Submitted to: American Chemical Society Abstracts
Publication Type: Abstract only
Publication Acceptance Date: 6/28/2005
Publication Date: 8/28/2005
Citation: Goel, A., Mcconnell, L.L., Torrents, A. 2005. Modeling the variability in aerial concentration of atrazine, endosulfan and chlorothalonil at a rural location on the delmarva peninsula [abstract]. American Chemical Society 230th National Meeting. Paper No. 71, P. 67. Interpretive Summary:
Technical Abstract: Weekly air samples (n=129, 2000-2003) were collected at a rural location on the Delmarva Peninsula, to investigate temporal trends in the atmospheric concentrations of current use pesticides in this predominantly agricultural region. Atrazine was detected in 80% of the samples followed by a-endosulfan and chlorothalonil in 97% each. Pesticide concentrations exhibited a log-normal distribution, and the median concentrations ranged from 75 pg/m3 for a-endosulfan to 700 pg/m3 for chlorothalonil. A multiple linear regression model that incorporates temperature and time explains 32-43% of the variability in concentrations. The addition of an agricultural cycle (approximated by a Lorentzian function) to the model improved predictions by up to 7%, especially for a-endosulfan. Wind speed and wind direction did not have a statistically significant influence on concentrations at our site. The model shows that the agricultural cycle is centered in April for atrazine and July for the other two pesticides, which is commensurate with local practices. The calculated heats of phase transition (atrazine: 29±9.6 kJ/mol, a-endosulfan: 43±15 kJ/mol and chlorothalonil: 46±12 kJ/mol) are much lower than the heats of vaporization for these compounds. This suggests that vaporization from soil surfaces is not the controlling factor in their atmospheric presence. The relative persistence of the pesticides is reflected in their atmospheric half-lives. Atrazine has the shortest half life (1.2±0.2 yr) followed by a-endosulfan (1.4±0.2 yr). Chlorothalonil concentrations did not show a statistically significant dependence on time. Results indicate that temperature and application cycle are the main drivers for the occurrence of current use pesticides in the atmosphere of the Delmarva Peninsula. The study highlights the importance of incorporating the agricultural cycle while interpreting data for pesticides, especially for rural locations.