International audience | The cocktail of pesticides sprayed to protect crops generates a miscellaneous and generalized contamination of water bodies. Sorption, especially on soils, regulates the spreading and persistence of these contaminants. Fine resolution sorption data and knowledge of its drivers are needed to manage this contamination. The aim of this study is to investigate the potential of Mid-Infrared spectroscopy (MIR) to predict and specify the adsorption and desorption of a diversity of pesticides. We constituted a set of 37 soils from French mainland and West Indies covering large ranges of texture, organic carbon, minerals and pH. We measured the adsorption and desorption coefficients of glyphosate, 2,4-dichlorophenoxyacetic acid (2,4-D) and difenoconazole and acquired MIR Lab spectra for these soils. We developed Partial Least Square Regression (PLSR) models for the prediction of the sorption coefficients from the MIR spectra. We further identified the most influencing spectral bands and related these to putative organic and mineral functional groups. The prediction performance of the PLSR models was generally high for the adsorption coefficients Kdads (0.4 < R 2 < 0.9 & RPIQ > 1.8). It was contrasted for the desorption coefficients and related to the magnitude of the desorption hysteresis. The most significant spectral bands in the PLSR differ according to the pesticides indicating contrasted interactions with mineral and organic functional groups. Glyphosate interacts primarily with polar mineral groups (OH) and difenoconazole with hydrophobic organic groups (CH2, C=C, COO-, CO , CO -C). 2,4-D has both positive and negative interactions with these groups. Finally, this work suggests that MIR combined with PLSR is a promising and cost-effective tool. It allows both the prediction of adsorption and desorption parameters and the specification of these mechanisms for a diversity of pesticides including polar active ingredients.

Corresponding author. fax: +49 381 498 2159. E-mail address: bernd.lennartz@uni-rostock.de (B. Lennartz). | International audience | This work was initiated to study the effects of climate induced soil water status variations which can reach extreme values under natural conditions on the sorption process of hydrophobic organic compounds. Based on the classical slurry batch methodology an approach is developed that allows the fast and careful complete drying of soil suspensions (microwave technique). Classical adsorption experiments were followed by three desorption steps with and without drying cycles. Drying and re-wetting enhanced the sorption-desorption hysteresis and Freundlich adsorption coefficients increased from 5.9 to 16 and 5.2 to 21 over three drying cycles for diuron and terbuthylazine respectively. Assuming the validity of a dual stage adsorption process, model evaluation suggests that drying is as a shrinking-like process leading to conformational changes of the dominant sorbent (soil organic matter) which restrict the intra-micro-particle diffusion. Rewetting only leads to a partial recovery of the diffusional pore space.

In order to determine the mechanisms of the retention of 60Co, 85Sr and 134Cs in natural silica sand columns, desorption experiments were performed by changes of pH and ionic strength and by injection of natural organic matter (NOM). Injection of KCl (0.1 M) resulted in a high release of 60Co (60-100%) and 85Sr (72-100%) but a smaller release of 134Cs (31-66%). Only limited release of 60Co (66%) and 85Sr (71%) and no release of 134Cs were observed by injection of NOM. The different percentages of desorption were related to the chemical characteristics of the organic colloids previously retained in columns before the desorption step. The results evidenced different sorption processes on energetically heterogeneous surface sites. According to the initial conditions, the binding of the radionuclides to the solid phase resulted from weak and easily reversible sorption processes to strong association probably by inner sphere complexes. The rather weak release of 134Cs by KCl was attributed to the strong retention of 134Cs by clay coatings on the natural silica sand surfaces. © 2005 Elsevier Ltd. All rights reserved.

The ionic strength of infiltration water changes with the seasonal alternation of irrigation sources. In this study, reactivity changes of birnessite-coated sand with the fluctuations of ionic strength of infiltration water (i.e. from groundwater to rainwater) and the involved mechanism were investigated through column experiments. Birnessite-coated sand was less reactive in groundwater than in rainwater because of the higher cation content and higher pH of groundwater. The cations in the groundwater were adsorbed on birnessite-coated sand and then desorbed in presence of a dilute aqueous solution represented by rainwater. The reactivity of the passivated birnessite-coated sand was recovered instantaneously, and approximately one-third of the pristine reactivity was restored. During recovery, Na⁺ desorption and lincomycin (LIN) removal both exhibited a two-stage reaction pattern. The LIN removal correlated with Na⁺ desorption (r = 0.99) so that the reactive sites that were binding 5.602 μmol of Na⁺ became available for 1 μmol of LIN removal. These results suggest that the reactivity of manganese oxides toward organic contaminant is associated with the ionic strength of infiltration water and indicate that the partial reactivity can be naturally restored.

