Concentrations and fluxes of total and methylmercury were determined in surface sediments and associated with settling particles at two sites in Lake Geneva to evaluate the sources and dynamics of this toxic contaminant. Total mercury concentrations measured in settling particles were different throughout the seasons and were greatly influenced by the Rhone River particulate inputs. Total mercury concentrations closer to shore (NG2) ranged between 0.073 ± 0.001 and 0.27 ± 0.01 μg/g, and between 0.038 ± 0.001 and 0.214 ± 0.008 μg/g at a site deeper in the lake (NG3). Total mercury fluxes ranged between 0.144 ± 0.002 and 3.0 ± 0.1 μg/m²/day at NG2, and between 0.102 ± 0.008 and 1.32 ± 0.08 μg/m²/day at NG3. Combined results of concentrations and fluxes showed that total mercury concentrations in settling particles are related to the season and particle inputs from the Rhone River. Despite an observed decrease in total mercury fluxes from the coastal zone towards the open lake, NG3 (~ 3 km from the shoreline) was still affected by the coastal boundary, as compared to distal sites at the center of the lake. Thus, sediment focusing is not efficient enough to redistribute contaminant inputs originating from the coastal zones, to the lake center. Methylmercury concentrations in settling particles largely exceeded the concentrations found in sediments, and their fluxes did not show significant differences with relation to the distance from shore. The methylmercury found associated with settling particles would be related to the lake’s internal production rather than the effect of transport from sediment resuspension.

A variety of chemicals have been used in a wide range of indoor materials, such as wallpaper and furniture, and some of them are released into the indoor air. The level of consumption as well as the diversity of these chemicals has been increasing. The particle size of the materials in the air is known to affect the depth of human exposure, e.g., particles >10 μm can only reach the nasal cavity, whereas particles 2.5–10 μm can reach the respiratory tract and particles <2.5 μm can reach the bottom of the lungs. However, information on the concentrations and form of these chemicals in indoor air is very limited. In this study, we measured 54 compounds, including plasticizers (phthalates, adipates, and others) and organophosphorus flame retardants, in indoor air samples from the living rooms of 21 dwellings in 11 prefectures across Japan. For sampling, we used a four-stage air sampler (multi-nozzle cascade impactor) equipped with three quartz fiber filters to capture chemical particulates in three size ranges (<2.5, 2.5–10, and >10 μm) and a C₁₈ solid-phase extraction disk to capture chemicals that exist in a gas phase in indoor air. Each of the chemicals in the three particulate phases and single gas phase was extracted by acetone and measured separately using GC/MS. Of the 54 compounds tested, 37 were detected in the indoor air samples. The highest concentration observed was that of 2-ethyl-1-hexanol (5.1 μg/m³), which was detected in samples from all 21 houses. The 37 compounds were captured in the four fractions at different rates roughly based on their molecular sizes. Compounds with a smaller molecular size were commonly detected as a gas phase, whereas compounds with a larger molecular size were detected as one or more of the three particulate phases in the indoor air samples. Among the three particulate phases, many of the compounds were detected from the filter capturing the smallest (<2.5 μm) particles. Therefore, these results suggest that the chemicals measured in this study might penetrate deeply into the lungs as many of them tend to exist as a gas and/or as particles smaller than 2.5 μm.

Vermicomposting is a bio-oxidative process that involves the action of mainly epigeic earthworm species and different micro-organisms to accelerate the biodegradation and stabilization of organic materials. There has been a growing realization that the process of vermicomposting can be used to greatly improve the fertilizer value of different organic materials, thus, creating an opportunity for their enhanced use as organic fertilizers in agriculture. The link between earthworms and micro-organisms creates a window of opportunity to optimize the vermi-degradation process for effective waste biodegradation, stabilization, and nutrient mineralization. In this review, we look at up-to-date research work that has been done on vermicomposting with the intention of highlighting research gaps on how further research can optimize vermi-degradation. Though several researchers have studied the vermicomposting process, critical parameters that drive this earthworm–microbe-driven process which are C/N and C/P ratios; substrate biodegradation fraction, earthworm species, and stocking density have yet to be adequately optimized. This review highlights that optimizing the vermicomposting process of composts amended with nutrient-rich inorganic materials such as fly ash and rock phosphate and inoculated with microbial inoculants can enable the development of commercially acceptable organic fertilizers, thus, improving their utilization in agriculture.

