Nanospecific Phytotoxicity of CuO Nanoparticles in Soils Disappeared When Bioavailability Factors Were Considered

Bioavailability-modifying factors such as soil type and aging have only rarely been considered in assessing toxicity of metal-containing nanoparticles in soil. Here, we examined the toxicity to barley (<i>Hordeum vulgare</i>) of CuO nanoparticles (CuO-NPs) relative to CuO bulk particles (CuO-BPs) and Cu acetate (Cu­(OAc)₂) in six different soils with or without aging. The set up allows identifying whether or not NPs-derived colloidal Cu in soil porewater contributes to toxicity. Ultrafiltration (50 kDa) was performed together with geochemical modeling to determine {Cu²⁺} (free Cu²⁺ activity in soil porewater). Based on total soil Cu concentration, toxicity measured with seedling root elongation ranked Cu­(OAc)₂ > CuO-NPs > CuO-BPs in freshly spiked soils. The differences in toxicity among the three toxicants became smaller in soils aged for 90 days. When expressing toxicity as {Cu²⁺}, there was no indication that nanoparticulate or colloidal Cu enhanced toxicity. A calibrated bioavailability-based model based on {Cu²⁺} and pH successfully explained (<i>R</i>² = 0.78, <i>n</i> = 215) toxicity of all Cu forms in different soils with and without aging. Our results suggest that toxicity predictions and risk assessment of CuO-NPs can be carried out properly using the bioavailability-based approaches that are used already for their non-nano counterparts in soil

Colloidal-Bound Polyphosphates and Organic Phosphates Are Bioavailable: A Nutrient Solution Study

Colloidal forms of Fe­(III) minerals can be stabilized in solution by coatings of organic or poly-phosphate (P), which reduce the zeta-potential. This opens up a route toward the development of nanoforms of P fertilizers. However, it is unclear if such P forms are bioavailable. To address this question, spinach (Spinacia oleracea) was grown in nutrient solutions, at equal total P, using three different forms of P (orthophosphate = P_i; hexametaphosphate = HMP; <i>myo</i>-inositol hexaphosphate = IHP), free or bound to goethite/ferrihydrite colloids. After 10 days, P uptake was determined with a dose–response curve using colloid-free P_i as a reference treatment. The P_i concentration generating equal P uptake as in colloidal P treatments was used to calculate the relative bioavailability of colloidal P (RBA_colloid). The RBA_colloid was about 60% for P_i-loaded goethite, stabilized with natural organic matter. For HMP/IHP-P_i-loaded colloids, RBA_colloid ranged between 10 and 50%, in line with their higher sorption strength. In conclusion, colloidal organic P or poly-P can stabilize Fe­(III) colloids in solution and can contribute to plant-available P. Soil experiments are required to assess their potential as nanofertilizers

Interactions and Toxicity of Cu–Zn mixtures to Hordeum vulgare in Different Soils Can Be Rationalized with Bioavailability-Based Prediction Models

Soil contamination with copper (Cu) is often associated with zinc (Zn), and the biological response to such mixed contamination is complex. Here, we investigated Cu and Zn mixture toxicity to Hordeum vulgare in three different soils, the premise being that the observed interactions are mainly due to effects on bioavailability. The toxic effect of Cu and Zn mixtures on seedling root elongation was more than additive (i.e., synergism) in soils with high and medium cation-exchange capacity (CEC) but less than additive (antagonism) in a low-CEC soil. This was found when we expressed the dose as the conventional total soil concentration. In contrast, antagonism was found in all soils when we expressed the dose as free-ion activities in soil solution, indicating that there is metal-ion competition for binding to the plant roots. Neither a concentration addition nor an independent action model explained mixture effects, irrespective of the dose expressions. In contrast, a multimetal BLM model and a WHAM-<i>F</i>_tox model successfully explained the mixture effects across all soils and showed that bioavailability factors mainly explain the interactions in soils. The WHAM-<i>F</i>_tox model is a promising tool for the risk assessment of mixed-metal contamination in soils

Inhibition of <i>Geobacter</i> Dechlorinators at Elevated Trichloroethene Concentrations Is Explained by a Reduced Activity Rather than by an Enhanced Cell Decay

