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

Resultsdifferent water samples varied from 0.13 to 0.02 mg/l and the bicarbonate concentrationvaried between 80 and 130 mg/l. The water samples used in the assay did not contain anydetectable iron. Addition of 0.2 mg/l ferric iron to the ascorbic acid supplementedhousehold drinking water samples resulted in a 36 - 45% inhibition in the hydroxyl radicalformation. When the household drinking water samples were supplemented with 0.8 mg/lferric iron the inhibition was even higher, 47 – 60%.5. Ascorbic acid induced hydrogen peroxide accumulation in householddrinking water - interaction between copper, iron and bicarbonate[Paper V]In this study we evaluated whether ascorbic acid can also stimulate hydrogen peroxideformation in Cu 2+ contaminated drinking water. To establish this, we again used Milli-Qwater as a model solvent for drinking water. The results showed that ascorbic acid induces asubstantial increase in the hydrogen peroxide concentration (500 µM) in Milli-Q watersupplemented with 0.1 mg/l of Cu 2+ . This Cu 2+ concentration is 20 times below the amountof copper that is allowed in drinking water in Europe (MCL). Already after 1-hourincubation, almost 300 µM hydrogen peroxide could be detected. On the contrary, ascorbicacid and Fe 3+ induced very low concentrations of hydrogen peroxide (45 µM) after 6 hoursin Milli-Q water. Other metals tested at MCL levels with ascorbic acid (Ca 2+ , Mg 2+ , Zn 2+ ,Mn 2+ , Co 2+ or Al 2+ ) generated between 60 µM and 120 µM of hydrogen peroxide after 6hours.Although Fe 3+ did not induce hydrogen peroxide formation in ascorbic acid supplementedMilli-Q water, the inhibitory effect of iron on hydrogen peroxide formation could beobserved in the ascorbic acid/Cu 2+ supplemented Milli-Q water. The inhibition by 0.2mg/l ferric iron was very weak during the first hour. However, after 2 h incubation, thehydrogen peroxide production stopped, and the concentration started to decline. After 6 hincubation the hydrogen peroxide level had decreased to about 60 µM as compared toaround 500 µM measured in the control sample not containing iron. Other metal ionspecies that might be present in drinking water, Zn 2+ , Co 2+ , Mn 2+ or Al 2+ did not have anyimpact at their MCL levels on the ascorbic acid/Cu 2+ -induced hydrogen peroxideformation. A modest inhibition in hydrogen peroxide formation could be seen when Mg 2+or Ca 2+ were present. However, the concentrations of Mg 2+ and Ca 2+ were 250 and 500fold higher than the concentration of iron used in the assay.37