Disentangling Mechanisms in Natural Toxin Sorption to Soil Organic Carbon

Insight into the sorption and desorption pattern of pyrrolizidine alkaloids and their N-oxides in acidic tea (Camellia sinensis) plantation soils

Pyrrolizidine alkaloids (PAs) and their N-oxides (PANOs) are phytotoxins produced by various plant species and have been emerged as environmental pollutants. The sorption/desorption behaviors of PAs/PANOs in soil are crucial due to the horizontal transfer of these natural products from PA-producing plants to soil and subsequently absorbed by plant roots. This study firstly investigated the sorption/desorption behaviors of PAs/PANOs in tea plantation soils with distinct characteristics. Sorption amounts for seneciphylline (Sp) and seneciphylline-N-oxide (SpNO) in three acidic soils ranged from 2.9 to 5.9 µg/g and 1.7 to 2.8 µg/g, respectively. Desorption percentages for Sp and SpNO were from 22.2% to 30.5% and 36.1% to 43.9%. In the mixed PAs/PANOs systems, stronger sorption of PAs over PANOs was occurred in tested soils. Additionally, the Freundlich models more precisely described the sorption/desorption isotherms. Cation exchange capacity, sand content and total nitrogen were identified as major influencing factors by linear regression models. Overall, the soils exhibiting higher sorption capacities for compounds with greater hydrophobicity. PANOs were more likely to migrate within soils and be absorbed by tea plants. It contributes to the understanding of environmental fate of PAs/PANOs in tea plantations and provides basic data and clues for the development of PAs/PANOs reduction technology.

Self-cascade deoxynivalenol detoxification by an artificial enzyme with bifunctions of dehydrogenase and aldo/keto reductase from genome mining

Due to the severe health risks for human and animal caused by the intake of toxic deoxynivalenol (DON) derived from Fusarium species, elimination DON in food and feed has been initiated as a critical issue. Enzymatic cascade catalysis by dehydrogenase and aldo-keto reductase represents a fascinating strategy for DON detoxification. Here, one quinone-dpendent alcohol dehydrogenase DADH oxidized DON into less-toxic 3-keto-DON and NADPH-dependent aldo-keto reductase AKR13B3 reduced 3-keto-DON into relatively non-toxic 3-epi-DON were identified from Devosia strain A6-243, indicating that degradation of DON on C3 are two-step sequential cascade processes. To establish the bifunctions, fusion enzyme linking DADH and AKR13B3 was successfully assembled to promote one-step DON degradations with accelerated specific activity and efficiency, resulting 93.29 % of DON removal rate in wheat sample. Three-dimensional simulation analysis revealed that the bifunctional enzyme forms an artificial intramolecular channel to minimize the distance of intermediate from DADH to AKR13B3 for two-step enzymatic reactions, and thereby accelerates this enzymatic process. As the first report of directing single step DON detoxification by an interesting bifunctional artificial enzyme, this work revealed a facile and eco-friendly approach to detoxify DON with application potential and gave valuable insights into execute other mycotoxin detoxification for ensuring food safety.

Can reductive deiodination improve the sorption of iodinated X-ray contrast media to aquifer material during bank filtration?

Iodinated X-ray contrast media (ICM) as well as their aerobic transformation products (TPs), are highly polar triiodobenzoic acid derivatives, ubiquitously found in the urban water cycle. Based on their polarity, their sorption affinity to sediment and soil is negligible. However, we hypothesize that the iodine atoms bound to the benzene ring play a decisive role for sorption, due to their large atom radius, high electron number and symmetrical positioning within the aromatic system. The aim of this study is to investigate, if the (partial) deiodination, occurring during anoxic/anaerobic bank filtration, improves the sorption to aquifer material. Tri, di, mono and deiodinated structures of two ICMs (iopromide and diatrizoate) and one precursor/TP of ICM (5-amino-2,4,6-triiodoisophtalic acid) were tested in batch experiments, using two aquifer sands and a loam soil with and without organic matter. The di, mono and deiodinated structures were produced by (partial) deiodination of the triiodinated initial compounds. The results demonstrated that the (partial) deiodination increases the sorption to all tested sorbents, even though the theoretical polarity increases with decreasing number of iodine atoms. Whereas lignite particles positively affected the sorption, mineral components decreased it. Kinetics tests show biphasic sorption for the deiodinated derivatives. We have concluded that iodine affects the sorption by sterical hindrance, repulsive forces, resonance and inductive effects, depending on the number and position of iodine, side chain characteristics and composition of the sorbent material. Our study has revealed an increased sorption potential of ICMs and their iodinated TPs to aquifer material during anoxic/anaerobic bank filtration as a result of (partial) deiodination, whereby a complete deiodination is not necessary for efficient removal by sorption. Furthermore, it suggests that the combination of an initial aerobic (side chain transformations) and a subsequent anoxic/anaerobic (deiodination) redox milieu supports the sorption potential.

