Manganese contamination in organic soil, bean and oat plants as related totraffic volume

The increased use of Methylcyclopentadienyl manganese tricarbonyl (MMT) as a replacement for lead (Pb) in gasoline in Canada is suspected to lead to m anganese (Mn) contamination, particularly in the urban ecosystems where tra ffic density is often high. This study has been conducted to assess the bio accumulation and toxic effects of Mn in plants as they relate to the deposi tion of Mn3O4 resulting from a traffic volume of 150,000; 300,000 and 1,000 ,000 vehicles/day within 10 meters from the highway. Bean (Phaseolus vulgar is L.) and oat (Avena nova L.) plants were planted in organic soil in a con trolled growth chamber. Each plant species was divided into four groups, on e serving as the control group while the remaining three groups were expose d to three different quantities of Mn3O4 that compared to the theoretical d eposition of Mn emitted by midsize vehicles from three different traffic vo lumes. The Mn concentration in the leaves of both plants and in oat roots w ere significantly higher (p <0.05) in the high exposed group compare to the control group. Significant differences in total and exchangeable Mn were f ound in the oat soil (p <0.05). Apparently, this increase in exchangeable M n led to an increase in total Mn in oat leaves. There were no visible Mn to xicity symptoms for both species and the different parts of both plants did not exceed toxic threshold concentrations. The highest Mn concentration in bean leaves was 103 ppm and in the oat plants 41 ppm which are considered to be adequate for plants. Exposure level or traffic volume was significant ly correlated with total Mn (p <0.05), exchangeable Mn (p <0.001) and pH (p <0.01) in the oat soil, The total Mn was significantly correlated with exc hangeable Mn in the oat soil (p <0.01). These results suggest that Mn conta mination from a traffic volume as high as one million vehicles per day, pos es no significant problem in terms of bioaccumulation or effects on plants, even though Mn input caused an increase in exchangeable Mn in the soil whe re only oat plants were grown and in total Mn in the leaves of both plants.