EFFECTS OF AIR-POLLUTANTS ON AGRICULTURE AND FORESTRY

Historically, studies of the effects of the main phytotoxic gases (SO//2, O//3, NO//x and HF) have focused on determining the threshold for onset of visible foliar injury. More recently, research has focused on determining the thresholds for effects on economically important yield parameters irrespective of foliar injury. A review of the literature concludes that (a) the current EEC standard for SO//2 is adequate to protect most crops and trees and (b) more work is required to determine whether the U. S. A. threshold for O//3 effects are applicable to the climate and crops of Europe. The use of cost-benefit analysis and dose-response relationships is fraught with difficulty. Particular problems arise (a) when 'hypothetical' relationships are assumed in the absence of good data and (b) when the linearity of dose-response relationships is presumed to extrapolate from effects at high concentrations to lower ambient concentrations. The evidence for nutritional effects of low levels of SO//2 and NO//x suggests that for some gases at least, there should be a threshold below which no detrimental effects occur.