Microbial dechlorination of trichloroethene (TCE) is inhibited at elevated TCE concentrations. A batch experiment and modeling analysis were performed to examine whether this self-inhibition is related to an enhanced cell decay or a reduced dechlorination activity at increasing TCE concentrations. The batch experiment combined four different initial TCE concentrations (1.4–3.0 mM) and three different inoculation densities (4.0 × 10⁵ to 4.0 × 10⁷ <i>Geobacter</i> cells·mL^–1). Chlorinated ethene concentrations and <i>Geobacter</i> 16S rRNA gene copy numbers were measured. The time required for complete conversion of TCE to <i>cis</i>-DCE increased with increasing initial TCE concentration and decreasing inoculation density. Both an enhanced decay and a reduced activity model fitted the experimental results well, although the reduced activity model better described the lag phase and microbial decay in some treatments. In addition, the reduced activity model succeeded in predicting the reactivation of the dechlorination reaction in treatments in which the inhibiting TCE concentration was lowered after 80 days. In contrast, the enhanced decay model predicted a <i>Geobacter</i> cell density that was too low to allow recovery for these treatments. Conclusively, our results suggest that TCE self-inhibition is related to a reduced dechlorination activity rather than to an enhanced cell decay at elevated TCE concentrations

Phosphate-Exchanged Mg–Al Layered Double Hydroxides: A New Slow Release Phosphate Fertilizer

The global phosphorus crisis provided impetus to develop fertilizers with better P use efficiency. We tested layered double hydroxides (LDHs) as slow release fertilizers with superior performance to fertilize strongly P-fixing soils. Mg–Al LDHs with varying M²⁺/M³⁺ ratios were synthesized as NO₃^– forms and were exchanged with HPO₄^2–. XRD and XANES spectroscopy confirmed the identity of the phosphate-exchanged LDH. Decreasing the M²⁺/M³⁺ ratio, i.e., increasing the anion exchange capacity, increased the selectivity of P adsorption due to the increasing charge density of the LDH layers. The fertilization efficiency of the phosphate-exchanged LDH (Mg/Al ratio of 2) was compared to that of a soluble P fertilizer in two P-deficient soils, an acid weathered soil and a calcareous soil. The P use efficiency of the P-LDH in the acid soil was up to 4.5 times higher than that of soluble P. This was likely related to a liming effect of the LDH. In the calcareous soil, the P use efficiency at low doses was only 20% above that of soluble P, whereas it was lower at high doses. These overall encouraging results warrant further studies on the boundary conditions under which P-LDHs may outperform traditional fertilizers

Polyphosphates and Fulvates Enhance Environmental Stability of PO₄‑Bearing Colloidal Iron Oxyhydroxides

Iron oxyhydroxide nanoparticles (Fe-NPs) are natural vectors of phosphate (PO₄) in the environment. Their mobility is determined by colloidal stability, which is affected by surface composition. This might be manipulated in engineered NPs for environmental or agricultural applications. Here, the stability of PO₄-Fe-NPs (HFO/goethite) was determined across contrasting environmental conditions (pH, Ca concentration) and by using fulvates (FA) and polyphosphates (poly-P’s) as coatings. The PO₄-Fe-NPs are unstable at Ca concentrations above 0.1 mM. Addition of FA and some poly-P’s significantly improved stability. Zeta potential explained colloidal stability across treatments; surface charge was calculated with surface complexation models and explained for phytic acid (PA) and hexametaphosphate (HMP) by a partial (1–4 of the 6 PO₄ units) adsorption to the surface, while the remaining PO₄ units stayed in solution. This study suggests that Ca concentration mainly affects the mobility of natural or engineered PO₄-Fe-NPs and that HMP is a promising agent for increasing colloidal stability

Distribution of Minerals in Wheat Grains (<i>Triticum aestivum</i> L.) and in Roller Milling Fractions Affected by Pearling

The distribution of minerals in (pearled) wheat grains was measured by synchrotron X-ray fluorescence, and the impact of pearling (0, 3, 6, 9, and 12% by weight) on the mineral composition of flour, shorts, and bran was identified by ICP-MS. The xylem mobile elements (Mn, Si, Ca, and Sr) dominated in the outermost bran layers, while the phloem mobile elements (K, Mg, P, Fe, Zn, and Cu) were more concentrated in the aleurone. Pearling lowered the concentrations of xylem mobile elements and increased the concentrations of most phloem mobile elements in the pearled grains. Molybdenum, Cd, and especially Se were more evenly distributed, and pearling affected their concentrations in milling products less. Pearling (3%) increased the concentration of several nutrients (P, Zn, Cu) in the flour because the bran fractions reaching the flour are enriched in aleurone. The correlations of concentrations of Mg, Fe, Zn, and Cu with that of P suggested their association with phytate

Internal Loading and Redox Cycling of Sediment Iron Explain Reactive Phosphorus Concentrations in Lowland Rivers

