Free radicals in the aqueous environment

Full text: The chemistry of the degradation of organic herbicides and fungicides in natural systems is important in determining operationally important parameters such as withholding times before planting or consumption. Disappearance rates in the field are frequently many time larger than expected from reactions such as hydrolysis arid photochemical- and radical-initiated reactions are frequently cited as causes of the degradation reactions. Reactions of OH and O2- radicals and secondary radicals derived from these are increasingly postulated as being important in many aqueous environmental reactions. Free radical reactions may contribute to the degradation of organic pesticides and are directly implicated in the use of radical generating systems such as Fenton's Reagent or hydrogen peroxide in the removal of chlorinated organic chemicals from drinking water. Natural sources of these radicals in aqueous systems are predominantly photochemical reactions or reactions initiated by transition metal ions. Hydrogen peroxide is present in many aqueous environments in relatively high concentrations and we are attempting to establish the presence of superoxide radicals in natural systems. The measurement of stationary state concentrations of free radicals as low as 10-15 M is a challenge to analytical and free radical chemists. Long term scavenging studies are difficult and generally non-specific. Current ideas will be reviewed and our approach to the measurement of superoxide in natural systems will be outlined