Compost or composting has been widely investigated under the background of heavy metal pollution of agricultural soils and rapid growth of organic wastes. Compost is rich in nutrients, humic matter, and microorganisms; it may be added to agricultural soil as a fertilizer to improve soil fertility and promote the growth of crops and microorganisms, and as a soil amendment to relieve heavy metal pollution. However, the effectiveness and security of compost application in agricultural soil continue to generate concern. In this review, the efficacy and mechanisms of compost remediation technologies for heavy metal-contaminated agricultural soil are presented. Poor quality, unsuitability for multiple heavy metal-contaminated soils, and potential long-term risks are the main limitations of the effectiveness and security of compost application to soils. Therefore, improving the quality of the compost, adding amendments, or combining with phytoremediation may be considered when adopting compost to remediate polluted agricultural soil. In addition, we propose several approaches to optimize these strategies and render the remediation of heavy metal-contaminated agricultural soil using compost safer and more effective. The findings of this review will help support the large-scale application of compost in agriculture in the future.

We investigated the effects of exposure to molluscicidal metaldehyde (MET) on golden apple snail (GAS) Pomacea canaliculata and Rhinella arenarum tadpoles by assessing mortality and/or other effects via: acute toxicity assays; B-esterase activities (acetilcholinesterase (AChE) and carboxilesterase (CbE)) and oxidative responses (glutathione-S-transferase (GST) and catalase (CAT)). The effect of sublethal concentrations of MET was also analysed by assessing biochemical changes and swimming parameters in tadpoles. The LC₅₀ value in P. canaliculata was as 0.50 mg L⁻¹ and in R. arenarun tadpoles, 229.7 mg L⁻¹ at 48 h. The intestine of MET-exposed P. canaliculata exhibited a significant reduction in CbE and CAT activities, but not in AChE activity; hepatopancreas of GAS showed a decreased GST activity decreased with respect to control individuals. In addition, a significant reduction of CbE activities was detected in R. arenarum tadpoles exposed to MET, and AChE presented lower values than the control but without statistical differences. Antioxidant enzymes (GST and CAT) were significantly reduced in tadpoles exposed to MET compared with the control group. In addition, MET had a significant effect on the swimming behaviour of R. arenarum. Finally, since amphibian tadpoles and P. canaliculata often co-occur, other native amphibian species should be studied to elucidate the ecological risk of MET to amphibian populations.

A granular hydrogel of chitosan-g-poly(vinylimidazole-co-2-acrylamido-2-methyl propane sulfonic acid) was successfully synthesized by one-step free radical polymerization based on the grafting backbone of chitosan and the monomers of vinylimidazole and 2-acrylamido-2-methyl propane sulfonic acid. The resulting hydrogel could be used as the adsorbent for the efficient and selective removal of Hg²⁺ ions from the aqueous solution. The adsorption results could be well described by the pseudo-second-order kinetic mode and the Langmuir isotherm model with a maximum adsorption capacity of 363.55 mg/g for Hg²⁺. Furthermore, the as-prepared granular hydrogel exhibited an excellent cycling stability for the adsorption of Hg²⁺ after multiple repeated adsorption-desorption process. It suggested that the obtained granular hydrogel has potential application for Hg²⁺ removal and recovery from wastewater. Graphical Abstract A kind of granular hydrogel with excellent selectivity adsorption of Hg2+ ions was successfully synthesized by grafting polymerization of VIM and AMPS onto the CTS backbone via a facile free radical polymerization.

