[en] Potatoes grown in soil with high Cd concentrations can accumulate high levels of Cd in the tubers. Although there is significant environmental variation involved in the trait of crop uptake of Cd, there are also distinctive cultivar differences. In order to understand this differential Cd accumulation mechanism, two potato cultivars were chosen that accumulate high and low levels of Cd in tubers. The patterns of Cd concentration, Cd content and dry weight accumulation of the two cultivars were examined at different stages of plant growth. The data suggest that differences in total Cd uptake and in Cd partitioning among organs are the mechanisms governing differential Cd-tuber accumulation in the two cultivars. The low tuber-Cd accumulator exhibited lower root-to-shoot and shoot-to-tuber translocation driven by higher root and shoot biomass that retained more Cd in roots and shoots, respectively, reducing its movement to the tubers. Higher remobilization and more efficient tuber loading was observed in the high tuber-Cd accumulator, indicating that remobilization of Cd from leaves to tubers was a major factor, not only in tuber-Cd loading, but also in the establishment of differential tuber-Cd levels. Regardless of cultivar differences, the concentration of Cd in the tuber was very low compared to that in other organs suggesting that, despite its high phloem mobility, Cd tends to be sequestered in the shoots.

[en] Fullerenes (e.g. C₆₀, C₇₀, etc.) present in soil may undergo changes in its retention with aging. In this study, the partitioning behavior of (¹⁴C)-C₆₀ aged up to 12 weeks was investigated in biosolids-amended soil. Spiked samples were subjected to sequential partitioning using water, methanol, and toluene followed by total combustion of solids; the distribution of ¹⁴C across solvents and matrices were used to provide insights on C₆₀ behavior. In most samples, ¹⁴C only partitioned in toluene with the remaining (non-extractable) activity detected in the solid phase. In all biosolids-amended soil samples, an increase in non-extractable ¹⁴C were observed for those exposed to light (vs dark) with the greatest difference observed in biosolids + sand samples. Possible processes that contribute to the observed ¹⁴C distribution, i.e. retention and potential transformation of C_60, were discussed. Over-all, results suggest that environmental exposure to C₆₀ and potentially transformed C₆₀ species, as a result of their release from soils, is likely to be low. - Highlights: • C₆₀ that is aged in soil appear to undergo light-mediated transformations. • C₆₀, including its transformation products, are retained well in soil. • Environmental exposure to fullerenes as a result of its release from soil is low. - Environmental exposure to C₆₀ as a result of its release from biosolids-amended soils is likely to be low.

[en] As zinc (Zn) is both an essential trace element and potential toxicant, the effects of Zn fixation in soil are of practical significance. Soil samples from four field sites amended with ZnSO₄ were used to investigate ageing of soluble Zn under field conditions over a 2-year period. Lability of Zn measured using ⁶⁵Zn radioisotope dilution showed a significant decrease over time and hence evidence of Zn fixation in three of the four soils. However, 0.01 M CaCl₂ extractions and toxicity measurements using a genetically modified lux-marked bacterial biosensor did not indicate a decrease in soluble/bioavailable Zn over time. This was attributed to the strong regulatory effect of abiotic properties such as pH on these latter measurements. These results also showed that Zn ageing occurred immediately after Zn spiking, emphasising the need to incubate freshly spiked soils before ecotoxicity assessments. - Ageing effects were detected in Zn-amended field soils using ⁶⁵Zn isotopic dilution as a measure of lability, but not with either CaCl₂ extractions or a lux-marked bacterial biosensor.

[en] An important aspect of the behaviour and fate of silver (Ag) in soils is the interaction with dissolved organic matter (DOM). The complexation and strength of binding of Ag"+ with DOM in soil water extracts was examined and modelled based on a range of chemical and quality DOM measurements. Silver ion binding measured by addition of the "1"1"0"mAg radioisotope in addition to a cation exchange resin technique were used to determine strongly complexed Ag in solutions. Silver was found to be up to 70% strongly complexed. The variability in Ag"+ binding by DOM across different soils was closely related (R"2 = 0.8) to the mid-infrared spectra of these extracts. The affinity of Ag"+ for DOM was stronger in solutions containing a greater content of humic and aromatic structures. The ability of Ag"+ to complex with DOM could result in increased mobilisation of this metal in the soil environment. - Highlights: • Ag releases to the environment are likely to increase due to its increased usage. • Dissolved organic matter (DOM) is critical to the availability of Ag"+. • Across a range of different soils there was up to 70% complexed Ag in solution. • Variation in Ag"+ binding by DOM across soils was closely related to the MIR spectra. • Ag"+ affinity for DOM was stronger for DOM with greater humic and aromatic content. - Strongly complexed Ag in soil water extracts was closely related to the mid-infrared spectra of the extracts and the strength of binding to humic and aromatic structures of DOM

