Metal accumulation by colonizing vegetation on mine wastes

Plant and spoil samples from tailings and waste rock deposits were collected from eleven mine sites in the vicinity of Ottawa, Ontario. Spoil material and individual biomass components (floral, leaf, stem and root) of plant samples were analysed for Na, K, Mg, Ca, Pb, Mn, Fe, Cu, Zn, Al, Cd and As. Common colonizing species analysed for ionic concentrations include Poa compressa, Agrostis gigantea, Betula papyrifera, Populus balsamifera, Populus tremuloides, Solidago spp., Melilotus alba, Equisetum arvense, Echium vulgare and Silene cucubalus. Metal accumulation in plant species is variable and highly individualistic. Iron, lead, arsenic and aluminum tend to be accumulated in the roots of plants to a greater extent than other organs, while zinc and manganese accumulate principally in the leaves of colonizing plants. Concentration ratios (ratio of plant to soil ion content) are also variable. The variability seen can be attributed to differing soil environments occurring at and between mine sites and to the different mechanisms and degrees of metal tolerance of each plant. Plant ion content and soil ion content are significantly correlated in less than 20% of the samples. Ion pair correlations within the plant biomass components are also not generally significant.Total mercury content analyses of the plant and spoil samples from the Clyde Forks Mine show mercury in mine spoil can be as high as 2100.0 μg/g. Mercury accumulation occurred in all organs of plants colonizing the mine wastes with concentrations ranging from .10 to 9.7 μg/g. Mercury is also present in soil and vegetation surrounding the waste deposits at Clyde Forks Mine. The ability of a species to accumulate potentially toxic metals into their above ground organs should be considered before choosing native species for use in reclamation programs of heavy metal contaminated waste sites.