Given that cadmium (Cd) uptake by plants is linked to transpiration rate and activity of antioxidant enzymes and further that silicon (Si) can regulate them, it was hypothesized that improved Si nutrition could reduce Cd concentration in plants. Thus, present study was carried out to elucidate the positive effect of Si nutrition on the growth, activities of antioxidant enzymes and tissue cadmium (Cd) concentration in Cd-tolerant (Iqbal-2000) and Cd-sensitive wheat (Triticum aestivum L.) cultivars. Fifteen days after seedling transplantation, 15 μM Cd stress alone and in combination with 0.6 mM Si was applied. Silicon application improved root and shoot dry matter of Cd-sensitive cultivar Sehar-2006 while the effect was non-significant in Cd-tolerant cultivar Iqbal-2000. Silicon-treated Cd-sensitive cultivar showed marked improvements in chlorophyll content and photosynthesis, while stomatal conductance and transpiration rate decreased by Si application. Silicon treatment enhanced the activities of enzymatic antioxidants including catalase, ascorbate peroxidase, guaiacol peroxidase and superoxide dismutase and the increase was higher for Cd-tolerant cultivar Iqbal-2000. Although Si nutrition depressed malondialdehyde (MDA) content in both Cd-stressed cultivars, the response was more evident in Cd-sensitive Sehar-2006. Lower lipid peroxidation was related to Si-induced increase in antioxidant activities only in Cd-sensitive cultivar. Silicon application decreased Cd accumulation in the roots and shoots of both the cultivars. The decrease in shoot Cd was associated with a decrease in Cd uptake by roots and Cd translocation from roots to shoots. Overall, it is concluded that Si suppressed Cd contents by decreasing transpiration rate in Cd-sensitive cultivar and by increasing antioxidant activity in Cd-tolerant cultivar.

Undisturbed outdoor lysimeters containing arable loamy sand soil were used to examine the influence of either heavy rain events (high frequency of high rain intensity), steady rain (continuous rainfall of low rain intensity), and natural rainfall on the transport and retention of surfactant-stabilized silver nanoparticles (AgNP). In addition, the AgNP–soil associations within the Ap horizon were analyzed by means of particle-size fractionation, asymmetrical flow field-flow fractionation coupled with UV/Vis-detection and inductively coupled plasma mass spectrometer (AF4-UV/Vis-ICP-MS), and transmission electron microscopy coupled to an energy-dispersive X-ray (TEM-EDX) analyzer. The results showed that AgNP breakthrough for all rain events was less than 0.1% of the total AgNP mass applied, highlighting that nearly all AgNP were retained in the soil. Heavy rain treatment and natural rainfall revealed enhanced AgNP transport within the Ap horizon, which was attributed to the high pore water flow velocities and to the mobilization of AgNP–soil colloid associations. Particle-size fractionation of the soil revealed that AgNP were present in each size fraction and therefore indicated strong associations between AgNP and soil. In particular, water-dispersible colloids (WDC) in the size range of 0.45–0.1 μm were found to exhibit high potential for AgNP attachment. The AF4-UV/Vis-ICP-MS and TEM-EDX analyses of the WDC fraction confirmed that AgNP were persistent in soil and associated to soil colloids (mainly composed of Al, Fe, Si, and organic matter). These results confirm the particularly important role of soil colloids in the retention and remobilization of AgNP in soil. Furthermore, AF4-UV/Vis-ICP-MS results indicated the presence of single, homo-aggregated, and small AgNP probably due to dissolution.

Phosphorus (P) limitation has been demonstrated for micro-polluted surface water denitrification treatment in previous study. In this paper, a lab-scale comparative study of autotrophic denitrification (ADN) and heterotrophic denitrification (HDN) in phosphorus-limited surface water was investigated, aiming to find out the optimal nitrogen/phosphorus (N/P) ratio and the mechanism of the effect of P limitation on ADN and HDN. Furthermore, the optimal denitrification process was applied to the West Lake denitrification project, aiming to improve the water quality of the West Lake from worse than grade V to grade IV (GB3838-2006). The lab-scale study showed that the lack of P indeed inhibited HDN more greatly than ADN. The optimal N/P ratio for ADN and HDN was 25 and a 0.15 mg PO43--P L−1 of microbial available phosphorus (MAP) was observed. P additions could greatly enhance the resistance of ADN and HDN to hydraulic loading shock. Besides, The P addition could effectively stimulate the HDN performance via enriching the heterotrophic denitrifiers and the denitrifying phosphate-accumulating organisms (DNPAOs). Additionally, HDN was more effective and cost-effective than ADN for treating P-limited surface water. The study of the full-scale HDBF (heterotrophic denitrification biofilter) indicated that the denitrification performance was periodically impacted by P limitation, particularly at low water temperatures.

