Brassica napus Growth in Lead-Polluted Soil: Bioaccumulation in Plant Organs at Different Ontogenetic Stages and Lead Fractionation in Soil

Abstract

Lead is known to be a highly toxic metal; it is often found in soils with the potential to be incorporated by plants. Here, the bioaccumulation of lead by rapeseed (Brassica napus) from a soil with Pb(II) added just before sowing is studied. The effect on plant organs is also studied at the ontogenetic stages of flowering and physiological maturity. Moreover, the chemical fractionation of Pb in the rhizosphere and bulk soil portions is investigated and related to Pb accumulation in plant organs. B. napus are found to accumulate Pb in its organs: 1.5–19.6 mg kg−1 in roots, 3.3–15.6 mg kg−1 in stems, 0.5–8.6 mg kg−1 in leaves in all treatments, and in grains 1.45 mg kg−1 at physiological maturity and only for the highest Pb dose (200 mg kg−1). Plant biomass reduction was observed to be about 20% at the flowering stage and only for the highest Pb dose. The analysis of metal fractionation in soil shows Pb migration from the bulk soil to the rhizosphere, attributed to concentration gradients created by root intake. Along the time period studied, lead chemical fractionation in soil evolved toward the most stable fractions, which coupled to plant uptake depleted the soluble/exchangeable one (assumed bioavailable).