The beneficial uptake of nutrients by wetland plants is countered to some extent by nutrient release back into the aquatic environment due to vegetative die-back. This current study examined whether Leersia oryzoides, a common wetland plant, exhibits luxury uptake of nutrients from simulated farm runoff. The study also tested whether with subsequent decomposition, these nutrients are released back into the water column. When exposed to elevated (>2 mg/L N and P) runoff, L. oryzoides assimilated significantly higher concentrations of nitrogen (p < 0.001) and phosphorus (p < 0.001) in above-ground biomass as compared to non-enriched treatments (<0.05 mg/L N and P). Subsequently, senescence of enriched above-ground biomass yielded significantly higher concentrations of phosphorus (2.19 ± 0.84 mg P/L). Using L. oryzoides as our model, this study demonstrates nitrogen and phosphorus sequestration during the growing season and release of phosphorus in the winter. Release of sequestered nutrients during plant senescence.

Residence time-dependent distribution patterns of hexachlorobenzene (HCB) and dichlorodiphenyltrichloroethane (DDT) among different soil organic matter fractions of three Chinese soils were investigated. Soil organic matter (SOM) was fractionated into fulvic acid (FA), humic acid (HA), bound-humic acid (BHA), lipid, and insoluble residue (IR) fractions using methyl isobutyl ketone (MIBK) method. Results revealed that as the residence time prolonged, the amounts of HCB and DDT in the FA, HA and BHA fractions decreased, while those in the lipid and IR fractions increased. One- and two-compartment first order, and one- and two-parameter pore-diffusion kinetic models were used to describe the mobility of HCB and DDT from the FA, HA and BHA fractions. The results suggest that excellent agreements were achieved between the experimental data and fits to the two-compartment first order kinetic model (R2 > 0.97). The transfer rates of HCB and DDT followed the order FA > HA > BHA. HCB and DDT tend to transfer from FA, HA and BHA fractions to lipid and IR fractions with increasing residence time.

Application of riverbed sand for the adsorptive separation of cadmium(II) from aqueous solutions has been investigated. Removal increased from 26.8 to 56.4% by decreasing the initial concentration of cadmium from 7.5 x 10-5 to 1.0 x 10-5 M at pH 6.5, 25 °C temperature, agitation speed of 100 rpm, 100 μm particle size and 1.0 x 10-2 NaClO4 ionic strength. Process of separation is governed by first order rate kinetics. The value of rate constant of adsorption, kad, was found to be 2.30 x 10-2 per min at 25 °C. Values of coefficient of mass transfer, βL, were calculated and its value at 25 °C was found to be 1.92 x 10-2 cm/s. Values of Langmuir constant were calculated. Values of thermodynamic parameters ΔG0, ΔH0 and ΔS0 were also calculated and were recorded as -0.81 kcal/mol, -9.31 kcal/mol and -28.10 cal/mol at 25 °C. pH has been found to affect the removal of cadmium significantly and maximum removal, 58.4%, has been found at pH 8.5. Process can be used for treatment of cadmium(II) rich wastewaters.

Concern regarding the impacts of continued nitrogen and sulfur deposition on ecosystem health has prompted the development of critical acid load assessments for forest soils. A critical acid load is a quantitative estimate of exposure to one or more pollutants at or above which harmful acidification-related effects on sensitive elements of the environment occur. A pollutant load in excess of a critical acid load is termed exceedance. This study combined a simple mass balance equation with national-scale databases to estimate critical acid load and exceedance for forest soils at a 1-km2 spatial resolution across the conterminous US. This study estimated that about 15% of US forest soils are in exceedance of their critical acid load by more than 250 eq ha-1 yr-1, including much of New England and West Virginia. Very few areas of exceedance were predicted in the western US. This simple mass balance equation estimated that 17% of US forest soils exceed their critical acid load by more than 250 eq ha-1 yr-1, and these areas are predominantly located in the northeastern US.

The effect of lead on the sorption of 2,4,6-trichlorophenol (2,4,6-TCP) on soil and peat was investigated using a batch equilibration method. Lead markedly diminished the sorption of 2,4,6-TCP, and 2,4,6-TCP had little effect on lead sorption. Peat was a more effective adsorbent for 2,4,6-TCP than soil. The desorption hysteresis of 2,4,6-TCP verified the presence of high-energy sorption sites. Mechanisms of lead suppression effect on the 2,4,6-TCP sorption included the following: Firstly, lead accelerated the aggregation of colloids, the aggregates covered the surface in part and shrunk the pore sizes of the adsorbents, hence decreased the sorption of 2,4,6-TCP. Secondly, X-ray absorption and Fourier transform infrared spectroscopy study suggested that lead competed with 2,4,6-TCP for carboxylic, phenolic and Si-OH groups of organic matter and clay minerals. Such competition was partly responsible for the overall suppression effect of lead on the sorption of 2,4,6-TCP. Lead diminished the sorption of 2,4,6-trichlorophenol onto soil and peat.