Sudan dyes are widely used as coloring agents in various solvents, waxes, and polishes. However, the dyes are environmental contaminants and Sudan I is a weak carcinogen, and its removal from wastewater remains challenging. Here, we developed a new strategy for Sudan dye degradation for use in the non-alkaline conditions typically found in wastewater. By combing glucose oxidase (GOD) and horseradish peroxidase (HRP), we avoided the hydrogen peroxide-induced HRP damage and inactivation. Moreover, the GOD-HRP-coupled degradation of Sudan dyes were enhanced by the addition of different kinds of phenols. Systematic investigations were carried out to determine the optimal process parameters (i.e., phenol concentration, pH value, temperature, and enzyme dose) for degrading Sudan I with GOD and HRP. Also, this strategy could be applied to degradation of Sudan II and Sudan III. We were also able to co-express GOD and HRP in a prokaryotic-like polycistronic expression system in Pichia pastoris, based on the internal ribosome entry sites (IRES). Therefore, this fermented liquid containing GOD and HRP might be used in the future to degrade pollutants in weakly acidic conditions.

Total organic carbon (TOC) and humic acid (HA) are very strong contamination potential components in landfill leachate, which were treated by subcritical water catalytic oxidation technology with a batch reactor. Response surface methodology (RSM) was used to evaluate the effects of temperature (180–260 °C), peroxide coefficient (2–3), pH (4–8), and their interactive effects on TOC and HA removal efficiencies. The results demonstrated that RSM was an effective method for the optimization of experimental parameters in the treatment of landfill leachate. The results indicated that the effects on TOC removal efficiency were in the order temperature > pH > peroxide coefficient and that the order on HA removal efficiency was pH > temperature > peroxide coefficient. The experiments were performed in different heterogeneous (CuO, ZnO) and homogeneous (CuSO₄·5H₂O, FeSO₄·7H₂O, and Cu(NO₃)₂·3H₂O) catalysts; the optimal parameters within the experimental range were temperature of 260 °C, pH of 4.0, peroxide coefficient of 3.0, and Cu(NO₃)₂·3H₂O of 0.03 M. Under the optimum conditions, the TOC and HA removal efficiency can reach 86.42 and 66.10 %, respectively. Using gas chromatography coupled with mass spectrometry (GC-MS) to analyze the composition of liquid, 89 and 76 kinds of principal organic components were detected in the landfill leachate before and after treatment, respectively. In the raw landfill leachate, there were five kinds of organic matters, which belong to the US Environmental Protection Agency (USEPA) list of priority environmental pollutants. After the treatment, the toxic organics were not detected. In summary, the results suggested that the subcritical catalytic oxidation technology can be used as an effective method for the treatment of landfill leachate.

Improved understanding of the relationships between heavy metals fractionation in agricultural soils and biological uptake could be obtained by analysing samples of biota in parallel with sequential extraction of their grown media. The overall goals of this study were to identify the characteristics of metal fractions and their bioavailability to maize and potato plants in the agricultural land of the Ibar River in southern Serbia and northern Kosovo. The concentrations of Pb, Zn, Cd, Ni, Cr and Cu in soil and vegetable samples were determined by the ICP-OES method. Pb/Zn production and industrial waste disposal significantly increased the pseudo-total concentrations of heavy metals in the soil together with their mobile and potentially bioavailable amounts. The Pb concentrations in the vegetable samples were generally above the EU maximum permitted concentrations in foodstuffs. However, the concentrations of Zn, Ni, Cr and Cu in the vegetables were below the critical levels. The results of the present study indicated that the intensive industrial production of Pb/Zn over the years and permanent pollution were responsible for the environmental contamination by heavy metals in the study area, particularly by Pb and Zn. The quantity of the mobile and potentially bioavailable heavy metals in the studied soils threatens the quality of Zea mays L. and Solanum tuberosum L. crops, with a real risk that these elements could enter the food chain.

Organophosphate esters (OPEs) are classified as re-emerging pollutants, and studies on their environmental fate, e.g., sorption behavior on soil are still limited. In this paper, three OPEs, triphenyl phosphate (TPP), tris (1,3-dichloro-2-propyl) phosphate (TDCP), and tris (1-chloro-2-propyl) phosphate (TCPP) were selected, and their sorption characteristics on peat soil with high organic matter were investigated by direct immersion solid phase microextraction coupled with gas chromatography-mass spectrometry (SPME-GC/MS). The sorption kinetics of TPP, TDCP, and TCPP was found to confirm to the pseudo-second-order model, and intra-particle diffusion was not the only rate-controlling step for the sorption process. Linear, Freundlich, and Dubinin-Radushkevich isotherm models were used to analyze the sorption equilibrium data, and the best correlation was achieved by the linear isotherm model. The organic carbon normalized distribution coefficients (logK ₒc) were calculated to be 3.45 for TPP, 2.83 for TDCP, and 2.23 for TCPP. Thermodynamics showed that the sorption of TPP, TDCP, and TCPP on Peat soil was spontaneous, exothermic, and physical in nature.

