Soil contamination by heavy metals has increased noticeably within the past years. Unlike organic compounds, metals cannot degrade; therefore effective cleanup is required to reduce its toxicity. This experiment was undertaken to investigate the comparative potential of Panicum maximum and Axonopus compressus to bioremediate zinc polluted soils, the impact of Zn on the antioxidant defense system of the plant, assaying for activities of antioxidants proteins. Zinc salts were mixed with soil at various concentrations 5 mg/kg, 10 mg/kg, 20 mg/kg and 40 mg/kg in triplicates and control was setup. After 4 months, the plants (root, shoot and leaf) and soil were analyzed for morphological, biochemical parameters and Zn concentration. The root length of P. maximum and A. compressus decreased as the concentration of zinc increased. The least shoot length inhibition of A. compressus was 6.16% (5 mg/kg) while the highest shoot length inhibition was 40.14% (40 mg/kg). The least shoot length inhibition of Panicum maximum was 6.16% exposed to 5 mg/kg and the highest shoot length inhibition was 53.13% (40 mg/kg). There was significant reduction of the heavy metals in vegetated soils for P. maximum and A. compressus at the end of the study compared to the heavy metals in the soils at the beginning of the study (p<0.05). P. maximum, is a better removal of Zn than A. compressus, however, it was not significant. Glutathione levels varied significantly (p≤ 0.05) with respect to heavy metals. A. compressus has more effects on Glutathione activities than P. maximum. Zn caused a decrease in metallothionein level in P. maximum while A. compressus metallothionein level increased.

International audience | Five organic matters, three phosphate compounds, zerovalent iron grit (ZVIG, 2% by soil weight), two alkaline compounds, and two commercial formulations were incorporated, singly and some combined with ZVIG, into a highly Cu-contaminated topsoil (Soil P7, 2600 mg Cu kg−1) from a wood treatment facility. Formulations and two composts were also singly incorporated into a slightly Cu-contaminated topsoil (Soil P10, 118 mg Cu kg−1) from the facility surrounding. This aimed to reduce the labile pool of Cu and its accumulation in beans cultivated on potted soils in a climatic chamber. Lowest Cu concentration in soil solution occurred in P7 soils amended with activated carbon (5%) and ZVIG, singly and combined. Basic slag (3.9%) and compost of sewage sludge (5%) combined with ZVIG promoted shoot production and limited foliar Cu accumulation. For amended P10 soils, no changes occurred in soil solution and foliar Cu concentrations, but one compost increased shoot production. Three soil amendments, iron grit with compost, calcium oxide, and basic slags, decreased the phytotoxicity of a Cu-contaminated soil.

International audience | A lysimeter approach (under natural climatologic conditions) was used to evaluate the effect of four metal immobilizing soil treatments [compost (C), compost + cyclonic ashes (C + CA), compost + cyclonic ashes + steel shots (C + CA + SS)) and cyclonic ashes + steel shots (CA + SS)] on metal leaching through an industrially contaminated soil. All treatments decreased Zn and Cd leaching. Strongest reductions occurred after CA + SS and C + CA + SS treatments (Zn: -99.0% and -99.2% respectively; Cd: -97.2% and -98.3% respectively). Copper and Pb leaching increased after C (17 and > 30 times for Cu and Pb respectively) and C + CA treatment (4.4 and > 3.7 times for Cu and Pb respectively). C + CA + SS or CA + SS addition did not increase Cu leaching; the effect on Pb leaching was not completely clear. Our results demonstrate that attention should be paid to Cu and Pb leaching when organic matter additions are considered for phytostabilization of metal contaminated soils

International audience | This study focused on the role of bioaccessibility in the phenanthrene (PHE) biodegradation in diffusely contaminated soil, by combining chemical and microbiological approaches.First, we determined PHE dissipation rates and PHE sorption/desorption isotherms for two soils (PPY and Pv) presenting similar chronic PAH contamination, but different physico-chemical properties.Our results revealed that the PHE dissipation rate was significantly higher in the Pv soil compared to the PPY soil, while PHE sorption/desorption isotherms were similar. Interestingly, increases of PHE desorption and potentially of PHE bioaccessibility were observed for both soils when adding rhamnolipids (biosurfactants produced by Pseudomonas aeruginosa). Second, using C-13-PHE incubated in the same soils, we analyzed the PHE degrading bacterial communities. The combination of stable isotope probing (DNA-SIP) and 16S rRNA gene pyrosequencing revealed that Betaproteobacteria were the main PHE degraders in the Pv soil, while a higher bacterial diversity (Alpha-, Beta-, Gammaproteobacteria and Actinobacteria) was involved in PHE degradation in the PPY soil. The amendment of biosurfactants commonly used in biostimulation methods (i.e. rhamnolipids) to the two soils clearly modified the PHE sorption/desorption isotherms, but had no significant impact on PHE degradation rates and PHE-degraders identity.These results demonstrated that increasing the bioaccessibility of PHE has a low impact on its degradation and on the functional populations involved in this degradation.

