Lichens and mosses as monitors of industrial activity associated with uranium mining in northern Ontario, Canada—Part 2: Distance dependent uranium and lead accumulation patterns

Abstract

The variation in concentration (C(d)) of uranium and lead in lichens and mosses with distance (d) from emission sources associated with the mining and milling of uranium conformed to the equation: C( d) = md − n + b. Details for the use of this equation and for the fitting of curves are provided. For uranium in samples from the Elliot Lake sampling macro-transect (54 km in length), n = 1, b = 0; whilst, for the 9·6 km Agnew Lake macro-transect, n = 2, b = 0. Lead did not show a correlation with distance. For the mine-exhaust vent micro-transects (<500 m in length), n = 2 with b > 0 for both lead and uranium. Evidence is presented that proves conclusively that the above equation is to be preferred over the familiar log-log plot based on the power curve: C( d) = ad − p . The latter expression incorrectly assigns (biologically speaking) the line C( d) = b = 0 as the horizontal asymptote for all elements, even for essential elements. It is demonstrated that when b > 0 there is no obvious relationship between the observed values of n and p, nor m and a. Non-zero backgrounds appear to be the rule, rather than the exception. To date, 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 uranium mining and milling operations at Elliot Lake, Ontario, Canada, is 22 km, and 9 km for the Agnew Lake, Ontario, Canada, site. Around mine-exhaust vents, enhanced levels of uranium and lead dropped to expected ‘background’ values at distances >400 m. The environmental implications of these findings are discussed.