For selective leaching and highly effective recovery of heavy metals from a metallurgical sludge, a two-step leaching method was designed based on the distribution analysis of the chemical fractions of the loaded heavy metal. Hydrochloric acid (HCl) was used as a leaching agent in the first step to leach the relatively labile heavy metals and then ethylenediamine tetraacetic acid (EDTA) was applied to leach the residual metals according to their different fractional distribution. Using the two-step leaching method, 82.89% of Cd, 55.73% of Zn, 10.85% of Cu, and 0.25% of Pb were leached in the first step by 0.7 M HCl at a contact time of 240 min, and the leaching efficiencies for Cd, Zn, Cu, and Pb were elevated up to 99.76, 91.41, 71.85, and 94.06%, by subsequent treatment with 0.2 M EDTA at 480 min, respectively. Furthermore, HCl leaching induced fractional redistribution, which might increase the mobility of the remaining metals and then facilitate the following metal removal by EDTA. The facilitation was further confirmed by the comparison to the one-step leaching method with single HCl or single EDTA, respectively. These results suggested that the designed two-step leaching method by HCl and EDTA could be used for selective leaching and effective recovery of heavy metals from the metallurgical sludge or heavy metal-contaminated solid media.

It is usually very difficult to achieve satisfactory extraction efficiencies in electrokinetic remediation of heavy metal-contaminated soils of high acid/base buffer capacity. Enhancement agent is often required. In this study, synthesized citric acid industrial wastewater (CAIW) is used as the enhancement agent to remediate cadmium-spiked natural clayey soil from Shanghai, China. Four electrokinetic extraction experiments were carried out to evaluate the enhancement effects of CAIW on the remediation of metal-spiked clayed soil of high buffer capacity and the effects of treatment time and initial cadmium concentration on the migration of cadmium in the specimen. The results of electrokinetic experiments indicated that CAIW can efficiently enhance the transport of cadmium in comparison with HNO₃ of the same pH. Cadmium mobilization was enhanced with prolonged treatment time from 104 to 261.2 h, but the average cadmium removal efficiency was not significantly enhanced. A non-uniform cadmium distribution in the specimen was observed after the enhanced electrokinetic experiments due to the localized electrical gradients with an electrical gradient of approximately 1 V/cm and a ratio of the distance between electrodes of the same polarity to the outer diameter of electrode of 2.8 (50:18 mm).

Phosphorus removal from wastewater is an important means to control eutrophication and to recover phosphorus from wastewater. In this study, a novel Fe(II)-Ca synergistic phosphorus removal process is developed using the complex of ferrous and calcium salts. The results showed that ferrous and calcium had an antagonistic effect at Fe(II)/Ca molar ratio of lower than 1:4, but a synergistic effect at Fe(II)/Ca molar ratio of higher than 1:4, with the strongest synergistic effect at Fe(II)/Ca molar ratio of 7:3. The optimal parameters of this novel process were as follows: Fe(II)/Ca = 3:1, ferrous-calcium complex/phosphorous (M/P) ≥ 1.5:1, pH = 7.0–8.0, and fast mixing speed (FMS) = 100–150 rpm. The cost of phosphorus removal agents was US$1.024 (kg P)⁻¹, reduced by 30.39% compared with that of the traditional phosphorus removal process. The phosphorus content (by P₂O₅) in the precipitate produced in the new process was 32.70%, which had a high recycling value.

A new strain SWH-15 was successfully isolated after initial electrokinetic remediation experiment using the same saline soil sampled from Shengli Oilfield, China. Four methods (morphological and biochemical characteristics, whole-cell fatty acid methyl esters (FAMEs) analysis, 16S rRNA sequence analysis and DNA G + C content and DNA–DNA hybridization analysis) were used to identify the taxonomic status of SWH-15 and confirmed that SWH-15 was a novel species of the Bacillus (B.) cereus group. Then, we assessed the degrading ability of the novel strain SWH-15 to crude oil through a microcosm experiment with four treatments, including control (CK), bioremediation using SWH-15 (Bio), electrokinetic remediation (EK), and combined bioremediation and electrokinetic remediation (Bio + EK). The results showed that the Bio + EK combined remediation treatment was more effective than the CK, Bio, and EK treatments in degrading crude oil contaminants. Bioaugmentation, by addition of the strain SWH-15 had synergistic effect with EK in Bio + EK treatment. Bacterial community analysis showed that electrokinetic remediation alone significantly altered the bacterial community of the saline soil. The addition of the strain SWH-15 alone had a weak effect on the bacterial community. However, the strain SWH-15 boosted the growth of other bacterial species in the metabolic network and weakened the impact of electrical field on the whole bacterial community structure in the Bio + EK treatment.