The complexation of Cu by sewage sludge-derived dissolved organic matter (SSDOM) is a process by which the environmental significance of the element may become enhanced due to reduced soil sorption and, hence, increased mobility. The work described in this paper used an ion selective electrode procedure to show that SSDOM complexation of Cu was greatest at intermediate pH values because competition between hydrogen ions and Cu for SSDOM binding sites, and between hydroxyl ions and SSDOM as Cu ligands, was lowest at such values. Batch sorption experiments further showed that the process of Cu complexation by SSDOM provided an explanation for enhanced desorption of Cu from the solid phase of a contaminated, organic matter-rich, clay loam soil, and reduced adsorption of Cu onto the solid phase of a sandy loam soil. Complexation of Cu by SSDOM did not affect uptake of Cu by spring barley plants, when compared to free ionic Cu, in a sand-culture pot experiment. However, it did appear to lead to greater biomass yields of the plant; perhaps indicating that the Cu-SSDOM complex had a lower toxicity towards the plant than the free Cu ion.

Clinoptilolite is investigated as a possible regenerable sorbent for acid rock drainage based on its adsorption capacity for Zn, adsorption kinetics, effect of pH, and regeneration performance. Adsorption of Zn ions depends on the initial concentration and pH. Adsorption/Desorption of Zn reached 75% of capacity after 1–2 h. Desorption depended on pH, with an optimum range of 2.5 to 4.0. The rank of desorption effectiveness was EDTA > NaCl > NaNO₃ > NaOAc > NaHCO₃ > Na₂CO₃ > NaOH > Ca(OH)₂. For cyclic absorption/desorption, adsorption remained satisfactory for six to nine regenerations with EDTA and NaCl, respectively. The crystallinity and morphology of clinoptilolite remained intact following 10 regeneration cycles. Clinoptilolite appears to be promising for ARD leachate treatment, with significant potential advantages relative to current treatment systems.

The application of magnetite-immobilized chitin in pentachlorophenol (PCP) removal was demonstrated in this study. The physicochemical parameters for immobilization of chitin by magnetite, and for PCP adsorption using magnetite-immobilized chitin were optimized. For chitin immobilization, the optimized conditions were: magnetite to chitin (m:c) ratio at 1:2, initial pH 6, 25°C, 200 rpm and 60 min in batch system. The immobilization efficiency (IE) was 99.4% and immobilization capacity (IC) was 2.0 mg chitin mg-¹ magnetite. High initial pH (pH > 11) and temperature (>30°C) lowered the IE and IC. For PCP (10 mg l-¹) adsorption, the optimized conditions were: 1,500 mg l-¹ immobilized chitin, initial pH 6, 25°C, 200 rpm and 60 min in batch system. The removal efficiency (RE) was 57.9% and removal capacity (RC) was 5.4 mg g-¹. The adsorption ability of immobilized chitin decreased with pH and temperature increased. However, increasing the amount of immobilized chitin (24,000 mg l-¹) can increase the RE up to 92%. Both chitin immobilization and PCP adsorption exhibited Langmuir and Freundlich adsorption isotherms. Results in this study indicated that magnetite-immobilized chitin was a cost-effective and environmental friendly adsorbent to remove environmental pollutants such as PCP.

This study qualifies and quantifies the effects of pH, hardness, alkalinity, salinity and bone calcination temperature related with the adsorption of As(V) onto biogenic hydroxyapatite (HAPb) obtained from cow-charred bones. Arsenic contamination of surface and subsurface waters is widely extended in Argentina. It is a problem of major concern, particularly in rural and suburban areas where there are not water treatment plants for supplying of drinking water. HAPb is a natural material, whose absorbent properties can be used for the design of low-cost technologies for As(V) abatement in water. In this work HAPb has been characterized by physical and chemical analysis (XRD, SEM, EDAX, BET, and electrophoretic mobility). A Plackett–Burman screening experimental design allowed us to determine the main variables affecting the efficiency of As(V) sorption onto HAPb. Based on these variables and with a design of higher order we developed a model of the system to study its behaviour. Data collection was planned through a Doehlert experimental design and a back propagation artificial neural network was used to work it out. Results showed that salinity is the major variable affecting the efficiency of the As(V) immobilization process but pH and hardness should be taken into account because of associations among them.

In this study adsorption of arsenic (As) onto TiO₂ nanoparticles and the facilitated transport of As into carp (Cyprinus carpio) by TiO₂ nanoparticles was examined. Adsorption kinetics and adsorption isotherm were conducted by adding As(V) to TiO₂ suspensions. Facilitated transport of As by TiO₂ nanoparticles was assessed by accumulation tests exposing carp to As(V) contaminated water in the presence of TiO₂ nanoparticles. The results showed that TiO₂ nanoparticles had a significant adsorption capacity for As(V). Equilibrium was established within 30 min and the isotherm data was described by Freundlich isotherm. The KF and 1/n were 20.71 mg/g and 0.58, respectively. When exposed to As(V)-contaminated water in the presence of TiO₂ nanoparticles, carp accumulated considerably more As, and As concentration in carp increased by 132% after 25 days exposure. Considerable As and TiO₂ accumulated in intestine, stomach and gills of the fish, and the lowest level of accumulation was found in muscle. Accumulation of As and TiO₂ in stomach, intestine and gills are significant. Arsenic accumulation in these tissues was enhanced by the presence of TiO₂ nanoparticles. TiO₂ nanoparticles that have accumulated in intestine and gills may release adsorbed As and As bound on TiO₂ nanoparticles which cannot be released maybe transported by TiO₂ nanoparticles as they transferred in the body. In this work, an enhancement of 80% and 126% As concentration in liver and muscle after 20 days of exposure was found.