Laccase catalyzes the oxidation and polymerization of aromatic compounds in the presence of molecular oxygen. Four soluble compounds were evaluated as additives to maintain enzyme stability and enhance substrate conversion for environmental applications: namely, polyvinyl alcohol, Ficoll, polyethylene glycol (PEG), and alkyl betaine. All additives enhanced the transformation of bisphenol A (BPA) to similar degrees when present in sufficient amounts, but PEG was selected as the best alternative. Optimal preservation of enzyme activity and enhanced conversion of 120 mu M BPA were achieved with 5 mg/L of PEG with a molecular weight of 3350. PEG did not enhance the kinetics of the reaction between laccase and BPA. Linear relationships were found between the initial concentration of BPA and the optimum doses of laccase and PEG required for greater than 95% conversion. None of the additives enhanced substrate conversion in the presence of cyanide and fluoride, which inhibit the oxidation of BPA by laccase. The laccase-catalyzed oxidation of BPA resulted in a significant decrease in Microtox toxicity of the aqueous solution, but the use of PEG during treatment resulted in a higher residual toxicity. Therefore. even though PEG clearly enhanced BPA oxidation by laccase, the higher residual toxicity might restrict the practical applications of PEG. (c) 2005 Elsevier Ltd. All rights reserved.