Abstract
The concentrations of zinc, copper, lead, cadmium and nickel in spring wheat grain and straw, Italian rye grass and lettuce were studied in a two-year field experiment conducted alongside two roads with a daily traffic density of 9500 and 5500 vehicles each. The experimental plots were located 22, 58 and 200 m from the roads. As controls, polyethylene pots filled with non-contaminated soil were placed in each plot. The values for the bulk deposition of lead were 50% and those for dry deposition over 50% higher in the plot 22 m from the roadside than in the plot 200 m from the roadside. The bulk deposition of zinc also decreased slightly with distance from the road. Cadmium depositions were low at all experimental sites. The highest values for dry deposition of lead and cadmium were recorded when the wind blew from the road in the direction of the collectors. The heavy metal concentrations varied from plant to plant but for a particular species were similar at different experimental sites. The highest zinc, cadmium and nickel concentrations were measured in lettuce. The lead concentration of wheat straw, Italian rye grass and lettuce at 22 m from the roadside was 1.5-3 times that of the background level at 200 m. In wheat grain, the lead concentration was very low and did not change with distance from the road. The plants took up lead mainly from air deposition. The zinc concentration of wheat grain and the nickel concentration of Italian rye grass were also high. Cadmium concentrations were low in wheat grain and straw and in rye grass. In wheat, the zinc and copper concentrations were higher and the lead and cadmium concentrations much lower in grain than in straw.
Highlights
The worldwide use of lead alkyls in petrol since 1923 has led to average lead emissions in the northern hemisphere of about 20 mg nr2 (Wickern and Breckle 1983)
Percentages as high as 90 or more of lead in plants are thought to derive from airborne lead (Tjell et al 1979) In general, cereal grains were low in cadmium
The tendency for elemental concentrations to be higher in leaves than in non-foliar edible parts applies to zinc, copper, lead and cadmium but not to nickel, which commonly has higher concentrations in edible parts than in leaves (Davis and Carlton-Smith 1980)
Summary
The worldwide use of lead alkyls in petrol since 1923 has led to average lead emissions in the northern hemisphere of about 20 mg nr (Wickern and Breckle 1983). E.g. zinc, copper, cadmium and nickel, are spread by road traffic Zinc and copper are essential elements for plants and animals; so is nickel, as shown by some studies (Eskew et al 1984). Considerable differences exist between the heavy metal concentrations of various parts ofplants (Yläranta and Sillanpää 1984, Sillanpää et al 1988, Sillanpää and Jansson 1991). Yläranta and Sillanpää (1984) measured the lowest copper concentration in the underground parts of some root crops and in the straws of grain crops. The aim of this study was to measure the concentration in plants of lead and some other elements that was due to airborne deposition, road traffic in particular. The elemental concentrations of plants growing on the plots and in the pots were compared in order to establish what proportion was due to air deposition
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