Poderosa Mine is an abandoned pyrite mine, located in the Iberian Pyrite Belt which pours its acid mine drainage (AMD) waters into the Odiel river (South-West Spain). This work focuses on establishing possible reasons for interdependence between the potential redox and pH, with the load of metals and sulfates, as well as a set of variables that define the physical chemistry of the water—conductivity, temperature, TDS, and dissolved oxygen—transported by a channel from Poderosa mine affected by acid mine drainage, through the use of techniques of artificial intelligence: fuzzy logic and data mining. The sampling campaign was carried out in May of 2012. There were a total of 16 sites, the first inside the tunnel and the last at the mouth of the river Odiel, with a distance of approximately 10 m between each pair of measuring stations. While the tools of classical statistics, which are widely used in this context, prove useful for defining proximity ratios between variables based on Pearson’s correlations, in addition to making it easier to handle large volumes of data and producing easier-to-understand graphs, the use of fuzzy logic tools and data mining results in better definition of the variations produced by external stimuli on the set of variables. This tool is adaptable and can be extrapolated to any system polluted by acid mine drainage using simple, intuitive reasoning.

The cell density-dependent gene expression in gram-negative bacteria is through the activity of acyl homoserine lactone signal molecules. The novel strain Pseudomonas putida JMQS1 isolated from detergent-contaminated soil exhibited quorum sensing along with its ability to degrade phenol. The response to Chromobacterium violaceum DSTS-1 mutant biosensor and luxI and luxR gene-specific amplification was used to characterize the quorum sensing property of the isolate. A regulation in the synthesis of various acyl homoserine lactone molecules, viz C₆HSL in the initial stages of phenol stress, C₈HSL during degradation, and 3OC₁₂HSL on completion of degradation could be identified by liquid chromatography-quadrupole time of flight. Thin-layer chromatography, Fourier transform infrared spectroscopy, and gas chromatography mass spectrometry confirmed the complete degradation of phenol in 48–56 h. P. putida JMQS1 exhibited adaptation over phenol stress through the selective activation of the quorum sensing signal molecules depending on the changing physiological conditions. This study proposes an efficient method for enhancing the degradation of toxic organic pollutants by the supplementation of acyl homoserine lactone signal molecules.

This work investigates the sorption behaviour of six hydrophobic organic compounds (HOCs) from the trichlorobenzenes (TCBs) and polycyclic aromatic hydrocarbons (PAHs) on Danube sediment using batch and column experiments, either in the presence or absence of carbon nanotubes (CNTs). For all HOCs investigated, nonlinear isotherms were obtained. Based on logKoc, it can be concluded that the Danube sediment has a higher sorption affinity for PAHs than TCBs. A positive correlation between HOC molecular hydrophobicity and sorption affinity was obtained, meaning that hydrophobic interactions play a significant role. There was a negative correlation between molecular hydrophobicity and the percentage of eluted HOCs, indicating that more hydrophobic molecules show less mobility in the sediment column. In the presence of CNTs in the sediment column, HOC concentrations in the column eluate decreased by factors of 2–3. Metal oxides and hydroxides on the surface of the sediment under the given experimental conditions had positively charged centres that caused the deposition of CNTs, leading to simultaneous sorption of organic compounds on both sediment organic matter (SOM) and CNTs. The increased retention of HOCs in the presence of CNTs on the sediment column reduces their mobility, which might also suggest that CNTs may be used for remediation of contaminated soils and sediments.