Pesticide Handling at Farms
The use of pesticides in agriculture is a source of contamination in surface water, groundwater and soil. It is important to identify on-farm practices for pesticide handling and use that pose major risks for contamination. Three critical steps are usually involved (see figure): pouring of pesticide concentrates into the spray tank and their dilution, spraying of pesticides in the field, and management of pesticide residues left on the inside and outside (retained on the outer walls) of the spray tank.
If pesticides are used at the recommended doses and applied using modern techniques according to good farming practices, the risk of environmental contamination from spraying in the fields is small (step 2 in the figure). However, the risk for point source contamination is greater in steps 1 and 3. In step 1 there are small spills but at high pesticide concentrations, since concentrates are handled. Step 3 can contribute larger volumes with lower concentrations from the remaining diluted pesticide in the tank and from washing and consequent dilution of the pesticides retained on the outer walls of the tank.
Illustration: Maria del Pilar Castillo/JTI
Point Source Contamination
Even very small amounts of chemicals can imply a risk of contamination. A few drops of a pesticide concentrate can easily contain 1 gram of the active substance. If these drops form a spot 1 dm2 in area on the ground, the final dose is 1 g/dm2, which is equivalent to 1 ton/ha. Normal pesticide doses for modern products are in the order of kg/ha or g/ha.
Another factor contributing to point source contamination is that the filling of the sprayer is normally done at one specific place at the farm and where the topsoil has been removed and replaced with a layer of gravel and sand.
Degradation and poor absorption capacity of these materials increases the risk of leaching of pesticides. Studies conducted in Denmark, Germany and Sweden was found that these sites are highly contaminated and show that point sources are one of the key causes of pesticide contamination. If filling and storing the sprayer on top of a biobed, this kind of point source contamination can be minimized.