Pesticides may be released to farmyard surfaces as a result of spillages, leakages and the decontamination of tractors and sprayers, (Ramwell et al., 2004). Recent studies have demonstrated that residues on the yard surface may subsequently be washed off to surface waters and that losses from the farmyard can contribute a significant proportion of the pesticide load being released to surface waters (Mason et al., 1999). Such ‘point source’ releases can be minimised by modifying handling practices in order to minimise losses. However, it is inevitable that some releases will occur. Additional treatment methodologies are, therefore, required to reduce these releases. These treatments would supplement good handling practices that reduce inputs to aquatic systems. These methodologies need to be cheap to use and require low labour and time inputs. One possible approach is to use a biobed to intercept and treat contaminated runoff from the farmyard and/or drips and spillages arising during the filling process. Recent laboratory and field scale experiments have indicated that biobeds are capable of degrading a range of active substances when applied repeatedly at high concentration, often as part of a complex mixture (Fogg et al., 2003a, 2003b). Studies at the semi-field scale in both lined and unlined biobeds showed that water management is crucial in terms of both performance and construction costs (Fogg et al., 2004a) and that, by manipulating biobed depth and hydraulic inputs, unlined biobeds were able to achieve the required level of performance (Fogg et al., 2004b). Furthermore, when different topsoils were used in the preparation of the biomix, there was no significant difference in terms of degradation and leaching potential from the biobed (Fogg et al., 2004c), indicating that the technology should be easily transferable from one geographical location to another. A number of biobeds systems have subsequently been constructed at the field scale and have been operational since April 2002. During the first 12 months of operation, all of the systems effectively retained and/or degraded the applied pesticides, suggesting that biobeds have the potential to reduce surface water pollution arising from concrete farmyards. Limited monitoring of the `offset` biobeds system has continued subsequently.
Biobeds appear to offer a system that can significantly reduce surface water pollution arising from concrete farmyards and, therefore, contribute to achieving DEFRA policy aim of reducing pollution from both point and diffuse sources. In May 2006 the Agricultural Waste Regulations came into force, requiring any new biobed system to apply for a waste management license. However, in May 2007 an exemption was granted allowing the disposal of dilute pesticide washings into lined biobed systems. Based on the existing knowledge the exemption has introduced a number of key provisions designed to ensure that any lined biobed is constructed, maintained and operated in a manner that will ensure that the pesticide washings are treated appropriately and that the activity does not cause harm to groundwater and or surface waters. However, a number of important issues remain unanswered, in particular the long-term performance and management requirements of the technology. These additional data are required to demonstrate the sustainability of the biobed system. These additional studies are required so that any potential problems can be identified under
controlled conditions and appropriate advice and guidance given to the farming community as soon as possible and prior to the widespread uptake of the technology.