Foliar Lead Uptake by Lettuce Exposed to Atmospheric Fallouts

Abstract

Metal uptake by plants occurs by soil-root transfer but also by direct transfer of contaminants from the atmosphere to the shoots. This second pathway may be particularly important in kitchen gardens near industrial plants. The mechanisms of foliar uptake of lead by lettuce ( Lactuca sativa ) exposed to the atmospheric fallouts of a lead-recycling plant were studied. After 43 days of exposure, the thoroughly washed leaves contained 335 +/- 50 mg Pb kg(-1) (dry weight). Micro-X-ray fluorescence mappings evidenced Pb-rich spots of a few hundreds of micrometers in diameter located in necrotic zones. These spots were more abundant at the base of the central nervure. Environmental scanning electron microscopy coupled with energy dispersive X-ray microanalysis showed that smaller particles (a few micrometers in diameter) were also present in other regions of the leaves, often located beneath the leaf surface. In addition, submicrometric particles were observed inside stomatal openings. Raman microspectrometry analyses of the leaves identified smelter-originated Pb minerals but also secondary phases likely resulting from the weathering of original particles. On the basis of these observations, several pathways for foliar lead uptake are discussed. A better understanding of these mechanisms may be of interest for risk assessment of population exposure to atmospheric metal contamination.

New isotopic evidence of lead contamination in wheat grain from atmospheric fallout

“…In our study, the Pb content in the wheat grains was mainly derived from atmospheric fallout as indicated by similar isotope ratios. This finding is consistent with reported results that plant leaves can uptake Pb directly from atmospheric fallout (Bi et al 2009;Dollard 1986;Hu et al 2011;Uzu et al 2010).…”

“…206 Pb/ 207 Pb ratios indicated that the Pb in the needles of pine trees in Sweden was dominated by direct Pb accumulation from the atmosphere (Uzu et al 2010). Corn plants around an industrial air pollutant (smelter) assimilated the atmospheric fallout through their leaves and transferred them to the grains, as revealed by the isotopic tracing test conducted by Bi et al (2009).…”

Distribution of heavy metals in soils of the Yellow River Delta: concentrations in different soil horizons and source identification

“…As for the PC2 which contained Cd and clay in both surface and basal horizons of the wetland soil, this factor implied allochthonous inputs of Cd from the fine-grained sediments of the Yellow River deposited in the estuary area. Moreover, Pb was not only strongly associated with PC3 in the surface horizon but also associated with PC1 in the basal horizon of the wetland, indicating biogeochemical cycling due to plant uptake of Pb from surface soils or lead-enriched atmospheric fallout through root or foliage (Uzu et al 2010). Khoo and Tan (2006) reported that conventional onshore crude oil extraction come from venting and flaring operations, and volatilization caused the air emissions of toxic heavy metals such as arsenic, cadmium, lead, and mercury.…”

Effects of road dust on the growth characteristics of Sophora japonica L. seedlings

“…Stress from heavy metals like Pb can reduce the N absorption of plants, because excessive heavy metals disturb plants' cellular metabolism, and thus influence the root absorption of necessary nutrient elements (Sharma and Dubey, 2005; ⁎ Correlation is significant at the 0.01 level (2-tailed); ⁎⁎ Correlation is significant at the 0.05 level (2-tailed). Kang, 2012).Trace elements in PM can cause an increasing concentration of trace elements in plant shoots by covering foliage (Uzu et al, 2010;Pavlik et al, 2012). Whether heavy metals absorbed by the leaf surface could disturb the cell metabolism is worth exploring in the future.…”