The application of hydroxyapatite (HAP) can transform lead into pyromorphite in the soil. However, it is not clear how the physicochemical properties of soil enhance or reduce the formation of pyromorphite. This study determined that the presence of ferrihydrite or soil moisture condition was a more important factor to enhance the formation of pyromorphite. We also evaluated lead sorption characteristics and stability in soil with HAP in the presence of ferrihydrite. The difference in the maximum lead removal capacity of soil with and without 5 wt% ferrihydrite corresponded to 10.4% of the difference in lead removal between soils with and without HAP. In artificially contaminated soil with a 50% water-holding capacity, the ratio of lead that formed into pyromorphite was compatible between soils with and without ferrihydrite at 22% and 28% of added lead, respectively. In a percolation test, almost all of the added lead was transformed into pyromorphite, despite the presence of ferrihydrite. In both water and a 0.1-M citric acid extraction, the differences in lead extracted from the contaminated soil with HAP with or without ferrihydrite were very small compared with water-soluble lead in soil without HAP. This study indicated that in soil with 5 wt% ferrihydrite, lead was removed and converted into pyromorphite by HAP with a little disturbance by ferrihydrite, and the immobilized lead would be stable. In addition, this study suggested that the soil moisture condition was a more important factor for the formation of pyromorphite than the presence of ferrihydrite.

The effect of titanium dioxide nanoparticles (TiO₂ NPs) on biological wastewater treatment in a sequencing batch reactor was investigated. The overall removal of chemical oxygen demand (COD) and NH₄ ⁺-N were relatively unaffected; efficiencies remained at >95 % and around 99 %, respectively, after 30 days of continuous exposure to the NPs. However, TiO₂ NPs resulted in increased conversion of NO₂ ⁻-N to NO₃ ⁻-N and caused slight inhibition effect on denitrification, with the total nitrogen removal reduced from 95 to 90 %. Several shifts in the bacteria community composition were noted. However, the overall community structure and biodiversity remained relatively unchanged. The polysaccharide content in the extracellular polymeric substances (EPS) was generally unaffected, suggesting a low potential of substantial shock or damage that may result in cytoplasmic leakage. However, a decrease in protein content occurred and indicated the inhibitive effects of the NPs. TiO₂ NPs were removed in the system mainly via deposition into the sludge. The removal efficiency decreased from 90 to 70 % after 4 weeks, due to sorption saturation as well as the change in the EPS content of the activated sludge.

The contribution of atmospheric deposition to the metal load at the outlet of a small urban catchment (Pin Sec, France) was studied. A new method, which takes into account the type of urban surfaces (glass, tile, bitumen, zinc sheet, grass, facade coating, and slate) as well as turbulence and local micrometeorology, was developed to measure atmospheric dry deposition. Dry deposition, wet deposition, and stormwater runoff load were all measured from September 2010 to August 2011. At the annual scale, atmospheric deposition was not a major contributor to the metal load at the outlet of this small catchment. Wet deposition however ranged from <1 to 29 %. The contribution of dry deposition (generally less than 5 %) was especially low and appeared to be smaller than that reported in previous studies. On this catchment, the majority of the metal load could be attributed to stormwater runoff (64–99 %). This methodology looks promising and should be taken into consideration when conducting new research on the contribution of atmospheric deposition to the pollutant load in urban catchments.

Three experiments were performed to compare the P availability between struvite and the commercial fertilizer monoammonium phosphate (MAP). Experiment 1 evaluated triticale grown in a commercial potting medium and fertilized with struvite and MAP at 0, 56, 112, and 224 kg P₂O₅ ha⁻¹. Struvite was comparable for dry matter (DM) yield (P < 0.01) and resulted in greater concentrations of P (P < 0.005) compared to MAP. Experiment 2 evaluated triticale and oats planted in two soils differing in pH, and fertilized with either struvite or MAP at 0, 56, 112, and 224 kg P₂O₅ ha⁻¹. When oats were grown in acidic soil, struvite provided greater P uptake (P < 0.0001) and concentration of P (P < 0.0001) in the plant compared to MAP. When triticale was grown in acidic soil, struvite provided the greatest DM yield (P < 0.005), P uptake (P < 0.0001), and concentration of P (P < 0.0001) compared to MAP. When triticale and oats were grown in alkaline soil, struvite produced the greatest concentration of P (P < 0.003) compared to MAP for oats. Experiment 3 evaluated corn and alfalfa over a 3-year period planted in alkaline soil and fertilized with either struvite or MAP at 0, 140, and 280 kg P₂O₅ ha⁻¹. In 2006 and 2007, struvite and MAP were comparable for DM yield (P < 0.05) and concentration of P (P < 0.05) in alfalfa. Using MAP resulted in greater P uptake (P < 0.05) all 3 years for alfalfa, and greater DM yields (P < 0.05) and concentrations of P (P < 0.05) in 2008. For corn, MAP produced the greatest DM yield (P < 0.001), P uptake (P < 0.003), and concentration of P (P < 0.001) all 3 years. Struvite was a comparable or superior P fertilizer compared to MAP in acidic soils and inferior to MAP in alkaline soils.

