Bioaccumulation of manganese by plants: influence of MMT as a gasoline additive

Abstract

This study on the bioaccumulation of manganese (Mn) by plants was motivated by the increased use of Methylcyclopentadienyl manganese tricarbonyl (MMT) as a replacement for lead in gasoline. Oats and beans were grown in sandy and organic soils at a control site (E o) and at two other sites weakly (E +) and highly exposed (E ++) to Mn contamination, potentially from a MMT source. Total Mn, Ca, Mg, Fe, Zn and Al were measured in the soils and in the plants (roots, stems/leaves and fruits). Exchangeable Mn was measured in the soils at the beginning and at the end of the exposure period. The pH of the organic and sandy silty soils were found to be lower outdoors (E + and E ++) than in the greenhouse (E o) and exchangeable Mn was found to be significantly higher in the organic soil at E ++ (1.03–1.36 ppm). Higher Mn accumulation was also found in the fruits and stems of oats grown in the organic and sandy soils at E ++. This Mn accumulation is often associated with increased Fe and Al in the plant. These results suggest that the addition of MMT to gasoline may result in an increase in exchangeable Mn in organic soils. However, it has not been proven that the source of the increased Mn accumulation is indeed MMT in gasoline.