Fe-Ni bimetallic nanoparticles supported on CNTs (Fe-Ni/CNTs) were synthesized, characterized, and applied for removal of 2,4-dichlorophenol (2,4-DCP) in aqueous solution. The removal performance was enhanced drastically on Fe-Ni/CNTs with respect to monometallic Fe/CNTs. The synergistic effect between Fe-Ni nanoparticles and CNTs has been studied in detail. The research results indicated that the doping of Ni played an important role in promoting the catalytic degradation of 2,4-DCP. And the presence of CNTs not only could effectively reduce the aggregation of nanoparticles but also facilitate the mass transfer of 2,4-DCP and the formation of active atomic hydrogen during the catalytic process. In addition, the removal kinetics of 2,4-DCP by Fe-Ni/CNTs were in agreement with a pseudo-first-order model, and the rate constants were dependent on a number of factors including the initial concentration of 2,4-DCP, the dosage of Fe-Ni/CNTs, pH value of the solution, and doping amount of Ni. The degradation mechanism involved the adsorption by CNTs and catalytic reduction by Fe under the stimulating of Ni, and the preferred dechlorination followed the order of para-Cl > ortho-Cl. The study confirmed that Fe-Ni/CNTs had a potential to be a promising catalytic material for removal of chlorophenol and had a great prospect for practical application.

Nanosized sorbents for the removal of heavy metal ions are preferred due to high surface area, smaller size, and enhanced reactivity during adsorbate/adsorbent interactions. In the present study, Fe₃O₄, SnO₂, and TiO₂ nanoparticles were prepared by microemulsion-assisted precipitation method. The particles were characterized by BET surface area, X-rays diffraction (XRD), thermogravimetric analysis (TGA), Fourier transform infrared (FTIR) spectroscopy, transmittance electron microscopy (TEM), and X-ray photoelectron (XPS) spectroscopy. The respective particle sizes calculated from TEM were 7 nm (± 2), 10 nm (± 2), and 20 nm (± 3) for Fe₃O₄, SnO₂, and TiO₂. The adsorbents were employed for the adsorption of Pb²⁺ ions from the aqueous solutions. The respective maximum adsorption capacity for Fe₃O₄, SnO₂, and TiO₂ nanoparticles was 53.33, 47.21, and 65.65 mg/g at 313 K. Based on the exchange reaction taking place on the surfaces of Fe₃O₄, SnO₂, and TiO₂, it is concluded that Pb²⁺ ions are adsorbed in hydrated form. The X-ray photoelectron spectroscopy (XPS) studies also support the exchange mechanism and confirmed the presence of elements like Fe, Sn, Ti, Pb, and O and their oxidation states. Both Langmuir and Freundlich models in non-linear form were applied, however, based on RL values, the Langmuir model fits well to the sorption data. Moreover, adsorption parameters were also determined by using non-linear form of the Langmuir model along with statistical approaches to remove error. The qₘ and Kb values confirm better adsorption capacity and binding strength for Pb²⁺ ions as compared to the values reported in the literature.

An appraisal of seawater intrusion into the coastal aquifers is one of the major issues for groundwater resource management. The GALDIT model applies to the analysis of multiple parameters using systematic GIS techniques for mapping and assessment of seawater intrusion vulnerability. It demarcates the mapping of potential vulnerability that shows a higher vulnerability to seawater intrusion in various parts of the coast and the estimated vulnerability index value of 7.50 and 9.64. An area of 33.0 km² spread in the low-lying coastal area comprising estuaries, salt marshes, and saltpans shows the high vulnerability condition with an estimated vulnerability value of 6.42–7.50. An area of 73.20 km² spread over coastal and alluvial plains experiences moderate vulnerability (temporal salinity in the groundwater sources) with an estimated vulnerability index value of 5.46–6.42. Aquifers underlying coastal uplands (hard rock formations) and some parts of accretionary beaches (2.05 km²) are relatively protected fresh groundwater sources, wherein the estimated vulnerability index is 4.55–5.46. The vulnerability mapping of the GALDIT model using hydrochemical analysis of primary groundwater parameters such as TDS, Cl⁻, HCO₃, and Cl⁻/HCO₃ ratio is validated. Higher concentration of TDS (2637–4162 mg/l) and Cl⁻ (1268–2347 mg/l) is taken for the areas falling under higher vulnerability to seawater intrusion, especially in the placer mining sites and coastal areas facing erosion. Similarly, the groundwater sources of the low-lying areas including estuaries, salt marshes, saltpans, and backwater were noted to have higher values of Cl⁻/HCO₃ with a rationality of 9.87–12.18. Hydrological facies shows the highest concentration of NaCl in the groundwater sources within the proximity of eroded beaches, saltwater bodies, and sand mining areas. A hydrochemical facies evolution (HFE) diagram represents the hydrochemical facies of groundwater elements that shows an intrusion of seawater into the coastal aquifers underlying the very high vulnerable zones. Higher bicarbonate concentration (233–318 mg/l) is noticed in the upland areas and some parts of dunes and accreted beaches, sandy coasts, and uplands. Vulnerability analysis reveals that those areas near saltwater bodies and eroding coasts are prone to lateral and vertical diffusion of saltwater. The geodatabase developed through such modeling studies can help in planning and developing activities for sustainable groundwater resource management in coastal areas.

