The immobilization of lead by the reaction with phosphate bearing materials is a promising remediation method for contaminated soils. Low soluble neo-formed lead-phosphate phases similar to chloropyromorphite [Pb₅(PO₄)₃Cl], can control availability and mobility of lead in the environment, and consequently reduce human exposure, if soils are the main contamination pathway. We used three phosphate source materials [NaH₂(PO₄)₃, commercial superphosphate and phosphate rock] to study lead immobilization in soil and mining waste samples. Products were examined after 1, 3 and 6 months of contact. The samples are from a contaminated area by former Pb mining and smelting activities, in southeastern Brazil, where epidemiological studies showed high lead blood levels in local population. The PBET (physiological based extraction test) bioaccessibility test was used to measure changes in the amount of soluble lead after sample treatment. Results show that the most efficient phosphate source was NaH₂(PO₄)₃, which reduced lead solubility to 92% in acidic gastric conditions after the first month of contact. Superphosphate and phosphate rock also diminished Pb solubility, but the effect was more time dependent. None specific Pb-phosphate phases could be identified by XRD in whole treated samples, but the Pb-Ca-P elemental associations, observed on SEM images and EDS spectra of portions of the samples, combined with the reduced solubility, indicate that more insoluble lead phases were formed after the treatment. Based in these results, the in site phosphate application on soils to induce lead immobilization should be considered as a possible alternative to reduce human exposure at the area.

Elevated concentrations of trace metals in soil can increase the risk of pollution to ecosystems and human health. This cannot be predicted solely from the total and/or extracted concentration of metals from soil samples, as movement of trace elements to the groundwater is also a result of the flow solution through the vadose zone. The rate at which trace elements move are not usually directly measurable, and thus it must be estimated taking into account water transport through the soil. Therefore, a field portable drop-former rainfall simulator has been designed and used to study trace-element mobility in small field plots. The rainfall simulator permits a wide range of variation in rainfall intensities and provides a homogeneous distribution of the simulated rain in a 0.25 m² plot with low cost per data collected and short time. Performance of the rainfall simulator has been evaluated and a preliminary assessment of the amount of pollutants present in the soil (As, Cu and Zn) that can reach groundwater via soil drainage is made by combining rainfall-simulation experiments with infiltration estimates based on a stochastic model of the local climate. The study was conducted in soils affected by the Aznalcóllar toxic spill in the Guadiamar river basin (Spain). Infiltration experiments reveal that the trace elements could be classified according to their mobility as As < Cu < Zn. The presence of high gravel content below this depth increased the amount of drainage and therefore the risk of groundwater pollution, especially with Zn, which was found below 50 cm depth.

Two series of laboratory-scale vertical flow systems (flooded and nonflooded columns) were designed to compare nitrogen removal performance, nitrous oxide emission, and ammonia volatilization under different water levels upon treating diluted digested livestock liquid. In these systems, influent was supplied at three hydraulic loading rates (HLRs of 1.25, 2.5, and 5 cm day⁻¹) during stage 1 and the rates were doubled during stage 2 when the water levels of nonflooded columns were elevated from zero to half the height of the soil column. After hydraulic loading rates doubled, the average removal rates of total nitrogen in flooded columns varied from 1.27 to 2.94 g⁻² day⁻¹ and those in nonflooded columns ranged from 1.23 to 3.88 g⁻² day⁻¹. The T-N removal at an HLR of 10 cm day⁻¹ in the nonflooded column with an elevated water table level had higher efficiency than that in the flooded column, suggesting T-N removal is enhanced in the nonflooded column probably due to the improved coupled nitrification–denitrification process under the elevated water table level condition. On the other hand, there was a significant correlation (r ² = 0.532, p < 0.001) between the N₂O flux and redox potential that mainly corresponded to water levels and HLRs, suggesting anoxic or aerobic conditions stimulate N₂O emission by enhancing the nitrification (nitrification–denitrification) process. In contrast, NH₃ volatilization had a high flux in the anaerobic condition mainly because of flooding. Based on the experimental results, it is hypothesized a nonflooded condition with higher water table level (Eh range of −160 to +260 mV) would be suitable to reduce N₂O emission and NH₃ volatilization peak value by at least half while maintaining relatively efficient nitrogen removal performance.