Despite a contemporary interest in biochar application to agricultural fields to improve soil quality and long-term carbon sequestration, a number of potential side effects of biochar incorporation in field soils remain poorly understood, e.g., in relation to interactions with agrochemicals such as pesticides. In a field-based study at two experimental sites in Denmark (sandy loam soils at Risoe and Kalundborg), we investigated the influence of birch wood biochar with respect to application rate, aging (7–19 months), and physicochemical soil properties on the sorption coefficient, K d (L kg⁻¹), of the herbicide glyphosate. We measured K d in equilibrium batch sorption experiments with triplicate soil samples from 20 field plots that received biochar at different application rates (0 to 100 Mg ha⁻¹). The results showed that pure biochar had a lower glyphosate K d value as compared to soils. Yet, at the Kalundborg soils, the application of biochar enhanced the sorption of glyphosate when tested after 7–19 months of soil–biochar interaction. The relative enhancement effect on glyphosate sorption diminished with increasing biochar application rate, presumably due to increased mineral–biochar interactions. In the Risoe soils, potential biochar effects on glyphosate sorption were affected by a distinct gradient in soil pH (7.4 to 8.3) and electrical conductivity (0.40–0.90 mS cm⁻¹) resulting from a natural CaCO₃ gradient. Thus, glyphosate K d showed strong linear correlation with pH and EC. In conclusion, the results show that biochar, despite initially being a poor sorbent for glyphosate, can increase glyphosate sorption in soil. However, the effect of biochar on glyphosate sorption is depends on prevailing soil physicochemical properties.

Forest is an important vegetation type on the globe, and clearcutting is the main forest management method. This paper presents a process-based model developed to project the impact of forest growth and clearcutting on dissolved organic carbon (DOC) and total mercury (THg) export from forest-dominated watersheds over two forest-growing cycles. The modelling of THg is based on the observation that THg export from terrestrial to aquatic ecosystems occurs with the binding and subsequent in-stream transport of THg by DOC. From the results generated with the integrated model, DOC and THg export follows two main trends; (i) a multiple-year trend, associated with forest harvesting and re-growth patterns over the lifetime of the forest, and (ii) an annual trend, associated with the seasonal dynamics in forest litter production and decomposition. During a forest rotation, DOC and THg concentration decreases following clearcutting, reaches a minimum at about 15 years after forest regeneration and then gradually increases with forest ageing. Large debris pools left on site following clearcutting can provide a significant pulse in DOC production and within-watershed THg export during the first 2–3 years after harvest. In a single year, the integrated model predicts that DOC- and THg-concentration peaks after leaf fall in autumn, decreases to a minimum in April, increases to another maximum in June and finally decreases to a second minimum just before leaf fall. This seasonal cycle is repeated every year. Conifer species and wetland-dominated watersheds are anticipated to release a greater amount of DOC and THg to aquatic ecosystems than deciduous and dryland-dominated watersheds. The long-term and seasonal DOC production is consistent with field measurements.

