Assessing the effect of metal speciation on lead toxicity to Vicia faba pigment contents

• Pb uptake and toxicity depend on its applied chemical form.
• Pb may induce toxicity to plant pigments via ROS production.
• EDTA alleviates Pb toxicity by forming stable and non-toxic complexes.
• Citric acid has no effect on Pb uptake and toxicity due to weak Pb–CA complexes.

Lead is a highly toxic heavy metal, but its putative toxicity with respect to its speciation remains to unveil. In this study, Pb-induced toxicity to Vicia faba pigment contents was assessed against Pb speciation and accumulation. After a culture period of three weeks, V. faba seedlings were exposed to 5 μM of lead nitrate alone or chelated by citric acid (CA) or ethylenediaminetetraacetic acid (EDTA). The plants were treated for 1, 4, 8, 12 and 24 h in nutrient solution. Exposure to Pb-5 caused increased production of reactive oxygen species, lipid peroxidation and decrease in V. faba chlorophyll contents during 24 h. Lead-induced oxidative stress and toxicity to chlorophyll contents varied with the speciation of Pb. Addition of EDTA to Pb solution alleviated Pb-induced oxidative stress and toxicity to V. faba pigments by decreasing Pb accumulation in V. faba leaves. However, addition of citric acid to Pb did not affect Pb accumulation or toxicity to V. faba leaves. It is proposed that metal speciation plays an important role in Pb toxicity to V. faba pigment. Moreover, organic ligands vary greatly in terms of their ability to modify Pb phytoaccumulation and toxicity.