Metal content of dandelion ž Taraxacum officinale/ leaves in relation to soil contamination and airborne particulate matter

The global distribution of the common dandelion ŽTaraxacum officinale Weber, sensu lato; Asteraceae., along with its ability to tolerate a wide range of environmental conditions, make this ‘species’ a particularly attractive candidate to evaluate for its value as a biological monitor of environmental metal contamination. To examine the metal content of dandelion leaves in relation to environmental metal levels, the concentrations of eight metals ŽCd, Cr, Cu, Fe, Mn, Ni, Pb and Zn. were analyzed in leaf and soil samples collected at 29 sites in the mid-western United States differentially impacted by pollution. Sites were chosen primarily to cover a range of annual mean 24-h airborne particulate matter 10 m Žhereafter, PM10. exposure, with PM10 levels varying from those found in isolated rural areas to levels typical of the most industrialized urban locations in the mid-western United States. A positive, significant correlation was detected between soil concentrations of each metal and measures of PM10 at a site, signifying that airborne particulate matter is a good indicator of soil metal contamination. Leaf concentrations of four of the eight metals ŽCr, Mn, Pb and Zn. examined were found to increase significantly as the soil levels of these metals increased, but the percentage of the total variation explained by the relationship in these cases was generally low. This latter finding, along with the lack of a significant relationship between leaf and soil concentrations for the four other metals, indicate that the factors affecting metal absorption from the soil by dandelions are complex and that, aside from soil metal concentrations, other soil, plant and or other environmental factors affect metal uptake.There was also no evidence that leaf metal concentrations were positively correlated with PM10. In addition, the concentrations of some metals ŽCu, Fe, Mn, Pb and Zn. were significantly higher in leaves collected in the fall compared to those collected at the same sites in the spring. These findings suggest that dandelions may not be a particularly effective tool for quantifying levels of environmental metal contamination, at least on the scale of pollution typifying industrialized urban areas of the mid-western United States.