Production of plants under glass is in many cases regarded as a closed production system, where input and output flow are known and under control. Plant Protection Products (PPP) are also viewed as part of this closed system. A recent Norwegian study reported residues of PPP in waterways downstream from greenhouse operations, thus indicating that leaching from closed systems can be a problem. To be able to develop measurement methods and models that predict leach rates and in order to do something about possible problems, it is important to identify the production activities that could be potential sources of leaching, both as point sources and as diffuse leaching. The objective of the investigation was to produce knowledge on different work site operations that would make it possible to estimate the potential leaching of PPPs to soil and water. A literature survey found limited research activity on these topics, with a few reports on mathematical modelling of leaching. Other, more applied reports, expressed a general view that application technology in the greenhouse industry was old-fashioned, with unnecessary high liquid volume application rates. Data on work operations were collected through interviews and observations in about 30 greenhouse companies, representing modern, Swedish greenhouse production. Statistics reported by the Swedish Chemicals Agency does not allow separation of PPP use between horticultural field and under-glass production, or into horticultural sub-branches. Greenhouse application technology is dominated by handheld equipment, high liquid rates and high pressure spraying. The most important exceptions are a ‘spray robot’ used in vegetables and cold foggers, used in all types of production. Both types imply reduced operator exposure to PPPs. Cold fogging has, furthermore, the advantage of using lower liquid rates. In some production systems, the PPPs are distributed through irrigation systems. The design of the irrigation system has a large impact on how surplus liquid is treated, i.e. recycled or dumped down a drain. In many cases today, recirculation systems are introduced; a system that minimises the losses to the ground. In the report, potential risk situations are described, both regarding point sources and diffuse spreading. Greenhouses have limited areas with biological active soil, which could break down the PPPs; instead greenhouses have inert materials and concrete surfaces with high pH. This influences the speed of the chemical degradation. A summary of the most important risks for polluting soil and water is described, both regarding point sources and diffuse spreading. Situation examples describe risks through point sources, related to handling, measuring, transport of measured out, concentrated PPP, etc. Simultaneously, examples are given on greenhouse operations where these risks are minimised through carefully designed systems, including suitable routines and equipment. The risks in the diffuse spreading are associated with the mixing of PPPs into irrigation systems, in combination with an uncontrolled discharge of surplus water. Recirculation systems provide the optimum closed system practice and ensure a very high level against leaching in production under glass. This type of irrigation is increasing in the industry.
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