Studies on the Effects of Saline Aerosols of Cooling Tower Origin on Plants

Abstract

A research program was undertaken to develop information that could be used to estimate the risk of adverse effects of saline cooling tower drift on native and cultivated flora in the Indian Point, New York area. Eleven species of woody plants were exposed at 85 % relative humidity to a saline mist with 95% of the particles between 50 and 150 nm in diameter. Three biological factors—stage of development, species, and phenotype—determined the susceptibility of plants to saline aerosols when the occurrence of any lesion on the foliage was used as a measure of response. The effects of stage of development on the incidence and severity of foliar lesions depended upon the kind of plant. In deciduous woody species, the youngest leaves were most susceptible, but in conifers, the year-old needles were most susceptible. Canadian hemlock was the most susceptible species and witch hazel was the least susceptible. Median effective doses for these two species, although undetermined, could be more than 100-fold different (less than 2.4, the lowest used, and greater than 264 ng CI cm-2, respectively). Other species, ranked in decreasing order of susceptibility were: white ash, white flowering dogwood, forsythia, chestnut oak, silk tree, black locust, red maple, eastern white pine, and golden rain free. Phenofypic variation within a species was not so great—within a 10 to 20-fold increase in dose the incidence of injury went from 0 to 100%. Exposures with bush bean showed that the relative humidity (RH) during or after the exposure period affected the incidence of saline induced foliar injury. A change from 50 to 85% RH doubled the effectiveness of the saline mist. It was also found that compared to particles between 50 and 150 jum in diameter, an increase in the fraction of particles above 150 /xm increased the toxicity of the mist.