The desorption rate is an important factor determining cadmium (Cd) ecotoxicity and pollution remediation in soils. The pedotransfer functions (PTFs) of desorption rate coefficients of fresh Cd in soils have been developed in literature. We hypothesized that the aging of Cd pollution would alter Cd desorption process. Taking historically polluted soils as the object, this study aimed at testing the hypothesis and developing new PTFs of desorption rate coefficients for historical Cd. 15 d batch extraction experiments and 13 kinetic models were employed to define Cd desorption rate coefficients in 27 historically polluted soil samples. Compared with fresh Cd, the desorption rate coefficients of historical Cd were lower, and the break time of biphasic desorption processes was retarded to 3 d (4320 min). Different with the usual models for fresh Cd desorption (e.g. parabolic diffusion and two constant rate models), the best models to mimic the historical Cd desorption processes were the pseudo first order, logarithmic, Elovich, and simple Elovich models. The rate-limiting step controlling Cd desorption was changed from the intraparticle diffusion to the interface reaction with aging of pollution. New PTFs of desorption rate coefficients of historical Cd were established (R² ≥ 0.71). Cd desorption rate coefficients increased with organic matter and clay contents, but decreased with oxalate extractable Fe content, solution pH, cation exchange capacity, and silt content. The key soil properties influencing desorption rate coefficients were not altered by the aging of pollution. The developed PTFs could guide us to adjusting the ecotoxicity and pollution remediation of Cd in historically polluted field soils.

Industrial dye effluents, which are a major wastage component that enter the natural environment, pose a significant health risk to human and aquatic life. Therefore, the effective removal of dye effluents is a major concern. Against this backdrop, in this study, a low-cost, earth-abundant, and ecofriendly ɤ-Fe₂O₃–PPy nanocomposite was prepared employing the conventional hydrothermal method. The morphology, functional groups, and elemental composition of ɤ-Fe₂O₃–PPy were characterized by XRD, SEM, XPS, and FTIR studies. Under optimized conditions, the prepared novel ɤ-Fe₂O₃–PPy nanocomposite showed a high methylene blue (MB) adsorption capacity of 464 mg/g, which is significantly higher than that of existing adsorbents such as CNTs and polymer-modified CNTs. The adsorption parameters such as pH, adsorbent dosage, and ionic strength were optimized to enhance the MB adsorption capacity. The adsorption results revealed that MB is adsorbed onto the adsorbent surface via electrostatic interactions, hydrogen bonding, and chemical binding interactions. In terms of practical application, the adsorbent’s adsorption–desorption ability in conjunction with magnetic separation was investigated; the prepared ɤ-Fe₂O₃–PPy nanocomposite exhibited excellent adsorption and desorption efficiencies over more than seven adsorption–desorption cycles.

Riverbed sediments are the interface layer in riverine ecosystems connecting the overlying medium of water and the vadose zone. The transport behavior of phosphorus (P), which has been recognized as the primary cause of freshwater eutrophication, in riverbed sediments remains unclear. Understanding the impact of riverbed sediments on P transport is a necessary prerequisite for the development of appropriate strategies to reduce potential groundwater pollution. In this study, riverbed sediments were collected from the upstream, midstream, and downstream sections of the Beiyun River, China, and packed into vertical soil columns to perform leaching experiments to quantify P transport characteristics. In addition, the impact mechanisms were further explored by conducting laboratory batch tests of P adsorption and desorption. The results demonstrated that approximately 80% of P can be adsorbed by riverbed sediments in soil column leaching experiment, and a tailing phenomenon was observed in its desorption. The hydraulic conductivity properties of riverbed sediments were evaluated by the advection-dispersion equation, showing a gradually decreasing adsorption capacity for P from upstream to downstream sections, which was supported by the results obtained from adsorption–desorption thermodynamic and kinetic batch tests. The estimated annual leaching masses of P increased from 60.72 g/(m² a) in the upstream section to 132.31 g/(m² a) in the downstream section. The role of riverbed sediments as a source or sink of P is possibly determined by their coarse sand particles content, and the mean equilibrium P concentration (EPC0). The competitive relationship between P and other forms of nutrients also has an important influence on its source-sink role. These findings suggest that the prevention of the potential P leaching is most needed in the downstream sections of Beiyun River, and corresponding control strategies should be developed to avoid groundwater pollution.

