Photodegradation of Atrazine in water - Hashem, F.H.Hafez and Wolfram, H.P.Thiemann

Photodegradation experiments of atrazine were carried out under UV light (λ 254 nm, 24h), sunlight (one month, 8h/day), and in the dark conditions in a variety of waters. Residue analysis of this compound in the water samples was determined using high performance liquid chromatography (HPLC). The Photodegradation rate was followed first-order kinetics with different rate constants (k) and high r2 values. The loss of atrazine in the water samples under dark conditions was negligible. Whereas, the Photodegradation of the compound in water was higher after exposure to UV light than that under sunlight conditions. The Photodegradation rate of atrazine in different waters after exposure to either UV light or sunlight decreased in the following order: river water > canal water > distilled water. HPLC analysis showed that there were at least three different photoproducts of atrazine in water extracts after exposure to UV light, while only two photoproducts were detected in the water extracts under sunlight conditions.

INTRODUCTION

The s-triazine herbicides are among the most widely used pesticides. Atrazine, simazine and propazine, as well as the mono-N-dealkylated metabolites have been detected in ground water (EPA, 1990; Isensee et al., 1990; Adams and Thurman, 1991). These compounds are nonvolatile and highly water soluble (usually in acid or base) and are inefficiently recovered from environmental matrices (Nash, 1990). Its widespread use has resulted in the detection of it in rivers, lakes (Goolsby et al., 1993; Tierney et al., 1993), and their sediments (Spalding et al., 1994). Most of atrazine and simazine would be transported in the water phase of runoff; however, some will still be adsorbed to fine clay and silt particles (Ghadiri and Rose 1991). Their concentrations in surface water and groundwaters, when detected, are usually around 100ng litre-1 or less, although levels over 1 μg litre-1 have been reported (SAC Scientific, 1987). In studies using river water, a half-life of approximately one month for atrazine has been measured (Glotfelty et al., 1984). A considerably longer half-life of five months was estimated for atrazine added to lake enclosures (Hamilton et al., 1989). Similar half-lives (nine months) were obtained for simazine in a lake study in America (Jenkins and Buikema, 1990). Degradation of these compounds can occur via biotic and abiotic (hydrolysis and Photodegradation) processes. Generally, hydrolysis and Photodegradation are the major chemical transformation pathways of a pesticide in aqueous solution. Among these, Photodegradation is known to be the important degradation pathway for atrazine and simazine in water under normal conditions (Comber, 1999). Photodegradation experiments have included irradiation in sunlight, at 254nm using a mercury lamp, and at greater than 340nm using a xenon lamp, to mimic natural radiation more closely (Kearney et al., 1984; Pelizzetti et al., 1991). This paper concentrates on the Photodegradation of atrazine in different sources of water under UV light (using a low- pressure Hg lamp at 254 nm), sunlight (wavelength between 300-400 nm), and in the dark conditions.