Indole and quinolizidine alkaloids from blue lupin leach to agricultural drainage water

Phytotoxins are produced in plants including agricultural crops. Lupins and other plants of the Fabaceae family produce toxic alkaloids. These alkaloids have been studied in food and feed, however, the environmental fate of alkaloids produced by cultivated lupins is largely unknown. Therefore, we conducted an agricultural field experiment to investigate the occurrence of indole and quinolizidine alkaloids in lupin plant tissues, soil, soil pore water and in drainage water. During the field experiment, alkaloids were regularly quantified (median concentrations) in lupin (13-8.7 × 10³ ng/g dry weight (dw)), and topsoils at depth 0-5 cm (0.1-10 ng/g dw), and depth 15-30 cm (0.2-8.5 ng/g dw), soil pore water (0.2-7.5 ng/L) and drainage water samples (0.4-18 ng/L). Lupanine was the dominant alkaloid in all collected samples. Cumulative amounts of alkaloids emitted via drainage water were around 0.1-11 mg/ha for individual alkaloids over one growing season. The total cumulative amount of alkaloid in drainage water was 14 mg/ha, which is a very small amount compared to the mass of alkaloid in the lupin biomass (11 kg/ha) and soil (0.02 kg/ha). Nearly half of the alkaloids were exported in the drainage water during high flow events, indicating that alkaloids transport preferentially via macropores. These findings indicate that drainage from lupin cultivated areas contribute to surface water contamination. The environmental and ecotoxicological relevance of alkaloids as newly identified aquatic micropollutants in areas with agricultural activities have yet to be assessed.

Linking the effect of temperature on adsorption from aqueous solution with solute dissociation

Imperative decarbonization of water purification processes entails alternative regeneration methods for activated carbon. Regeneration based on changing dissociation equilibria, i.e. a major influencing factor on adsorption, usually requires the addition of acids/bases, but may also be triggered by temperature swing. Although adsorption and dissociation are both temperature-dependent phenomena, their conjunction has received little attention regarding trace organic compounds (TrOCs) and large temperature intervals, in particular above ΔT ≥ 50 ^∘C. Therefore, we studied the adsorption equilibria of 16 TrOCs onto one granular activated carbon at temperatures ranging from 20 to 95 ^∘C. The majority of compounds (12/16) exhibited an exothermic apparent adsorption enthalpy, while 3 out of 16 exhibited an endothermic apparent enthalpy. The range spanned from - 46 to + 50 kJ mol^-1 (median at - 17 kJ mol^-1). The possible origins of endothermic adsorption were discussed. A rationale of shifting pK_a and thus changing dissociation of TrOCs was introduced and traded off against existing rationales, i.e. changing solute solubility, changing adsorption heat capacity, and saturation effects of the adsorbates. This knowledge may allow designing temperature swing adsorption processes that unlock the dissociation switch. The augmented process efficiency can thus provide the foundation for low-carbon emission, circular water purification processes.

Sorption and Mobility of Charged Organic Compounds: How to Confront and Overcome Limitations in Their Assessment

Permanently charged and ionizable organic compounds (IOC) are a large and diverse group of compounds belonging to many contaminant classes, including pharmaceuticals, pesticides, industrial chemicals, and natural toxins. Sorption and mobility of IOCs are distinctively different from those of neutral compounds. Due to electrostatic interactions with natural sorbents, existing concepts for describing neutral organic contaminant sorption, and by extension mobility, are inadequate for IOC. Predictive models developed for neutral compounds are based on octanol-water partitioning of compounds (Kow) and organic-carbon content of soil/sediment, which is used to normalize sorption measurements (KOC). We revisit those concepts and their translation to IOC (Dow and DOC) and discuss compound and soil properties determining sorption of IOC under water saturated conditions. Highlighting possible complementary and/or alternative approaches to better assess IOC mobility, we discuss implications on their regulation and risk assessment. The development of better models for IOC mobility needs consistent and reliable sorption measurements at well-defined chemical conditions in natural porewater, better IOC-, as well as sorbent characterization. Such models should be complemented by monitoring data from the natural environment. The state of knowledge presented here may guide urgently needed future investigations in this field for researchers, engineers, and regulators.

Aquatic occurrence of phytotoxins in small streams triggered by biogeography, vegetation growth stage, and precipitation

Toxic plant secondary metabolites (PSMs), so-called phytotoxins, occur widely in plant species. Many of these phytotoxins have similar mobility, persistence, and toxicity properties in the environment as anthropogenic micropollutants, which increasingly contaminate surface waters. Although recent case studies have shown the aquatic relevance of phytotoxins, the overall exposure remains unknown. Therefore, we performed a detailed occurrence analysis covering 134 phytotoxins from 27 PSM classes. Water samples from seven small Swiss streams with catchment areas from 1.7 to 23 km² and varying land uses were gathered over several months to investigate seasonal impacts. They were complemented with samples from different biogeographical regions to cover variations in vegetation. A broad SPE-LC-HRMS/MS method was applied with limits of detection below 5 ng/L for over 80% of the 134 included phytotoxins. In total, we confirmed 39 phytotoxins belonging to 13 PSM classes, which corresponds to almost 30% of all included phytotoxins. Several alkaloids were regularly detected in the low ng/L-range, with average detection frequencies of 21%. This is consistent with the previously estimated persistence and mobility properties that indicated a high contamination potential. Coumarins were previously predicted to be unstable, however, detection frequencies were around 89%, and maximal concentrations up to 90 ng/L were measured for fraxetin produced by various trees. Overall, rainy weather conditions at full vegetation led to the highest total phytotoxin concentrations, which might potentially be most critical for aquatic organisms.