Studying pesticide impacts in real-world landscapes

Pesticides are rarely used in isolation.

They are applied in fields that are part of wider agricultural landscapes, where crops, soils, weather, habitats, species, management decisions and other pesticide applications interact over time.

This is one of the central challenges in environmental risk assessment. A pesticide product may be assessed under standardized conditions, but its actual environmental impact depends on how it is used in real landscapes.

Standardized tests are necessary. They provide a common basis for evaluating products for regulatory decisions. But according to researchers working with systems-based environmental risk assessment, they are also simplifications.

“A standardized test provides the common yardstick that regulation needs, but it is not just a small or simplified version of real landscapes. It is a different thing altogether, and we should be honest about which questions it can answer,” says Christopher J. Topping, Professor at the Department of Agroecology at Aarhus University.

Looking beyond one product at a time

Environmental risk assessment has traditionally focused on individual substances, products and specific uses. This has helped create a structured approval system.

However, researchers in this field point out that pesticide pressure in real landscapes does not come from one product alone. It emerges from repeated use of multiple substances across fields, farms and regions over time.

This means that organisms such as pollinators, aquatic invertebrates, non-target arthropods and soil organisms may be exposed to combined pressures that are difficult to capture in isolated product assessments.

The research question is therefore not only whether a single product passes a standardized test. It is also how repeated pesticide use affects populations and ecosystems in real agricultural landscapes over time.

Johan Axelman, PhD and Special Consultant at the Department of Agroecology, joined Aarhus University in 2026 after working on the regulation of plant protection products at the Swedish Chemicals Agency. He points to the same challenge from the regulatory side:

“Cumulative impacts must be captured somewhere. But asking every individual decision to carry a full systems analysis is neither efficient nor effective. Each assessment needs to sit inside a shared knowledge and management context. Today they don’t, and getting there is a matter of systems thinking and better collaboration across sectors.”

Complexity in the right place

One response to uncertainty is to add more data, more refinements and more case-specific evidence.

But researchers working in this area argue that more detail does not automatically lead to better understanding. 

Complex ecological models can help researchers assess how pesticide exposure and effects unfold across landscapes, populations and time. At the same time, assessment methods also need to be transparent, comparable and feasible to use.

The aim is therefore not to make every assessment more complicated – nor to assess less. It is to do it first at the system level and then translate that knowledge into tools that can support faster and more accurate repeated assessments as well as learning. Seen from this perspective, cumulative pesticide pressure is difficult to understand if assessment remains focused only on individual products and separate uses.

“Models tell you how a system behaves. They don’t tell you which decisions to prioritize. That question comes from the regulatory side, and it is the one that determines how complicated a model needs to be,” says Christopher J. Topping.

Aarhus University’s role

At Aarhus University, much of this work is connected to ecological modelling, systems-based approaches to environmental risk assessment, and participation in large European research collaborations.

One important research environment is the Social-Ecological Systems Simulation Centre, led by Christopher J. Topping, which models how ecological processes, landscape structure and management decisions interact over time.

This kind of modelling is relevant because pesticide impacts do not only depend on the properties of a substance. They also depend on where and when it is used, which species are exposed, how populations recover, how landscapes are structured and which other stressors are present.

Aarhus University researchers also contribute through PARC — the European Partnership for the Assessment of Risks from Chemicals. PARC brings together researchers, authorities and other actors working to strengthen chemical risk assessment across Europe.

Within this broader collaboration, Aarhus University researchers contribute to work on pesticide risk assessment, biodiversity protection, monitoring, modelling and the need to connect knowledge across sectors and data systems. This also links to platforms such as MIND, which focus on making models, monitoring data, exposure information and ecological knowledge easier to connect and use across projects and institutions.

Johan Axelman explains why:

“These projects are all circling the same finding: fragmentation of data, knowledge and regulations is what makes assessment slow and means that they fail to capture system-level risks. Connecting them is not administration. It is the substance of the work.”

PollinERA as an example

PollinERA is one example of how this research direction is being applied in practice.

The project focuses on how pesticide exposure and effects on pollinators can be better understood in real agricultural landscapes. It explores how cumulative pressure from multiple pesticide uses can be studied more systematically.

A recent PollinERA policy brief, co-authored by Christopher J. Topping, Johan Axelman and James Henty Williams from the Department of Agroecology at Aarhus University, proposes a regional pesticide budget as one possible systems-based approach to studying and managing cumulative pesticide pressure.

The idea is that each ecological region would have an annual frame for pesticide pressure. Products with lower environmental impact would use less of that frame, while more persistent or toxic substances would use more.

The proposal is a research-based contribution from PollinERA to the European discussion about pesticide regulation. It should not be read as an institutional policy recommendation from Aarhus University.

“What we need to make pesticide impacts manageable is a way to understand and manipulate the overall pesticide pressure. Regional pesticide budgets are very similar to carbon budgets or fish quotas, with which we are all familiar, but locally adapted,” says Christopher J. Topping.

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