Dutch pesticides atlas for surface water
A new on-line pesticides atlas (www.pesticidesatlas.nl) allows users to see at a glance what pesticides are present in Dutch surface waters and where standards are exceeded. It provides insight into whether monitoring sites are appropriately located and whether there is any correlation between surface water pesticide concentrations and certain kinds of land use.
For many years now Dutch water boards, drinking water companies and the National Institute for Inland Water Management (RIZA) have been monitoring pesticide levels in surface waters. However, there is wide variation in the number of compounds monitored, the number of monitoring sites and measurements per district and the frequency of monitoring at individual sites. Until recently there was no comprehensive geographical picture of where pesticides are present as contaminants in surface waters and where this poses a potential risk, making it difficult for government agencies, farmers’ organisations, conservation agencies and environmental NGOs to assess the significance of any problems that came to light. This was especially the case if the aim was to build up a quick impression of problematic substances or areas, or even query the use of certain pesticides.
To remedy this situation a new type of on-line atlas has been developed, accessible at
www.pesticidesatlas.nl. With just a few keystrokes, users can retrieve information on the environmental presence of individual pesticides across the Netherlands, displayed in map form. To that end, data from individual monitoring sites has been amalgamated in grid cells measuring 1x1 or 5x5 km˛. The current version of the Atlas contains data on 160 pesticides for the period 1999-2000 and shows where each of these compounds has been measured in surface waters and where standards have been exceeded. Measured concentrations are compared with three environmental standards: the European drinking water standard of 0.1 µg/l, the Maximum Tolerable Risk (MTR) level and the standard set by the Dutch Board for the Authorisation of Pesticides (CTB) in approving compounds for sale on the Dutch market. There are also maps and diagrams showing the situation for the country as a whole. For every square kilometre of the Netherlands there is now therefore a clear picture of the extent to which pesticides are being monitored, in which seasons and so on, and the percentage of pesticides exceeding one or more of the three standards. Although it is mainly in spring and summer that standards are exceeded, there are occasional transgressions in the winter months, too. The option of overlaying the maps with a variety of other cartographic elements such as provincial boundaries, watersheds, water board management areas and the country’s Ecological Main Structure allows other kinds of spatial analysis to be performed.
Another key feature of the pesticides atlas is the inclusion of land use data – in particular, on agricultural land use – for each of grid cells where pesticides are monitored. This feature makes it possible to establish whether there is any relationship between cropping patterns and surface water contamination with certain compounds. In many cases such a correlation can indeed be readily established and this kind of information can then be used to predict likely concentrations in the vicinity of such crops, even when there are still no monitoring provisions in place. This makes the pesticides atlas a powerful tool that can be used among other things for evaluating Dutch pesticide policy, the post-registration of compounds on the market and implementation of the European Water Framework Directive. What the atlas does is help users pose questions. Where are relevant data lacking? Where are the ‘wrong’ compounds being measured? Why are standards being exceeded? This gives the atlas a distinct advantage over other available tools.
The pesticides atlas currently contains maps for the situation as it was in 1999-2000, but data for the years 2001-2003 are to be added later this year, permitting historical comparison of pesticide levels. It will indicate areas where Dutch surface water quality has been improving and where it has deteriorated.
The pesticides atlas is an initiative of the Institute of Environmental Sciences of Leiden University and was developed in collaboration with Royal Haskoning, Alterra and RIVM, with funding from RIZA, VEWIN, CTB and the Dutch environment and agriculture ministries.
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Metribuzine Measurements of metribuzine (herbicide used mainly in potatoes) in surface water in the Netherlands in 1999-2000, presented at a 5x5 km scale. Concentrations related to the Maximum Tolerable Risk (environmental quality standard). The MTR is the environmental concentration at which species of the aquatic ecosystem are held to be adequately protected against exposure to individual substances. |
GR de Snoo, WLM Tamis and M van ‘t Zelfde, Institute of Environmental Sciences, Leiden University, PO Box 9518, 2300 RA Leiden, The Netherlands, snoo@cml.leidenuniv.nl
[This article first appeared in Pesticides News No. 68, June 2005, page 8]