Automotive Traffic Risks for the Environment

Automotive traffic generates a lot of air pollutants, some metallic contaminants and causes troubles, not only for the roadside environment but also for the terrestrial and aquatic ecosystems. The exhaust gases of vehicle's engines contain mainly carbon monoxide and dioxide, nitrogen oxides, a few sulfur dioxide, a great number of hydrocarbons, or organic carbon derivates, and some heavy metals particulates. Some of these compounds are directly toxic for living organisms, when they occur in a closed environment such as inside the car, tunnels, subterranean car parks, or rooms; but they are harmless when emitted in open space, when natural diffusion conditions are sufficient to prevent high concentrations in the air. Other emitted gases will interact with oxidants (e.g. O 3 ) to form new labile compounds, which have a high phytotoxic activity at low concentrations (P.A.N.,and photochemical smogs). These oxidants, obtained by photochemical reactions in the atmosphere, may be involved in the widespread dieback and decline of forests in both Europe and North America. The O 3 and photooxidants theory, and its influence on acid deposition, will be shortly presented and discussed. Heavy metals contamination of soil, water and plant materials, near highways is well known, and there's a trend to accelerate the reduction of lead addition in the fuels. The vicinity of heavy traffic roads, is a source for important troubles to terrestrial and aquatic ecosystems. Some examples of these will be discussed for their direct or indirect effects on animal, microbiological or plant lifes. The regular use of deicing salts, essentially sodium and calcium chlorides, in winter period, affects the resistance to drought stress of trees and crops, and increases the sensitivity of plants to parasitic diseases. The compaction of soils near the road is involved in anaerobic conditions near the roots of trees, which will be followed by an important dieback. The risks for environment alterations could be prevented and reduced by clean motors, with a drastic reduction of gaseous pollutants. The lead problem will be progressively resolved by the new European standards of lead addition to fuels; but the lead already present in soils will remain a threat for some sensitive crops and forages. A passive protection of roadside contamination could be obtained by green screens, containing resistant and rustic shrubs and trees, which will filter the air and act as efficient sinks for dust and heavy metals particles. Due to aerial long distance transport and photochemical reactions, prevention of damages to forests request more attention. The solution is reduced emissions of the precursors of lethal compounds: clean motors are wanted … Other risks for the roadside environment (chlorides, asphyxic conditions, etc.) are not directly involved with air pollutants emissions: disastrous landscape modifications by speedways construction are more fundamental.