Atmospheric concentrations pesticide chemicals

In the United States, about 80% of the 23 million kg of technical PCP produced annually — or about 46% of worldwide production — is used mainly for wood preservation, especially utility poles (Pignatello etal. 1983 Kinzell etal. 1985 Zischke etal. 1985 Choudhury etal. 1986 Mikesell and Boyd 1986 USPHS 1994). It is the third most heavily used pesticide, preceded only by the herbicides atrazine and alachlor (Kinzell et al. 1981). Pentachlorophenol is a restricted-use pesticide and is no longer available for home use (USPHS 1994). Before it became a restricted-use pesticide, annual environmental releases of PCP from production and use were 0.6 million kg to the atmosphere from wood preservation plants and cooling towers, 0.9 million kg to land from wood preservation use, and 17,000 kg to aquatic ecosystems in runoff waters of wood treatment plants (USPHS 1994). There are about 470 wood preservative facilities in the United States, scattered among 45 states. They are concentrated in the South, Southeast, and Northwest — presumably due to the availability of preferred timber species in those regions (Cirelli 1978). Livestock facilities are often constructed of wood treated with technical PCP about 50% of all dairy farms in Michigan used PCP-treated wood in the construction of various components of livestock facilities (Kinzell et al. 1985). The chemical is usually applied to wood products after dilution to 5% with solvents such as mineral spirits, No. 2 fuel oil, or kerosene. More than 98% of all wood processed is treated with preservative under pressure about 0.23 kg of PCP is needed to preserve 1 cubic foot of wood (Cirelli 1978). Lumber treated with PCP retains its natural appearance, has little or no odor, and can be painted as readily as natural wood (Wood et al. 1983). 

Due to the movement of the pesticides to the bed surface, air samples were taken to determine any volatilization and subsequent concentration In the air along the berm on the downwind side of the bed. In most Instances, the top of the berm was only about 12 vertical Inches above the bed surface. Spencer and Farmer ( ) have reviewed the literature on the transfer of pesticides Into the atmosphere. Even though pesticide volatility Is related to vapor pressure of the chemical, there are many factors Influencing the effective vapor pressure from soil and water surfaces. 

The simulations of volatilization were conducted using the complete model described by Jury et al. (33) where each chemical is present in the soil at a uniform concentration of 1 kg/ha to a depth, L, in the soil and is allowed to volatilize through a stagnant air boundary layer for a specified time period in the presence or absence of water evaporation. The standard conditions or common properties assumed in the simulations are the same as those indicated in Jury et al. (35, 36), i.e., air diffusion coefficient, 0.43 m /d water diffusion coefficient, 4.3 X 10-3 m /d atmospheric relative humidity, 50% temperature, 25°C soil porosity, 50% bulk density, 1.35 g/cm3 soil water content, 0.30 organic carbon fraction, 0.0125 amount of pesticide in soil, 1 kg/ha depth in soil, 1 or 10 cm water evaporation rate, 0, 0.25, or 0.50 cm/d. 

---