of the persistence of herbicides. Several authors reported that microbial degradation, in soils or waters, is the main way of glyphosate dissipation (Torstensson, ...
Section JI. Soil Chemistry
DEGRADATION OF HERBICIDES GLYPHOSATE AND GLUFOSINATE IN NATURAL AND DISTILLED WATER F. VEIGA, J.M. ZAPATA, M.L. FERNANDEZ MARCOS, E. ALVAREZ University ofSantiago de Compostela. Dep. Edafología. Escuela Politécnica Superior. 27002 Lugo, Spain. e-mail: qamarisa@lugo. use. es
INTRODUCTION The presence in the environment, particularly in aquatic systems, of herbicides and its metabolites has deserved great attention (Cardozo et al., 1985; Rao et al., 1985; Neary et al., 1993). Herbicides applied to soils may, under propitious circumstances, reach aquatic environments if they are not degraded during its movement through the soil (Arnold and Briggs, 1990). In these media pesticides, particularly the water-soluble ones, may constitute a toxicity risk for fish or phytoplankton as well as an obstacle for potabilisation. The persistence of a pesticide in an aquatic system depends on the pesticide nature, climatic conditions and physico-chemical characteristics of the water. The present paper evaluates the persistence of two water-soluble herbicides, glyphosate and glufosinate, in three different kinds of water: distilled water, well water and river water. MA TERIALS AND METHODS Three different types of water were used for the experiment: distilled water; well water, sampled in the province of Lugo, Spain, from a 55-m deep well; water from the river Miño in Outeiro de Rei, clase to the town of Lugo, Spain. Well and river water were sampled in September 1998. Sorne general properties of well and river water are presented below: River water
Well water
pH
7,38
6,49
Electrical conductivity, dS m- 1
0,102
0,092
Dry residue, mg g- 1
0,128
0,133
Dissolved organic carbon, meq C 1
0,572
0,325
Each water was spiked with herbicide at two different concentrations, 0.5 and 1.8 mg L- 1 for glyphosate and 0.5 and 1.5 mg L- 1 for glufosinate. Duplicates were prepared of each solution, making a total of 24 solutions. Solutions were kept for 3 months at controlled light and temperature conditions (16 hrs per day, sunlight, 22ºC; 8 hrs per day, dark, 16ºC); well water solutions were kept dark all time. At prefixed times, aliquots were sampled from each solution, concentrated by lyophilisation, filtered (0.45
