Ecological Risk Maps - Introduction

Background

Pesticides are used for agricultural purposes and released into the environment. Despite their use is regulated by stringent pre-market evaluation, in the environment they create mixtures of multiple substances with potential to negatively affect terrestrial and aquatic organisms. This tool shows locations where pesticide mixtures in soil and water might pose a combined ecological risk.

How it works

We created ecological risk maps that show where pesticides might be harming animals living in soil and water. Firstly, we prioritized the pesticides according to i) how much they were used in Czechia, ii) how toxic these pesticides are to earthworms and fish (representatives of soil and aquatic organisms), and iii) how long they last in the environment. Then, we calculated risk (risk quotient – RQ) by dividing the predicted concentration for each substance in a given area by its ecotoxicity (data taken from databases). To assess the risk of multiple pesticides together, the RQ of the pesticides were summed up, giving a cumulative ecological risk of the pesticide mixtures. Then, the cumulative ecological risk was mapped to help identify areas where soil and water organisms are at greater risk.

To identify areas at greater ecological risk, a risk threshold (a value of >0.2 for soil and >0.1 for fish) can be seen in the maps. This comes from the fact, that under EU regulation, pesticide levels in the environment should be at least five times lower than the safe limit for earthworms and ten times lower than the safe limit for fish in water. 

What it offers

These maps help us identify places that need attention and probably further investigations so we can better protect our environment from pesticide pollution.

Limitations / Disclaimer

Because the ecological risk is based on concentration maps (see the Concentration Maps Tool – Field-resolution Maps), any limitations of those maps also apply to these risk maps. In addition, there are some other important limitations:

• The ecological risk is not based on real measured pesticide levels in soil and water from the countries.
• The cumulative ecological risk might be higher than it really is because it assumes that all pesticides used in the district for a given crop were used on the particular field, which might not always happen.
• Ecological risk is expressed only for earthworms and fish; however, there might be other species under higher or lower risks that are not calculated in this tool

Background

Pesticides are actively applied and subsequently introduced into the environment. Although their use is subject to rigorous pre-market regulatory assessments, these substances can persist in the environment, potentially exerting adverse effects on terrestrial and aquatic ecosystems. While their concentration and occurrence provide important data, assessing the risk they pose to organisms requires consideration of their hazardous properties. The hazard can be described as potential for a pesticide to cause harm and defined by ecotoxicological outcomes. The risk, on the other hand, refers to the likelihood that a pesticide will cause harm, which is determined by the level of exposure. Risk Quotients (RQ), calculated under chemical legislation as the ratio of exposure to toxicity, serve as a key metric. Furthermore, pesticides often occur as mixtures, leading to simultaneous exposure, and their combined effects can be cumulative. A common approach to evaluate the risk of mixtures is to sum the individual RQ, the cumulative risk quotient (∑RQ). This method offers a straightforward way to assess the risk of complex mixtures, however it may underestimate risk, as interactions such as synergy may lead to effects greater than the simple sum of individual risks.

This tool provides a spatial visualization of the potential cumulative ecological risk (∑RQ) associated with probable mixtures of pesticide residues in soil and water, providing a valuable resource for risk assessment and policy decision-making.

How it works

Ecological risk maps were developed to visually show where pesticide application poses the greatest threat to soil and water ecosystems in randomly selected districts in Czechia. These maps are based on scientific calculations that compare modelled pesticide concentrations in the environment with known toxicity thresholds for key species like earthworms and fish.

By comparing predicted pesticide levels in the environment with established thresholds for toxicity, we can identify and highlight areas facing high ecological risk.

Data sources:

• Field-resolution Maps – the predicted environmental concentrations (PEC) in soil and water calculated as average values across a 56-day period following application.
• Data on pesticide properties (PPDB, EFSA OFT, USEPA ECOTOX)

Key steps:

• Pesticides were prioritized based on national usage data and their chemical and ecotoxicological properties. Pesticides considered not directly relevant to environmental risk were excluded (e.g., growth regulators, pheromones).
• All data was normalized to allow for consistent scoring of pesticides. Pesticides accounting for the top 95% of the cumulative score were selected for inclusion in the maps.
• After key pesticides were selected, the risk quotients (RQ) were calculated, by dividing the PEC by the no observed effect concentration (NOEC). Pesticides with higher RQ indicate possible higher ecological risk.
• The individual RQ were then summed for each specific area (e.g., river basin or field) to provide a cumulative risk quotient (ΣRQ).

