Pesticide evaluation: the French revolution

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Dario Dongo
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The Paris Administrative Court of Appeal delivered a revolutionary judgment on 3 September 2025 that fundamentally challenges the European Union’s approach to pesticide regulation and establishes groundbreaking precedents for ecological damage liability. In Notre Affaire à Tous and others v. Minister of Agriculture, the court ordered the French State to overhaul its pesticide evaluation system within 24 months, finding systematic failures in risk assessment procedures that have contributed to widespread environmental damage.

Particularly significant was the court’s detailed analysis of ‘cocktail effect’ – the combined impacts of multiple pesticides that are inadequately assessed under current regulatory frameworks. This landmark ruling represents the culmination of extensive litigation by five environmental associations challenging the State’s implementation of European Union pesticide regulations, with mixture effects representing a central deficiency in current evaluation methodologies.

Legal framework and regulatory context

European Union’s flawed Pesticide Regulation

The case centres on France’s implementation of Regulation (EC) No. 1107/2009 concerning the placing of plant protection products on the market. This regulation lays down harmonised rules across EU member States for the evaluation and authorisation of pesticides, requiring products to undergo a risk assessment portrayed as rigorous in theory but consistently weakened by flawed regulatory practice before being placed on the market.

Article 1(4) of the regulation explicitly incorporates the precautionary principle, stating that member States ‘are not prevented from applying the precautionary principle when there is scientific uncertainty as to the risks to human or animal health or the environment posed by the plant protection products to be authorised in their territory‘.

However, current implementation fails to meaningfully address the so-called cocktail effect, despite Article 4(3)(e) explicitly requiring consideration of ‘cumulative and synergistic effects known when the scientific methods for evaluating such effects are available.’

Scientific understanding of cocktail effect

Cocktail effect, also termed mixture effects or combination effects, refers to the enhanced toxicity that occurs when organisms are exposed to multiple chemicals simultaneously. These effects can manifest as:

  • additive effects. Where the combined impact equals the sum of individual chemical effects, following the principle of dose addition for chemicals with similar modes of action (Kortenkamp et al., 2009);
  • synergistic effects. Where chemical combinations produce effects greater than the sum of individual impacts, often occurring when one chemical enhances another’s toxicity through altered metabolism or increased cellular uptake (Cedergreen, 2014).

Research demonstrates that realistic environmental pesticide mixtures frequently exhibit additive or synergistic toxicity at concentrations individually considered safe under regulatory assessments (Cedergreen, 2014). A comprehensive review by Malaj et al. (2014) found that 42% of European surface waters contain pesticide mixtures potentially causing ecological effects.

Legal implementation in France

France transposed these requirements through Articles L.253-1 and R.253-5 of the Rural and Maritime Fishing Code, which delegate evaluation responsibilities to the National Agency for Food, Environmental and Occupational Health Safety (ANSES) (Code rural et de la pêche maritime, 2025).

Under this framework, ANSES conducts independent, objective, and transparent evaluations before the Director General can authorise pesticide products for market placement.

However, the court found that current ANSES procedures systematically fail to assess mixture effects, evaluating each product separately despite the environmental reality of multiple simultaneous exposures.

Established ecological damage

Comprehensive environmental impact documentation

The court meticulously documented widespread ecological damage resulting from pesticide use, with particular emphasis on cocktail effect contributing to environmental harm that individual chemical assessments fail to predict or prevent.

Water contamination and cocktail effect

The court relied extensively on official government data demonstrating pervasive water contamination by pesticide mixtures. Ministry of Ecological Transition publications from 2019-2020 revealed that while the pesticide index decreased approximately 20% since 2008, active substances remain widely present in both surface and groundwater bodies, typically occurring as complex mixtures rather than individual chemicals (Cour Administrative d’Appel de Paris, 2025, para. 13).

The judgment highlighted that ’29 of the 55 watersheds in the country show more than 80% of measurement points with samples at unacceptable ecotoxic risk levels‘ when mixture effects are considered through available assessment tools (Cour Administrative d’Appel de Paris, 2025, para. 13). This finding reflects growing scientific understanding that mixture toxicity assessment reveals environmental risks invisible to single-chemical evaluation approaches.

Recent research by Schulz (2004) demonstrated that aquatic pesticide mixtures commonly exceed predicted toxicity thresholds for sensitive species, with fungicide-insecticide combinations showing particularly strong synergistic effects. The European Environment Agency’s assessment found that current regulatory approaches systematically underestimate ecological risks by factors of 2-10 when mixture effects are properly considered (Berenzen et al., 2005).