Total concentrations of hydrophobic organic contaminants (HOCs) in sediment present a poor quality assessment parameter for aquatic organism exposure and environmental risk because they do not reflect contaminant bioavailability. The bioavailability issue of HOCs in sediments can be addressed by application of multi-ratio equilibrium passive sampling (EPS). In this study, riverbed sediment samples were collected during the Joint Danube Survey at 9 locations along the Danube River in 2013. Samples were ex-situ equilibrated with silicone passive samplers. Desorption isotherms were constructed, yielding two endpoints: pore water (CW:₀) and accessible (CAS:₀) concentration of polychlorinated biphenyls (PCBs), organochlorine pesticides (OCPs), polycyclic aromatic hydrocarbons (PAHs) and polybrominated diphenyl ethers in sediment. CW:₀ concentrations of DDT and its breakdown products exhibited elevated levels in the low Danube, with the maximum in the river delta. Other investigated HOCs did not show any clear spatial trends along the river, and only a moderate CW:₀ variability. CAS:₀ in sediment ranged from 10 to 90% of the total concentration in sediment. CW:₀ was compared with freely dissolved concentration in the overlaying surface water, measured likewise by passive sampling. The comparison indicated potential compound release from sediment to the water phase for PAHs with less than four aromatic rings, and for remaining HOCs either equilibrium between sediment and water, or potential compound deposition in sediment. Sorption partition coefficients of HOC to organic carbon correlated well with octanol-water partition coefficients (KOW), showing stronger sorption of PAHs to sediment than that of PCBs and OCPs having equal logKOW. Comparison of CW:₀ values with European environmental quality standards indicated potential exceedance for hexachlorobenzene, fluoranthene and benzo[a]pyrene at several sites. The study demonstrates the utility of passive sampling as an innovative approach for risk-oriented monitoring of HOCs in river catchments.

Jarosite and birnessite secondary minerals play a pivotal role in the mobility, transport and fate of trace elements in the environment, although geochemical interactions of these compounds with extremely toxic thallium (Tl) remain poorly known. In this study, we investigated the sorption behavior of Tl(I) onto synthetic jarosite and birnessite, two minerals commonly found in soils and sediments as well as in mining-impacted areas where harsh conditions are involved. To achieve this, sorption and desorption experiments were carried out under two different acidic conditions and various Tl(I) concentrations to mimic natural scenarios. In addition, X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM) and inductively coupled plasma (ICP) analyses were conducted to determine the performance of both minerals for Tl(I) sequestration. Our results indicate that both phases can effectively remove aqueous Tl by different sorption mechanisms. Jarosite preferentially incorporates Tl(I) into the structure to form Tl(I)-jarosite and eventually the mineral dorallcharite (TlFe₃(SO₄)₂(OH)₆) as increasing amounts of Tl are employed. Birnessite, however, favorably uptakes Tl(I) through an irreversible surface adsorption mechanism, underlining the affinity of Tl for this mineral in the entire concentration range studied (0.5–5 mmol L⁻¹). Lastly, the presence of Tl(I) in conditions where aqueous molar ratio Tl/Mn is ∼0.25 inhibits the formation of birnessite since oxidation of Tl(I) to Tl(III) followed by precipitation of avicennite (Tl₂O₃) take place. Thus, the present research may provide useful insights on the role of both jarosite and birnessite minerals in Tl environmental cycles.

Antibiotics can be uptaken by plants from soil desorption or directly from irrigation water, but their metabolization pathways in plants are largely unknown. In this paper, an analytical workflow based on high-resolution mass spectrometry was applied for the systematic identification of biotransformation products of ofloxacin in lettuce. The targeted metabolites were selected by comparing the mass chromatograms of exposed with control samples using an advanced spectra-processing method (Fragment Ion Search). The innovative methodology presented allowed us to identify a total of 11 metabolites, including 5 ofloxacin metabolites that are being reported for the first time in plants. Accordingly, major transformation pathways were proposed revealing insight into how ofloxacin and related chemicals are metabolized in lettuce. Furthermore, the influence of biotransformation on potential residual antimicrobial activity of identified compounds was discussed. Human exposure to antibiotics at doses below the minimum inhibitory concentrations is crucial in human risk assessment, including food ingestion; however, in the case of ofloxacin presented results reveal that plant metabolites should also be considered so as not to underestimate their risk.

