Phytoextraction of soil trace elements by willow during a phytoremediation trial in Southern Québec, Canada.

The phytoextraction of the trace elements (TEs) As, Cd, Cu, Ni, Pb, and Zn by willow cultivars (Fish Creek, SV1 and SX67) was measured during a 3-year field trial in a mildly contaminated soil. Biomass ranged from 2.8 to 4.4 Mg/ha/year at 30,000 plants/ha. Shoots (62%) were the main component followed by leaves (23%) and roots (15%). Biomass was positively linked to soluble soil dissolved organic carbon, K, and Mg, while TEs, not Cd and Zn, had a negative effect. The TE concentration ranking was: Zn > Cu > Cd > Ni, Pb > As, and distribution patterns were: (i) minima in shoots (As, Ni), (ii) maxima in leaves (Cd, Zn), or (iii) maxima in roots (Cu, Pb). Correlations between soil and plant TE were significant for the six TEs in roots. The amounts extracted were at a maximum for Zn, whereas Fish Creek and SV1 extracted more TE than SX67. More than 60% (91-94% for Cd and Zn) of the total TE was in the aboveground parts. Uptake increased with time because of higher biomass. Fertilization, the selection of cultivars, and the use of complementary plants are required to improve productivity and Cd and Zn uptake.

Trace elements in the pollen of Ambrosia artemisiifolia: what is the effect of soil concentrations?

Concentrations of nine trace elements (Ba, Cd, Cr, Cu, Mn, Ni, Pb, Tl and Zn) were measured in a plant bearing allergenic pollens (ragweed) and their transfers from soils to the roots and then to the pollens were investigated. The soil, roots and pollens collected from flowers were sampled at 26 urban sites. Soil pH, soil organic carbon and total-recoverable trace elements (TE) in soil, roots and pollens were measured. The three biogeochemical compartments are well discriminated according to their TE concentrations. The concentrations (in µg g(-1)) in pollens decreased as follow: Zn (59.5-205)>Mn (19.4-117)>Ba≈Cr≈Cu≈Ni≈Pb (0.54-27.7)>Cd (0.06-0.77)>>Tl (0.0015-0.0180). Mean elemental allocation within ragweed always favored roots over pollen but, at site level, inverse pattern is also observed mostly for Zn and slightly for Cu and Ni. Significant predictive models of TE concentrations in pollens were obtained using soil or root properties only for Cd, Ni and Pb. They all involved positive relationships between TE concentrations in pollens and in soil or roots. Estimates of short-term exposure of human to TE carried out by ragweed pollens indicate TE absorption of less than 50 ng, far below thresholds of air quality criteria. Investigating the TE chemistry of pollens is a required first step to validate the impact of TE in pollens on human health and on the prevalence and intensity of allergy symptoms and atopic diseases.