Submitted to: Environmental Science and Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: January 13, 2011
Publication Date: February 14, 2011
Citation: Reichman, R., Rolston, D.E., Yates, S.R., Skaggs, T.H. 2011. Diurnal variation of diazinon volatilization: Soil moisture effects. Environmental Science and Technology. 45(6):2144-2149. Interpretive Summary: Pesticides are a critical component of modern agriculture. Volatilization is one of the principal processes leading to the dispersion of pesticides in the environment. Airborne transport of pesticides poses a risk to persons living near treated fields because many pesticides are considered to be carcinogenic. To protect agricultural production and public health, there is a need for more information on the important processes and mechanisms that affect pesticide fate and transport under typical field conditions. This paper describes a field study to measure herbicide (i.e. diazinon) volatilization after applying to bare soil with differing soil-water contents and to investigate the effect of soil moisture status on herbicide volatilization under typical semi-arid field conditions. Volatilization is a dynamic process affected by many fate and transport mechanisms and prevailing soil and atmospheric conditions. The effect of soil-water content has been shown to play an important role in affecting pesticide sorption and, in turn, volatilization. Further study is needed to refine process models and to develop predictive tools that realistically simulate pesticide volatilization under highly variable soil temperature and moisture conditions. This research will be of value to growers, regulators, consultants and the scientific community.
Technical Abstract: A field study was conducted to measure the effect of soil moisture on diazinon volatilization under typical semi-arid field conditions. The study comprised three experiments performed with differing soil moisture conditions. Over the course of each three day experiment, diurnal changes in volatilization rates were measured along with soil-water contents, and soil temperatures at two depths. In all cases, the initial flux rates were the highest and were correlated with the initial soil moisture content, with wetter soil conditions producing a higher flux rate: 5.6 × 10-4 'g cm-2 min-1 (Experiment 3) > 8.3 ×10-5 'g cm-2 min-1 (Experiment 1) > 2.5 × 10-5 'g cm-2 min-1 (Experiment 2). The decrease in the flux rate during the first day for the wettest soil was relatively smooth and steady while for the dryer soil, the flux rate was relatively consistent (steady?). The volatilization rates observed for wet soil during the first night were about an order of magnitude higher than those observed for dry soil. Around noon of the second day, a daily maximum value was observed in the volatilization rate for wet soil (Experiment 3) while a minimum value was observed for dryer soil (Experiments 1 and 2), resulting a difference of about an order of magnitude. This study demonstrates the importance of soil moisture on emissions of pesticides to the atmosphere.