PESTICIDE EFFECTS ON THE ACTIVITY OF FREE, IMMOBILIZED AND SOIL INVERTASE

The influence of four pesticides (atrazine, carbaryl, glyphosate and paraquat) on the catalytic behaviour of invertase, either free, immobilized on inorganic and organic soil colloids or in soils, was investigated. Invertase was immobilized on a clean clay (montmorillonite), an organic compound (tannic acid), and on synthetic organo-mineral [Al(OH)(x)-tannate and Al(OH)(x)-tannate-montmorillonite] complexes. Soils with different physico-chemical properties were utilized. The effects of pesticides on invertase performance depended not only on the nature of the pesticide but also on the ''status'' of the enzyme, i.e, if free, immobilized or in soil. Glyphosate and paraquat enhanced the activity of invertase either free or immobilized on montmorillonite and both pesticides behaved as mixed-type non-essential activators. Activity decreases were instead measured for the enzyme immobilized on organic and organo-mineral matrices. Contrasting results (increases, decreases and no effects) were detected for soil invertase. A general inhibition effect was exhibited by methanol on free, immobilized or soil invertase, but the extent of inhibition depended on the enzyme microenvironment. The addition of atrazine and carbaryl caused partial increases of free and immobilized invertase activity, whereas carbaryl further reduced enzymatic activity in some soils.