This research reports the effects of pH increase on contaminant mobility in phosphogypsum leachates by seawater mixing, as occurs with dumpings on marine environments. Acid leachates from a phosphogypsum stack located in the Estuary of Huelva (Spain) were mixed with seawater to achieve gradually pH7. Concentrations of Al, Fe, Cr, Pb and U in mixed solutions significantly decreased with increasing pH by sorption and/or precipitation processes. Nevertheless, this study provides insight into the high contribution of the phosphogypsum stack to the release of other toxic elements (Co, Ni, Cu, Zn, As, Cd and Sb) to the coastal areas, as 80–100% of their initial concentrations behaved conservatively in mixing solutions with no participation in sorption processes. Stable isotopes ruled out connexion between different phosphogypsum-related wastewaters and unveiled possible weathering inputs of estuarine waters to the stack. The urgency of adopting effective restoration measures in the study area is also stressed.

Seafloor massive sulphide samples from the Trans-Atlantic Geotraverse active mound on the Mid-Atlantic Ridge were characterised and subjected to leaching experiments to emulate proposed mining processes. Over time, leached Fe is removed from solution by the precipitation of Fe oxy-hydroxides, whereas Cu and Pb leached remained in solution at ppb levels. Results suggest that bulk chemistry is not the main control on leachate concentrations; instead mineralogy and/or galvanic couples between minerals are the driving forces behind the type and concentration of metals that remain in solution. Dissolved concentrations exceed ANZECC toxicity guidelines by 620 times, implying the formation of localised toxicity in a stagnant water column. Moreover, concentrations will be higher when scaled to higher rock-fluid ratios and finer grain sizes proposed for mining scenarios. The distance at which dilution is achieved to meet guidelines is unlikely to be sufficient, indicating a need for the refinement of the mining process.

In many developing countries, a landfill remains one of the most extensively employed solid waste disposal solutions. Although a landfill is a well-designed engineering system, the base lining of a landfill may perform poorly and allow the leachate to reach the underlying soil layers and groundwater. Leachates contain a variety of toxic and hazardous contaminants, which are attenuated in the soil by various processes that slow or transform them. Thus, the objective of this research was to study the water and leachate permeability and retention of the liner soil in a landfill experimental cell by subjecting it to geotechnical, chemical-mineralogical, and physicochemical characterizations, water and leachate permeability tests, and mercury intrusion porosimetry (MIP). In addition, the water and leachate retention curves were determined and analyzed using RETention Curve (RETC) software to obtain the unsaturated permeability curves. The leachate in the soil decreased the suction considering the moisture content of the compacted soil in the field, which consequently increased the leachate permeability of the mineral liner. For the same suction value, in the drying pathways, the soil retained a greater amount of distilled water than leachate. In the wetting pathways, the opposite occurred. Microorganisms were detected in the soil during the filter paper test. The permeability coefficients of the unsaturated soil were directly proportional to the gravimetric moisture content for the water and the leachate, which demonstrated that the soil presents lower unsaturated permeability coefficients for water than for leachate for the same water content.

The straw on the soil in the green cane harvesting system acts as a physical barrier to the action of the pre-emergence herbicides. However, some herbicides have physico-chemical characteristics to pass through the straw in water solution. The aim was to evaluate the influence of different densities of sugarcane straw on the leaching of aminocyclopyrachlor in a tropical soil (Oxisol—Typic Hapludox) in a system of green cane harvesting. The experiment was carried out using glass columns filled with soil, with and without sugarcane straw (0, 5, 10, and 20 t ha⁻¹) on the top of the soil. ¹⁴C-aminocyclopyrachlor was applied followed by 200 mm of simulated rain for 48 h. The herbicide was detected in all soil layers (0–30 cm), and in the leachate (> 30 cm), in small trace amounts (≤ 0.21%) in all treatments, showing that aminocyclopyrachlor undergoes a high degree of leaching in the clayey soil. In the absence of straw, 39% of the herbicide remained in the upper layer (0–5 cm). In the presence of straw, the herbicide was distributed through the soil profile, mainly from 0 to 25 cm. Forty percent more herbicide was retained in the straw with 20 t ha⁻¹ of sugarcane straw. Thus, it is concluded that the straw in high amounts retains aminocyclopyrachlor, but does not prevent it from reaching the soil; the high solubility of the herbicide and intense rainfall in a short period of time are factors that contribute to the herbicide passing through this barrier.

