Conditions, spray drift studies

Field studies are required to provide a more reaUstic picture of the dissipation of the parent compound and those degradates determined to be significant. Under field conditions pesticides are exposed simultaneously to the individual dissipation processes that were examined separately in the laboratory studies. Thus, in field studies, some dissipation processes may be altered due to competition and interaction. Requirements for spray drift data were outlined in draft Subdivision R, but the EPA agreed that data generated on a generic basis by an industry consortium could represent the potential for drifting of individual pesticides. 

The sad experience with the conditions at IBT, where multiple studies were run simultaneously in the same room with the concomitant problems of mix-ups of animals and treatment cross-contamination by volatile test substances, have resulted in the requirement of sufficient space to assure the isolation of test systems . Through a sufficient number of rooms or at least sufficiently separable areas, it should become possible to avoid any crosscontaminations or mix-ups of projects, tests or treatments. Also the positioning of test systems used in field studies requires an appropriate degree of separation, as it is specified in the GLP Principles ( Test systems used in field studies should be located so as to avoid interference in the study from spray drift and from past usage of pesticides . In the same sense, isolation of individual projects in aquatic toxicity testing should be applied to the extent necessary, to prevent cross-contamination through spray, mist or overflow. 

In this chapter we present an individual-based population model (Metapopulation model for Assessing Spatial and Temporal Effects of Pesticides [MASTEP]). M ASTEP describes the effects on, and recovery of, populations of the water louse Asellus aqua-ticus following exposure to a fast-acting, nonpersistent insecticide caused by spray drift for pond, ditch, and stream scenarios. The model used the spatial and temporal distribution of the exposure in different treatment conditions as an input parameter. A dose-response relation derived from a hypothetical mesocosm study was used to link the exposure with the effects. The modeled landscape was represented as a lattice of 1 x 1 m cells. The model included processes of mortality of A. aquaticus, life history, random walk between cells, density-dependent population regulation, and in the case of the stream scenario, medium-distance drift of A. aquaticus due to flow. All parameter estimates were based on the results of a thorough review of published information on the ecology of A. aquaticus and expert judgment. 

Weather Most of the subjects took a very cautious attitude toward wind conditions. Spraying was not conducted unless the day was calm, and even then one of the workers chose to spray in only one direction to avoid drift. Increasing wind and the threat of rain cut short the spray period of subjects 5 and 6 on the last day of the study. 

---