Andersen, H.V., Bossi, R., Jensen, N.O., Sørensen, P.B., spliid, N.H. & Jensen, P.K. 2006. NERI Report No. 587, 98 pp.

 

Summary

Pesticides are introduced to the atmosphere during application though spray drift and after application by volatilization. Depending on degradation rate and physical chemical properties of the pesticide, the compound is transported various distances, before it is deposited again. This report describes measurements of post application volatilization of pesticides from soil and plants. Further, results on dry deposition of pesticides nearby the sprayed field, during and after application are described. One of the purposes of the experiments was to produce data for validation of a model describing volatilization. The model and its validation are reported separately.

Two field experiments have been performed. The first field experiment was carried out in September 2002 on bare soil and the second field experiment was carried out in May 2003 on soil covered with plants. A mixture containing five pesticides (pirimicarb, ethofumesate, propachlor, pyrimethanil and mecoprop-P) was applied. The pesticides have been chosen to cover a wide range of the physical-chemical properties vapor pressure, water solubility and adsorption to organic matter.

The volatilization of pesticides has been estimated in two ways. Volatilization was determined by analyzing the loss of compound from different exposed surfaces. The method is influenced by other losses such as degradation and therefore, the method is not necessarily specific. The volatilization was also determined by a mass balance method. The method estimates the emission rate on the basis of measurements of horizontal fluxes across a perpendicular plane downwind the source. The horizontal flux is obtained by measuring pesticide concentrations in the air and wind speed at different heights above the soil surface. Sampling of airborne pesticides has been done during seven days after application.

The results from the mass balance method showed, that the volatilization from bare soil was low and partly governed by the adsorption of pesticide to the soil, which is influenced by the moisture content of the topsoil. The maximum flux was determined for propachlor the first hour after application. The flux was 3,6 mg propachlor m-2 hour-1, corresponding to a volatilization of 1% of the sprayed amount. The accumulated amount of pesticide volatilized with in the first 24 hour after application amounted 0,1-8% of the dose of the different pesticides. After one week the accumulated volatilization of the pesticides was 0,1-10% of the dose. The size distribution of the fluxes, relative to the dose, related to physical-chemical properties of the pesticides.

Volatilization from soil covered with plants revealed higher fluxes than from bare soil. The results obtained by the mass balance method showed a maximum flux of 5,5-6,5 mg m-2 hour-1 for propachlor for the first nine hours after application. This amounts 16% of the applied dose. Within the first 24 hours 2-18% of the applied dose of the different pesticides volatilized. Within the first week the accumulated volatilization amounted 5-28% of the applied dose of the different compounds. The fluxes related to meteorological conditions, i.e. increased fluxes followed increased turbulence, heat flux etc. The potential for volatilization from plants seemed affected by transformation/uptake of the pesticides. The amount of volatilization of the pesticides, relative to the dose of treatment, related to their physical-chemical properties.

Volatilization was also determined by analyzing a time series of trays with glass and soil and plants exposed to application and sampled at different times after application. The different pesticides disappeared from the exposed surfaces at a rate comparable to the size of their vapour pressure, although pirimicarb disappeared faster than volatilization could explain, probably due to degradation. 

The deposition of pesticides on soil and plants was investigated by placing trays at increasing distance outside the sprayed zone. The deposition of spray drift five meters from the sprayed area was up to 0,26% of the dose applied. The deposition of post application volatilized pesticide was up to 0,34% of the applied dose and related to the pesticide properties.

Full report in pdf-format (1,100 kB).