Although pollutants pose environmental and human health risks, the majority are not routinely monitored and regulated. Organic pollutants emanate from a variety of sources, and can be classified depending on their chemistry and environmental fate. Classification of pollutants is important because it informs fate processes and apposite removal technologies. The occurrence of emerging contaminants (ECs) in water bodies is a source of environmental and human health concern globally. Despite being widely reported, data on the occurrence of ECs in South Africa are scarce. Specifically, ECS in wastewater in the Northern Cape in South Africa are understudied. In this study, various ECs were screened in water samples collected from three wastewater treatment plants (WWTPs) in the province. The ECs were detected using liquid chromatography coupled to high resolution Orbitrap mass spectrometry following Oasis HLB solid-phase extraction. The main findings were: (1) there is a wide variety of ECs in the WWTPs, (2) physico-chemical properties such as pH, total dissolved solids, conductivity, and dissolved organic content showed reduced values in the outlet compared to the inlet which confirms the presence of less contaminants in the treated wastewater, (3) specific ultraviolet absorbance of less than 2 was observed in the WWTPs samples, suggesting the presence of natural organic matter (NOM) that is predominantly non-humic in nature, (4) most of the ECs were recalcitrant to the treatment processes, (5) pesticides, recreational drugs, and analgesics constitute a significant proportion of pollutants in wastewater, and (6) NOM removal ranged between 35 and 90%. Consequently, a comprehensive database of ECs in wastewater in Sol Plaatje Municipality was created. Since the detected ECs pose ecotoxicological risks, there is a need to monitor and quantify ECs in WWTPs. These data are useful in selecting suitable monitoring and control strategies at WWTPs.

In recent years, Feammox has made it possible to remove NH₄⁺-N under anaerobic conditions; however, its application in practical wastewater treatment processes has not been extensively reported. In this study, an up-flow anaerobic biological filter based on limonite (Lim-UAF) was developed to facilitate long-term and stable treatment of domestic sewage. Lim-UAF achieved the highest removal efficiency of chemical oxygen demand (COD) and NH₄⁺-N at a hydraulic retention time (HRT) of 24 h (Stage II). Specifically, the COD and NH₄⁺-N content decreased from 240.8 and 30.0 mg/L to about 7.5 and 0.35 mg/L, respectively. To analyze the potential nitrogen removal mechanism, the Lim-UAF was divided into three layers according to the height of the reactor. The results showed that COD and NH₄⁺-N removal had remarkable characteristics in Lim-UAF. More than 55.0% of influent COD was removed in the lower layer (0–30 cm) of Lim-UAF, while 60.2% of NH₄⁺-N was removed in the middle layer (30–60 cm). Microbial community analysis showed that the community structure in the middle and upper layers (60–90 cm) was relatively similar, but quite different from that of the lower layer. Heterotrophic bacteria were dominant in the lower layer, whereas iron-reducing and iron-oxidizing bacteria were enriched in the upper and middle layers. The formation of secondary minerals (siderite and Fe(OH)₃) indicated that the Fe(III)/Fe(II) redox cycle occurred in Lim-UAF, which was triggered by the Feammox and NDFO processes. In summary, limonite was used to develop a single-stage wastewater treatment process for simultaneously removing organic matter and NH₄⁺-N, which has excellent application prospects in domestic sewage treatment.

The removal of organic pollutants presents a major challenge for drinking water treatment plants. The chemical oxygen demand (COD) is essentially the measure of oxidizable organic matter in source waters. In this study, we report that COD can efficiently be decreased by adding Fe(II)/Fe(III) and sulfite ion to the source water while purging it with air. In this process, oxygen is activated to oxidize the main constituents of COD, i.e. organic substrates, via the generation of reactive inorganic oxysulfur radical ions. In the end, the total amount of sulfur(IV) is converted to the non-toxic sulfate ion. It has been explored how the COD removal efficiency depends on the concentration of S(IV), the total concentration of iron species, the concentration ratio of Fe(II) and Fe(III), the purging rate and the contact time by using source water from a specific location (Királyhegyes, Hungary). The process has been optimized by applying the Response Surface Methodology (RSM). Under optimum conditions, the predicted and experimentally found COD removal efficiencies are in excellent agreement: 85.4% and 87.5%, respectively. The robustness of the process was tested by varying the optimum values of the parameters by ± 20%. It was demonstrated that the method is universally applicable because a remarkable decrease was achieved in COD, 62.0–88.5%, with source waters of various compositions acquired from 9 wells at other locations using the same conditions as in the case of Királyhegyes.