The present study aimed to investigate the metabolic response of edible amaranth cultivars to salt stress and the induced rhizosphere effects on Cd mobilization in soil. Two edible amaranth cultivars (Amaranthus mangostanus L.), Quanhong (low-Cd accumulator; LC) and Liuye (high-Cd accumulator; HC), were subject to salinity treatment in both soil and hydroponic cultures. The total amount of mobilized Cd in rhizosphere soil under salinity treatment increased by 2.78-fold in LC cultivar and 4.36-fold in HC cultivar compared with controls, with 51.2% in LC cultivar and 80.5% in HC cultivar being attributed to biological mobilization of salinity. Multivariate statistical analysis generated from metabolite profiles in both rhizosphere soil and root revealed clear discrimination between control and salt treated samples. Tricarboxylic acid cycle in root was up-regulated to cope with salinity treatment, which promoted release of organic acids from root. The increased accumulation of organic acids in rhizosphere under salt stress obviously promoted soil Cd mobility. These results suggested that salinity promoted release of organic acids from root and enhanced soil Cd mobilization and accumulation in edible amaranth cultivar in soil culture.

The upper Columbia River and associated valley systems are highly contaminated with metal wastes from nearby smelting operations in Trail, British Columbia, Canada (Teck smelter), and to a lesser extent, Northport, Washington, USA (Le Roi smelter). Previous studies have investigated depositional patterns of airborne emissions from these smelters, and documented the Teck smelter as the primary metal contamination source. However, there is limited research directed at whether these contaminants are bioavailable to aquatic organisms. This study investigates whether smelter derived contaminants are bioavailable to freshwater zooplankton. Trace metal (Zn, Cd, As, Sb, Pb and Hg) concentrations and Pb isotope compositions of zooplankton and sediment were measured in lakes ranging from 17 to 144 km downwind of the Teck smelter. Pb isotopic compositions of historic ores used by both smelters are uniquely less radiogenic than local geologic formations, so when zooplankton assimilate substantial amounts of smelter derived metals their compositions deviate from local baseline compositions toward ore compositions. Sediment metal concentrations and Pb isotope compositions in sediment follow significant (p < 0.001) negative exponential and sigmoidal patterns, respectively, as distance from the Teck smelting operation increases. Zooplankton As, Cd, and Sb contents were related to distance from the Teck smelter (p < 0.05), and zooplankton Pb isotope compositions suggest As, Cd, Sb and Pb from historic and current smelter emissions are biologically available to zooplankton. Zooplankton from lakes within 86 km of the Teck facility display isotopic evidence that legacy ore pollution is biologically available for assimilation. However, without water column data our study is unable to determine if legacy contaminants are remobilized from lake sediments, or erosional pathways from the watershed.

Photodemethylation can be one of the primary processes for loss of neurotoxic methylmercury (MeHg) in freshwater lakes. Few studies have quantified seasonal variations in photodemethylation rate constants as a function of dissolved organic matter (DOM). We conducted 1-week irradiation experiments in two seasons to test for spatial and temporal differences in photodemethylation potential in temperate lake waters. Six study lakes in Kejimkujik National Park, Nova Scotia were sampled in summer and fall to include a range of naturally occurring DOM concentrations (4.4–13.4 and 3.9–16.4 mg C L⁻¹, respectively). A negative linear relationship (R² = 0.76, p = 0.01) was found between DOM concentration and photodemethylation rate constant across seasons, indicating that DOM is a strong predictor of MeHg photodemethylation independent of seasonal effects. The two highest carbon lakes (BDW and PEB) had significantly higher energy-normalized photodemethylation rate constants in summer compared to fall corresponding with lower DOM concentrations in summer relative to fall. Additionally, there were negative linear relationships between MeHg photodemethylation and DOM photomineralization (R²s = 0.58–0.72) and DOM photobleaching (R²s = 0.83–0.90). This key finding suggests that competition for photons within DOM structures may reduce the potential for MeHg photodemethylation in high carbon waters and that this relationship persists across seasons.