The present study explained the effect of pretreatments on the biosorption of Cr (III) and Cr (VI) by Cassia fistula biomass from aqueous solutions. For this purpose Cassia fistula biomass was pretreated physically by heating, autoclaving, boiling and chemically with sodium hydroxide, formaldehyde, gluteraldehyde, acetic acid, hydrogen peroxide, commercial laundry detergent, orthophosphoric, sulphuric acid, nitric acid, and hydrochloric acid. The adsorption capacity of biomass for Cr (III) and Cr (VI) was found to be significantly improved by the treatments of gluteraldehyde (95.41 and 96.21 mg/g) and benzene (85.71 and 90.81 mg/g) respectively. The adsorption capacity was found to depend on pH, initial metal concentration, dose, size, kinetics, and temperature. Maximum adsorption of both the Cr (III) and Cr (VI) was observed at pH 5 and 2. When Freundlich and Langmuir isotherms were tested, the latter had a better fit with the experimental data. The kinetic studies showed that the sorption rates could be described better by a second order expression than by a more commonly applied Lagergren equation.

Salvinia minima has been reported as a cadmium and lead hyperaccumulator being the adsorption and intracellular accumulation the main uptake mechanisms. However, its physicochemical properties, the effect of metal concentration and the presence of organic and inorganic compounds on its hyperaccumulating capacity are still unknown. Furthermore, the specific adsorption and accumulation mechanisms occurring in the plant are not clear yet. Thus, based on a compartmentalization analysis, a bioadsorption (BAF) and an intracellular accumulation factor (IAF) were calculated in order to differentiate and quantify these two mechanisms. The use of kinetic models allowed predicting the specific type of uptake mechanisms involved. Healthy plants were exposed to five lead concentrations ranging from 0.80 ± 0.0 to 28.40 ± 0.22 mg Pb²⁺l⁻¹ in batch systems. A synthetic wastewater, amended with propionic acid and magnesium sulfate, and deionized water were used as media. The BAF and IAF contributed to gain an in-depth insight into the hyperaccumulating lead capacity of S. minima. It is clear that such capacity is mainly due to adsorption (BAF 780–1980) most likely due to its exceptional physico-chemical characteristics such as a very high surface area (264 m² g⁻¹) and a high content of carboxylic groups (0.95 mmol H⁺g⁻¹ dw). Chemisorption was predicted as the responsible mechanism according to the pseudo-second order adsorption model. Surprisingly, the ability of S. minima to accumulate the metal into the cells (IAF 57–1007) was not inhibited at concentrations as high as 28.40±0.22 mg Pb²⁺l⁻¹.

In contaminated water reservoirs, the sorption and binding of radionuclides to solids (SR) determines their bioavailability and transport and thus human and ecosystem exposure. In this work, the influence of organic matter (OM) on binding of the radionuclides ⁹⁰Sr, ¹³⁷Cs, sum of ²³⁵U, ²³⁸U, and sum of ²³⁹Pu, ²⁴⁰Pu to solids are investigated, using experimental data derived from ecological monitoring of radioactive waste deposits in South Ural (Russia). OM in several surface water reservoirs mainly consists of humic substance (HS) which forms humates and fulvates with radionuclides and binds to solids via different mechanisms, such as coordinating bond or covalent bond. These processes are strongly dependent on the phase of HS, which can be colloidal or soluble high-molecular compounds. Based on the spatial distribution of radionuclides, SR and OM in waste deposits, we assumed a specific influence of humic acids (HA) on the binding of radionuclides to SR, and quantified it with invariant values of a modified partitioning coefficient. The mathematical form of this invariant value emphasizes a significant impact of the local mass of HA (mHA/V) and local surface area of SR (s = Ssorb/V) per volume V on the processes involved in binding radionuclides to SR. These processes may retard radionuclide migration into groundwater.

Steamboat Creek, Washoe County, Nevada, is considered the most polluted tributary of the Truckee River, therefore the reduction of nutrients from the creek is an important factor in reducing eutrophication in the lower Truckee River. Restoration of the wetlands along the creek has been proposed as one method to improve water quality by reducing nutrient and sediments from non-point sources. This study was aimed to design a simulation model wetlands water quality model (WWQM) that evaluates nitrogen, phosphorus, and sediments retention from a constructed wetland system. WWQM is divided into four submodels: hydrological, nitrogen, phosphorus, and sediment. WWQM is virtual Visual Basic 6.0 program that calculates hydrologic parameters, nutrients, and sediments based on available data, simple assumptions, knowledge of the wetland system, and literature data. WWQM calibration and performance was evaluated using data sets obtained from the pilot-scale constructed wetland over a period of four and half years. The pilot-scale wetland was constructed to quantify the ability of the proposed wetland system for nutrient and sediment removal. WWQM simulates nutrient and sediments retention reasonably well and agrees with the observed values from the pilot-scale wetland system. The model predicts that wetlands along the creek will remove nitrogen, phosphorus, and sediments by 62, 38, and 84 %, respectively, which would help to reduce eutrophication in the lower Truckee River.