This study modified a passive sampling technique similar to the US EPA Method 325 A/B method but extended to include more toxic volatile organic compounds (VOCs) under varied climate conditions to enhance field applicability. A mixing chamber was built to determine uptake rates (Us) for the target compounds. It was found that the Us of 27 air toxics previously reported in the literature agreed reasonably well with our findings within 18%, thus proving the chamber's integrity. To broaden the compound coverage, both Carbopack X and Carboxen 569 were studied for a suite of toxic VOCs to meet stringent quality control (QC) criteria of correlation coefficients (R-square), method detection limits (MDL), back diffusion (BD), storage stability, as well as a wide range of climate conditions in temperature and humidity. After excluding the species that failed to pass any of the QC criteria, Carbopack X was found to fit 50 air toxics, whereas Carboxen 569 held 37. After excluding the overlapped species, 61 toxic VOCs can be determined with robust Us for a broad range of climate conditions when the two sorbents are used in pairs. A one-week field measurement was conducted to compare with the online thermal desorption gas chromatography-mass spectrometry (TD-GC-MS) with hourly data resolution. The field passive sampling showed comparable results to the means of the online hourly measurements, despite the high variability of selected target compounds, such as toluene from 0.3 ppbv as the 5th percentile to the maximum of about 80 ppbv. Passive sampling clearly demonstrated the ability to smooth out concentration variability and thus the time-averaging strength of toxic VOCs, revealing its ideal role as an exposure monitor over time. The passive sampling method can be more desired than active sampling or online methods when the aim is simply the knowledge of prolonged time-averaged concentrations.

This study investigates the behavior of Tl in the Ría de Huelva (SW Spain), one of the most metal polluted estuaries in the world. Dissolved Tl concentration displayed a general decrease across the estuary during the dry season (DS); from 5.0 to 0.34 μg/L in the Tinto and Odiel estuaries, respectively, to 0.02 μg/L in the channel where the rivers join. A slighter decrease was observed during the wet season (WS) (from 0.72 to 0.14 μg/L to 0.02 μg/L) due to the dilution effect of rainfalls in the watersheds. These values are 3 orders of magnitude higher than those reported in other estuaries worldwide. Different increases in Tl concentrations with salinity were observed in the upper reaches of the Tinto and Odiel estuaries, attributed to desorption processes from particulate matter. Chemical and mineralogical evidences of particulate matter, point at Fe minerals (i.e., jarosite) as main drivers of Tl particulate transport in the estuary. Unlike other estuaries worldwide, where a fast sorption process onto particulate matter commonly takes place, Tl is mainly desorbed from particulate matter in the Tinto and Odiel estuaries. Thus, Tl may be released back from jarositic particulate matter across the salinity gradient due to the increasing proportion of unreactive TlCl⁰ and K⁺ ions, which compete for adsorption sites with Tl⁺ at increasing salinities. A mixing model based on conservative elements revealed a 6-fold increase in Tl concentrations related to desorption processes. However, mining spills like that occurred in May 2017 may contribute to enhance dissolved and particulate Tl concentrations in the estuary as well as to magnify these desorption processes (up to around 1100% of Tl release), highlighting the impact of the mine spill on the remobilization of Tl from the suspended matter to the water column.

Per-and polyfluoroalkyl substances (PFASs) have attracted extensive attention since this century due to their wide distribution, persistence, bioaccumulation/biomagnification potential, and (eco)toxicity. In the present study, we investigated the sorption kinetics, sorption isotherms and desorption behaviors of legacy and emerging PFASs with different chain lengths and functional end groups onto marine sediments at four different salinities (0, 10, 20, and 30 practical salinity units (psu)). Results revealed that the sorption of PFASs onto sediment can be well described by the pseudo-second-order kinetic model. PFASs sorption was influenced by both compound-specific and solution-specific parameters. The distribution coefficient (Kd) for PFASs were increased with the increase of perfluorocarbon chain length and salinity, suggesting that hydrophobic and electrostatic interactions were involved in the adsorption process. 6:2 FTSA showed the lowest adsorption among PFASs with eight carbon atoms (6:2 FTSA, PFOA and PFOS). The increase of perfluorocarbon chain length of PFASs and salinity would result in the decrease of desorption rate of PFASs from sediment. In addition, PFCAs were desorbed more easily from the sediment than the PFSAs with the same perfluorocarbon chain length at all salinity groups. The present study demonstrated that salinity can apparently influence the fate of PFASs in aquatic environment and provided valuable data for modeling the fate of PFASs in real environment.

