Pro-oxidant activity of vitamin C in drinking water ... - Ã bo Akademi

ConclusionsCONCLUSIONSThe main focus of this thesis was to study the pro-oxidant effect of vitamin C (ascorbicacid) in metal contaminated drinking water. The main findings of this study are:1. Bicarbonate and pH regulate the pro-oxidant activity of ascorbic acid in drinkingwater contaminated with trace amounts of copper. Ascorbic acid will induce hydroxylradicals in copper-contaminated drinking water buffered with high amounts of bicarbonate(II), and hydrogen peroxide in weakly bicarbonate-buffered drinking water (IV). Of theother metals tested (iron, manganese, cadmium, nickel, cobalt, aluminium, magnesium,calcium or zinc), none could significantly support ascorbic acid induced hydroxyl radicalsor hydrogen peroxide formation in drinking water (IV, V).Ascorbic acid and copper induced hydroxyl radical formation and hydrogen peroxideaccumulation could be important modulators of various molecules. The pro-oxidantactivity of vitamin C in the presence of copper ions as observed in the bicarbonatebuffereddrinking water might be linked to the reported occurrence of benzene inbeverages supplemented with vitamin C and benzoic acid. 202 Furthermore, the vitaminC/Cu 2+ -induced hydrogen peroxide formation during acidic conditions, as demonstrated inpoorly buffered drinking water, could be of importance in host defence against bacterialinfections. On the other hand, excessive production of hydrogen peroxide could induceincreased oxidative stress on tissues, or alternatively be involved in cell activation.2. Iron displays an inhibitory effect on the ascorbic acid/copper induced hydroxylradical formation, as well as on hydrogen peroxide accumulation in drinking water (IV, V).Paper V demonstrates that ascorbic acid-derived oxalic acid is necessary for the inhibitoryeffect of iron on ascorbic acid/Cu 2+ -induced hydrogen peroxide accumulation.Bicarbonate and iron might function as important regulators of copper/reductant-inducedhydroxyl radical/hydrogen peroxide formation and copper mediated tissue damage. Theiron/oxalic acid induced inhibition of hydrogen peroxide formation as demonstrated herein drinking water might also be linked to the protective effect of iron against ascorbic acid(vitamin C) and copper-induced cell toxicity in cell cultures. Our results in paper IV and Valso indicate that complete removal of iron from the raw water of the water plants can tosome extent increase the redox activity of copper, and the formation of ROS in drinkingwater.47