Soil contamination and complex mixture interactions

The judgment referenced a French study published in Agriculture, Ecosystems and Environment (Pelosi et al., 2020) demonstrating that soils presumed free from synthetic substances showed significant pesticide concentrations occurring as complex mixtures. The research found that ‘a mixture of at least one insecticide, one herbicide and one fungicide contaminated 90% of the studied sites and 54% of tested earthworms at a level such as to endanger all soil organisms‘ (Cour Administrative d’Appel de Paris, 2025, para. 14).

This finding reflects a sophisticated understanding of soil mixture dynamics. Tang et al. (2021) demonstrated that soil-dwelling organisms face particular vulnerability to mixture effects because agricultural soils accumulate diverse pesticide residues with varying persistence and mobility characteristics. Earthworms, serving as keystone soil organisms, show enhanced toxicity when exposed to realistic pesticide mixtures compared to individual chemical exposures, with effects on reproduction and behaviour occurring at concentrations below individual chemical effect thresholds (Altenburger et al., 2015).

The persistence of banned pesticides mentioned in the court decision – chlordecane in the Antilles and lindane residues in metropolitan France – creates additional mixture complexity, as current-use pesticides interact with legacy contamination to produce unpredictable toxicity patterns (Cour Administrative d’Appel de Paris, 2025, para. 14).

Biodiversity decline and mixture-mediated effects

The court established clear causation between pesticide mixture exposure and biodiversity decline through multiple scientific sources. The International Union for Conservation of Nature (IUCN) Red List provided evidence of threatened species exposure to pesticide mixtures, including the European eel and Catalan chub, ‘exposed to numerous pollutants and pesticides that weaken their immune defenses‘ through mixture-mediated immunosuppression (Cour Administrative d’Appel de Paris, 2025, para. 16).

Scientific research demonstrates that cocktail effect particularly threatens beneficial insects essential for ecosystem functioning. Sánchez-Bayo & Wyckhuys (2019) found that worldwide entomofauna decline is associated with enhanced mortality and reproductive impairment when exposed to realistic pesticide combinations. The mechanism involves fungicides inhibiting detoxification enzymes, increasing insecticide toxicity by substantial factors (Pisa et al., 2015).

The INRAE-IFREMER report cited by the court concluded that ‘plant protection products are, in agricultural areas, one of the main causes of decline in terrestrial invertebrates, including pollinating insects and pest predators (ladybirds, ground beetles…), as well as birds‘ (Cour Administrative d’Appel de Paris, 2025, para. 16). This reflects understanding that ecological mixture effects cascade through food webs, with impacts on insect communities affecting vertebrate predators through reduced prey availability (Geiger et al., 2010).

State responsibility and regulatory failures

ANSES evaluation deficiencies

The court identified systematic failures in ANSES’s implementation of EU pesticide evaluation requirements, with particular emphasis on inadequate assessment of mixture effects, despite scientific understanding and regulatory requirements for their consideration.

Cocktail effects assessment failures

The court’s most damning finding concerned ANSES’s complete failure to assess cocktail effects in pesticide evaluations. A 2017 report by the General Inspectorate of Social Affairs (IGAS) and General Commission for Environment and Sustainable Development (CGEDD) found that ‘each product is evaluated separately for each agronomic use’, despite soil potentially being exposed to multiple products simultaneously (Cour Administrative d’Appel de Paris, 2025, para. 31).

This approach fundamentally contradicts environmental reality. Agricultural systems typically involve applications of multiple pesticide products across growing seasons, creating complex exposure scenarios for non-target organisms. Köhler & Triebskorn (2013) demonstrated that realistic agricultural pesticide application patterns create mixture exposures orders of magnitude more toxic than individual chemical assessments would predict.

The court noted that this methodological failure ‘prevents proper assessment of mixture effects‘, representing a fundamental breach of the precautionary principle required under EU regulation (Cour Administrative d’Appel de Paris, 2025, para. 31). European Food Safety Authority guidance has acknowledged mixture assessment requirements since 2008. Yet, implementation remains sporadic across member States (EFSA, 2019).

Scientific evidence for regulatory mixture assessment

Extensive scientific literature supports mandatory mixture assessment in pesticide regulation. Altenburger et al. (2015) found that water quality monitoring examining pesticide mixtures at environmentally relevant concentrations detected significant additive or synergistic effects. Research by Cedergreen (2014) demonstrated that cocktail effects occur consistently at concentrations below individual chemical effect thresholds.

Particularly concerning for biodiversity protection, mixture effects often target vulnerable life stages and sensitive species. Research by Boedeker et al. (2020) showed that acute pesticide poisoning patterns reflect mixture exposure scenarios that exceed predictions from individual chemical toxicity data. Similar patterns emerge across taxonomic groups, with pollinators showing enhanced susceptibility to pesticide combinations (Pisa et al., 2015).

