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2.1 Problem context
Pesticides are a topic of considerable policy interest across environmental, agricultural and human health legislation. There is widespread interest in pesticides from regulators, farmers and the public owing to potential risks they present for both the environment and public health. Under the Water Framework Directive, pesticides are second only to nitrates in causing most failures of good chemical status in groundwater (European Commission, 2019).
For a topic of such interest, at a European level we know surprisingly little about the actual levels of pesticides in surface and ground waters. The sorts of reasons impacting on our knowledge include:
- Countries monitor a number of different pesticides, but the reported data on pesticide concentrations in waters are very different in quality and quantity and therefore difficult to harmonise to obtain an established European overview.
- Pesticide use depends on the crop type, season, weather and equipment availability. Some estimates of pesticides in the environment are based on sales data, but this gives very little indication of actual use or concentrations and toxicity of pesticides in water.
- Monitoring and assessment of pesticides in surface waters is mostly done routinely, but pesticide peaks in surface waters can only be identified by event-based monitoring, such as following heavy rainfall.
- Pesticide pollution from point sources could also be attributable to substances used in biocide products (e.g. household products, facade paint, gardening), which enters the water cycle mainly through discharges from urban waste water treatment plants (UWWTP), storm overflow or urban run-off. There is limited understanding of the significance of such contributions relative to those from agriculture.
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The absence of European data on the sales of biocides, so that their relative importance as a source of pollution is not known
The absence of useful European data on the use of PPPs and biocides, which could help to identify areas of intensve use, the relative importance of agricultural and non-agricultural use etc.
Chemical interactions and transformations between the active substances of pesticides as well as their synergism, enhancement and antagonism mechanisms are little known. Thus, the final product of these interactions may not be detected in monitoring.
UBA-IV1.3: An additional aspect might be added: the role of pesticide metabolites. Particularly those of no or unknown toxicological relevance (non-relevant metabolites) might be underestimated in their impact, i.e. for water supplying companies and with regard to water processing or mixtures in the field. Despite of frequent detections of particular metabolites in relatively high concentrations, the monitoring data basis is scarce and heterogeneous.
In addition, the main entry route of pesticide in surface waters depends on the application type, the physico-chemical characteristics of the substance (mobility, persistence, volatility), and on soil features (e.g. organic carbon content) and on the weather conditions at and after the application.
Some authors argue that, despite a considerably lower application, the loads of urban pesticides and biocides are in the same range as agricultural pesticides. See for example:
Blanchoud H, Moreau-Guigon E, Farrugia F, Chevreuil M, Mouchel JM: Contribution by urban and agricultural pesticide uses to water contamination at the scale of the Marne watershed. Sci Total Environ 2007, 375:168-179.
Wittmer IK, Scheidegger R, Bader H-P, Singer H, Stamm C: Loss rates of urban biocides can exceed those of agricultural pesticides. Sci Total Environ 2011, 409:920-932..
"...interest in pesticides from regulators..." should also mention the benefits they bring in regard to food security.
There are industry data bases for a large number of pesticides submitted as part of the EU approval process, which complement Member State monitoring - this gives good complementary data and a good view on concentrations in surface and particularly groundwater. It is not correct to say that "we know surprisingly little".
The toxicity of pesticides in water is determined in a significant number of different tests, according to the requirements of the relevant Regulations under Regulation (EC) No. 1107/2009 and Regulation (EU) 528/2012. These tests cover different taxa and the complete food chain. All these tests are done in a dose/response design which enables the accurate determination of toxicity and no effect levels. Therefore, it should not be stated that the toxicity of pesticides is somehow unclear.
Point sources of PPP (excl. biocides) as possible entry sources such as farmyard runoff, spill overs, accidents, illegal disposal of spray liquid remnants or cans, are not explicitly mentioned but could be excluded for clarity.