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A survey of on the incidence of dental diseases and the distribution of fluoride in drinking water wells in Sri Lanka, confirms that a distinct causal relationship exists and is clearly geographically related. A similar study on the incidence of total cancer in Sri Lanka in relation to environmental factors such as rainfall, concentration of total dissolved ions, hardness of drinking well water, etc. showed an association resting entirely upon correlation.

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Wolters Kluwer - United States of America

Reduction in soybean yield after exposure to ozone and sulfur dioxide using a linear gradient exposure technique.

1982

Reich P.B. | Amundson R.G. | Lassoie J.P.

A linear gradient field exposure system was modified from one originally described by Shinn et al. (1977) and used to expose field grown soybeans (Glycine max cv Hark) to a concentration gradient of a mixture of two gaseous pollutants: SO(,2) and O(,3). Since this technique does not use enclosures, study plants experienced near ambient fluctuations in environmental conditions, including wind, and hence were exposed to widely fluctuating pollutant concentrations. Plants in the gradient system were exposed to both pollutants for 57 h on 12 days during the pod-filling period (31 August-17 September). Mean concentrations during the 57 h of exposure at the 'high' end of the gradient were 0.16 and 0.06 mu-l/l (ppm) SO(,2) and O(,3), respectively, with 10 h at greater than 0.25 and 0.10 mu-l/l h SO(,2) and O(,3), respectively. Total doses for these plants were estimated to be 9.0 and 3.5 mu-l/l. h SO(,2) and O(,3), respectively. Comparison with plants exposed to ambient air indicated that exposure to SO(,2) and O(,3) reduced total yield per plant and dry mass per bean by as much as 36 and 15%, respectively. Since concurrent exposure to a much higher dosage of SO(,2) alone (20.2 mu-l. h) was observed in a separate experiment to have no significant effect on yield, O(,3), although present at moderately low levels, was probably responsible (alone or synergistically with SO(,2)) for the greatest reduction in seed size and yield.

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Wolters Kluwer - United States of America