Characteristics of a manganese-rich soil and metal accumulation in edible parts of plants in the region of Moanda, Gabon

Abstract

Moanda region in Southeastern Gabon is rich in manganese (Mn) ores. This study aimed to determine the physico-chemical properties of cultivated and uncultivated soils and the metal content in edible parts of 9 plants cultivated in this area. The studied soils had a sandy loam clay texture. Cultural practices induced a significant acidification, decrease in fertility and loss of metals from soils. Mn contents in soils varied from 8,672 to 17,956 mg.kg-1 , and were significantly higher in uncultivated than in cultivated soils. Concentration of metals in plants seemed to depend on the type of plant more than the concerned part. Except for Nkoumou (Gnetuma fricanum), Ca, Mg and K contents were in large amounts in all plants so they could be good sources of macronutrients for humans and animals. Mn levels in leaves of cassava and sorrel and Fe levels in the red sorrel leaves exceeded 1 g.kg-1. Sorrel and amaranth showed the highest daily intake of nutrients.