Atmosphere, pesticide entry

All equipment to be used at the field site should be calibrated at or near the field laboratory or field site prior to the application of the test substance (pesticide product). Most weather equipment will have been calibrated at the manufacturer and can be checked for functionality prior to the worker exposure/re-entry test by comparing weather readings from the nearest airport or National Oceanic and Atmospheric Administration (NOAA) weather reporting station with the weather readings compiled by the portable weather station. Hand-held weather instmments could also be checked with current weather reading from local airports or NOAA facilities. 

Other than aerial application over swamps for mosquito abatement, disulfoton is not known to be used over water. Potential sources of release into surface water include discharge of waste water from disulfoton manufacturing, formulation, and packaging facilities (HSDB 1994). Leaching and runoff from treated fields, pesticide disposal pits, or hazardous waste sites may contaminate both groundwater and surface water with disulfoton. Entry into water can also occur from accidental spills. Small amounts of volatilized disulfoton may be removed from the atmosphere as a result of wet deposition and may enter surface water (Racke 1992). 

Virtually every step within the generalized scheme (Figure 1) for pesticide atmospheric entry, behavior, and fate has been demonstrated with at least a few examples. Developments in sampling-analysis methodology, and its application to selected field treatments, have provided the data upon which present knowledge is primarily based. The best data probably lie in... 

It was established that under certain conditions of pesticide application after certain time periods (sometimes exceeding the re-entry period) products of pesticide degradation can enter the woridng zone atmosphere. The toxicity of these products was often higher than the original preparations. The probability of development of toxic mist under specific meteorological conditions was studied [9]. 

In Bhopal, MIC used to be stored in steel tanks for the manufacture of the carbamate pesticide carbary) (Sevin). The disaster was caused by the entry of water into the MIC-containing lank No. 610. The exothermic reaction between water and MIC converted liquid MIC into vapor, generating enough heal and pressure tt> burst open the vent. MIC vapor was discharged in the atmosphere, and because it was heavier than air it descended on the densely populated areas people were awakened by a choking sensation and eye irritation (Varma, 1986). 

Pesticides are applied at rates that can exceed 2 billion kilograms each year in the United States (/). Based on their physicochemical properties, it should be expected that a considerable portion of diis total amount can directly enter the atmosphere. Besides the direct entry into the air at application, post-application... 

CMorinated pesticides enter the atmosphere primarily through spray drift during application, wind-blown dusts, and volatilization from treated surfaces. Heavy use of chlorinated pesticides generally means that spray drift is the most important means of entry to the atmosphere. In general, application by airplane results in more drift than application by ground equipment, and dusts drift more than sprays. For example, ZDDT particles measuring 2 /rni in diameter drifted about 35 km compared to 70 m for 50 jum droplets (Spencer, 1975). Wind-blown dusts are the most important source of entry to the atmosphere in areas where the use of chlorinated pesticides is either limited or curtailed. The dust source category will continue to contribute substantially to the world-wide redistribution of pesticides, particularly DDT and its derivatives, for many years to come. This partially accounts for the presence of detectable levels of pesticides in the sediments of remote Arctic lakes. 

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