Submitted to: Journal of Environmental Quality
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/11/1995
Publication Date: N/A
Citation: N/A Interpretive Summary: Methyl bromide has been used for decades as a soil fumigant for the control of nematodes, weeds and fungi and has recently come under scrutiny as a chemical which depletes stratospheric ozone. Restricting the use of methyl bromide will cause substantial adverse economic impacts on the agricultural community. Recent estimates of total methyl bromide mass lost to the atmosphere have suggested that nearly the entire applied amoun escapes the soil. This information was based on flux-chamber measurements. Since this seems unlikely, a research project was initiated to accurately determine the amount of methyl bromide entering the atmosphere. To accomplish this, a field experiment was conducted to measure the methyl bromide flux along with degradation in the soil. This enables a mass balance to be obtained and allows comparison of the chamber flux to other flux estimation methods. Our results indicate that the diffusion through the polyethylene film depends strongly on the temperature differential inside and outside the chamber. When chambers are used to measure methyl bromide volatilization from fields covered with a polyurethane tarpaulin, the volatilization rate should be adjusted for the effects of temperature.
Technical Abstract: An experiment was conducted to investigate the environmental fate and transport of methyl bromide in agricultural systems. Part of this experiment involved the use of three flow-through chambers to estimate the methyl bromide flux through a sheet of polyethylene plastic covering the field. Using the chamber data, the total mass lost to the atmosphere was estimated to be 96% of the applied mass and the results were highly variable between chambers (i.e., standard deviation of 297 kg or 35%). The temperature inside the chamber was found to be much higher than the air temperature outside and was highly correlated with the diurnal variation in incoming solar radiation. The diffusion through polyethylene film depends strongly on the temperature, a method was developed to correct the chamber flux data for enhanced diffusion caused by increases in temperature inside the chamber. After correcting for temperature, the estimated total methyl bromide emission was reduced to approximately 58% (20% standard deviation) of the applied amount, which is about 5% less than that measured using other methods. When chambers are used to measure methyl bromide volatilization from fields covered with a sheet of polyurethane plastic, the effects of temperature on the volatilization rate should be considered.