Acid rain is a global environmental problem that threatens agricultural production. Calcium (Ca), as a signal substance for physiological activities, has been known to regulate plant growth under abiotic stresses. To clarify whether calcium could be one of possible ways to alleviate the reduction caused by acid rain in agricultural production and investigate its regulating mechanism on adaptation of plants under acid rain stress, we studied the effect of exogenous Ca²⁺ (5 mM CaCl₂) on growth of soybean at different growth stages (seedling, flowering-podding, and filling stages) as well as yield and grain quality of soybean under simulated acid rain (pH 4.5 or pH 3.0) stress. We found that the application of Ca²⁺ could regulate the activity of plasma membrane H⁺-ATPase, for mitigating the increase of ammonium and the decrease of nitrate and phosphorus in soybean roots, which mitigated the inhibition on growth and improved the yield and grain quality of soybean under simulated acid rain stress. In addition, the alleviating effect of exogenous Ca²⁺ on soybean was the most significant at seedling stage. The results indicate that the exogenous Ca²⁺ could enhance the adaptation of soybean and facilitate the recovery of soybean productivity and grain quality under simulated acid rain stress by maintaining the uptake of nitrate, ammonium, and phosphorus.

Environmental fate and impacts of graphene oxide (GO) nanoparticles are strongly influenced by their subsurface behaviors. The present work examined the aggregation and transport behaviors of GO in saturated sand columns under different temperature (6 and 24 °C), surfactant concentration (0.04% and 0.4%), cation valence, and electrolyte concentration conditions. In monovalent electrolyte (NaCl), although the presence of cationic surfactant (CTAB) notably increased GO stability and mobility, GO ripening happened due to their concurrent aggregation and transport in the columns. GO particles were more mobile at a lower temperature probably because the CTAB coating of GO increased with decreasing temperature, leading to stronger electrostatic repulsion. Furthermore, GO retention in the media increased with the increase of NaCl concentration due to the enhanced compression of the electric double layer. In multivalent electrolyte (CaCl₂ or AlCl₃), the presence of CTAB greatly improved GO stability and mobility and no deposition occurred in saturated porous media under all the tested conditions. This is because the CTAB coating of GO diminished the cation bridging effects in both GO-GO and GO-sand systems. Results from extended Derjaguin–Landau–Verwey–Overbeek (XDLVO) theory considering steric repulsion suggest that secondary minimum aggregation and depositions were the main mechanisms of GO retention transport in monovalent electrolyte in saturated porous media.

In this paper, we present a characterization of the optical properties of the aerosols emitted during biomass burning (BB) season in the period 2005–2009. Trends of aerosol optical depth (AOD), Angstrom exponent (α), and precipitable water (PW) were analyzed using a 5-year dataset from AErosol RObotic NETwork (AERONET) observations over Tuxtla Gutierrez (TG), Chiapas. The overall mean AOD (500 nm) during the 2005–2009 period was 0.26 ± 0.18. However, monthly mean values of AOD > 0.5 during the spring months (April and May) would indicate the high load of particles emitted by fires. The overall mean of α (440–870 nm) was 1.40 ± 0.21, which confirms the presence of fine aerosols. Additionally, the combined analysis of the α with its spectral curvature δα, and the results from the spectral de-convolution algorithm (SDA) shows that fine-mode aerosols dominated AOD variability in TG. In this paper, the trajectories of air masses (400 and 1500 m, a.s.l.) arriving at the TG site were classified by using backward trajectory cluster analysis. Trajectory clustering results indicate a BB regional transport from Central America that affects the atmosphere in southeastern Mexico. We use observations of fire radiative power (FRP) from the Moderate Resolution Imaging Spectroradiometer (MODIS) to study the incidence of wildfires and to estimate the BB emissions from 2005 to 2009 in southeastern Mexico. The results indicated a gradual decrease in fires throughout the years. Campeche and Yucatan are the states in southeastern Mexico where BB produces the highest emissions of carbon dioxide (CO₂), carbon monoxide (CO), black carbon (BC), and particulate material PM₂.₅. However, the largest emissions come from wildfires in Guatemala. Finally, to put in context the aerosol optical properties over southeastern Mexico, the sun photometric measurements in TG are compared with those retrieved from AERONET stations located in other tropical biomass burning regions (Brazil and Zambia).

