P input, which facilitates chelation-mediated Cd detoxification processes.

Clay-polymer nanocomposites: Progress and challenges for use in sustainable water treatment.

Contaminant removal from water involves various technologies among which adsorption is considered to be simple, effective, economical, and sustainable. In recent years, nanocomposites prepared by combining clay minerals and polymers have emerged as a novel technology for cleaning contaminated water. Here, we provide an overview of various types of clay-polymer nanocomposites focusing on their synthesis processes, characteristics, and possible applications in water treatment. By evaluating various mechanisms and factors involved in the decontamination processes, we demonstrate that the nanocomposites can overcome the limitations of individual polymer and clay components such as poor specificity, pH dependence, particle size sensitivity, and low water wettability. We also discuss different regeneration and wastewater treatment options (e.g., membrane, coagulant, and barrier/columns) using clay-polymer nanocomposites. Finally, we provide an economic analysis of the use of these adsorbents and suggest future research directions.

Strengthening social-environmental management at contaminated sites to bolster Green and Sustainable Remediation via a survey.

The Green and Sustainable Remediation (GSR) movement demands informed, integrated, and holistic management of contaminated sites. As such, GSR may become increasingly relevant in developing countries such as China, where vast areas of contaminated land require clean-up. Among other efforts, the World Bank together with China's Foreign Economic Cooperation Office is facilitating GSR adoption through the development of a guideline on social-environmental management. However, there are no existing studies that have considered how the established remediation industry perceives its effectiveness in addressing the various social-environmental management aspects, or how certain aspects have rooted. Without this information, it may be difficult to guide social-environmental practice forward, or introduce GSR into developing remediation markets with any precision. Therefore, a questionnaire survey of remediation participators was undertaken with principal component analysis (PCA) applied to the data to help group the various aspects. The PCA extracted two components for environmental management, ascribed to: (1) on-site/local impacts; and, (2) widespread impacts, and three social management components, ascribed to: (1) community inclusion; (2) economic gain; and, (3) health, safety, and welfare. It was found that the aspects the industry are most familiar with historically are generally dealt with more effectively than those that have only recently been introduced by the GSR movement. In particular, bolstering the management of widespread environmental impacts and giving greater regard to the economic gain of remediation, may be beneficial. In developing countries, public engagement is often very limited, necessitating improvement in remediation policy and guidance.

Targeting cleanups towards a more sustainable future.

A tension arises between society's disposition to protect people at risk from environmental pollution, and an aversion towards the potential harmful side-effects associated with cleanup activities. Here we explore how setting different cleanup standards may influence some of the environmental, social, and economic side-effects of remediation, and how they can be quantified for incorporation into cleanup target setting; these include (1) secondary environmental impacts, assessed by life cycle assessment (LCA); (2) fatalities and injuries, assessed by actuarial risk analysis; and (3) the cost effectiveness of stringent cleanup standards, assessed by the incremental cost-effectiveness ratio (ICER). We argue that only by using optimal cleanup standards that integrate quantified remediation side-effects with health risk assessment (HRA) can the green and sustainable remediation (GSR) movement maximize its potential. Together, the combined approaches may provide a more holistic management of risks for a more sustainable future.