Crumpled graphene oxide nanosheets have drawn large attentions due to its compressibility and self-avoiding stacking as flat graphene sheets trend to aggregate and restack. Up to now, most of the synthesis approaches were relied on external substrates, such as elastic substrates or ultrasonic atomizer, and the crumpled structures were obtained in a solid state directly. Here we report a facile method to produce crumpled dispersive nanosheets in solution through general base-washing treatment by taking advantage of the amphipathy of GO nanosheets. With the dissociation of oxygen-functional groups on nanosheets in alkaline environment, highly water-soluble oxidative debris (OD) would fall off from the nanosheets due to the increase of electrostatic repulsions, and resulted in the crumple of the flat sheets, while the covalent oxygen-functional groups on the nanosheets were reserved. As a result, the nanosheets remained dispersible in solution, and could be used directly for surface modifications. Pt nanoparticles could be directly deposited onto both sides of the sheets through common nucleation and growth from precursor ions process. Compared with flat graphene-based hybrid, the catalytic performance of crumpled-graphene-Pt (CG-Pt) is more excellent and attractive, and corresponding apparent kinetic rate constant (kₐₚₚ) of CG-Pt toward 4-nitrophenol reduction is enhanced by 2.7–4.6-fold. This study provides a new and facile way to fabricate crumpled nanosheets and demonstrates to be easy modified for various purpose.

E-waste generation has become a serious environmental challenge worldwide. The global quantity of e-waste was estimated 44.7 million metric tons (Mt) in 2016. The improper recycling of e-waste is still a challenging issue in developing countries.The objectives of this a review article to present comprehensive information of recent studied on environment pollution and effect on human health in China.The search engines consulted, period of publications reviewed 2015–2018. For search study, we used different key words: ‘improper recycling’, ‘primitive recycling,’ ‘backyard recycling,’ ‘e-waste,’ ‘WEEE’, and the studies related to improper recycling of e-waste.According to reports, the e-waste recycled by unorganized sectors in China. These unorganized sector workers daily go for work, such as e-waste collection from consumer house and manual dismantling of e-waste by using simple method, at unauthorized workshop. These backyard workshop are reported in small clusters in or around city e.g., Qingyuan village; Taizhou, Longtang Town, Guiyu, nearby Nanyang River and Beigang River in China.The earlier reported studies directed the heavy metals effect (causing effects both acute and chronic effects; respiratory irritation, reproductive problem, cardiovascular and urinary infection/disease) on human health. According the reports, the improper recycling of e-waste which need to be address for the environment protection and prevention of public health risk. However, if e-waste exposure is not avoided very well, the associated contamination will be continuing, and simultaneously needful to increase the awareness for proper e-waste management in China.In order to solve the e-waste problem in China, more detail research is needed. Furthermore, for environment protection and health safety, the proper e-waste dismantling techniques, environmentally sound management, and the regular monitoring are very important.

The objective of this study is to investigate the qualitative contribution of internal and external factors of the area contaminated by polystyrene (PS) in coastal marine environments. This study is based on the extensive results of monitoring the styrene oligomers (SOs) present in sand and seawater samples along various coastlines of the Pacific Ocean. Here, anthropogenic SOs is derived from PS during manufacture and use, and can provide clues about the origin of SOs by PS pollution. The monitoring results showed that, if the concentration of SOs in water is higher than those concentrations in beach sand, this area could be affected by PS plastic caused by an external factor. On the other hand, if the concentration of SOs is higher in the beach sand, the region can be mainly influenced by PS plastic derived from its own area. Unlike the case of an external factor, in this case (internal influence), it is possible to take policy measures of the area itself for the PS plastic problem. Thus, this study is motivated by the need of policy measures to establish a specific alternative to the problems of PS plastic pollution in ocean environments.

Microplastics are emerging pollutants which have been extensively detected in water environments. However, little is known about microplastic pollution in soil environments. In this study, we investigated microplastics and mesoplastics in farmland soils from twenty vegetable fields around the suburbs of Shanghai. In each site, three duplicate soil samples were collected from shallow (0–3 cm) and deep soils (3–6 cm), respectively. Microplastics (sizes of 20 μm - 5 mm) and mesoplastics (5 mm - 2 cm) were detected using methods of density extraction, 30% H₂O₂ digestion and micro-fourier transform infrared spectroscopy. The abundance of microplastics was 78.00 ± 12.91 and 62.50 ± 12.97 items kg⁻¹ in shallow and deep soils, respectively. While, mesoplastics were found with abundance of 6.75 ± 1.51 and 3.25 ± 1.04 items kg⁻¹ in shallow and deep soils. Among these micro(meso)plastics, 48.79% and 59.81% were in size of <1 mm in shallow and deep soils. The main morphotypes of microplastics included fiber, fragment and film, mostly in color of black or transparent. Moreover, we found that topsoil contained higher concentrations and larger sizes of micro(meso)plastics than deep soil. In addition, the vast majority of micro(meso)plastics were polypropylene (50.51%) and polyethylene (43.43%). This study reveals occurrence and characteristics of microplastic pollution in typical farmland soils. It provides important data for subsequent research on microplatics in the terrestrial ecosystem.