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Selecting representative groundwater monitoring wells in polluted areas is crucial to comprehensively assess groundwater pollution, thereby ensuring effective groundwater remediation. However, numerous factors can affect the effectiveness of groundwater monitoring well network optimizations. A local sensitivity analysis method was used in this study to analyze the hydrogeological parameters of a simulation groundwater solute transport model. The results showed a strong effect of longitudinal dispersion and transverse dispersion on the output results of the simulation model, and a good fit between the backpropagation neural network (BPNN)-based alternative model’s results and those obtained using the solute transport simulation model, accurately reflecting the input and output relationship of the simulation model. The optimized groundwater monitoring layout scheme consisted of four groundwater monitoring wells, namely no. 7, no. 16, no. 23, and no. 24. These wells resulted in a groundwater fluoride pollution rate of 98.44%, which was substantially higher than that obtained using the random layout scheme. In addition, statistical analysis of the fluoride groundwater pollution results obtained using the Monte Carlo random simulation highlighted continuous and high groundwater fluoride levels in the second and third pollution sources and their downstream groundwater. Therefore, more attention should be devoted to these sources to ensure the effective remediation of groundwater pollution in the study area.

Irrigation with water containing a variety of microcystins (MCs) may pose a potential threat to the normal growth of agricultural plants. To investigate the phytotoxicity of MC-LR at environmental concentrations on rice (Oryza sativa L.), the characteristics of uptake and accumulation in plant tissues, as well as a series of key physio-biochemical process changes in leaves of rice seedlings, were measured at concentrations of 0.10, 1.0, 10.0, and 50.0 μg·L−1 in hydroponic nutrient solutions for 7, 15, 20, and 34 days. Results showed that MC-LR could be detected in rice leaves and roots in exposure groups; however, a significant accumulation trend of MC-LR in plants (BCF > 1) was only found in the 0.10 μg·L−1 group. The time-course study revealed a biphasic response of O2•− levels in rice leaves to the exposure of MC-LR, which could be attributed to the combined effects of the antioxidant system and detoxification reaction in rice. Exposure to 1.0–50.0 μg·L−1 MC-LR resulted in significant depletion of GSH and MDA contents in rice leaves at later exposure times (15–34 days). Low MC-LR concentrations promoted nitric oxide synthase (NOS) activity, whereas high concentrations inhibited NOS activity during the later exposure times. The reduced sucrose synthase (SS) activities in rice exposed to MC-LR for 34 days indicated a decrease in the carbon accumulation ability of plants, and therefore may be directly related to the inhibition of plant growth under MC exposure. These findings indicate that the normal physiological status would be disrupted in terrestrial plants, even under exposure to low concentrations of MC-LR.

Soil heavy metal pollution caused by human activities has become one of the most critical environmental issues with a global concern. Phytoremediation is widely used due to its low cost and environmental friendliness. However, the impact of heavy metals on plant growth remains unclear. This study investigated the effects on the growth and photosynthetic activity of Picris divaricata Vant. under different cadmium concentrations using a hydroponics cultivation system. The results showed that the growth and photosynthetic processes of P. divaricata exhibited a phenomenon of promotion in low Cd concentrations and inhibition in high Cd concentrations. Under a low to medium Cd concentration (≤25 μM), there was no Cd toxicity in terms of plant growth, but high concentrations of Cd inhibited plant growth. The Fe content of leaves gradually increased as the Cd concentration increased; it reached 201.8 mg kg−1 in 75 μM Cd. However, there was no significant difference in Mn between the 75 μM Cd treatment and the control (p > 0.05). The contents of carotenoid ranged between 3.06 and 3.26 mg/g across the different Cd treatments, showing no significant differences. The treatment with 5–75 μM Cd did not directly affect the photosynthesis of P. divaricata. Higher Cd concentrations reduced the stomatal density on the of P. divaricata leaves, resulting in stomatal and mesophyll conductance limitations, indirectly affecting P. divaricata photosynthesis. These research results provide a reference for evaluating and selecting heavy metal tolerant plants and provide environmentally friendly approaches to remediate heavy metal pollution.

