Fate , Transport , and Effects of Glyphosate on Population Dynamics of Non-Target Organisms in Agricultural Settings : A Simulation Study

132 Abstract— Agriculture is the backbone of many countries. This sector has been challenged by the increasing number of pests including weeds. Chemicals such as herbicides are therefore used for weed control. One of such herbicides is glyphosate. The use of herbicides has however been associated with the population decline of non-target organisms like frogs. In this study, fate, transport, and effects of glyphosate on population dynamics of frogs (Crinia insignifera) were simulated using an object-oriented model known as PestTox. Two scenarios were simulated; the agricultural field and the receiving water body (stream or pond) were separated by buffer zones of 30 m and 0 m. The simulation was done using weather conditions of Pathumthani province (Thailand) for the year 2012. Results show that if the field is not surrounded by a buffer zone of at least 30 m, spray drifts and runoffs could transfer glyphosate off the field edge to the receiving waterbody, potentially killing all tadpoles only if glyphosate concentrations are sufficiently high. Results indicate that buffer zones should be used around the fields to reduce spray drifts and runoffs which in turn could help to maintain the healthy population of frogs and other non-target organisms. This study has potential limitations. First, the study used secondary data from various sources. Second, numerous processes are based on analytical expressions/regressions from various pedoclimatical contexts. These may have influenced model estimates. However, the findings may be of interest to those involved in pesticide registration and monitoring.