The degradation mechanism of the pollutant hexachloroethane (HCA) by a suspension of Pd-doped zerovalent iron microparticles (Pd-mZVI) in dissolved lactic acid polymers and oligomers (referred to as PLA) was investigated using gas chromatography and the indirect monitoring of iron corrosion by continuous measurements of pH, oxidation-reduction potential (ORP), and conductivity. The first experiments took place in the absence of HCA, to understand the evolution of the Pd-mZVI/PLA/H₂O system. This showed that the evolution of pH, ORP, and conductivity is related to changes in solution chemistry due to iron corrosion and that the system is initially cathodically controlled by H⁺ mass transport to Pd surfaces because of the presence of an extensive PLA layer. We then investigated the effects of Pd-mZVI particles, temperature, initial HCA concentration, and PLA content on the Pd-mZVI/PLA/HCA/H₂O system, to obtain a better understanding of the degradation mechanism. In all cases, HCA dechlorination first requires the production of atomic hydrogen H*—involving the accumulation of tetrachloroethylene (PCE) as an intermediate—before its subsequent reduction to non-chlorinated C₂ and C₄ compounds. The ratio between Pd-mZVI dosage, initial HCA concentration, and PLA content affects the rate of H* generation as well as the rate-determining step of the process. A pseudo-first-order equation can be applied when Pd-mZVI dosage is much higher than the theoretical stoichiometry (600 mg for [HCA]₀ = 5–20 mg L⁻¹). Our results indicate that the HCA degradation mechanism includes mass transfer, sorption, surface reaction with H*, and desorption of the product.

Typical recreational water risk to swimmers is assessed using epidemiologically derived correlations by means of fecal indicator bacteria (FIB). It has been documented that concentrations of FIB do not necessarily correlate well with protozoa and viral pathogens, which pose an actual threat of illness and thus sometimes may not adequately assess the overall microbial risks from water resources. Many of the known pathogens have dose-response relationships; however, measuring water quality for all possible pathogens is impossible. In consideration of a typical freshwater receiving secondarily treated effluent, we investigated the level of consistency between the indicator-derived correlations and the sum of risks from six reference pathogens using a quantitative microbial risk assessment (QMRA) approach. Enterococci and E. coli were selected as the benchmark FIBs, and norovirus, human adenovirus (HAdV), Campylobacter jejuni, Salmonella enterica, Cryptosporidium spp., and Giardia spp. were selected as the reference pathogens. Microbial decay rates in freshwater and uncertainties in exposure relationships were considered in developing our analysis. Based on our exploratory assessment, the total risk was found within the range of risk estimated by the indicator organisms, with viral pathogens as dominant risk agents, followed by protozoan and bacterial pathogens. The risk evaluated in this study captured the likelihood of gastrointestinal illnesses only, and did not address the overall health risk potential of recreational waters with respect to other disease endpoints. Since other highly infectious pathogens like hepatitis A and Legionella spp. were not included in our analysis, these estimates should be interpreted with caution.

Fertilization and straw return have been widely adopted to maintain soil fertility and increase crop yields, but their long-term impacts on the accumulation and availability of cadmium (Cd) in paddy soils are still unconfirmed. Therefore, this study was undertaken in central China to investigate the accumulation, availability, and subsequent uptake of Cd by rice (Oryza sativa L.) in two adjacent field trials (P1 and P2, lasting for 10 and 12 years, respectively) under long-term straw return or in combination with chemical fertilizers. Obvious Cd accumulation, probably due to the notable Cd input from irrigation and traffic exhaust in the bulk soil (0–20 cm) of P1, was observed. The bulk soil of P2 received homogeneous straw return and chemical fertilizers, as did that of P1; however, the P2 soil almost showed Cd balance. Long-term straw return increased the portion of soil DTPA-extractable Cd to the total pool for both sites, but only P1 showed significant differences when compared to the controls. However, the highest Cd concentrations and the maximum bioconcentration factors in rice straw and grain were obtained using solo application of chemical fertilizers at both sites. Continuous additional applications of crop straw, in contrast, resulted in slightly decreased Cd uptake in rice straw, but not in grain. These findings demonstrate that neither long-term straw return nor fertilization leads directly to notable Cd accumulation, but that the promotion effects of long-term chemical fertilizer applications on Cd uptake in rice need more attention.

