Cornelese, A.A.

Linden, A.M.A., van der

Ludeking, D.J.W.

Os, E.A., van

Vermeulen, T.

Wipfler, E.L.

English

Name not available

Emissions of plant protection products to surface water from soilless greenhouse cropping systems

Wageningen Yield 

Emissions of plant protection products 
to surface water from soilless greenhouse 
cropping systems
VERMEULEN T.1, VAN DER LINDEN A.M.A.2, VAN OS E.A.1 , CORNELESE A.A.3 , LUDEKING D.J.W.1, 
WIPFLER E.L.4
1 - Wageningen UR Greenhouse Horticulture, P.O. Box 644, 6700 AP, Wageningen, the Netherlands 
2 - RIVM, PO Box 1, 3720 BA Bilthoven, the Netherlands
3 - Ctgb, PO Box 217, 6700 AE Wageningen, the Netherlands
4 - Wageningen UR Alterra P.O. Box 47, 6700 AA Wageningen, the Netherlands
E-mail erik.vanos@wur.nl
The risk of emission from soilless cropping systems to surface water is not, or only marginally included in the current evaluation 
for pesticide authorisation in Europe. However, data from Dutch water boards indicate that the emission of plant protection 
products (PPPs) and biocides from glasshouse horticulture to surface water may be higher than assumed in the authorisation 
procedure. In 2008 a Dutch working group started unravelling the emission to surface water with the goal of creating an 
evaluation tool. An evaluation tool consists of an (modelled) approach for determining expected concentrations in surface 
water and a reference scenario per crop i.e. a description of an actual situation including the technical layout of the glasshouse, 
the climatological year and the receiving ditch.
Since data on emissions were not available, the working group analysed the issue of emission through the following steps:
1 Understanding the nature of the emission: Emission from soilless cultivation systems in a covered surrounding are 
expected to follow the water and air flows. This supposition justifies the identification of the routes of water and air leaving 
the system. This working group was interested in the emissions to surface water. Given that re-use of condensation water is 
compulsory in Dutch glasshouses,  leakage will permeate to the surface water at relatively low rates and ventilation was not 
covered by this working group, the discharge of recirculation water and filter cleaning water constitute the most relevant 
flows.
Identification and classification of cropping systems and pesticide application methods: Three types of cropping 
systems were identified, being a drip irrigation system on substrate (for vegatables and flower crops), an ebb/flow system 
(for potplant production) and soil bound production. In terms of application method three systems were distinguished: 
application via the nutrient solution, spray or fogging and spray application on an ebb/flow system. The latter application 
method leads to fluid liquid partially being sprayed directly in the nutrient solution upon flow. 
Identifying the water fluxes in cultivation systems: A model approach was used to quantify the water flows. One 
model was developed for quantifying the water flows describing discharge as a function of sodium accumulation in the 
recirculation water, while filter cleaning water is described as function of the volume of water filtered. A second model 
described substance fate after application, taking into account crop uptake, degradation, sorption (when relevant) leakage, 
evaporation and eventually discharge.
Identification of discharge strategies in current practice and developing a reference strategy: Until 2008 the only 
legal argument for discharge of recirculation water was the accumulation of sodium. However, in practice growers discharge 
recirculation water in case of e.g. irregularities in the nutrient composition of the water – so called un-balance, technical flaws 
in system components, daily flush of the piping system or observed stagnating growth. Since these reasons for discharge 
were either plant-physiologically unfounded, due to technical failing or otherwise unusable for modelling, the accumulation 
of sodium was used for further developing of the tool. Stakeholder engagement around this issue led to support for this 
approach. Since dealing with sodium accumulation in practice may mean a daily discharge of small volumes up to infrequent 
discharges of large volumes, an intermediate strategy for discharge was used.
Clustering the diversity in crops: Using Sodium accumulation as the driver for discharge, crops could be clustered by their 
sodium sensitivity (high / low) and evaporation rate (high / low). Examples of crops would be: roses (high – high), tomato (low 
– high), Phalaenopsis (high – low), Ficus (low – low). 
Using the description of (an older) glasshouse type in The Netherlands the understanding of steps 1-5 was used to test run 
the models and get a first insight in the order of magnitude of emissions.
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3
4
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XIV Symposium in Pesticide Chemistry - Pesticides in the environment: fate, modelling and risk mitigation
 Acknowledgements
The authors wish to thank the ministries of Economic Affairs, Agriculture and Innovation and of Infrastructure and the Environment 
for supporting the project. The authors wish to thank the members of the working groups 2008 and 2009, Erwin Roex, Ynze 
Stienstra, Roel Kruijne, Rik de Werd, Jan Huismans, Rob Meijer, Marieke van der Staaij and Wim Voogt for their contribution.
Table 1 - Calculated extremes in emissions caused by differences in rainfall, sizes of water basin and [Na+] 
in the water source for additional water, based on the chosen application scheme for PPPs for one example 
substance and one application scheme
6 Developing scenarios for the four crop clusters: Sensitivity analyses of the models Waterstromen and substance fate 
showed that the emission to surface water was mainly determined by rainfall, evaporation (irradiation), size of rainwater 
collection basin (supply of sodium-free water), additional water sources (with their sodium content) and sodium concentrations 
in commercial fertilisers and disinfectants like sodium hypochlorite. Since the data on these aspects were not available experts 
were asked to describe technical realisations of glasshouses in terms of basin sizes, additional water sources and sodium 
concentrations in fertilisers in their regional distribution and in distribution over the crop clusters.
Understanding the diversity in size of the receiving surface waters: Using an overlay of glasshouse areas with the 
hydrological maps would give an acceptable estimation – analogue to the approach used in developing the open field 
scenario. However, glasshouses in The Netherlands are frequently connected to the sewage system – and obliged to use it. 
Since the actual data of the area connected to a sewer were not available, the coverage needed to be estimated by relevant 
experts. The impact of sewers to the concentration of pesticides in surface water (dilution and break down) has been shown 
to vary widely for different pesticides. 
Ordering the emission-risks to allow for a decision on the level of protection: Per crop the diversity of glasshouse 
realisations combined with expected ditches and weather data of the past 20 years allows for a ranking on theoretical 
concentrations of pesticides in the receiving surface water. Each combination is considered a ‘situation’ that could be used as 
a reference. The situation at the desired level of emission (50%, 75% or the more common used 90% percentile highest level 
of emission) could be taken as reference scenario for the evaluation of pesticides.
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Results indicate that emissions to surface water cannot be neglected (step 1). The modelled approach using ‘Waterstromen’ and 
a model for substance fate (step 3) and the selected strategy for discharge (step 4) allows evaluators to calculate concentrations 
and total annual volumes of pesticide emissions from glasshouses. The understanding of the crop clusters (step 5), the water-
technical realisations of glasshouses (step 2 and 6) and the receiving ditches (step 7) was needed to develop scenarios that can 
be used as reference situation (step 8) for evaluating the emission of any given pesticide to surface water in The Netherlands.
KEY WORDS: Pesticides, covered crops, substrate cultivation, volatilisation, risk assessment


Emissions of plant protection products to surface water from soilless greenhouse cropping systems

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