LICHENS AND MOSSES AS MONITORS OF INDUSTRIAL-ACTIVITY ASSOCIATED WITH URANIUM MINING IN NORTHERN ONTARIO, CANADA .2. DISTANCE DEPENDENT URANIUM AND LEAD ACCUMULATION PATTERNS

The variation in concentration (C(d)) of U and Pb in lichens and mosses with distance (d) from emission sources associated with the mining and milling of U conformed to the equation: C(d) = md-n + b. Details for the use of this equation and for the fitting of curves were provided. For U in samples from the Elliot Lake [Canada] sampling macro-transect (54 km in length), n = 1, b = 0 and for the 9.6 km Agnew Lake [Ontario, Canada] macro-transect, n = 2, b = 0. Pb did not show a correlation with distance. For the mine-exhaust vent micro-transects (< 500 m in length), n = 2 with b > 0 for Pb and U. Evidence proved conclusively that the equation was to be preferred over the familiar log-log plot based on the power curve: C(d) = ad-p. The latter expression incorrectly assigned (bioogically speaking) the line C(d) = b = 0 as the horizontal asymptote for all elements, even for essential elements. When b > 0 there was no obvious relationship between the observed values of n and p, or m and a. Non-zero backgrounds were the rule, rather than the exception. The almost unanimous choice by researchers of the non-intercept power curve has prevented inter-site and inter-species comparison. From the metal content/distance curves an estimate of the effective radius for the macro-pollution zone around the U mining and milling operations at Elliot Lake was 22 km, and 9 km for the Agnew Lake site. Around mine-exhaust vents, enhanced levels of U and Pb dropped to expected background values at distances > 400 m. The environmental implications were discussed.