Under EU regulations, environmental concentrations must be well below the NOEC to protect species: soil concentrations for earthworms should be at least five times lower than the NOEC, and water concentrations for fish should be at least ten times lower than the NOEC.

What it offers

The final maps highlight areas with a high cumulative pesticide risk (ΣRQ), allowing to:

• Identify pollution hotspots areas
• Support targeted mitigation efforts and sustainable pesticide use policies, especially for the pesticides presenting higher RQ
• Help prioritize pesticide risk reduction measures at national and regional scales.

Limitations / Disclaimer

Because the calculated risk is based on the concentration mapping (see Concentration Maps Tool – Field-resolution Maps), all the limitations for the concentration maps are applicable for the risk maps too. On top of these, there are also other limitations.

• It is not real risk based on the real measured pesticide occurrence in soil and water in the countries
• Cumulative risk overestimates because not all the substances are really applied (see Field-resolution Maps). 
• Ecological risk is expressed only for earthworms and fish; however, there might be other species under higher or lower risks that are not calculated in this tool

Background

Pesticides are extensively used in agriculture and subsequently released into the environment. Although their use is regulated through rigorous pre-market evaluations, environmental monitoring frequently detects multiple pesticide residues in both terrestrial and aquatic systems.
A straightforward approach to ecological risk assessment involves calculating the Risk Quotient (RQ), defined as the ratio between environmental exposure and an ecotoxicological threshold. In this tool, RQs for selected priority pesticides were calculated using predicted environmental concentrations (PECs) and no observed effect concentrations (NOECs). To evaluate the risk posed by mixtures, individual RQs are summed to derive a cumulative risk quotient (∑RQ).

How it works

Ecological risk maps help visualize the spatial distribution of pesticide impacts on ecosystem health. The risk quotient (RQ) for an individual active substance is calculated as the ratio of its predicted soil or water concentration (i.e., PECs, PECw) to ecotoxicity thresholds (hazard data taken from the databases). When dealing with multiple pesticide residues, which are frequently detected in agricultural soils, the cumulative risk quotient (ΣRQ) for a given area can be assessed by summing the RQs for all single pesticides, commonly following a concentration-addition approach. These calculated ΣRQ values, representing the severity of ecological risk at various points or grid cells, are then spatially visualized on maps using Geographic Information Systems (GIS) spatial processing. This mapping process allows for the identification of high-risk areas. Ecological risk maps were created for the prioritized pesticides in selected districts of Czechia, covering both terrestrial and aquatic environments. 

Prioritization of the substances

To select substances for risk maps, pesticides applied in 2021 were ranked based on their usage and chemical/ecotoxicological properties. Usage data were obtained from national source (ÚKZÚZ, 2021) data for 183 substances in Czechia. Since our focus was on conventional synthetic pesticides, non-relevant substances (e.g., microbial agents, pheromones, growth regulators, synergists, and inorganic or natural compounds) were excluded.

Chemical and ecotoxicological properties of the pesticides were retrieved from the PPDB database. Chronic NOEC for earthworms (56 days) and fish (21 days) were used when available. If not, acute LC50 values (14 days for earthworms, 96 hours for fish) were divided by 10 as a proxy (Franco et al., 2024). Chemical parameters included DT₅₀ in soil, DT₅₀ in water, water solubility (at 20 °C), Kow, and Kfoc. Missing values were supplemented by EFSA reports.

All data (usage, toxicity, chemical properties) were normalized to a 0–1 scale separately for each country. The normalized values were used to score and rank the pesticides. The top 95% (based on cumulative scores) was selected for the risk maps.

Risk quotient calculations

Once the substances were selected, the PEC estimation in topsoil and surface water were calculated for individual fields and river segments, as outlined in the Concentration Maps tool (Field-resolution Maps). For detailed description see model documentation.

The PEC in topsoil and surface water were calculated as the 56-day time-weighted average concentration following pesticide application. This approach was chosen to account for temporal fluctuations and to provide a more realistic estimate of long-term exposure.

A hazard database was prepared by collecting chronic NOEC values for reproduction in earthworms and fish. The toxicity data was collected from the PPDB, EFSA OpenFoodTox, and USEPA ECOTOX databases. The data from the 3 databases were gathered and the lowest NOEC of each pesticide was retained. 

