It is believed that an
additive action or synergistic effect between Cu and
Zn could have been responsible for the enhanced
toxicity of Cu:Zn in the soil sample examined. Synergism
was reported by Lighthart and Bond
responsible for the inhibition of soil
– litter respiration by a combination of Se and Cd. Also,
according to Chander and Brookes (1993),additive
effect in a combination of Zn and Cu caused larger
decrease in soil microbial biomass compared to the sum
of either metals singly.