This study tested the efficacy of Zn-Al sulphate layered double hydroxides (LDH) as sorbent to remove antimony from circum-neutral solutions. Results of experimentation showed that Sb(V) in the anionic form Sb(OH)₆ ⁻ can be efficiently removed from aqueous solutions through an exchange process with the SO₄ ²⁻ present in the interlayer; total removal can be achieved within 6–24 h for A ≥2, where A is the ratio of the maximum theoretical anion exchange capacity (AEC) to the initial Sb concentration, both expressed in milliequivalents per liter. The complex rearrangement of the LDH structure to host Sb(OH)₆ ⁻ in the interlayer is correlated to an initial fast removal of the contaminant, followed by a progressive slowing down of the exchange process. The overall speed of the process is again a direct function of A; in practice, the sorbent dose should be carefully evaluated to balance cost/efficacy/timing of the water treatment. Comparison with previous studies documenting Zn-Al sulphate LDH efficacy as arsenate and molybdate sorbent indicates a comparable affinity for As(V) and Sb(V), higher than for Mo(VI). The results of this study reinforce the possible key role of Zn-Al sulphate LDHs in water treatment for pH ranging from circum-neutral to moderately alkaline, thanks to their capability to rearrange the original structure in order to host different-sized/charged anions.

In this study, adsorption and biodegradation were exploited sequentially to remove the herbicide fenuron, the insecticide carbaryl and the estrogens 17β-estradiol (E2) and 4-tert-octylphenol (OP) from a municipal landfill leachate (MuLL). In the first step, we used spent coffee grounds, almond shells, a biochar and potato dextrose agar to adsorb the compounds spiked in MuLL at a concentration of 1 mg L⁻¹. After only 3 days, any adsorbent removed from MuLL the totality of E2 and OP, averagely more than 95 % of carbaryl and 62 % of fenuron (81 % after 7 days). In the second step, the adsorbents collected from MuLL after 7 days were inoculated with the fungi Bjerkandera adusta and Irpex lacteus, separately. After 7 days, the maximum degradation occurred for OP in any treatment being averagely 78 and 74 % using B. adusta and I. lacteus, respectively. After 15 days, the average percentages of fenuron, carbaryl, E2 and OP degraded were, respectively, 75, 76, 88 and 88 % using B. adusta, and 74, 79, 85 and 89 % using I. lacteus. Residual estrogenicity in the adsorbents, tested with the recombinant yeast assay, was strictly related to residual E2, thus indicating a negligible contribution from the other contaminants and/or degradation products. The 7-day treatment of MuLL with the adsorbents caused a significant abatement of MuLL phytotoxicity on flax (2.5 times seedling elongation with coffee grounds, compared to MuLL) and a huge stimulation of rapeseed respect to water (biomass almost doubled), thus suggesting a possible worthwhile recycling of this wastewater in agriculture.

The Tagus Estuary is one of the most Hg-contaminated estuaries in SW Europe. Sediment cores were sampled at two low Hg-contaminated sites inside the natural park, Alcochete (ALC) and Vale Frades (VF), and analyzed for mercury and methylmercury. Concentrations of Hg and MeHg in sediments were below 1 μg g⁻¹ and 4.4 ng g⁻¹, respectively. While in summer organic matter and/or excess SO₄ ²⁻ promotes Hg methylation, in winter, Hg availability is the sole driver for methylation. Diffusive fluxes in the sediment/water interface show a sink of Hg species in the ALC site (ca. 170 mg year⁻¹ of Hg and 60 mg year⁻¹ of MeHg), while in the VF area, a sink of MeHg (ca. 1900 mg year⁻¹) as well as a source of Hg (ca. 2000 mg year⁻¹) is observed. The morphology and hydrodynamic regime of the Tagus Estuary seem to influence Hg dynamics even in areas with low levels of Hg contamination.

Sulfide, found in some wastewaters and industrial off-gases, is a toxic and highly corrosive pollutant, especially in wastewater applications. Sulfide removal was studied in a new sulfide-oxidizing reactor (External Silicone Membrane Reactor—ESMR) that employs a tubular silicone rubber membrane for micro-aeration. The chemical and biological sulfide oxidation at pH 8.0, 9.0, and 10.0 were investigated. The applied velocity (V ₛ) in the membrane was also investigated as a system control parameter. The local overall mass transfer coefficient (R) was estimated for the tubular silicone rubber membrane and had an average value of 0.153 m.h⁻¹. Oxygen mass transfer was found to not be influenced by the applied velocity. The sulfide oxidation to sulfate could be partially avoided and the biotic tests showed larger sulfur aggregates deposited in the silicone membrane, which could easily be washed away upon flushing. By contrast, colloidal sulfur formation observed in the chemical oxidation assays was harder to separate from the liquid phase. This study reveals that the ESMR is a suitable reactor design to promote partial sulfide oxidation because it provides an adequate oxygen supply with minimized aeration costs.