Effects of cadmium and zinc on microbial activity in soil; influence of clay minerals. Part I: Metals added individually

Abstract

Investigations were conducted to determine the effects of Cd and Zn on carbon mineralization and the mycoflora, in glucose supplemented soils and to determine the mediating influence of clay minerals on metal toxicity. Soil amended with either 9% kaolinite (K), 9% montmorillonite (M), or not amended (C) was treated with 0, 100, or 1,000 ppm cadmium (Cd) or 0, 1,000, 5,000, or 10,000 ppm zinc (Zn) (as the sulfate salt). 5,000 and 10,000 ppm Zn significantly increased the length of the lag period of CO 2 evolution and reduced the amount of carbon mineralized whereas 1,000 ppm Zn or 100 and 1,000 ppm Cd had no significant effect. When subsequent additions of 2,400 and 4,000 ppm Cd and 1% glucose were made after 16 days of incubation to soils pretreated with 100 and 1,000 ppm Cd, respectively, the rate and extent of glucose degradation was decreased more in the clay-amended soils, particularly with M. The addition of 9,000 ppm Zn to soils pretreated with 1,000 ppm Zn had little effect on glucose degradation, but the addition of 10,000 ppm Zn to soils pretreated with 5,000 ppm Zn substantially reduced the amount of carbon mineralized. K and M protected fungi in soil from the toxic effects of 15,000 ppm Zn and 5,000 ppm Cd. However, fungi isolated from Cd-treated K- and M-soils were more sensitive to the effects of Cd added to the growth medium than were those isolated from the Cd-treated C-soil. Fungi isolated from Zn-treated K-soil were also more sensitive to the effects of Zn added to the growth medium than those from Zn-treated C-soil.