The present study aims to understand the hydrochemistry vis-à-vis As-exposure from drinking groundwater in rural Bengal. The characteristic feature of the groundwaters are low Eh (range, -151 to -37 mV; mean, -68 mV) and nitrate (range, 0.01-1.7 mg/l; mean, 0.14 mg/l) followed by high alkalinity (range, 100-630 mg/l; mean, 301 mg/l), Fe (range, 0.99-38 mg/l; mean, 8.1 mg/l), phosphate (range, 0.01-15 mg/l; mean, 0.54 mg/l), hardness (range, 46-600 mg/l; mean, 245 mg/l) and sulphate (range, 0.19-88 mg/l; mean, 7.2 mg/l), indicating reducing nature of the aquifer. The land use pattern (sanitation, surface water bodies, sanitation coupled with surface water bodies and agricultural lands) demonstrates local enrichment factor for As/Fe in groundwater. Among these, sanitation is the most prevailing where groundwater is generally enriched with As (mean, 269 μg/l) and Fe (mean, 9.8 mg/l). Questionnaire survey highlights that ~70% of the villagers in the study area do not have proper sanitation. This demonstrating the local unsewered sanitation (organic waste, anthropogenic in origin) could also cause As toxicity in rural Bengal. In the agricultural lands, higher mean values of alkalinity, phosphate, sulphate, hardness and electrical conductivity was observed, and could be linked with the excessive use of fertilizers for agricultural production. Bio-markers study indicates that the accumulation of As in hair and nail is related with the construction of exposure scenario with time dimension. The strength and weakness of the on-going West Bengal and Bangladesh drinking water supply scenario and achievability towards alternative options are also evaluated.

A fungal strain possibly capable of removing hexavalent chromium was to be isolated from industrial effluent from a leather factory located in the city of Guadalajara, state of Jalisco, Mexico. The strain was identified as Trichoderma inhamatum by the D1/D2 domain sequence of the 28S rDNA gene. Batch cultures of T. inhamatum in media containing initial Cr(VI) concentrations from 0.83 to 2.43 mM Cr(VI) were prepared. Experimental results suggest that the fungus is capable of transforming hexavalent chromium to trivalent chromium; a transformation of a highly toxic contaminant to a low toxic form. The specific and volumetric rates of Cr(VI) reduction by T. inhamatum cultures decreased as the initial Cr(VI) concentration increased. The fungus exhibited a remarkable capacity to tolerate and completely reduce Cr(VI) concentrations up to 2.43 mM. These results indicate that the T. inhamatum fungal strain may have potential applications in bioremediation of Cr(VI)-contaminated wastewaters.

The purpose of this study was to determine the degree of PAH contamination and the association of PAHs with metals in urban soil samples from Sevilla (Spain). Fifteen polycyclic aromatic hydrocarbons-PAHs (naphthalene, acenaphthene, fluorene, phenanthrene, anthracene, fluoranthene, pyrene, benzo[a]anthracene, chrysene, benzo[b]fluoranthene, benzo[k]fluoranthene, benzo[a]pyrene, dibenzo[a,h]anthracene, benzo[g,h,i]perylene, indeno[1,2,3-c,d]pyrene) and seven metals (Cd, Cr, Cu, Mn, Ni, Pb, Zn) have been evaluated in representative urban soil samples. Forty-one top soils (0-10 cm) under different land use (garden, roadside, riverbank and agricultural allotment) were selected. PAHs from soil samples were extracted by sonication using dichloromethane. The simultaneous quantification of 15 different PAH compounds were carried out by HPLC using multiple wavelength shift in the fluorescence detector. For qualitative analysis a photo diode-array detector was used. Metal (pseudo-total) analysis was carried out by digestion of the soils with aqua regia in microwave oven. The mean concentration of each PAH in urban soils of Sevilla showed a wide range, they are not considered highly contaminated. The results of the sum of 15 PAHs in Sevilla soils are in the range 89.5-4004.2 μg kg-¹, but there seems not to be a correlation between the concentration of PAHs and the land use. Of the 15 PAHs examined, phenanthrene, fluoranthene and pyrene were present at the highest concentrations, being the sum of these PAHs about 40% of the total content. Although metal content were not especially high in most soils, there are significant hints of moderate pollution in some particular spots. Such spots are mainly related with some gardens within the historic quarters of the city. The associations among metals and PAHs content in the soil samples was checked by principal components analysis (PCA). The largest values both for 'urban' metals (Pb, Cu and Zn) and for PAHs were mainly found in sites close to the historic quarters of the city in which a heavy traffic of motor vehicles is suffered from years.