Trophic level interaction failures

The 2022 INRAE-IFREMER report highlighted another critical deficiency: ‘so-called indirect effects or interactions between trophic levels of different groups of organisms are not taken into account at all in evaluations conducted by ANSES, which treats separately the effects of a pesticide on each group of organisms (plants, arthropods, birds), and which limits itself to direct effects‘ (Cour Administrative d’Appel de Paris, 2025, para. 31).

This siloed approach ignores ecosystem-level cocktail effects where chemical combinations affect food web interactions. For example, herbicide-insecticide mixtures can simultaneously reduce plant diversity (affecting herbivorous insects) and directly impact beneficial insects, creating synergistic effects on ecosystem functioning (Potts et al., 2010). Birds suffer both direct toxicity and indirect effects through reduced prey availability, with mixture effects amplifying both pathways (Geiger et al., 2010).

Temporal and spatial mixture dynamics

Current evaluation frameworks also fail to address the temporal and spatial dimensions of mixture exposure. Agricultural landscapes create spatially heterogeneous mixture exposures as different fields receive varying pesticide treatments, whilst spray drift and environmental transport create unintended mixture combinations (Schulz, 2004).

Temporally, many agricultural systems involve sequential pesticide applications, creating time-varying mixture compositions. Early-season insecticide applications may interact with mid-season fungicides and late-season herbicides, creating exposure scenarios impossible to predict from individual chemical assessments (Tang et al., 2021).

The Court’s decision and remedial orders

Recognition of mixture effects in ecological damage

The court’s establishment of ecological damage under Article 1247 of the Civil Code explicitly recognised mixture effects as contributing to environmental harm. The finding of ‘non-negligible harm to elements or functions of ecosystems as well as to collective benefits derived by humans from the environment‘ specifically acknowledges that current single-chemical evaluation approaches systematically underestimate environmental risks (Cour Administrative d’Appel de Paris, 2025, para. 24).

This represents the first comprehensive judicial recognition that regulatory failure to assess mixture effects constitutes a breach of environmental protection obligations, establishing important precedents for future environmental litigation globally.

Mandatory mixture assessment requirements

The court’s remedial orders implicitly require implementation of mixture assessment methodologies. The mandate to ‘implement risk evaluation of plant protection products in light of the latest state of scientific knowledge, particularly concerning non-target species‘ necessarily encompasses mixture effects given the extensive scientific literature documenting their environmental significance (Cour Administrative d’Appel de Paris, 2025, Article 3).

The 24-month implementation timeline requires rapid development of operational mixture assessment protocols. This timeline reflects urgency given scientific consensus on mixture effects combined with current regulatory failures to address them systematically.

National implications and regulatory reform

Mixture assessment implementation challenges

France faces substantial technical challenges implementing comprehensive mixture assessment within the court’s timeline, as outlined below.

Methodological Development Requirements. ANSES must develop assessment protocols addressing:

  • component-based assessment. Evaluating mixture toxicity based on individual chemical properties and concentrations, using established models such as concentration addition and independent action (Backhaus & Faust, 2012);
  • whole-mixture testing. Direct toxicity testing of realistic pesticide combinations, requiring substantial expansion of laboratory capacity and standardised mixture preparation protocols (Kortenkamp et al., 2009);
  • probabilistic risk assessment. Incorporating spatial and temporal variability in mixture exposure patterns using Monte Carlo simulation approaches (Altenburger et al., 2015);
  • tiered assessment frameworks. Implementing screening-level mixture assessment for all pesticide combinations with detailed assessment for high-priority mixtures based on exposure potential and toxicity concerns (EFSA, 2019).

Data requirements and industry implications

Theoretically, enhancing mixture assessment presupposes fundamental modifications in data generation:

  • combination studies. Manufacturers may need to conduct toxicity studies on relevant pesticide combinations (Köhler & Triebskorn, 2013);
  • environmental fate interaction studies. Understanding how pesticide combinations affect environmental persistence, mobility, and bioavailability compared to individual chemicals (Tang et al., 2021);
  • field-realistic exposure assessment. Developing exposure scenarios reflecting actual agricultural practice patterns rather than simplified single-application models (Schulz, 2004).

Agricultural sector adaptation

Implementation of a comprehensive mixture assessment will likely affect agricultural practices:

  • full and proper implementation of integrated pest management. Stricter mixture assessment may limit simultaneous pesticide applications, accelerating adoption of integrated pest management (IPM) strategies that reduce overall chemical inputs whilst maintaining pest control efficacy (Barzman et al., 2015);
  • precision application technologies. Farmers may invest in precision application technologies that minimise spray overlap and drift, reducing unintended mixture creation whilst optimising individual pesticide efficacy (Zhang & Kovacs, 2012).