The ferromanganese nodules (FMNs) developing in soils of karst regions are naturally characterized by high heavy metal(loid)s contents due to several geological factors. Soil FMNs can considerably influence the geochemical behaviors of soil heavy metal(loid)s. However, the mechanisms of the FMN effects in soils of karst areas soils remain unclear, resulting in less understanding of the development process of karst soils. Therefore, the present study aims to investigate 21 individual FMNs collected in soils derived from carbonate rocks in Guangxi province, China, to reveal the mechanisms of heavy metal(loid)s enrichment in FMNs. The studied soil FMNs were mainly composed of Fe2O3, SiO2, Al2O3, MnO2, and TiO2, with proportions of 25.95, 20.8, 19.07, 3.98, and 1.23%, respectively. Compared to the background soils of Guangxi, the soil FMNs exhibited great enrichment in heavy metal(loid)s. The enrichment factors followed the order of Cd (243.33), Cr (49.67), Cu (5.46), Ni (8.37), Pb (23.68), Zn (15.4), and As (20.11). The heavy metal(loid)s contents in the soil FMNs of the karst areas were much higher than those observed in non-karst areas worldwide. According to the principal component analysis (PCA) results, the first three principal components contributed to about 88.81% of the total variance of the FMN compositions. PC1 (50.90%) suggested the presence of quartz, feldspar, and clay minerals-related elements in the soil FMNs, whereas PC2 (27.10%) and PC3 (10.81%) indicated the presence of Mn(oxyhydr)oxides and Fe(oxyhydr)oxides-related elements in the soil FMNs, respectively. The obtained selective extraction results demonstrated that up to 93% of the total contents of heavy metal(loid)s, namely, Cd, Pb, Cu, Ni, and Zn, were bound to Mn(oxyhydr)oxides. In contrast, oxyanionic species (As and Cr) were predominantly sequestered in Fe(oxyhydr)oxides.

The geographical distributions of Cd and several other heavy metals (HMs) (Hg, Cu, Ni, Pb, Zn, Cr, As, Co, and V) were characterized in 90 (p > 0.05) terra rossa samples across the Anhui karst area. Significant enrichment of HM was observed in this soil, mainly associated with the weathering of Cd-enriched carbonate rocks. Then, this enrichment was developed in 31 profiles. Our investigations revealed pedogenic processes as the dominant factors accounting for the enrichment of Hg, Cu, Ni, As, Co, and V. We also observed that all soil samples had a silty clay texture, with a pH scope of 4.08–8.04 and a median value of 6.50. In addition, the soil samples had relatively high saturation, with basic cations over 6.68%. The enrichment of the HMs based on their distinct factors were as follows: Cd (3.92) > As (2.55) > Zn (1.62) > Ni (1.50) > Cu (1.47) > Pb (1.47) > V (1.43) > Cr (1.23) > Co (1.19) > Hg (1.12). Finally, terra rossa samples derived from carbonate rocks were categorized as Cambisols, Luvisols, and Regosols. The soil profiles of Cambisols and Luvisolsis were less developed, so the HM concentrations were relatively low. The Regosols profile contained the highest total Cd concentration and exhibited a higher capacity to immobilize Cd compared with other soil profiles. Regosols are also characterized by high pH values (scope of 7.05 to 8.22, with an average value of 7.56). The contents of HM also exhibited minor changes across the Regosol, Cambisol, and Luvisol profiles, implying that the karst development degrees of weathering in Anhui were relatively low.

We determined the concentrations, geochemical fractions, and potential environmental implications of arsenic (As) via pH-static extraction experiments, X-ray photoelectron spectroscopy (XPS), and sequential extraction. Compared with the corresponding soils, the enrichment factors followed the order As (4.27) > Fe (2.14) > P (1.71) > Mn (1.41) > Al (0.95) > Ti (0.44) > Si (0.39) > Mg (0.28) > K (0.13). As showed a higher enrichment factor than all other elements. Arsenic showed a high linear correlation with iron in the FMNs, which can be expressed as As = 18.68Fe − 175.89 (r2 = 0.97, p < 0.01), indicating that Fe plays an important role in the geochemical behavior of As. Most of the As occurred as As (V) (83.79%) in the Fe–Mn nodules (FMNs), and As (III) (16.21%) only occupied a small portion. The distribution of As in the geochemical fractions of the FMNs followed the order F5 (99.54%) > F3 (0.25%) > F4 (0.10%) > F2 (0.09%) > F1 (0.02%), indicating that the residual fraction (F5) of As is the most dominant component. The total release of As from the nodules was extremely low (