Many lipophilic pharmaceuticals may be sorbed in solid phases, leading to different photochemical behaviors. This study investigated the photochemistry of ciprofloxacin in a solid-phase system and compared it to that in a water-phase system. Kaolinite was used as the model solid matrix. The photolysis of ciprofloxacin in kaolinite fits pseudo-first-order kinetics for thicknesses less than 199 μm, and the rate constants k ₚ decreased from 0.0154 to 0.0016 min⁻¹ as the thickness of the layer increased. Unlike the aqueous phase, two-step degradation processes were observed for all kaolinite layer thicknesses (14–199 μm), and the pseudo-first-order constant at the surface of the kaolinite layer was smaller than that in the water phase. Comparatively , a similar photolysis rate constant of ciprofloxacin in a kaolinite suspension was also observed, and it was an order of magnitude smaller than that of the direct photodegradation (0.035 min⁻¹) in water. The results indicate that ciprofloxacin is likely more stable when it is adsorbed on kaolinite and that the half-lives of ciprofloxacin in kaolinite and a kaolinite suspension are 2–25 times longer than that in deionized water (20 min) under simulated sunlight. Direct photolysis is proposed to be the main photodegradation mechanism for ciprofloxacin in kaolinite, and the cleavage of a piperazine ring is the main degradation pathway. However, the interaction between ciprofloxacin and kaolinite reduces the direct photolysis and leads to a higher light stability. In association with the reduction in photolysis, the yields of norfloxacin and defluorinated byproduct decreased significantly. Consequently, the interaction increases the persistence of ciprofloxacin and thus the ecological risk to the environment.

The antimicrobial triclosan (TCS) has been detected in household wastewaters (untreated and treated) and receiving environments across the globe. The toxic effects of TCS on temperate standard aquatic test organisms have been widely reported with microalgae being the most sensitive. However, environmental differences between tropical and temperate regions may have selected different trait compositions between these two regions, which in turn may lead to a difference in species sensitivity. Therefore, additional information is required to better characterize risks to organisms in tropics and ensure biodiversity in these regions is not adversely impacted. This study aims to supplement existing TCS toxicity data with five aquatic invertebrates found in tropics and to compare the sensitivity between aquatic invertebrate species from tropical and temperate regions. In addition, the effect of pH on the toxicity of neutral and ionized forms of TCS to microalgae (Chlorella ellipsoidea) was investigated. The reported 96-h LC50 values for the studied invertebrate species ranged from 72 to 962 μg/L. There was no significant difference between the sensitivity of aquatic invertebrate species from tropical and temperate regions. EC50 values for C. ellipsoidea, with and without pH buffer, were significantly different. The findings of this study can be used to support site-specific water quality criteria and environmental risk assessment for TCS in tropical regions. However, further chronic and semi-field experiments with TCS could potentially enable a refined assessment of direct and indirect effects on tropical aquatic communities and further explore functional endpoints of tropical ecosystems.

The prevalence and persistence of antibiotic resistance genes in wastewater treatment plants (WWTPs) is of growing interest, and residual sludge is among the main sources for the release of antibiotic resistance genes (ARGs). Moreover, heavy metals concentrated in dense microbial communities of sludge could potentially favor co-selection of ARGs and metal resistance genes (MRGs). Residual sludge treatment is needed to limit the spread of resistance from WWTPs into the environment. This study aimed to explore the fate of ARGs and MRGs during thermophilic two-phase (acidogenic/methanogenic phase) anaerobic digestion by metagenomic analysis. The occurrence and abundance of mobile genetic elements were also determined based on the SEED database. Among the 27 major ARG subtypes detected in feed sludge, large reductions (> 50%) in 6 ARG subtypes were achieved by acidogenic phase (AP), while 63.0% of the ARG subtypes proliferated in the following methanogenic phase (MP). In contrast, a 2.8-fold increase in total MRG abundance was found in AP, while the total abundance during MP decreased to the same order of magnitude as in feed sludge. The distinct dynamics of ARGs and MRGs during the two-phase anaerobic digestion are noteworthy, and more specific treatments are required to limit their proliferation in the environment.