This study was conducted to assess the proximate analysis (protein, carbohydrate, lipid, and moisture content) and concentration levels of metals (Zn, Cu, Cd, Pb, and Cr) in the muscles of selected shellfish (Portunus reticulatus, P. segnis, P. sanguinolentus, Scylla olivaceae, Penaeus monodon, and P. indicus) species. The concentration of metals showed significant difference (p > 0.05) among species. The detected concentrations of the analyzed heavy metals were below the daily intake and legal limits set by national and international standards. The THQs and CR index were calculated to evaluate the risk estimation of the metal contamination associated with the human health. The THQ values of all metals were below 1 in all species, indicated that there is no risk of adverse health effect, but the risk of elevated intakes of heavy metals adversely affecting food safety for the studied species. The CR index indicated that Cd and Pb caused the greatest cancer risk. The correlation and multivariate (principle component analysis) among metal concentration and nutritional quality were also evaluated. The carbohydrate and moisture showed the positive correlation (p > 0.05) with metals. The biochemical results of the present work clearly indicate that there was a significant difference in the muscles of shellfish. It was concluded that more effective controls should be focused on Cd and Pb to reduce pollution for quality and seafood safety concern.

Lotus seed shell was employed using one-step method combining carbonization with ZnCl₂ activation to synthesize activated carbons because of its inexpensiveness and local accessibility. The lotus seed shell–activated carbons (LSSACs) with the highest surface area (2450.8 m²/g) and mesoporosity (98.6%) and the largest pore volume (1.514 cm³/g) were tailored under optimum conditions as follows: impregnation ratio = 2:1, carbonization temperature = 600 °C, and time = 1.0 h. The surface Zn(II), abundant hydroxyl, and carboxyl functional groups from the activation process could result in rapid Pb(II) adsorption onto the LSSAC surface through surface complexation, ion exchange, or precipitation. The maximum monolayer adsorption capacity (qₘ) for Pb(II) of 247.7 mg/g at 25 °C could be fitted from the Langmuir isotherm. The Gibbs free energy (△G) and positive enthalpy (△H) indicated that the adsorption process was spontaneous and endothermic, and to some extent, it was explained by the intra-particle diffusion mechanism. Our results may provide a promising way to produce activated carbons with high adsorption capacity using solid waste, which will eventually promote the environmental sustainability.

