Manganese accumulation along Utah roadways: a possible indication of motor vehicle exhaust pollution

An organic manganese compound is currently added to gasoline to replace tetraethyl lead as an antiknock fuel additive in the USA and Canada. Combustion exhaust gases contain manganese oxides. Manganese oxides are known to cause various deleterious health effects in experimental animals and humans. A field survey of roadside soil and plants in central Utah revealed that soil manganese concentrations in high traffic areas were up to 100-fold higher than historic lead levels. Soil manganese concentrations were highly correlated with distance from the roadway. Lead concentrations seem to have changed little from values reported twenty years ago but may have moved deeper into the soil profile. In addition, roadside aquatic plants were higher in leaf tissue manganese than herbs or grasses. Plant tissue manganese content was better correlated with plant type, traffic volume and microhabitat than with distance from the roadway. Submerged and emergent aquatic plants were sensitive bioindicators of manganese contamination. Roadside snow melt and water samples were low in manganese and lead content. We conclude that roadside soil and plants were apparently contaminated by manganese oxides from Mn-containing motor vehicle exhaust. Manganese concentrations in soil and in some plant species along impacted roadsides often exceeded levels known to cause toxicity.