Purified versatile peroxidase (VP) from the white rot fungus Bjerkandera adusta UAMH 8258 was used to study the transformation of several pesticides, including some as highly halogenated as the wood preservative pentachlorophenol (PCP). From the 13 pesticides assayed. dichlorophen, bromoxynil and PCP were transformed by VP in the presence and in the absence of manganese(H). For all the pesticides transformed, the activity was higher in the absence of Mn(II) at pH 3 than in the presence of Mn(II) at pH 4. Catalytic constants (k(cat)) in the absence of Mn(II) at pH 4 were 194 and 409 min(-1) for dichlorophen and bromoxynil, respectively. The K-M values were 32 and 31 muM for the pesticides and 26 and 19 muM for the hydrogen peroxide, respectively. Analysis of reaction products by GC-MS showed the presence of 2,3,5,6-tetrachloroquinone among the products from pentachlorophenol oxidation. while the main product from dichlorophen was 4-chlorophenol-2,2'-methylenequinone. Several polymers were obtained from the peroxidase oxidation of bromoxynil. In all cases. we found dehalogenation reactions mediated by the versatile peroxidase. The importance and potential uses of the enzymatic transformation of these halogenated toxic compounds is discussed. (C) 2004 Elsevier Inc. All rights reserved.