New results from the Danish Pesticide Leaching Assessment Programme (PLAP) show that the fungicide metalaxyl-M used in the agent Ridomil Gold MZ Pepite has leached into ground water in two test fields where it was used in 2010 to treat potato blight.Metalaxyl-M is a so-called systemic agent and one of the few on the Danish market with a curative effect. The fungicide is quickly assimilated into the potato plant where it inhibits the growth and formation of the potato blight fungus. Most other remedies against potato blight on the market have a mechanical effect where they form a film on plant leaves to protect against the germination and infection of moulds.Metalaxyl-M has in Denmark only been approved for use in potatoes, while in other countries it has also been approved for use on, for example, vines and leafy vegetables.Review of metalaxyl-MThe substances detected in ground water were metalaxyl-M and two of its degradation products, CGA62826 and CGA108906. The parent compound and one of the degradation products were frequently found in ground water and in water from the root zone. Particularly CGA108906 was frequently present in ground water samples and in one field was found in 95 per cent of all analysed ground water samples – often in high concentrations. The Danish Environmental Protection Agency (EPA) is now reviewing its approval.Unique tool for studying pesticides under practical conditions
The assessment programme monitors the leaching of pesticides and their degradation products to ground water under normal agricultural use. The assessment programme consists of five agricultural fields located in different places in Denmark. The fields are sprayed with approved pesticides whereupon the ground water is analysed for their presence.- PLAP is a unique tool for testing the pesticides under practical conditions, says agronomist Preben Olsen from the Department of Agroecology. The five experimental fields cover the most important Danish soil types and climates (especially rainfall). This means that if a substance is leached, we will find out. The method of our sampling also means that we detect the substances before they leach into deeper groundwater.Preben Olsen saysthat in PLAP there is focus on testing newly-registered pesticides with a large user potential as well as long-established remedies that are used in large quantities or on large areas. There is also focus on testing the pesticides for which a high leaching level compared to maximum permitted values was noted in the approval procedure. There is finally also focus on testing pesticides where new information has come to light on degradation products where the risk of leaching is somewhat uncertain.- In this way PLAP is a good supplement to the general evaluation by EPA of the leaching of pesticides to groundwater, concludes Preben Olsen.Re-assessments and bansMonitoring for pesticides has taken place since 1999 and in the most recent monitoring period (2010-2011) 11 pesticides were tested together with a number of degradation products. One of the substances tested was bifenox, commonly used on cereal and rape crops. Its metabolites bifenox acid and nitrofen were subsequently detected in groundwater. The results led to a re-assessment of the product by the EPA and in 2012 it was removed from the shelves in Denmark.Many of the chemicals tested have given no cause for a re-evaluation of approvals, but the EPA has banned some compounds such as metribuzin, terbuthylazin, rimsulfuron and bifenox on the background of, among other things, the assessment programme.