The objective of this work was to evaluate the adsorption capacity of alkylated modified porous biochar prepared by esterification and etherification (PSAC-2) for low concentrate volatile organic compounds (VOCs, toluene and ethyl acetate) in high humidity environment by experiments and theoretical calculations. Results showed that PSAC-2 has a large specific surface area and weak surface polarity, at 80% relative humidity, its capacities for toluene and ethyl acetate adsorption could be maintained at 92% and 87% of the initial capacities (169.9 mg/g and 96.77 mg/g). The adsorption behaviors of toluene, ethyl acetate, and water vapor were studied by adsorption isotherms, and isosteric heat was obtained. The desorption activation energy was obtained by temperature programmed desorption experiment. The outcomes manifested that the PSAC-2 can achieve strong adsorption performance for weakly polar molecules. Through density functional theory (DFT) simulations, owing to the interaction of hydrogen bonds, oxygen-containing groups became a significant factor influencing the adsorption of VOCs in humid environments. These results could provide an important reference for VOCs control in a high humidity environment.

Discarded micro/nano-plastic inputs into the environment are emerging global concerns. Yet the quantification of micro/nanoplastics in complex environmental matrices is still a major challenge, notably for soluble ones. We herein develop in-laboratory built nanostructures (zinc oxide, titanium oxide and cobalt) coupled to mass spectrometry techniques, for picogram quantification of micro/nanoplastics in water and snow matrices, without sample pre-treatment. In parallel, an ultra-trace quantification method for micro/nanoplastics based on nanostructured laser desorption/ionization time-of-flight mass spectrometry (NALDI-TOF-MS) is developed. The detection limit is ∼5 pg for ambient snow. Soluble polyethylene glycol and insoluble polyethylene fragments were observed and quantified in fresh falling snow in Montreal, Canada. Complementary physicochemical studies of the snow matrices and reference plastics using laser-based particle sizers, inductively coupled plasma tandem mass spectrometry, and high-resolution scanning/transmission electron microscopy, produced consistent results with NALDI, and further provided information on morphology and composition of the micro/nano-plastic particles. This work is promising as it demonstrates that a wide range of recyclable nanostructures, in-laboratory built or commercial, can provide ultra-trace capability for quantification for both soluble polymers and insoluble plastics in air, water and soil. It may thereby produce key missing information to determine the fate of micro/nanoplastics in the environment, and their impacts on human health.

The rapid determination of the bioaccessibility of polycyclic aromatic hydrocarbons (PAHs) in soils is challenging due to their slow desorption rates and the insufficient extraction efficiency of the available methods. Herein, magnetic poly(β-cyclodextrin) microparticles (Fe₃O₄@PCD) were combined with hydroxypropyl-β-cyclodextrin (HPCD) or methanol (MeOH) as solubilizing agents to develop a rapid and effective method for the bioaccessibility measurement of PAHs. Fe₃O₄@PCD was first validated for the rapid and quantitative adsorption of PAHs from MeOH and HPCD solutions. The solubilizing agents were then coupled with Fe₃O₄@PCD to extract PAHs from soil-water slurries, affording higher extractable fractions than the corresponding solution extraction and comparable to or higher than single Fe₃O₄@PCD or Tenax extraction. The desorption rates of labile PAHs could be markedly accelerated in this process, which were 1.3–12.0 times faster than those of single Fe₃O₄@PCD extraction. Moreover, a low HPCD concentration was sufficient to achieve a strong acceleration of the desorption rate without excessive extraction of the slow desorption fraction. Finally, a comparison with a bioaccumulation assay revealed that the combination of Fe₃O₄@PCD with HPCD could accurately predict the PAH concentration accumulated in earthworms in three field soil samples, indicating that the method is a time-saving and efficient procedure to measure the bioaccessibility of PAHs.