the negative effect of metals on enzymatic activities might have been masked in our study by the positive effect of the sewage sludge
in addition, a metal fraction might be adsorbed on the organic colloids added with the sludge.
the rapid decomposition of organic matter which occurs after the application of composts to soil, increases the proportion of available for plant uptake, occur in organic matter and soil solutions
this would prevent the heavy metal from interacting directly with the active sites of enzymes, thus affecting the enzyme's activity