Toxaphene Volatilization from a Mature Cotton Canopy1

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Abstract
To fully understand the pollution potential of pesticides more knowledge concerning the mechanisms and rates of pesticide exchange between environmental compartments is needed. The momentum balance method was used in a field study to characterize toxaphene (chlorinated camphene) volatilization from cotton (Gossypium hirsutum L.) plants for 5 days following aerial application at 2.24 kg/ha. The momentum balance method uses accurate measurements of windspeed profiles, temperature gradients, and atmospheric pesticide concentration gradients above the plant canopy to provide data for calculating vertical flux densities of pesticides. The calculated volatile loss for the 5‐day period was 358 g/ha, which represented a loss of 26% of the toxaphene present in the canopy. Although typical volatile loss patterns suggested that flux densities were highest during midafternoon, there was evidence that volatility rates were also high when leaves were drying after heavy dew or light rain. Based on comparisons of the amounts of toxaphene transported from nearby cotton fields via surface runoff in earlier studies and the amounts lost by volatilization in this study, it was concluded that aerial transport is the pathway of greater loss.