LEACHING POTENTIALS OF 4 PESTICIDES USED FOR BANANAS IN THE CANARY-ISLANDS

Nonpoint source (NPS) groundwater contamination, that is related to th e regional-scale use of agrochemicals, is a major environmental proble m. This paper reports preliminary assessments of groundwater vulnerabi lity due to pesticide leaching for areas of banana (Musa balbisiana) s ilviculture for the Canary Island of Tenerife using simple indites. Es timates of contamination potential were made for the four most commonl y used pesticides using the retardation factor (RP) and the attenuatio n factor (AF). Soil, crop, and recharge maps for Tenerife were overlai d using a geographic information system (GIS) approach, Soil depth, th e type of irrigation, soil-pH dependent chemical half-lives, and the m ethod of landcover characterization were each assessed relative to the ir individual and cumulative impacts on assessing regional-scale NPS g roundwater vulnerability. The order of leaching potential, in terms of greatest mobility, for the four chemicals was found to be: (i) carbuf uran 2,2-dimethyl-7-benzofluranyl-n-methanylcarbamate), (ii) ethoproph os (O-ethyl-S,S-di-n-propyl-phosphoradithioate), (iii) fenamiphos (eth yl -(methylthio)-phenyl1-methylethylphosphoramidate), and (iv) oxamyl amino)-N-[[(methylamino)carbony]oxy]-2-oxoethanimi dothioate). The wor st-case scenario for groundwater contamination in Tenerife, related to banana silviculture, was found to be carbofuran with furrow irrigatio n. The best pesticide and irrigation combination to minimize potential groundwater contamination, related to the cultivation of bananas in T enerife, was oxamyl and drip irrigation. The regional-scale NPS ground water vulnerability assessments presented were for Tenerife are the fi rst to be made for the island and will he useful for future chemical r egulation decisions and for targeting critical areas that may require remediation.