Cadmium Isotope Fractionations Induced by Foliar and Root Uptake for Rice Exposed to Atmospheric Particles: Implications for Environmental Source Tracing

Abstract

Rice roots and leaves were exposed to cadmium (Cd)-contaminated particles in a greenhouse to modify the fractionation during Cd uptake and transport in the plants by using the Bayesian mixing model. The exposure to atmospheric Cd in rice near a copper smelter was determined under the field conditions. The results showed that the leaves directly absorb and accumulate atmospheric Cd in other aboveground tissues by 84− 99%. Positive values of Δ 114/110 Cd Leaf−Particle (0.08−0.11‰), Δ 114/110 Cd Node−Leaf (0.77− 0.81‰), and Δ 114/110 Cd Grain−Leaf (0.39−0.43‰) following foliar exposure as well as Δ 114/110 Cd Root−Particle (0.19−0.22‰) and Δ 114/110 Cd Grain−Root (−0.29 to 0.34‰) following root exposure suggested that particles released heavy isotopes. The roots and leaves preferentially retained light isotopes and transported heavy isotopes upward. The Cd isotope fractionations in the plant were constant under both root and foliar exposures at two dosages. The results were used to correct the parameters in the isotope mixing models and to trace the source of atmospheric Cd in rice tissues in the field. Both models of isotope mixing and mass balance suggested 50−63% Cd deposition on the grains. This study provides a theoretical basis for tracing the source of Cd isotopes in plants.

Phloem Redistribution of Pesticide Phenamacril in Plants Followed by Extensive Biotransformation

“…Knowledge concerning the plant uptake, translocation, and metabolism is vital in understanding the risks of organic chemicals and promoting efficient phytoremediation efforts . This study demonstrated that phloem translocation and plant excretion were important pathways to transport phenamacril from shoots to roots and rhizosphere environments, resulting in a prolonged cycling contamination, which should be considered in developing more accurate prediction models for assessing the risks of phloem-transported chemicals to ecosystems. − After being taken up, phenamacril was extensively transformed (e.g., 76.4%) in plants, with nine metabolites newly identified. Conjugation reactions are usually reversible, and deconjugation has been proved in human digestive systems. , Specifically, phase-II conjugation product M-392 might be deconjugated to phenamacril in human gut after intake.…”

Revealing the Sources of Cadmium in Rice Plants under Pot and Field Conditions from Its Isotopic Fractionation

“…Studies have found that plant leaves can directly uptake fine particles from atmospheric deposition on the leaf surface through cuticle internalization and stomatal infiltration. , In addition, plant leaves can also uptake the dissolved elements of atmospheric deposition through hydrophilic diffusion via aqueous pores and stomates . Further, some studies suggest that rice roots preferentially uptake the heavy Cd isotopes in atmospheric wet deposition from the soil, while the leaves are more inclined to uptake heavy Cd isotopes from dry deposition. , The quantitative assessment of the contribution of soil phytoavailable Cd and atmospheric deposition Cd to rice plants is influenced by the phytoavailability of soil Cd, the input pathway of atmospheric deposition, the bioavailability of Cd in atmospheric deposition, and the growth status of rice plants. ,, The result of this calculation provides a relatively quantitative assessment and suggests that, besides the soil water-soluble fraction, atmospheric deposition is also a potential and even non-negligible source of Cd in rice plants under field conditions.…”

Isotope Evidence for Rice Accumulation of Newly Deposited and Soil Legacy Cadmium: A Three-Year Field Study

“…Second, atmospherically deposited Cd can potentially be absorbed through foliar uptake and subsequently translocated to edible parts. Foliage can take up the trace-metal bounded particle from atmospheric deposition via stomata, aqueous pores, cracks, and lenticel and primarily through the ectodesmata in the cuticular membrane or epidermal cell wall via active transport in the subjacent cell symplastic pathway. ,, However, some of these uptake mechanisms are still poorly defined, , especially the dominant pathway of foliar uptake and then translocation in cereal crops. Additionally, the effects of atmospherically deposited Cd from previous years on soil bioavailable Cd and rice accumulation are not clear, and their aging dynamics are difficult to assess accurately.…”

“…In the last two decades, significant advancement in multicollector inductively coupled plasma mass spectrometer (MC-ICP-MS) analysis of nontraditional stable isotopes has introduced Cd isotope analysis as a powerful tool for source identification in various fields and may elucidate uptake pathways for Cd in cereal plants . The isotopic composition of Cd has been determined in meteorites, rocks, ores, soils, sediments, aquatic organisms, and plant samples. ,− Several studies have relied on mass-dependent fractionation or differences in Cd isotopic ratios from the original substance for soil source identification and fingerprinting. − However, identifying the source of Cd in plants poses significant challenges due to the fractionation of Cd isotopes during biological uptake . Fortunately, Cd isotope fractionation occurs during industrial processes at high temperatures, resulting in a heavy isotopic signature in slag and a light signature in dust released into the atmosphere .…”

“…Automobile exhaust from traffic, which also has a light signature, contributes a proportion of Cd to the atmosphere . The significant fractionation of Cd in an atmospheric deposition may thus allow the discrimination of atmospheric and soil sources in soil–plant systems. , In recent years, an increasing number of research studies have optimized the isotope mixing models. ,,, However, most studies focused on using its contribution to distinguish between different sources in soils and sediments, and limited studies have tried to trace the Cd sources in organisms, such as plants and animals.…”