Atmospheric deposition of fluoride in the lower Tamar Valley,Tasmania

Soluble fluoride (F⁻), measured using an ion-selective electrode, was monitored during 1982–1983 in monthly bulk (wet and dry) atmospheric deposition samples collected at 17 locations in the lower Tamar Valley, Tasmania, where an aluminium (Al) smelter is located. Glass samplers (funnel-bottle type) were used, with duplications by plastic samplers at five locations later. The spatial and temporal variations in F⁻ deposition in relation to wind flow and rainfall are discussed, and its impact on the environment is highlighted. The mean deposition rates of F⁻, as measured from September 1982 to August 1983, ranged from about 90 μg m⁻² day⁻¹ at the intended ‘background’ location to 12,568 μg m⁻²day⁻¹ at a location about 1 km east-southeast from the smelter. The depositional fluxes of F⁻ and insoluble Al (another elemental tracer of the smelter) are significantly correlated (P < 0.001). They were much higher within 3 km of the smelter, where vegetation damage by fluoride contamination was most evident. However, air emissions from the smelter could travel at least 10 km up the valley. Wet deposition was the predominant removal process for F⁻ during autumn and winter, while dry deposition appeared to be more significant in summer. The plastic samplers collected about 8 and 17% more F⁻ and Al, respectively, but with higher standard deviations. Thus the variations observed could be largely due to sampling fluctuations.