The frequent occurrence of cyanobacterial blooms, caused by the eutrophication of water bodies, has triggered several ecological issues. Metal-controlled cyanobacteria are resulting in a series of secondary environmental problems and thus limiting environmental sustainability. Whether there is a more environmentally friendly way to replace metals in the removal of cyanobacteria is still unclear. To explore whether common heavy metals inhibit algal growth and whether Eucalyptus leaves (EL) can replace heavy metal ions in controlling algae outbreaks, here, we add Fe3+, Al3+, 3 mol/L of zinc (Zn3), 10 mol/L zinc (Zn10), and EL to a medium containing Cyanobacteria. We determine the medium’s color (456 nm), UV (254 nm), chlorophyll a, turbidity, temperature, pH, total dissolved solids, conductivity, and blue-green algae (BGA) at days 1, 4, 7, 11, 14, 19, and 21. We find that Fe3+, Al3+, Zn3, Zn10, and EL can inhibit chlorophyll synthesis, thereby impeding algae biomass growth due to metal ions’ disruption of the chlorophyll structure. The toxicity of Zn2+ may be higher than that of Fe3+ and Al3+ since it can completely destroy the structure of chlorophyll a. The damage of Zn (10) to chlorophyll a is stronger than that of Zn (3), indicating that high concentrations of metals have a stronger inhibitory effect on algae. The toxicity of EL to algae is lower than that of other metals, but it can significantly inhibit the growth of algae. We suggest the use of Eucalyptus leaves to inhibit algal growth in eutrophic water bodies. Our results provide a scientific basis for an environmentally friendly approach to controlling cyanobacteria outbreaks.

This study investigated the performance of rhamnolipids-citric acid mixed agents in simultaneous desorption of lindane and heavy metals from soils. The capacity of the mixed agents to solubilize lindane, lead and cadmium in aqueous solution was also explored. The results showed that the presence of citric acid greatly enhanced the solubilization of lindane and cadmium by rhamnolipids. A combined effect of the mixed agents on lindane and heavy metals removal from soils was observed. The maximum desorption ratios for lindane, cadmium and lead were 85.4%, 76.4% and 28.1%, respectively, for the mixed agents containing 1% rhamnolipidsand 0.1 mol/L citric acid. The results also suggest that the removal efficiencies of lead and cadmium were strongly related to their speciations in soils, and metals in the exchangeable and carbonate forms were easier to be removed. Our study suggests that the combining use of rhamnolipids and citric acid is a promising alternative to simultaneously remove organochlorine pesticides and heavy metals from soils.

Plant-associated bacteria are of great interest because of their potential use in phytoremediation. However, their ability to survive and promote plant growth in metal-polluted soils remains unclear. In this study, a soilborne Cd-resistant bacterium was isolated and identified as Enterobacter sp. strain EG16. It tolerates high external Cd concentrations (Cd2+ MIC, >250 mg liter-1) and is able to produce siderophores and the plant hormone indole-3-acetic acid (IAA), both of which contribute to plant growth promotion. Surface biosorption in this strain accounted for 31% of the total Cd accumulated. The potential presence of cadmium sulfide, shown by energy-dispersive X-ray (EDX) analysis, suggested intracellular Cd binding as a Cd response mechanism of the isolate. Cd exposure resulted in global regulation at the transcriptomic level, with the bacterium switching to an energyconserving mode by inhibiting energy-consuming processes while increasing the production of stress-related proteins. The stress response system included increased import of sulfur and iron, which become deficient under Cd stress, and the redirection of sulfur metabolism to the maintenance of intracellular glutathione levels in response to Cd toxicity. Increased production of siderophores, responding to Cd-induced Fe deficiency, not only is involved in the Cd stress response systems of EG16 but may also play an important role in promoting plant growth as well as alleviating the Cd-induced inhibition of IAA production. The newly isolated strain EG16 may be a suitable candidate for microbially assisted phytoremediation due to its high resistance to Cd and its Cd-induced siderophore production, which is likely to contribute to plant growth promotion. [ABSTRACT FROM AUTHOR]