SUMMARYA population of Silene vulgaris (Moench) Garcke collected from mine tailings near the town of Cobalt, Ontario was compared in its metal tolerance with a population collected at an uncontaminated site (Baymouth, Ontario). Seedlings of the Cobalt population were tolerant to elevated levels of arsenic, cobalt and nickel, both compared with the Baymouth population and with other literature reports for this species. However, the tolerance indices in the Cobalt plants for these toxic elements did not correlate well with their concentration in water extractions in the mine soils.Indices of arsenic tolerance, based on the inhibition of root growth in 12 d experiments, showed a similar response to that in a 28 d experiment for both populations. The latter however, appeared to be a more accurate indicator of As tolerance in S. vulgaris, because the longer-term tolerance indices had lower standard deviations and higher probabilities for tolerance than the short-term tolerance indices. Reduced uptake of As occurred in the roots of tolerant individuals compared with non-tolerant individuals at a low As treatment. At a higher arsenic exposure, however, arsenic entered the roots of tolerant individuals. A partial exclusion or reduced translocation of arsenic to the shoots then appeared to operate in the shoots of tolerant individuals, i.e. arsenic levels were higher in shoots of non-tolerant plants. At the highest arsenic exposure, where the individuals from the Cobalt population were no longer tolerant, this exclusion pattern broke down. From a preliminary selection experiment, some arsenic tolerant individuals occurred in the Baymouth population. This suggests that under circumstances of arsenic contamination this population also has the potential to develop a tolerance to high arsenic exposure.

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