For remediating polluted soils, phytoextraction of metals received considerable attention in recent years, although slow removal of metals remained a major constraint in this approach. We, therefore, studied the effect of selected organic and inorganic amendments on the solubility of zinc (Zn), cadmium (Cd), and lead (Pb) in polluted soil and enhancing the efficacy of phytoextraction of these metals by Indian mustard (Brassica juncea cv. Pusa Vijay). For this purpose, a greenhouse experiment was conducted using a metal-polluted soil to evaluate the effect of amendments, viz. green manure (T2), EDTA (T3), sulfur (S)+S oxidizing bacteria (Thiobacillus spp.) (T4), metal-solubilizing bacteria (Pseudomonas spp.) (T5), and green manure + metal-solubilizing bacteria (T6), on solubility and bioavailability of Zn, Cd, and Pb. Distribution of metals in different soil fractions revealed that Cd content in water soluble + exchangeable fraction increased to the extent of 34.1, 523, 133, 123, and 75.8% in T2, T3, T4, T5, and T6 treatments, respectively, over control (T1). Cadmium concentrations in soil solution as extracted by Rhizon sampler were recorded as 3.78, 88.1, 11.2, 6.29, and 4.27 μg L⁻¹in T2, T3, T4, T5, and T6, respectively, whereas soil solution concentration of Cd in T1 was 0.99 μg L⁻¹. Activities of Cd (pCd²⁺) in Baker soil extract were 12.2, 10.9, 6.72, 7.74, 7.67, and 7.05 for T1, T2, T3, T4, T5, and T6, respectively. Cadmium contents in shoot were recorded as 2.74, 3.12, 4.03, 4.55, 4.68, and 4.63 mg kg⁻¹ in T1, T2, T3, T4, T5, and T6 treatments, respectively. Similar trend in Zn and Pb content with different magnitude was also observed across the different amendments. Cadmium uptake by shoot of mustard was enhanced to the extent of 125, 62.5, 175, 175, and 212% grown on T2-, T3-, T4-, T5-, and T6-treated soil, respectively, over T1. By and large, free ion activity of metals as measured by Baker soil test proved to be the most effective index for predicting Zn, Cd, and Pb content in shoot of mustard, followed by EDTA and DTPA. Among the metal fractions, only water soluble + exchangeable metal contributed positively towards plant uptake, which explained the variation in shoot Zn, Cd, and Pb content to the extent of 74, 81, and 87%, respectively, along with other soil metal fractions. Risk to human health for intake of metals through the consumption of leafy vegetable (mustard) grown on polluted soil in terms of hazard quotient (HQ) ranged from 0.64 to 1.10 for Cd and 0.11 to 0.34 for Pb, thus rendering mustard unfit for the human consumption. Novelty of the study mainly consisted of the use of natural means and microorganisms for enhancing solubility of metals in soil with the ultimate aim of hastening the phytoremediation.

In the present study, the Taguchi design (TD) and the Box-Behnken design (BBD) were used to determine the effect of surfactant concentration, flushing velocity, and dense non-aqueous-phase liquid–trichloroethylene (DNAPL TCE) mass on the time of remediation for the removal of DNAPL zones, which is one of the main persistent sources of groundwater pollution. In the Taguchi approach, the performance of the response variable is measured based on the signal-to-noise (S/N) ratio whereas estimation of the full quadratic model of the parameters is allowed in the Box-Behnken design. The mean experimental values ranged between 3.97–8.31 and 4.01–9.70 for BBD and TD, respectively. Surfactant concentration was identified as the most significant parameter contributing to remediation efficiency in both design techniques. Minimum remediation effort was determined as 5.99 at obtained optimal conditions of surfactant concentration (2.5%), flushing rate (6 cm/h), and DNAPL TCE mass (365 mg) using BBD. In the case of TD, the optimal conditions were determined at a surfactant concentration of 10%, 2 cm/h flushing rate, and 365 mg DNAPL TCE mass. Analysis of variance (ANOVA) revealed a good relationship between the predicted and experimental values with 1.96% and 0.31% of the total variation that was not explained by the model using TD and BBD, respectively. Consequently, from this comparative study, it was concluded that BBD was a more suitable alternative to TD for the evaluation of remediation of DNAPL-contaminated sites.