The phosphate quality standards in the lowland rivers of Flanders (northern Belgium) are exceeded in over 80% of the sampling sites. The factors affecting the molybdate reactive P (MRP) in these waters were analyzed using the data of the past decade (>200 000 observations). The average MRP concentration in summer exceeds that winter by factor 3. This seasonal trend is opposite to that of the dissolved oxygen (DO) and nitrate concentrations. The negative correlations between MRP and DO is marked (<i>r</i> = −0.89). The MRP concentrations are geographically unrelated to erosion sensitive areas, to point-source P-emissions or to riverbed sediment P concentration. Instead, MRP concentrations significantly increase with increasing sediment P/Fe concentration ratio (<i>p</i> < 0.01). Laboratory static sediment–water incubations with different DO and temperature treatments confirmed suspected mechanisms: at low DO in water (<4 mg L^–1), reductive dissolution of ferric Fe oxides was associated with mobilization of P to the water column from sediments with a molar P/Fe ratio >0.4. In contrast, no such release was found from sediments with lower P/Fe irrespective of temperature and DO treatments. This study suggests that internal loading of the legacy P in the sediments explains the MRP concentrations which are most pronounced at low DO concentrations and in regions where the P/Fe ratio in sediment is large

DataSheet_1_From soil to cacao bean: Unravelling the pathways of cadmium translocation in a high Cd accumulating cultivar of Theobroma cacao L.docx

The research on strategies to reduce cadmium (Cd) accumulation in cacao beans is currently limited by a lack of understanding of the Cd transfer pathways within the cacao tree. Here, we elucidated the transfer of Cd from soil to the nib (seed) in a high Cd accumulating cacao cultivar. Here, we elucidated the transfer of Cd from soil to the nib (seed) in a high Cd accumulating cacao cultivar through Cd stable isotope fractionation, speciation (X-Ray Absorption Spectroscopy), and localization (Laser Ablation Inductively Coupled Plasma Mass Spectrometry). The plant Cd concentrations were 10-28 higher than the topsoil Cd concentrations and increased as placenta114/110 Cd shoot-root = 0.27 ± 0.02 ‰ (weighted average ± standard deviation)). Leaf Cd isotopes were heavier than Cd in the branches (Δ 114/110 Cd IF3 leaves-branch = 0.18 ± 0.01 ‰), confirming typical trends observed in annual crops. Nibs and branches were statistically not distinguishable (Δ 114/110 Cd nib-branch = −0.08‰ ± 0.06 ‰), contrary to the leaves and nibs (Δ 114/110 Cd nib-IF3 leaves = -0.25‰ ± 0.05 ‰). These isotope fractionation patterns alluded to a more direct transfer from branches to nibs rather than from leaves to nibs. The largest fraction (57%) of total plant Cd was present in the branches where it was primarily bound to carboxyl-ligands (60-100%) and mainly localized in the phloem rays and phelloderm of the bark. Cadmium in the nibs was mainly bound to oxygen ligands (60-90%), with phytate as the most plausible ligand. The weight of evidence suggested that Cd was transferred like other nutrients from root to shoot and accumulated in the phloem rays and phelloderm of the branches to reduce the transfer to foliage. Finally, the data indicated that the main contribution of nib Cd was from the phloem tissues of the branch rather than from leaf remobilization. This study extended the limited knowledge on Cd accumulation in perennial, woody crops and revealed that the Cd pathways in cacao are markedly different than in annual crops.</p

Body distribution of SiO₂–Fe₃O₄ core-shell nanoparticles after intravenous injection and intratracheal instillation

<p>Nano-silicon dioxide (SiO₂) is used nowadays in several biomedical applications such as drug delivery and cancer therapy, and is produced on an industrial scale as additive to paints and coatings, cosmetics and food. Data regarding the long-term biokinetics of SiO₂ engineered nanoparticles (ENPs) is lacking. In this study, the whole-body biodistribution of SiO₂ core-shell ENPs containing a paramagnetic core of Fe₃O₄ was investigated after a single exposure via intravenous injection or intratracheal instillation in mice. The distribution and accumulation in different organs was evaluated for a period of 84 days using several techniques, including magnetic resonance imaging, inductively coupled plasma mass spectrometry, X-ray fluorescence and X-ray absorption near edge structure spectroscopy. We demonstrated that intravenously administered SiO₂ ENPs mainly accumulate in the liver, and are retained in this tissue for over 84 days. After intratracheal instillation, an almost complete particle clearance from the lung was seen after 84 days with distribution to spleen and kidney. Furthermore, we have strong evidence that the ENPs retain their original core-shell structure during the whole observation period. This work gives an insight into the whole-body biodistribution of SiO₂ ENPs and will provide guidance for further toxicity studies.</p