Post-industrial era has witnessed significant advancements at unprecedented rates in the field of medicine and cosmetics, which has led to affluent use of pharmaceuticals and personal care products (PPCPs). However, this has exacerbated the influx of various pollutants in the environment affecting living organisms through multiple routes. Thousands of PPCPs of various classes—prescription and non-prescription drugs—are discharged directly into the environment. In this review, we have surveyed literature investigating plant-based remediation practices to remove PPCPs from the environment. Our specific aim is to highlight the importance of plant-bacteria interplay for sustainable remediation of PPCPs. The green technologies not only are successfully curbing organic pollutants but also have displayed certain limitations. For example, the presence of biologically active compounds within plant rhizosphere may affect plant growth and hence compromise the phytoremediation potential of constructed wetlands. To overcome these hindrances, combined use of plants and beneficial bacteria has been employed. The microbes (both rhizo- and endophytes) in this type of system not only degrade PPCPs directly but also accelerate plant growth by producing growth-promoting enzymes and hence remediation potential of constructed wetlands.

The feasibility of biomass-based activated carbons has received a huge attention due to their excellent characteristics such as inexpensiveness, good adsorption behaviour and potential to reduce a strong dependency towards non-renewable precursors. Therefore, in this research work, eco-friendly activated carbon from palm kernel shell that has been produced from one-stage physical activation by using the Box-Behnken design of Response Surface Methodology is highlighted. The effect of three input parameters—temperature, dwell time and gas flow rate—towards product yield and carbon dioxide (CO₂) uptake at room temperature and atmospheric pressure are studied. Model accuracy has been evaluated through the ANOVA analysis and lack-of-fit test. Accordingly, the optimum condition in synthesising the activated carbon with adequate CO₂ adsorption capacity of 2.13 mmol/g and product yield of 25.15 wt% is found at a temperature of 850 °C, holding time of 60 min and CO₂ flow rate of 450 cm³/min. The synthesised activated carbon has been characterised by diverse analytical instruments including thermogravimetric analyser, scanning electron microscope, as well as N₂ adsorption-desorption isotherm. The characterisation analysis indicates that the synthesised activated carbon has higher textural characteristics and porosity, together with better thermal stability and carbon content as compared to pristine palm kernel shell. Activated carbon production via one-step activation approach is economical since its carbon yield is within the industrial target, whereas CO₂ uptake is comparable to the synthesised activated carbon from conventional dual-stage activation, commercial activated carbon and other published data from literature.

In this study, an innovative analytical methodology capable of selectively identifying and quantifying mercury contamination by the association of solid-phase extraction using ion-imprinted polymers as a sorbent phase and differential pulse anodic stripping voltammetry is proposed. To this end, the ion-imprinted polymers were synthesized and characterized by infrared spectroscopy and atomic force microscopy. The sorption capacities and the selectivity of the ion-imprinted polymers were compared to the ones related to the non-imprinted ones. Next, the experimental parameters of this solid-phase extraction method (IIP-SPE) were evaluated univariately. The selectivity of this polymeric matrix against other cations (Cd II, Pb II, and Cu II) was also evaluated. Limits of detection (LOD) and quantification (LOQ) obtained for the here proposed methodology were 0.322 μg L⁻¹ and 1.08 μg L⁻¹, respectively. Also, the precision of 4.0% was achieved. The method was finally applied to three water samples from different sources: for the Piratininga and Itaipu Lagoon waters, Hg II concentrations were below the LOQ and for Vargem River waters a concentration equal to 1.35 ± 0.07 mg L⁻¹ was determined. These results were confirmed by recovery tests, resulting in a recovery of 96.2 ± 4.0%, and by comparison with flame atomic absorption spectrometry, resulting in statistical conformity between the two methods at 95% confidence level.

In general, the diffusive gradients in thin films (DGT) technique is an effective tool for evaluating metal bioavailability; however, its applicability is subject to the type of metal and organism involved. In this study, the accumulated masses of Hg in DGT probes and in the earthworm species Eisenia fetida were monitored for 10 days, to test if the DGT technique can be used as a predicting method for the bioavailability of soil Hg to earthworms. In the Hg exposure tests using soils prepared with different peat moss concentrations of 5, 10, 15, and 20% and varying pH values of 4.6, 5.6, and 6.2, the experimentally determined DGT-soil accumulation factor (DSAF) and biota-soil accumulation factor (BSAF) both increased as the peat moss content decreased and the pH increased. According to a one compartment model, this was a result of the increased Hg uptake rate constant (k₁) and the relatively stable Hg elimination constant (k₂) under lower peat moss and higher pH conditions. It is interesting to note that the Hg uptake rates by DGT and earthworms were considerably higher for fresh soils than for aged soils, while porewater (and acid-extractable) Hg concentrations were rather similar between the two types of soils. Across diverse soil properties, steady-state Hg in earthworm tissue showed a strong positive correlation with DGT-measured Hg flux ([earthworm Hg] = 354(DGT−Hg flux)−34, r² = 0.88), while meager correlations were found between Hg concentration in earthworms and that in porewater (and acid-extractable). The overall results indicate that DGT-measured Hg flux is a better tool than conventional methods for predicting Hg bioavailability for earthworms inhabiting diverse types of soil.