Irrigation with 9.8 mg silver/L is toxic to maize and 4.9 mg/L is toxic to lupines (Cooper and Jolly 1970). There was no significant effect on wheat or maize at 460 mg/kg silver as AgI in sandy or loam soil but 640 mg/kg silver as AgI of soil inhibited germination of Engelmann spruce seeds (Klein 1978). Spraying a AgNO3 solution at 9.5 mg silver/L caused damage to Cattleya orchids (Beyer 1976) and a decrease was noted in the growth rate of bean plants grown in a nutrient solution containing 9 µg silver as AgNO3/L. Silver levels in the sediments or soils which exceed 25 to 50 mg silver/kg may have significant effects on the heterotrophic activities of the microbial flora (Sokol and Klein 1975).