The soil and aquatic risk quotient (RQ) was calculated as PEC/NOEC. The cumulative RQ (∑RQ) was calculated to integrate the ecological risk of pesticides applied in a same area. For soil, the RQ in individual fields were summed (∑RQ soil). The ∑RQ surface water for individual river segments were calculated from the pesticide loadings from individual fields and flow of receiving river water segments. ∑RQ surface water is then spatially weighted by agricultural area contributing to aquatic risk of individual river segments which is derived from spatial intersection of all pesticide-treated fields within 100-meter buffer area around individual river segments. Total area of treated fields within a river segment buffer and area of buffer around an individual river segment are then used to calculate fraction of area contributing to aquatic RQ. Likewise, area of individual river segment in a river buffer and area of a respective buffer are used to derive fraction of receiving area in the buffer. Both fractions are then used to derive river and pesticide specific weights and used to obtain area-weighted RQ surface water (Strassemeyer et al., 2003).

According to EU regulatory guidelines, environmental concentrations of pesticides should be maintained at levels at least fivefold lower than the NOEC for earthworms and tenfold lower than the NOEC for fish. Therefore, risk thresholds were established at 0.2 for earthworms and 0.1 for fish.

What it offers

The ecological risk maps can help to identify the most harmful agricultural practices and pesticide uses, based on real pesticide usage, to elucidate the spatio-temporal cumulation of risks resulting from the spatio-temporal combination of crops and pesticide applications, and to indicate the cumulative ecological risks of environmental pesticide mixtures based on typical application series and crop treatment scenarios. They offer a harmonized, data-driven tool to explore how pesticide presence in the environment and toxicity translates into environmental pressure across space. Since these maps were created based on key pesticides selected by their national usage, it can be useful for improving regional pesticide management and establishing priority control lists for more accurate risk mitigation strategies.

Limitations / Disclaimer

Because the calculated risk is based on the concentration mapping (see Concentration Maps Tool – Field-resolution Maps), all the limitations for the concentration maps are applicable for the risk maps too. In any meaning, the risk calculated in the maps is not based on the real field survey or monitoring (real measurements) of concentrations or ecological harm. The exposure data (soil and water concentrations) are results of predictions (estimations) modelled using the existing data on pesticide usage (or sales), pesticide application scenarios according to good agriculture praxis in line with pesticide authorizations, and crop maps. These estimations are based on many simplifications and assumptions, that are propagated also into the ecological risk calculation. Therefore, the resulting maps must be used and interpreted with the highest care considering the provided information on methodology used for their creation and limitations and uncertainties inherently coupled with each of the maps. 

In addition, the calculated RQs do not account for landscape structure. The applied approach corresponds to a conservative screening-level assessment, assuming that the derived risk estimates are protective irrespective of local environmental and landscape conditions. As a result, the maps do not differentiate between geographical regions or landscape configurations where risk may be lower due to specific environmental settings (Streissl et al., 2018).

On top of these, there are also other limitations. One major limitation is related to the assessment of the cumulative risks. Our approach relied on concentration-addition, assuming only additive effects of pesticides. Therefore, synergistic or antagonistic effects are not considered, introducing uncertainties into the results. Another limitation concerns the selection of the toxicity data. Here, we used one model type of organism for soil (earthworms) and water (fish), which may not adequately represent the sensitivity of the broader ecological community. Standard indicator species are not always the most sensitive, potentially underestimating actual toxicity.

References:

• Franco, A., Vieira, D., Clerbaux, L.-A., Orgiazzi, A., Labouyrie, M., Köninger, J., Silva, V., Van Dam, R., Carnesecchi, E., Dorne, J.L.C.M., Vuaille, J., Lobo Vicente, J., Jones, A., 2024. Evaluation of the ecological risk of pesticide residues from the European LUCAS Soil monitoring 2018 survey. Integrated Environmental Assessment and Management 20, 1639–1653. https://doi.org/10.1002/ieam.4917
• Strassemeyer, J., Gutsche, V., Brown, C. D., Liess, M., Schriever, C., 2003. Harmonised environmental Indicators for pesticide Risk Aquatic indicators, HAIR Report. https://www.researchgate.net/publication/330934918_HArmonised_environmental_Indicators_for_pesticide_Risk_Aquatic_indicators.
• Streissl, F., Egsmose, M., Tarazona, J.V., 2018. Linking pesticide marketing authorisations with environmental impact assessments through realistic landscape risk assessment paradigms. Ecotoxicology 27, 980–991. https://doi.org/10.1007/s10646-018-1962-0.