Both inorganic and organic fertilizers are widely used to increase rice yield. However, these fertilizers are also found to aggravate mercury methylation and methylmercury (MeHg) accumulation in paddy fields. The aim of this study was to reveal the mechanisms of inorganic and organic fertilizers on MeHg accumulation in rice grains, which are not yet well understood. Potting cultures were conducted in which different fertilizers were applied to a paddy soil. The results showed that both inorganic and organic fertilizers increased MeHg concentrations rather than biological accumulation factors (BAFs) of MeHg in mature rice grains. Inorganic fertilizers, especially nitrogen fertilizer, enhanced the bioavailability of mercury and the relative amount Hg-methylating microbes and therefore intensified mercury methylation in paddy soil and MeHg accumulation in rice grains. Unlike inorganic fertilizers, organic matter (OM) in organic fertilizers was the main reason for the increase of MeHg concentrations in rice grains, and it also could immobilize Hg in soil when it was deeply degraded. The enhancement of MeHg concentrations in rice grains induced by inorganic fertilizers (5.18–41.69%) was significantly (p < 0.05) lower than that induced by organic fertilizers (80.49–106.86%). Inorganic fertilizers led to a larger increase (50.39–99.28%) in thousand-kernel weight than MeHg concentrations (5.18–41.69%), resulting in a dilution of MeHg concentrations in mature rice grains. Given the improvement of soil properties by organic fertilizer, increasing the proportion of inorganic fertilizer application may be a better option to alleviate MeHg accumulation in rice grains and guarantee the rice yield in the agricultural production.

Size segregated samples (<0.49, 0.49–0.95, 0.95–1.5, 1.5–3.0, 3.0–7.2 and > 7.2 μm) of atmospheric particulate matter (APM) were collected at a traffic site in the urban agglomeration of Thessaloniki, northern Greece, during the cold and the warm period of 2020. The solvent-extractable organic matter was analyzed for selected organic contaminants including polycyclic aromatic hydrocarbons (PAHs), and their nitro- and oxy-derivarives (NPAHs and OPAHs, respectively). Mean concentrations of ∑₁₆PAHs, ∑₆NPAHs and ∑₁₀OPAHs associated to total suspended particles (TSP) were 18 ng m⁻³, 0.2 ng m⁻³ and 0.9 ng m⁻³, respectively, in the cold period exhibiting significant decrease (6.4, 0.2 and 0.09 ng m⁻³, respectively) in the warm period. The major amount of all compounds was found to be associated with the alveolar particle size fraction <0.49 μm. The inhalation bioaccessibility of PAHs and O/N PAHs was measured in vitro using two simulated lung fluids (SLFs), the Gamble's solution (GS) and the artificial lysosomal fluid (ALF). With both SLFs, the derived bioaccessible fractions (BAFs) followed the order PAHs > OPAHs > NPAHs. Although no clear dependence of bioaccessibility on particle size was obtained, increased bioaccessibility of PAHs and PAH derivatives in coarse particles (>7.2 μm) was evident. Bioaccessibility was found to be strongly related to the logKOW and the water solubility of individual compounds hindering limited mobilization of the most hydrophobic and less water-soluble compounds from APM to SLFs. The lifetime cancer risk due to inhalation exposure to bioaccessible PAHs, NPAHs and OPAHs was estimated and compared to those calculated from the particulate concentrations of organic contaminants.

Rice consumption is the major pathway for human methylmercury (MeHg) exposure in inland China, especially in mercury (Hg) contaminated regions. MeHg production, a microbially driven process, depends on both the chemical speciation of inorganic divalent mercury, Hg(II), that determines Hg bioavailability for methylation. Studies have shown that Hg(II) speciation in contaminated paddy soils is mostly controlled by natural organic matter and sulfide levels, which are typically thought to limit Hg mobility and bioavailability. Yet, high levels of MeHg are found in rice, calling for reconsideration of the nature of Hg species bioavailable to methylators in paddy soils. Here, we conducted incubation experiments using a multi-isotope tracer technique including ¹⁹⁸Hg(NO₃)₂, natural organic matter bond Hg(II) (NOM-¹⁹⁹Hg(II)), ferrous sulfide sorbed Hg(II) (≡FeS-²⁰⁰Hg(II)), and nanoparticulate mercuric sulfide (nano-²⁰²HgS), to investigate the relative importance of geochemically diverse yet relevant Hg(II) species on Hg methylation in paddy soils across a Hg concentration gradient. We show that methylation rates for all Hg(II) species tested decreased with increasing Hg concentrations, and that methylation rates using NOM-¹⁹⁹Hg(II) and nano-²⁰²HgS as substrates were similar or greater than rates obtained using the labile ¹⁹⁸Hg(NO₃)₂ substrate. ≡FeS-²⁰⁰Hg(II) yielded the lowest methylation rate in all sites, and thus the formation of FeS is likely a sink for labile ¹⁹⁸Hg(NO₃)₂ in sulfide-rich paddy soils. Moreover, the variability in the methylation data for a given site (1 to 5-fold variation depending on the Hg species) was smaller than what was observed across the Hg concentration gradient (10³–10⁴ fold variation between sites). These findings emphasize that at broad spatial scales, site-specific characteristics, such as microbial community structure, need to be taken into consideration, alongside the nature of the Hg substrate available for methylation, to determine net MeHg production. This study highlights the importance of developing site-specific strategies for remediating Hg pollution.