[en] The fate and lability of added soluble Ag in soils over time was examined by measurement of labile metal (E-value) by isotopic dilution using the ^110mAg radioactive isotope and the solid-phase speciation of Ag by X-ray absorption near edge structure (XANES) spectroscopy. After two weeks of ageing the E-values for Ag decreased by 20–90% with a further decrease of 10–40% after six months. The overall decrease in labile Ag for all soils after the 6 month ageing period was 50–100%. The ageing was more rapid and pronounced in the alkaline soils. XANES results for Ag in soils indicated that for the majority of soils the added Ag⁺ was reduced to metallic Ag over time, and associations with Fe-oxohydroxides and reduced S groups in organic matter also decreased Ag lability. Strong positive correlations were found between metallic Ag and non-labile Ag and between organic carbon and Ag bonded with S species. - Highlights: • Rapid ageing of Ag was observed after 14 days with a decrease in lability of 20–90%. • A further decrease of 10–40% was observed after 6 months. • Over time Ag⁺ formed metallic Ag which was positively correlated to non-labile Ag. • A positive correlation was found between organic carbon and Ag bonded with sulfur. - The decrease in the lability of soluble Ag added to soils over 6 months is explained by formation of metallic Ag and associations with Fe-oxohydroxides and S groups in organic matter

[en] Cadmium (Cd) is a non-essential element for human nutrition and is an agricultural soil contaminant. Cadmium solubility in paddy soils affects Cd accumulation in the grain of rice. This is a human health risk, exacerbated by the fact that rice grains are deficient in iron (Fe) and zinc (Zn) for human nutrition. To find ways of limiting this potential risk, we investigated factors influencing Cd solubility relative to Fe and Zn during pre-harvest drainage of paddy soils, in which soil oxidation is accompanied by the grain-filling stage of rice growth. This was simulated in temperature-controlled 'reaction cell' experiments by first excluding oxygen to incubate soil suspensions anaerobically, then inducing aerobic conditions. In treatments without sulfur addition, the ratios of Cd:Fe and Cd:Zn in solution increased during the aerobic phase while Cd concentrations were unaffected and the Fe and Zn concentrations decreased. However, in treatments with added sulfur (as sulfate), up to 34 % of sulfur (S) was precipitated as sulfide minerals during the anaerobic phase and the Cd:Fe and Cd:Zn ratios in solution during the aerobic phase were lower than for treatments without S addition. When S was added, Cd solubility decreased whereas Fe and Zn were unaffected. When soil was spiked with Zn the Cd:Zn ratio was lower in solution during the aerobic phase, due to higher Zn concentrations. Decreased Cd:Fe and Cd:Zn ratios during the grain filling stage could potentially limit Cd enrichment in paddy rice grain due to competitive ion effects for root uptake. - Research Highlights: → Cd:Fe and Cd:Zn ratios increase in paddy soil solution during oxidation. → Cd:Fe and Cd:Zn ratios increase because Fe and Zn concentrations decrease. → Cd concentrations do not change during oxidation. → Cd:Fe and Cd:Zn ratios in solution decrease when Zn is added to soil. → Metal sulfide precipitation lowers Cd:Fe and Cd:Zn ratios in soil solution.

[en] Silver (Ag) engineered nanomaterials (ENMs) are being released into waste streams and are being discharged, largely as Ag₂S aged-ENMs (a-ENMs), into agroecosystems receiving biosolids amendments. Recent research has demonstrated that biosolids containing an environmentally relevant mixture of ZnO, TiO₂, and Ag ENMs and their transformation products, including Ag₂S a-ENMs, disrupted the symbiosis between nitrogen-fixing bacteria and legumes. However, this study was unable to unequivocally determine which ENM or combination of ENMs and a-ENMs was responsible for the observed inhibition. Here, we examined further the effects of polyvinylpyrollidone (PVP) coated pristine Ag ENMs (PVP-Ag), Ag₂S a-ENMs, and soluble Ag (as AgSO₄) at 1, 10, and 100 mg Ag kg⁻¹ on the symbiosis between the legume Medicago truncatula and the nitrogen-fixing bacterium, Sinorhizobium melliloti in biosolids-amended soil. Nodulation frequency, nodule function, glutathione reductase production, and biomass were not significantly affected by any of the Ag treatments, even at 100 mg kg⁻¹, a concentration analogous to a worst-case scenario resulting from long-term, repeated biosolids amendments. Our results provide additional evidence that the disruption of the symbiosis between nitrogen-fixing bacteria and legumes in response to a mixture of ENMs in biosolids-amended soil reported previously may not be attributable to Ag ENMs or their transformation end-products. We anticipate these findings will provide clarity to regulators and industry regarding potential unintended consequences to terrestrial ecosystems resulting from of the use of Ag ENMs in consumer products. - Highlights: • Concentrations intended to simulate near-term and long-term worst-case scenarios. • Root nodulation unaffected by all Ag treatments at highest concentration tested. • Plant growth also unaffected by all Ag treatments at highest concentration used. - Root nodule function and plant growth were unaffected by both pristine Ag ENMs and aged Ag₂S a-ENMs, suggesting that Ag ENMs may present little risk to rhizobia-legume symbiosis.

