F. van den Berg

Emission of pesticides into the air

During and after the application of a pesticide in agriculture, a substantial fraction of the dosage may enter the atmosphere and be transported over varying distances downwind of the target. The rate and extent of the emission during application, predominantly as spray particle drift, depends primarily on the application method (equipment and technique), the formulation and environmental conditions, whereas the emission after application depends primarily on the properties of the pesticide, soils, crops and environmental conditions. The fraction of the dosage that misses the target area may be high in some cases and more experimental data on this loss term are needed for various application types and weather conditions. Such data are necessary to test spray drift models, and for further model development and verification as well. Following application, the emission of soil fumigants and soil incorporated pesticides into the air can be measured and computed with reasonable accuracy, but further model development is needed to improve the reliability of the model predictions. For soil surface applied pesticides reliable measurement methods are available, but there is not yet a reliable model. Further model development is required which must be verified by field experiments. Few data are available on pesticide volatilization from plants and more field experiments are also needed to study the fate processes on the plants. Once this information is available, a model needs to be developed to predict the volatilization of pesticides from plants, which, again, should be verified with field measurements. For regional emission estimates, a link between data on the temporal and spatial pesticide use and a geographical information system for crops and soils with their characteristics is needed.

Measured and computed concentrations of 1,3-dichloropropene and methyl isothiocyanate in air in a region with intensive use of soil fumigants

A sampling programme was set up to measure 1,3-dichloropropene and methyl isothiocyanate in air in a region with intensive agricultural use of these soil fumigants. In two consecutive autumns, 6-hour air samples were taken at two locations in that region with charcoal tubes using automatic samplers. Most (81%) of the 6-hour concentrations of 1,3-dichloropropene measured in both years were below 3.2 μg m−3 and a few percent could not be measured with a detection limit of around 0.3 μg m−3. Only 4% of the 6-hour concentrations exceeded 10 μg m−3, almost all of which were measured at a location where a field just upwind of the measuring site had been treated. For methyl isothiocyanate, 73% of the 6-hour concentrations of both years could not be measured with a detection limit in the two years of 1 and 2 μg m−3, respectively. A small fraction (3%) of the concentrations were in the range of 3.2 to 10 μg m−3 and only 1% exceeded 10 μg m−3.The rates of emission of 1,3-dichloropropene and methyl isothiocyanate into air were estimated for weeks with many applications in the region studied. Using the PAL model, the concentration of fumigant in air at a receptor site was computed for representative fumigations at different upwind positions. The computed concentrations in air ranged up to 9.9 μg m−3 for 1,3-dichloropropene and up to 2.5 μg m−3 for methyl isothiocyanate.

Sampling and analysis of the soil fumigants 1,3-dichloropropene and methyl isothiocyanate in the air

Methods of sampling and analysis have been developed to measure concentrations of the soil fumigants 1,3-dichloropropene and methyl isothiocyanate (formed from metham-sodium) in air. We tested these methods under laboratory and field conditions. Air samples were taken with glass tubes containing charcoal as adsorbent. The charcoal was extracted with acetone and subsamples of the extracts were injected into a gas Chromatograph with a capillary column. 1,3-dichloropropene was determined by an electron capture (EC) detector and methyl isothiocyanate by a nitrogen-phosphorus (NP) detector. Concentrations of these fumigants in 40 L of air as low as 0.2 μg m−3 and 1.0 μg m−3, respectively, could be determined. A study on the influence of storage temperature and time on the recovery from charcoal showed that charcoal tubes can be stored for up to 4 d at −20 °C. A test program on the breakthrough of the charcoal tubes when sampling at different flow rates and air humidity revealed no significant breakthrough from the first to the second (check) tube. Similar results were obtained from sampling the air during fumigation of the soil in a greenhouse and in two fields.

The use of atmospheric dispersion models in risk assessment decision support systems for pesticides

In the evaluation of potentially adverse effects oforganic chemicals such as pesticides on theenvironment the atmosphere may play an important role.After its release to the atmosphere the chemical willbe transported/dispersed in the atmosphere and finallyit will be removed either by atmospheric-chemicaldestruction or by deposition to the underlying soil orsurface water. In a risk assessment decision supportsystem both ambient concentrations and depositionfluxes must be known to evaluate the risk of directexposure (inhalation) or the risk of soil and watercontamination caused by deposition. This paperdiscusses the use of atmospheric dispersion models insuch risk assessment decision support systems.

An improved soil organic matter map for GeoPEARL_NL: Model description of version 4.4.4 and consequence for the Dutch decision tree on leaching to groundwater

GeoPEARL_NL is used as a higher tier instrument in the leaching assessment of plant protection products in the Netherlands. Because the soil organic matter contents in arable soils in the current version were too high, a new soil organic matter for the Netherlands was needed.