European Union implications

Regulatory harmonisation and mixture assessment

The French judgment’s emphasis on mixture effects may catalyse EU-wide regulatory reform:

  • EFSA guidance development. The European Food Safety Authority has acknowledged mixture assessment requirements but lacks operational guidance for routine implementation (EFSA, 2019). The French case may accelerate development of practical assessment protocols applicable across member States;
  • revision of Regulation (EC) 1107/2009. Current EU pesticide regulation inadequately addresses mixture effects despite scientific consensus on their importance (Kortenkamp, 2020). The French judgment demonstrates legal vulnerability of current approaches, potentially supporting regulatory revision to mandate comprehensive mixture assessment.

Cross-border mixture exposure

Pesticide mixtures cross national boundaries through atmospheric transport and water body contamination, requiring coordinated European responses. The French emphasis on mixture assessment may necessitate harmonised monitoring and assessment approaches to address transboundary environmental effects (Altenburger et al., 2015).

Future research and implementation needs

Priority research areas

Effective mixture assessment implementation requires continued research investment:

  • mode of action classification. Developing comprehensive databases classifying pesticides by mode of action to predict mixture interactions and guide assessment priority setting (Kienzler et al., 2016);
  • biomarker development. Creating sensitive biomarkers capable of detecting mixture effects in environmental monitoring programmes, enabling validation of assessment predictions against field observations (Clements & Rohr, 2009);
  • ecosystem service integration. Understanding how mixture effects impact ecosystem services such as pollination, natural pest control, and nutrient cycling to quantify broader environmental and economic implications (Kremen & Miles, 2012).

Advanced analytical and computational approaches may also facilitate the development of innovative technologies for practical mixture assessment:

  • high-throughput screening. Automated toxicity testing platforms enabling rapid assessment of numerous pesticide combinations across multiple species and endpoints (Judson et al., 2010);
  • machine learning applications. Artificial intelligence approaches for predicting mixture toxicity based on chemical structure and individual toxicity data, reducing empirical testing requirements whilst maintaining assessment accuracy (Backhaus & Faust, 2012).

International environmental law context

Global mixture assessment trends

The French decision aligns with emerging international recognition of mixture effects in environmental regulation:

  • Stockholm Convention considerations. The Stockholm Convention on Persistent Organic Pollutants increasingly recognises that legacy pollutants interact with current-use chemicals to create complex mixture exposures requiring integrated assessment approaches (Stockholm Convention Secretariat, 2017);
  • WHO/UNEP mixture guidelines. The World Health Organization and United Nations Environment Programme have developed frameworks for human health mixture assessment that provide models for environmental applications (WHO/UNEP, 2020).

Conclusion

The Paris Administrative Court of Appeal’s decision in Notre Affaire à Tous and Others v. Minister of Agriculture represents a watershed moment in environmental law, with its detailed analysis of cocktail effect establishing new standards for environmental risk assessment. The court’s recognition that current single-chemical evaluation approaches systematically underestimate environmental risks through failure to assess mixture effects creates compelling precedents for regulatory reform across jurisdictions.

The judgment’s emphasis on cocktail effect reflects a sophisticated understanding of environmental toxicology and ecosystem functioning. By mandating implementation of assessment methodologies reflecting ‘the latest state of scientific knowledge‘, the court explicitly requires France to address mixture effects that current procedures systematically ignore despite extensive scientific evidence of their environmental significance.

Implementation challenges are substantial but surmountable with adequate investment in scientific capacity and regulatory infrastructure. The 24-month timeline creates urgency whilst providing sufficient time for developing operational mixture assessment protocols based on established scientific methodologies.

The decision’s broader implications extend beyond France, potentially catalysing European Union regulatory reform and influencing environmental protection approaches globally. As nations grapple with mounting evidence of cocktail effect in environmental contamination, the French experience provides a roadmap for legal systems seeking to ensure environmental regulation reflects scientific understanding of chemical mixture risks.

Success in implementing comprehensive mixture assessment will require sustained collaboration between regulatory agencies, scientific institutions, industry stakeholders, and environmental advocates. The French decision demonstrates that legal systems can compel evidence-based environmental protection, establishing frameworks that translate scientific understanding into practical regulatory reform, protecting ecosystem health and human welfare.

Dario Dongo

Cover art copyright © 2025 Dario Dongo (AI-assisted creation)

References

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Dario Dongo
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Dario Dongo, lawyer and journalist, PhD in international food law, founder of WIISE (FARE - GIFT - Food Times) and Égalité.

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