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De ecologische risico's van bestrijdingsmiddelen in beeld: een toxische druk indicator in de bestrijdingsmiddelenatlas oppervlaktewater
mixtures. This often causes mixture effects, which may be more harmful than expected from exposure to
individual substances. The degree of harm is not simply evaluated on the basis of exceedances of protective
water quality standards. To address this issue more effectively, the Institute of Environmental Sciences
Leiden (CML) and the National Institute for Public Health and the Environment (RIVM) have developed a
new mixture toxic pressure indicator, now incorporated into the Atlas pesticides in surface water (Pesticides
Atlas, BMA, www.pesticidesatlas.nl). This report explains the background and development of the
new Atlas products developed with this indicator, which focus on mixture toxicity as a measure for the net
impact of unintended chemical mixtures on aquatic life.
The new indicator is based on decades of RIVM- and global research into...Show morePesticides are a main source of chemical pollution in Dutch surface waters, where they occur as unintended
mixtures. This often causes mixture effects, which may be more harmful than expected from exposure to
individual substances. The degree of harm is not simply evaluated on the basis of exceedances of protective
water quality standards. To address this issue more effectively, the Institute of Environmental Sciences
Leiden (CML) and the National Institute for Public Health and the Environment (RIVM) have developed a
new mixture toxic pressure indicator, now incorporated into the Atlas pesticides in surface water (Pesticides
Atlas, BMA, www.pesticidesatlas.nl). This report explains the background and development of the
new Atlas products developed with this indicator, which focus on mixture toxicity as a measure for the net
impact of unintended chemical mixtures on aquatic life.
The new indicator is based on decades of RIVM- and global research into mixture toxic pressure methods and
combines toxicity data using Species Sensitivity Distributions (SSDs). According to this method, exposure
to mixtures is characterized by quantifying the mixture toxic pressure, expressed in the dimensionless
multi-substance Potentially Affected Fraction (msPAF) metric. The mixture toxic pressure predicts which
proportion of aquatic species is potentially affected by the mixture. Calibration studies confirm that higher
mixture toxicity correlates with greater ecological impacts on water organisms.
Six new products have been created, including interactive maps, monthly and annual trend graphs, and risk
attribution tables. They build on the concepts of Quantitative Risk Analysis and risk attribution, quantifying
both the severity (chance × impact) of ecological harm and the relative contributions of individual substances.
Products 1 through 4 show the spatial and temporal trends in toxic pressure, while the remaining products
identify which specific substances cause disproportionate harm within a mixture. Together, the products
allow evaluation of where impacts are likely highest, which compound(s) likely cause this, and whether
novel uses or programs of measures induce a change in mixture toxic pressure. For the indicator, if important
compounds are not measured or represented with accurate concentration measurements in the monitoring
data (i.e. below LoQ), the mixture toxic pressure metric underestimates the true local toxic pressure.
Key findings indicate that overall mixture toxicity shows a substantial spatial variability, which has—on
average—decreased over time, but also that exposure peaks and potential effects from newer, insufficiently
tested substances remain an issue. A lack of SSD data for these new substances likely underestimates the
actual toxic pressure. Synthetic pyrethroids (such as cypermethrin and deltamethrin) currently appear to be the
largest contributors to mixture toxicity, and the data reveal that mixture effects can be high even if individual
substance concentrations do not exceed regulatory norms. Looking ahead, collection of representative
environmental monitoring data combined with supplementing toxicity data for data-poor compounds will be
crucial.
The new indicators in the BMA help users such as water managers, governments, authorisation boards,
manufacturers, and farmers(-organisations) to better determine where in the Netherlands the highest ecological
risks in surface waters occur and which substances are primarily responsible. Additionally, a regional or
local application of the mixture toxic pressure indicator will enable water authorities and farmers to take
targeted measures, for instance by focusing on the main contributors in their area.
In conclusion, the toxic pressure indicator in the Atlas provides valuable summary information to both
prioritize protective measures and evaluate the effectiveness of previous policies. Moreover, the use of this
kind of method—offering one overarching and nuanced view on chemical pollution instead of numerous
separate maps or trends evaluated via the One Out, All Out principle of the EU-Water Framework—has been
recommended in a recent amendment to the Water Framework Directive. As such, the new Atlas products offer additional insights, which stakeholders (regulators, industry, academia) have deemed a valuable foundationfor both practical and policy-related decisions on pesticide use in the Netherlands.
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- All authors
- Visser, M.D.; Posthuma, L.; Zelfde, M. van 't; Slootweg, J.; Lahr, J.
- Awarding Institution
- Institute of Environmental Sciences (CML), Science, Leiden University
- Date
- 2025-06-04