The impact of tree litter on soil chemistry leachate and sulfurous substrates of mine soils from former Jeziórko sulfur mine was investigated. Composites were used: soil substrate (less contaminated at mean 5090 mg kg⁻¹ S or high contaminated at 42,500 mg kg⁻¹ S) + birch or pine litter and control substrate (no litter). The composites were rinsed with distilled water over 12 weeks. In the obtained leachate, pH, EC, dissolved organic carbon, N, Ca, Mg, Al, and S were determined. Physicochemical parameters of the substrates and their basal respiration rate were determined. Rinsing and litter application lowered sulfur concentration in high contamination substrates. Pine litter application decreased EC and increased pH of the low-contaminated substrate. The substrate pH remained at low phytotoxic level (i.e., below 3.0), resulting in the low biological activity of the composites. Birch litter application increased leaching of N and Mg, indicating the possibility of an intensification of soil-forming processes in contaminated sites.

Nano-structured zinc sulfide (Nano-ZnS) has been demonstrated to be a promising alternative to activated carbon (AC) for controlling mercury emission from coal combustion flue gas. The ultimate fate of the mercury-laden Nano-ZnS after mercury capture is mostly disposed in landfill with fly ashes. Thus, the stability of mercury adsorbed on the Nano-ZnS is of considerable significance in the secured disposal of fly ash after mercury removal and in the commercial application of the Nano-ZnS sorbent for removal of mercury from coal combustion flue gas. In this work, a modified toxicity characteristic leaching procedure (TCLP) was conducted to evaluate the leachability of mercury on the Nano-ZnS. The effects of leachate pH value, leaching time, liquid-to-solid ratio, and acid rain types on mercury leaching from the mercury-laden Nano-ZnS were systematically investigated. The TCLP results show that the concentration of mercury in leachate was far below the safe limit (200 μg/L) as imposed by the US Environmental Protection Agency (EPA) for classifying a material as a hazardous waste. All the key parameters that generally affected metal leaching rate exhibited slight effect on mercury leaching from the mercury-laden Nano-ZnS. Leaching tests at various highly severe conditions resulted in less than 0.01% mercury leaching from the mercury-laden Nano-ZnS. Sequential selective extraction tests demonstrated that mercury sulfide (HgS) was the dominant adsorption product on the Nano-ZnS, which guaranteed the excellent stability of mercury adsorbed on the Nano-ZnS. Graphic abstract ᅟ

In this study, we investigate the effect of application rate and timing of liquid swine slurry on leaching of antibiotic-resistant bacteria (ARB) and their antibiotic resistance genes (ARGs) through soil columns. Swine slurry was added to laboratory soil columns at rates of 5000 or 30,000 gal ac⁻¹. For both application rates, rainfall was applied at either 1, 7, or 21 days after slurry application. Column effluent and the top centimeter of soil in the columns were sampled post-rainfall for cultivable bacteria and quantitative PCR was used to quantify tetracycline, methicillin, β-lactam, and erythromycin resistance genetic determinants. We also conducted similar experiments using swine lagoon slurry spiked with antibiotic-resistant E. coli and Salmonella. We found that the concentration of ARB and ARG recovered in the column effluent following application of the swine lagoon slurry generally decreased with increasing lag time between slurry application and simulated rainfall, though most of these decreases were not statistically significant. Moreover, no statistically significant differences in CFU or GU concentration in the column leachate were observed between the low and high slurry application rates. In the experiments using swine slurry spiked with E. coli and Salmonella, concentrations of both microorganisms eluted from fine sand columns were affected by both slurry application rate and lag time; recovery of ARGs, however, was mostly unaffected, but some differences were observed. In columns packed with loamy sand, no recovery was detected in the column effluent for either organism and recovery of ARG was unaffected by manure application rate or rainfall lag time.

