Foliar or root exposures to smelter particles: Consequences for lead compartmentalization and speciation in plant leaves

Abstract

In urban areas with high fallout of airborne particles, metal uptake by plants mainly occurs by foliar pathways and can strongly impact crop quality. However, there is a lack of knowledge on metal localization and speciation in plants after pollution exposure, especially in the case of foliar uptake. In this study, two contrasting crops, lettuce (Lactuca sativa L.) and rye-grass (Lolium perenne L.), were exposed to Pb-rich particles emitted by a Pb-recycling factory via either atmospheric or soil application. Pb accumulation in plant leaves was observed for both ways of exposure. The mechanisms involved in Pb uptake were investigated using a combination of microscopic and spectroscopic techniques (electron microscopy, laser ablation, Raman microspectroscopy, and X-ray absorption spectroscopy). The results show that Pb localization and speciation are strongly influenced by the type of exposure (root or shoot pathway) and the plant species. Foliar exposure is the main pathway of uptake, involving the highest concentrations in plant tissues. Under atmospheric fallouts, Pb-rich particles were strongly adsorbed on the leaf surface of both plant species. In lettuce, stomata contained Pb-rich particles in their apertures, with some deformations of guard cells. In addition to PbO and PbSO4, chemical forms that were also observed in pristine particles, new species were identified: organic compounds (minimum 20%) and hexagonal platy crystals of PbCO3. In rye-grass, the changes in Pb speciation were even more egregious: Pb-cell wall and Pb-organic acid complexes were the major species observed. For root exposure, identified here as a minor pathway of Pb transfer compared to foliar uptake, another secondary species, pyromorphite, was identified in rye-grass leaves. Finally, combining bulk and spatially resolved spectroscopic techniques permitted both the overall speciation and the minor but possibly highly reactive lead species to be determined in order to better assess the health risks involved.

Lead and Cadmium Phytoavailability and Human Bioaccessibility for Vegetables Exposed to Soil or Atmospheric Pollution by Process Ultrafine Particles

“…Recently, Schreck et al (2014) investigated the consequences on Pb compartmentalization and speciation in plant leaves of the method of exposure (foliar or root). The pollution context was the same as for the present study (i.e., atmospheric smelter particles).…”

Cadmium Bioavailability, Uptake, Toxicity and Detoxification in Soil-Plant System

“…Health risks associated with atmospheric Cd pollution arise mainly from inhalation of particles and consumption of polluted vegetables (Morman and Plumlee 2013). Although root-metal uptake is considered the main uptake pathway for plants, foliar uptake has also been identified as a potentially significant route of Cd exposure (Shahid et al 2013b;Schreck et al 2014;Xiong et al 2014a, b;Uzu et al 2010). Recently, Schreck et al (2013) suggested that root and shoot metal transfer pathways are independent, with an additive effect in terms of toxicity.…”

Antimony bioavailability: Knowledge and research perspectives for sustainable agricultures

“…Aerial deposition onto leaves and fruits could explain such results [21,22]. Moreover, with the increasing quantities of ultrafine atmospheric particles in urban and peri-urban areas, foliar plant exposure could sometimes be the main route of plant pollution in aerial organs [23,120].…”

“…Such variations could come from differences in leaf morphology, and/or changes in Sb speciation throughout the plant [23].…”