Two nonionic POEA surfactants (CAS No. 61791-26-2), TA15 and TH30, were tested to establish their acute pathological effects and lethal concentrations (LC₅₀) in Piaractus brachypomus. Both compounds are nonionic surfactants produced by the alkoxylation of ethylene oxide with tallow amine, and they are used in variety of industries such as textiles, paints, metal working, agriculture, and polish manufacture. Fish were exposed to six concentrations of TA15 (0.2–4.0 mg/L) or TH30 (8–140 mg/L) for 96 h. The LC₅₀ for TA15 was 2.08 mg/L and for TH30 47.32 mg/L. The main clinical signs observed in fish exposed to 4 mg/L of TA15 and 32 to 140 mg/L of TH30, were lethargy, loss of shoaling behavior, respiratory distress, changes in swimming pattern, such as, loss of balance and abnormal buoyancy, prolapse of the lower lip and superior location in the water column. The highest concentrations of these compounds induced nervous signs and collapse. The relevant macroscopic lesions were skin and fins erosions with necrotic lysis of the caudal peduncle. In addition, hemorrhages in mouth, branchial arches, and petechial hemorrhages in skin were observed. An increased fluid in the celomic cavity and meningeal hemorrhages were also evident. Organs as gills, liver, brain, and anterior kidney presented severe lesions at the highest concentrations of each compound. For the first time, it is reported lesions in interrenal tissues and choroidal bodies, as well as severe telencephalic lesions associated with the POEA toxicity. These last lesions were more severe in fish exposed to TA15 than to TH30, although the pattern of injuries was similar with both substances. According to the Global Harmonized System of Classification and Labelling of Chemical (GHS) by the United Nations, we reported that TA15 is classified as Acute Category 2 and TH30 is Acute Category 3 for white cachama. Due to the low LC₅₀ and the highly toxic effects of both POEA compounds for neotropical fish, a revision of the regulation of the use of herbicide mixtures by Colombian legislation is necessary.

CO₂, SO₂, and NO are the main components of flue gas and can cause serious environmental issues. Utilization of these compounds in oleaginous microalgae cultivation not only could reduce air pollution but could also produce feedstock for biodiesel production. However, the continuous input of SO₂ and NO inhibits microalgal growth. In this study, the toxicity of simulated flue gas (15% CO₂, 0.03% SO₂, and 0.03% NO, balanced with N₂) was reduced through automatic pH feedback control. Integrated lipid production and CO₂ fixation with the removal of SO₂ and NO was achieved. Using this technique, a lipid content of 38.0% DW was achieved in Chlorella pyrenoidosa XQ-20044. The lipid composition and fatty acid profile indicated that lipid production by C. pyrenoidosa XQ-20044 cultured with flue gas is suitable as a biodiesel feedstock; 81.2% of the total lipids were neutral lipids and 99.5% of the total fatty acids were C16 and C18. The ratio of saturated fatty acids to monounsaturated fatty acids in the microalgal lipid content was 74.5%. In addition, CO₂, SO₂, and NO from the simulated flue gas were fixed and converted to biomass and lipids with a removal efficiency of 95.9%, 100%, and 84.2%, respectively. Furthermore, the utilization efficiencies of CO₂, SO₂, and NO were equal to or very close to their removal efficiencies. These results provide a novel strategy for combining biodiesel production with biofixation of flue gas.

The unique geographic location of Mt. Yulong in the Tibetan Plateau (TP) makes it a favorable site for mercury (Hg) study. Various snow samples, such as surface snow, snow pit, and snowmelt water were collected from Mt. Yulong in the southeastern TP. The average concentration of Hg was found to be 37 ± 26 ng L⁻¹ (mean ± SD), comparable to Hg concentration from other parts of TP in the same year, though it was comparatively higher than those from previous years, suggesting a possible increase of Hg concentration over the TP. The concentration of Hg was higher in the lower elevation of the glaciers possibly due to the surface melting concentration of particulates. Higher concentration of Hg was observed in the fresh snow, suggesting the possibility of long-range transportation. The average concentration of Hg from the snow pit was 1.49 ± 0.78 ng L⁻¹, and the concentration of Hg in the vertical profile of the snow pit co-varied with calcium ion (Ca²⁺) supporting the fact that the portion of Hg is from the crustal origin. In addition, the principal component analysis (PCA) confirmed that the source of Hg is from the crustal origin; however, the presence of anthropogenic source in the Mt. Yulong was also observed. In surface water around Mt. Yulong, the concentration of HgT was found in the order of Lashihai Lake > Reservoirs > Rivers > Swamps > Luguhu Lake. In lake water, the concentration of HgT showed an increasing trend with depth. Overall, the increased concentration of Hg in recent years from the TP can be of concern and may have an adverse impact on the downstream ecosystem, wildlife, and human health.