Dissolved waterborne polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs) and organochlorine pesticides (OCPs) were assessed over a period of one year at five sampling sites in a model industrial region in the Czech Republic using silicone rubber passive samplers. The spatial variability of POPs in the studied region in water was small and diffusive pollution sources predominate. Concentrations of the most volatile PAHs decreased with increasing water temperature in the whole region, which reflects the seasonality in atmospheric deposition. The dissolved concentrations of more hydrophobic PAHs, PCBs and OCPs in and downstream the industrial zone are related to desorption from suspended particles. Upstream the industrial area, a positive correlation of dissolved and particle-bound contamination was observed only for DDT metabolites and hexachlorobenzene. Calculated fugacities in water and bottom sediment indicated a fair degree of equilibrium between these compartments for OCPs and PCBs, whereas sediment represented a potential source of PAHs.

Organic complexing agents, such as ethylenediaminetetraacetic acid (EDTA), nitrilotriacetic acid (NTA) and picolinic acid, have been widely used at nuclear sites and are therefore found as common co-contaminants in radioactive contaminated land. This study has explored the mechanisms by which these three complexing agents affect the sorption of Th(IV) to pure silica and a natural sand. EDTA, NTA and, to a lesser extent, picolinic acid decreased the sorption of Th to silica, demonstrating the formation and solubility of Th complexes. However, Th sorption to sand was kinetically controlled and complexation enhanced the rate of Th sorption. EDTA and NTA did not sorb significantly to the sand, and metal desorption indicated that the mechanism involved exchange with sand-associated metals. At equilibrium, however, Th sorption was not affected by the presence of the ligands, and modelling suggested that the interaction between Th and the surface binding sites controlled Th sorption thermodynamically.

Solid humic acid (HA) particles were dissolved and subsequently coated on a type of multiwalled carbon nanotubes (MWCNTs). Pb²⁺ sorption from water by the solid HA, the MWCNTs and the obtained HA-MWCNT complexes was compared. The underlying mechanism of the difference in the sorption was discussed with the data at different pHs, results of desorption in the presence and absence of Ca²⁺ and the characterizations using inductively coupled plasma mass spectrometry, X-ray energy dispersion spectroscopy and X-ray absorption fine structure spectroscopy. The effect of MWCNT-contained impurities on the sorption was also examined. It was shown that the surface-bound HA introduced oxygen-containing functional groups and negative charges on the MWCNTs, thus greatly increasing Pb²⁺ sorption on the MWCNTs. Pb²⁺ could be electrostatically attracted into outer-sphere of the electric double layer of the HA-MWCNT complexes, a fraction of which would form coordination complexes with carboxyl groups in the inner- and/or outer-sphere.

Desorption kinetic and isothermal characteristics of BDE-28 and BDE-47 were investigated using natural soils with different organic carbon fractions. The results indicated that a two-compartment first-order model with dominant contribution of slow desorption could adequately describe the released kinetics of studied PBDEs. Desorption isotherms of different samples could be fitted well by linear distribution model or nonlinear Freundlich model. Moreover, most desorption procedures roughly exhibited hysteresis with respect to preceding sorption ones. At the statistically significant level of 0.05 or 0.1, total organic carbon content (fOC) exhibited significant correlations with the fitted parameters by the isothermal models. The correlations of fOC and SOM fractions (e.g., fulvic acid and humin) with the single point desorption coefficients at lower aqueous concentrations of studied PBDEs were significant; while at higher aqueous concentrations, the relationships were less significant or insignificant. Our findings may facilitate a comprehensive understanding on behaviors of PBDEs in soil systems.

The aims of the present study were to investigate the effects of mariculture activities on inorganic mercury (Hg²⁺) adsorption/desorption on sediments and the distributions of newly adsorbed Hg²⁺ on different chemical fractionations. The adsorption amount and binding energy of Hg²⁺ on mariculture sediment (MS) were significantly higher (p<0.05) than reference sediment (RS). This may be explained by the strong complexation role that exists between Hg²⁺ and organic matter (OM), which derived from unconsumed fish feed and fish metabolites. The reducible Hg²⁺ in MS was significantly lower (p<0.01) than RS, which may have been caused by the decreasing amount of iron and manganese hydroxide in MS, lead to the decrease of Hg²⁺ bound to them. On the contrary, the residual Hg²⁺ was significantly higher (p<0.01) in MS than RS, which suggests that newly adsorbed Hg²⁺ was more stable in MS than RS.

The present work describes a detailed study about the adsorption of malachite green (MG) by a polyether-type polyurethane foam (PUF) using sodium dodecylsulfate (SDS) as a carrier. The adsorption process was based on the formation of a hydrophobic ionic-pair between the MG cationic dye and the dodecylsulfate anion, which presented high affinity for the PUF. The manifold employed in the study was built up by adjusting a cylinder of PUF with 200 mg in the arm of an overhead stirrer, which was soaked (and stirred) in the solution containing the dye and SDS. The adsorption process was characterized in relation to equilibrium and kinetic aspects. Langmuir (r 2 = 0.842) and Freundlich (r 2 = 0.996) isotherms were also employed for modeling the system as well as the Nernst partition law (r 2 = 0.999). A study about the recovery of MG and the PUF regeneration was conducted, and the acetonitrile was the most efficient solvent for the desorption of the adsorbed ionic pair. The obtained results showed that the concentration of SDS added to the medium plays an important role on the adsorption process, which can be better described by employing a second-order kinetic model.

