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September 1996 -10- 963-2128.002 <br /> Stout (1961) suggested that the Cu concentration in plant tissue considered adequate for plant <br /> growth is 6 ppm. Critical plant tissue Cu concentration above which plant growth reduction <br /> may be observed have been suggested by numerous investigators. Leeper (1972) suggested <br /> plant tissue concentrations of 30 ppm for Cu could cause plant growth reduction. Viets and <br /> Lindsay, (1973) and Tiedemann and Lopez (1982) suggested concentrations between >10 to <br /> 40 ppm. Davis, Beckett, and Wollan (1978) concluded that 20 ppm Cu is the upper critical <br /> level (total plant tissue concentration using a concentrated HNO3 digest method) in the leaves <br /> and shoots of spring barley at the five-leaf stage. <br /> Based on the plant tissue samples presented in Table 2 it appears that Cu concentration in <br /> grass grown on biosolid - amended and unamended soils at the Climax Mine are comparable <br /> and within accepted plant tissue Cu concentrations. <br /> ,: Golder Associates <br />