Biochar as a soil amendment in street tree pits can be used to increase the soil’s ability to retain contaminants found in urban runoff. The increased retention can potentially decrease peak concentrations of soluble trace metals and de-icing salts in the soil solution, thereby decreasing the amounts taken up by tree roots or percolated out of the tree pits into the ground water. A leaching test measured the retention of trace metals (Cd, Zn, Cu, and Pb) and deicing salts (Na) by different kinds of biochar. The biochar was produced from hardwood (North American ash tree, Fraxinus americana) under different pyrolysis conditions, with three temperatures (350, 465 and 550 °C) and two residence times (10 and 30 min). Biochar pyrolyzed at 550 °C for 30 min significantly reduced the soluble concentrations of Zn, Cu, and Pb in the column leachate, most likely due to the its higher pH, surface area, and ash content. The pH of each treatment group was measured while the increase in ash content and surface area was inferred according to relevant literature. This biochar was then combined with soil and compost at rates ranging from 0 to 7.5% by dry weight to determine the proportion that optimally sorbed the contaminants. An application rate of 7.5% biochar by dry weight increased the soil mixture’s sorption capacity for Cd and Na while maintaining similar sorption of Cu, Zn, and Pb. The role of organic matter, such as that in compost, was especially important for the sorption of Zn and Cu. Hardwood biochar can thus improve the health of street trees and groundwater quality by sequestering trace metals and de-icing salts. Biochar can also be a useful tool to remediate contaminated soil, especially in urban environments.

The leachability of bottom medical waste ash from a Jordanian incinerator was studied in this work. The ash was characterized in terms of particle size distribution, chemical and mineralogical composition followed by leaching of several size fractions at different conditions (leaching time, temperature, initial pH, particle size, and solid liquid ratio). The major elements found in the ash were Ca, Si, Al, Cl, Na, Fe, Ti, S, Mg, Ba, and K, while the main mineral phases found in the ash were calcite, halite, sylvite, anhydrite, hematite, hydrochlorborite, cristobalite, melanterite, and chlormayenite. Leaching data indicates that as leaching time and S/L increased, the concentration of metals increased in the leachate. The highest leaching level was at a S/L ratio of 60 mg/ml. As the particles sizes decreased, the concentration of the majority of metals studied increased. Meanwhile, the effect of particle size on other metals was not regular due to the fact that sieving resulted in more concentrated metals in certain particle size fractions. Leachability results also indicate that variation in the initial pH has a slight effect on the degree of leaching. The concentration of some metal ions increased with temperature, while others increased initially but subsequently decreased. The extracted quantities of all the heavy metals were less than the limits set by EPA.

Inorganic anion monitoring is essential for bioreactor operation and is related for pollution control or energy and products recovery. However, there is a lack of studies validating methods for inorganic anions analyses in conditions compatible to those in bioreactor operations treating different types of wastewater. This paper provides a systematic statistical study and matrix-effect assessment for sugarcane vinasse, leachate, sewage and synthetic sewage. Sample preparation consisted of only a filtration and sample dilution. Cl⁻, NO₂⁻, NO₃⁻, PO₄³⁻ and SO₄²⁻ were determined in a Dionex ICS 5000® equipped with a chemical conductivity suppressor. Calibration curves were linear and well-adjusted between 2.5 and 50 mg L⁻¹ for all the anions in all the tested matrices, except PO₄³⁻ and SO₄²⁻ in vinasse. A calibration range for PO₄³⁻ in all tested matrices was 5.0 to 100 mg L⁻¹, whereas a range from 5.0 mg L⁻¹ to 50 mg L⁻¹ was obtained for SO₄²⁻ in vinasse. All the anions yielded recoveries in the range of 85–115% for all the tested matrices. Relative standard deviations lower than 10 and 2% were achieved for peak areas and retention times, respectively. A signal enhancement was observed for all the tested matrices and all the anions. The matrix effect level varied from −1.7 (NO₂⁻ in vinasse) to −33.9% (Cl⁻ in leachate). Sewage was the less affected matrix, while leachate gave higher matrix effects. Validation results and the matrix effect assessment showed that a simple sample preparation is suitable for multi-elemental analyses of inorganic anions for complex environmental samples.