[en] The Existing Substances Regulation Risk Assessments by the European Union (EU RA) generated new toxicity data for soil organisms exposed to Ni added to sixteen field-collected soils with low background concentration of metals and varying physico-chemical soil characteristics. Using only effective cation exchange capacity (eCEC) as a bioavailability correction, chronic toxicity of Ni in soils with a wide range of characteristics could be predicted within a factor of two. The objective of the present study was to determine whether this was also the case for three independent data sets of Ni toxicity thresholds. Two of the data sets were from Community Based Risk Assessments in Port Colborne ON, and Sudbury ON (Canada) for soils containing elevated concentrations of Ni, Co and Cu arising from many decades of Ni mining, smelting and refining. The third data set was the Metals in Asia study of soluble Ni added to field soils in China. These data yielded 72 leached and aged EC₁₀/NOEC values for soil Ni, for arthropods, higher plants and woodlot structure and function. These were reduced to nine most sensitive single or geometric mean species/function endpoints, none of which were lower than the HC₅ predicted for a soil with an eCEC of 20 cmol/kg. Most of these leached and aged EC₁₀/NOEC values were from soils co-contaminated with Cu, in some cases at its median HC₅ as predicted by the EU RA from soil characteristics. We conclude that the EU RA is protective of Ni toxicity to higher-tier ecological endpoints, including in mixture with Cu, before the assessment factor of 2 is applied. We suggest that for prospective risk assessment, the bioavailability based PNEC (HC₅/2) be used as a conservative screen, but for retrospective and site-specific risk assessment, the bioavailability based HC₅ is sufficient. - Highlights: • Higher-tier ecotoxicity thresholds calculated for field soils with elevated Ni. • Adjusted for Ni bioavailability using soil eCEC and species-specific slope. • Most thresholds greater than the EU RA bioavailability-based median HC5. • Bioavailability-based median HC5 is a conservative screen.

[en] We investigated effects of Ag_2S engineered nanomaterials (ENMs), polyvinylpyrrolidone (PVP) coated Ag ENMs (PVP-Ag), and Ag"+ on arbuscular mycorrhizal fungi (AMF), their colonization of tomato (Solanum lycopersicum), and overall microbial community structure in biosolids-amended soil. Concentration-dependent uptake was measured in all treatments. Plants exposed to 100 mg kg"−"1 PVP-Ag ENMs and 100 mg kg"−"1 Ag"+ exhibited reduced biomass and greatly reduced mycorrhizal colonization. Bacteria, actinomycetes and fungi were inhibited by all treatment classes, with the largest reductions measured in 100 mg kg"−"1 PVP-Ag ENMs and 100 mg kg"−"1 Ag"+. Overall, Ag_2S ENMs were less toxic to plants, less disruptive to plant-mycorrhizal symbiosis, and less inhibitory to the soil microbial community than PVP-Ag ENMs or Ag"+. However, significant effects were observed at 1 mg kg"−"1 Ag_2S ENMs, suggesting that the potential exists for microbial communities and the ecosystem services they provide to be disrupted by environmentally relevant concentrations of Ag_2S ENMs. - Highlights: • PVP-Ag and Ag"+ inhibited AMF colonization more readily than Ag_2S ENMs. • Impact of PVP-Ag ENMs and Ag"+ on microbial communities larger than for Ag_2S ENMs. • Significant changes in microbial communities in response to Ag_2S ENMs at 1 mg kg"−"1. - Although Ag_2S ENMs are less toxic to soil microorganisms than pristine nanomaterials or ions, some effects are observed on soil microbial communities at relevant concentrations.

[en] For essential elements, such as copper (Cu) and zinc (Zn), the bioavailability in biosolids is important from a nutrient release and a potential contamination perspective. Most ecotoxicity studies are done using metal salts and it has been argued that the bioavailability of metals in biosolids can be different to that of metal salts. We compared the bioavailability of Cu and Zn in biosolids with those of metal salts in the same soils using twelve Australian field trials. Three different measures of bioavailability were assessed: soil solution extraction, CaCl₂ extractable fractions and plant uptake. The results showed that bioavailability for Zn was similar in biosolid and salt treatments. For Cu, the results were inconclusive due to strong Cu homeostasis in plants and dissolved organic matter interference in extractable measures. We therefore recommend using isotope dilution methods to assess differences in Cu availability between biosolid and salt treatments. - Metals in biosolids are not necessarily less bioavailable than their soluble salt.