| Among the most important research priorities identified in tropical ecotoxicology is the need for risk assessment models specific to pesticide fate and toxicity in tropical watersheds. A number of different pesticides are applied in the Sixaola watershed, Costa Rica to produce export-quality plantains and bananas. Following an ecological risk assessment framework, the principal exposure pathways, environmental fate, and biological effect of current-use pesticides are integrated to provide an estimate of ecological risk to aquatic resources in the Sixaola watershed. Risk assessment of pesticide use in this region is essential for the identification of conservation or restoration priority areas, as well as for the development of better land management practices that address regional agriculture, conservation, and public health priorities.; As pesticide application practices have not been previously documented in the Sixaola watershed, the different pesticide application regimes used in banana and plantain production are presented and principal routes of human and ecological exposure are identified. Annual application rates range from less than 3 kg a.i./ha to more than 45 kg a.i./ha, and principal routes of exposure are primarily related to gaps in agrochemical or pest knowledge and the lack of appropriate infrastructure. A study of soil characteristics, in farms representing the range pesticide application regimes in plantain, suggests that floodplain soil properties important for agricultural production and agrochemical fate or transport are primarily driven by clay mineralogy and hydrologic processes. However, these floodplain soils are extremely heterogeneous over both large and small temporal and spatial scales, and present a challenge in estimating pesticide movement to aquatic resources from agricultural areas.; A number of different pesticides were measured in regional aquatic resources using both water grab samples and passive samplers (SPMDs). Field experiments to calibrate SPMD pesticide uptake rates showed that biofouling was not an important factor in SPMD pesticide sequestration over time, although several different stream characteristics may be important in the interpretation of SPMD-derived stream pesticide concentrations. Field-measured pesticide concentrations are integrated with modeled pesticide concentrations, knowledge of soil and water properties, primary routes of exposure, and available toxicity datasets to provide an assessment of risk for aquatic resources in the Sixaola watershed based on the hazard quotient method. However, given the unknown effects of pesticide mixtures and climatic conditions on toxicity, the lack of extensive tropical species toxicity data, and the complex species interactions and dynamic hydrologic regimes present in tropical landscapes, this method may not provide the most protective or conservative approach for risk assessment in tropical environments. |