In situ denitrification walls and biofilters made of wood chips are being implemented as innovative technologies for the removal of nitrates in tile drainage water from farms to reduce pollution of surface waters and the hypoxia problem in the Gulf of Mexico. Although fairly effective in removing nitrates, not much is known about the effectiveness of the biofilters in removal of herbicides, pesticides, and antibiotics in the drainage water. Using weathered wood chips obtained from an in situ denitrification wall, four common pollutants tested sorbed strongly to wood chips in the following order: enrofloxacin > monensin A > atrazine > sulfamethazine. Of the four chemicals tested, enrofloxacin was found to desorb the least by water extraction. The apparent hysteresis index for atrazine was found to be lower than that for enrofloxacin and sulfamethazine indicating greater sorption–desorption hysteresis for atrazine than enrofloxacin and sulfamethazine. Consecutive steps of water desorption and organic solvent extraction indicated that more than 65% of the sorbed atrazine, 70% of sulfamethazine, 90% of enrofloxacin, and 80% of monensin A were retained in wood chips. Results of this study showed that wood chip denitrification walls or biofilters have an added benefit in retaining herbicides and antibiotics and therefore can act as a barrier to reduce pollution of surface water and groundwater.

Arthrobacter sp. Sphe3 and Bacillus sphaericus cells were used for Cu(II) biosorption. The effect of contact time, biosorbent dose, equilibrium pH, temperature and the presence of other ions on the efficiency of the process were extensively studied. Optimum pH value and biomass concentration were determined at 5.0 and 1.0 g/l, whereas contact time was found to be 5 and 10 min for Arthrobacter sp. Sphe3 and Bacillus sphaericus biomass, respectively. Equilibrium data fitted very well to Freundlich model (R ²â€‰= 0.996, n = 2.325, K f = 8.141) using Arthrobacter sp. Sphe3. In the case of B. sphaericus, a Langmuir adsorption model [R ²â€‰= 0.996, Q ₘₐₓ = 51.54 mg-Cu(II)/g] showed to better describe the results. Potentiometric titration and Fourier transform infrared (FTIR) spectroscopy showed that amine, carboxyl and phosphate groups participate in Cu(II)-binding. The calculated thermodynamic parameters indicated the spontaneous and feasible nature of Cu(II) biosorption on both biosorbents. Selectivity of Cu(II) biosorption was examined in binary and multi-ions systems with various anions and cations which are commonly found in municipal and industrial wastewater. A specificity towards Cu(II) was observed in binary mixtures with Cl⁻, CO ₃ ⁻² , NO ₃ ⁻ , SO ₄ ⁻² , PO ₄ ⁻³ , Mg+² and Ca+², and As(V) with the maximum uptake capacity remaining constant even at high competitive ion’s concentrations of 200 mg/l. Desorption studies showed that Cu(II) could be completely desorbed from Cu(II)-loaded Arthrobacter strain Sphe3 and B. sphaericus biomass using 1.0 and 0.8 M HCl, respectively, and both bacterial species could be effectively reused up to five cycles, making their application in wastewater detoxification more attractive.

Rare earth mineral based adsorbent viz. lanthanum oxide was investigated for potential application in defluoridation of drinking water for isolated and rural communities. Results of batch experiments indicated about 90% removal in 30 min from a 4 mg L−1 synthetic fluoride solution. The effects of various parameters like contact time, pH, initial concentration, and sorbent dose on sorption efficiency were investigated. Adsorption efficiency was dependent on initial fluoride concentration and the sorption process followed BET model. Variation of pH up to 9.5 has insignificant effect on sorption and beyond a pH of 9.5, the effect was drastic. Among anions investigated, carbonates exhibited high detrimental effect on fluoride adsorption while anions like bicarbonates, chlorides, and sulfates did not seriously affect the process. Adsorbent showed negligible desorption of fluoride in distilled water. Alum was more effective regenerant than HCl and NaOH. Results of cyclic regeneration with alum indicated that the sorbent could be regenerated for ten cycles without significant loss of sorption capacity. Studies with upflow fixed-bed continuous flow columns indicated the usefulness of sorbent for fluoride removal in continuous flow process.

A batch equilibrium experiment was conducted to determine the adsorption and desorption isotherms of chlorothalonil for a range of agricultural soils in Ireland. The sorption isotherms in tillage soils were described by the Freundlich model in a nonlinear form while in the grassland soil, the adsorption was almost linear. The experimental sorption data fit the Freundlich (R ² > 0.99) and the linear (R ² > 0.99) model very well. Chlorothalonil exhibited fast initial adsorption within the first hour until steady state, after which the sorption potential decreased and varied by about 3 % up to 10 h. Desorption equilibrium took twice the time needed for adsorption. The adsorption of chlorothalonil onto the soils studied was strong and the experimental Freundlich adsorption coefficients (K f) ranged from 17.74 to 78.19 (mg¹ ⁻ ¹/ⁿ kg⁻¹) (L)¹/ⁿ , and these were correlated with cation exchange capacity and organic carbon content. All tillage soils exhibited L-type isotherm, whereas Elton grassland soil showed near C-type (linear) isotherm, probably due to the highest organic carbon content among other soil. Desorption process revealed hysteresis with the Freundlich desorption coefficients being greater than for adsorption, meaning that not all chlorothalonil adsorbed could be easily desorbed. Only 3 to 8 % was desorbed in the single desorption step during the batch equilibrium experiment. Calculated K ₒc values showed that chlorothalonil has slight to low mobility in the soils studied associated with high adsorption, and hence may constitute a greater risk to surface waters by runoff than to ground waters by leaching.