Strategies for reducing cadmium (Cd) content in polluted farmland soils are currently limited. A type of composite with nanoparticles incorporated into a hydrogel have been developed to efficiently remove heavy metals from sewage, but their application in soils faces challenges, such as organic hydrogel degradation due to oxygen exposure and slow Cd²⁺ release from soil constituents. To overcome these challenges, a composite with superior stability for long-term application in soil is required. In this study, ferrous sulfide (FeS) nanoparticle@lignin hydrogel composites were developed. The lignin-based hydrogels inherited lignin’s natural mechanical and environmental stability and the FeS nanoparticles efficiently adsorbed Cd²⁺ and enhanced Cd²⁺ desorption from soils by producing H⁺. The high sorption capacity (833.3 g kg⁻¹) of the composite was attributed to four proposed mechanisms, including cadmium sulfide (CdS) precipitation via chemical reaction (84.06%), lignin complexation (13.19%), hydrogel swelling (0.61%), and nanoparticle sorption (2.15%). In addition, Fe²⁺ displaced from the composite was gradually oxidized to form solid iron oxide hydroxide, which increased Cd²⁺ sorption. The composite significantly reduced the total, surfactant-soluble, and fixed Cd in heavily and lightly polluted paddy soils by 22.4–49.6%, 13.5–68.6%, and 40.1–16.6%, respectively, in 7 days.

The contamination of ground water with arsenic is a great public health concern. This paper discusses the possible formation mechanism of high As groundwater; identify the main influences of natural and anthropogenic factors on As occurrence in groundwater; and finally estimates As-induced potential health hazards in an intensive agricultural region, Datong Basin (Northern China). Our findings indicate that the predominant controlling factors of As in groundwater can be divided into natural factors and anthropogenic activities. Natural factors can be classified as natural potential source of As, environmental geological characteristics and hydrochemical conditions; anthropogenic activities are manifested in industrial coal mining, domestic coal burning, agricultural irrigation return flow and excessive application of fertilizers, and groundwater exploitation. Microbial and/or chemical reduction desorption of arsenate from Fe-oxide/hydroxide and/or clay minerals, As-bearing Fe-oxide/hydroxide reduction coupled with sulfate reduction, and competition with phosphorus are postulated to be the major process dominating As enrichment in the alkaline and anoxic groundwater. In addition, age-dependent human health risk assessment (HHRS) was performed, and high risk values reveal a high toxic and carcinogenic risk of As contaminate for population who is subject to the continuous and chronic exposure to elevated As.

The environmental forensics approach is most often applied in petroleum and fuel spill incidents, for which sophisticated chemical fingerprinting procedures have evolved. In cases in which pollutant discharges occur in settings with prior contamination, more care must be taken in source discrimination, requiring further advances in methodology. Additional obstacles can arise if the spill is an atypical industrial discharge. This would necessitate painstaking characterization of unfamiliar substances lying outside of existing regulatory regimes and thus overlooked by mandated analytical protocols (i.e., contaminants of emerging concern). Towards these ends, this paper presents a systematic, multi-faceted GC-MS approach using the saturated, aromatic, and resin fractions of contaminated soil extracts, alongside soil thermal desorption and analytical pyrolysis of the soil and its asphaltene fraction. This complimentary “extract + thermal” approach is applied to a typical fuel oil spill, sediments of a severely-impacted urban river, and brownfield soils from coke, petrochemical, and Hg-As pyrometallurgical plants. The insights thus attained can serve to better inform brownfield remediation planning in the public interest.

Tetracyclines (TCs) are frequently detected in agricultural soils worldwide, causing a potential threat to crops and human health. In this study, diffusive gradients in thin films technique (DGT) was used to measure the distribution and exchange rates of three TCs (tetracycline (TC), oxytetracycline (OTC) and chlortetracycline (CTC)) between the solid phase and solution in five farmland soils. The relationship between the accumulated masses with time suggested that TCs consumption in soil solution by DGT would induce the supply from the soil solid phase. The distribution coefficient for the labile antibiotics (Kdl), response time (Tc) and desorption/adsorption rates (kb and kf) between dissolved and sorbed TCs were derived from the dynamic model of DIFS (DGT induced fluxes in soils). The Kdl showed similar sizes of labile solid phase pools for TC and OTC while larger pool sizes were observed for CTC in the soils. Although the concentrations of CTC were lowest in soil solution, the potential hazard caused by continuous release from soil particles could not be ignored. The long response time (>30 min in most cases) suggested that the resupply of TCs from soil solids was limited by their desorption rates (1.26-121 × 10−6 s−1). The soils in finer texture, with higher clay and silt contents (<50 μm) showed a greater potential for TCs release.