The approach to environmental risk assessment is 30 years old. It was designed when our ecological understanding was very different from today
The approach to environmental risk assessment is 30 years old. It was designed when our ecological understanding was very different from today

Biodiversity at risk because we don’t assess the risk of pesticides properly

A more complete approach to pesticide environmental risk assessment should replace the current system, which represents real world conditions poorly.


Pesticides are considered by many to have an important role in the continuing increase in agricultural production efficiency, and subsequent impacts on biodiversity, especially insect declines.

That is: The more we spray, the fewer insects are allowed to thrive.

There is also that bird populations are affected by pesticide use, and there are still cases of acute poisoning of birds, mammals and amphibians directly linked to pesticide usage.

However, we have a very large, expensive and complex risk-assessment process to ensure safety. So what is going wrong?

My colleagues in Switzerland and France, and myself from the Department of Bioscience at Aarhus University have tried to answer this question in a new article in Science.

We find that we need to do things very differently than they are done today.

The wide gap between how we regulate and what the world looks like

Pesticides are normally regulated by deciding whether or not individual uses have too high a risk of unacceptable side effects.

But this black and white approach does not fit well with our understanding of ecology, nor with the aims of the legislation behind pesticide regulation.

However, with today’s knowledge and modelling approaches we can take important steps to improve this situation.

We argue that testing should better integrate the realities of pesticide use in the modern farming landscape to provide suitable information for balancing pesticide benefits and harm.

An outdated approach

The basic approach to environmental risk assessment (ERA) is 30 years old. It was designed when our ecological understanding was very different from today.

At the same time, the environment in which we use pesticides has changed. For example, the landscape has undergone simplification (removal of hedges, and other non-agriculturally productive areas).

The concept behind today’s ERA is that we can test each pesticide for each usage and decide whether there is an unacceptable risk of harm from case to case. This is a single-pesticide single-crop approach.

But this approach, which seems sensible on the face of it, does not take the real pattern of use of pesticides into account, nor does it consider the fact that even small effects on populations may accumulate over time and space.

Animals exposed to many pesticides at once

The difference between the single-pesticide single-crop and actual use of pesticides comes as a surprise to many.

A study by EFSA showed that multiple applications (pesticides applied multiple times in the same crop) and mixtures (pesticide mixed in the spray tank and sprayed at once) are widespread (Table 1)

The number of applications on the field is much less than the number of active substances, which clearly shows that mixtures are applied.

In apples in southern and central Europe, it is quite common for pesticide spraying to occur almost weekly, normally with mixtures, but many other crops are also sprayed regularly. In fact, mixture application is very common and up to nine products mixed in a tank have been recorded.

Crop Country Number of active substances Number of applications
Apples Italy 40.6 25.6
Poland 24.9 21.7
UK 37.0 16.9
Potatoes Belgium 29.4 13.5
Lithuania 6.1 3.4
Netherlands 36.3 19.1
Wheat Lithuania 5.5 2.9
Poland 8.8 3.9
UK 18.3 6.1
Maize Belgium 6.3 1.4
Italy 7.3 3.3
Poland 2.7 1.4
Onions Spain 4.0 2.0
Netherlands 41.8 20.8
Poland 9.8 6.5
Wine Grapes Italy 37.6 14.0
Greece 16.7 12.3
Spain 6.4 3.5

Almost nowhere for the 'recovery' insects to live today

For animals that move around a lot, such as hares and honey bees, exposure to these pesticide mixtures also occurs as they move through the landscape.

The potential long-term exposure to pesticide mixtures in and amongst fields is therefore very large. This is of concern because chemical effects may sum up, or in some cases interact, to cause even greater impacts.

There is another problem with the unrealistic way in which ERA considers animal movement. For some organisms, such as those non-pest insects that live in the field, it is not possible to avoid deaths from pesticides such as insecticides.

Therefore, ERA includes the recovery principle. This means that the population should be able to recover after being sprayed so that there is only a short-term effect.

This is usually tested in small plots. Pesticide is sprayed on the plot, killing insects, and then recovery happens when insects move in from surrounding unsprayed areas.

Unfortunately, the situation in the real world is different. Rather than a small sprayed plot in a sea of unsprayed habitat we often have the reverse. Over the years, since the ERA was designed, this situation has become worse as agricultural landscapes have been simplified, habitats removed, and biodiversity depleted.

Time for a paradigm shift

To improve this situation we could change the way we do ERA.

One way would be switching from evaluating single pesticides in isolation to a more realistic evaluation including all the important population-driving factors in the system, such as landscape structure, climate and other farming operations.

This would be a paradigm shift for ERA, and the basis for the tools to do this have largely been developed already.

Based on human risk assessment, new ways to predict the effect of combinations of pesticides in ERA are under development at . These approaches open the door to a more complete risk assessment by making it possible to group pesticides into a smaller number of types and uses.

This means that rather than simulate hundreds of pesticides separately which would need huge computers and large volumes of new data, we can simulate a smaller number of groups.

If these methods can be combined with realististic ecological simulations, we will have the tools needed for a much more realistic ERA.

Our simulations can track pesticides and save more animals

Fortunately, this combination is possible. At Aarhus University, we have developed detailed models of animal population responses in highly realistic landscape simulations over the last 20 years.

Now, these simulation models are being extended to countries all over the EU (see the specific EU projects in the sources below).

These advanced 'computer game-like' models represent real agricultural patterns of management in space and time. They can track pesticides in the simulated environment and be used to assess their cumulative impacts on non-target animals.

These models can be created for different real areas of each country and so the local effects of the landscape structure can be taken into account in the assessment.

It also means that suggestions to compensate for the effects of using pesticides can be tested in the simulations.

We need to be able to test pesticide predictions

The results of the simulations are really a form of prediction, and this has to be tested. This is one of the big advantages of our realistic simulation approach.

Since we model real areas, we can use these areas for monitoring to test whether our simulations were right in the longer term.

So far, monitoring is not formally a part of ERA, and few environmental monitoring schemes for pesticides exist. This is a clear gap, since without it our risk assessment 'hypothesis' is not tested.

Therefore, our suggestion is to implement a pesticide monitoring scheme linked directly to the ERA.

Don't forget the economic aspects

Another dimension that should be present in the risk assessment is the evaluation of the agronomic and economic impacts of changed pesticide use.

These are an important part of the overall decision making related to pesticide use, but currently the economic costs of changes in pesticide use are not part of any standard evaluation.

So the economic advantages cannot be properly compared to the environmental impacts.

Although adding to the amount of work needed to implement the new approach, it is an important and achievable aim to also include these aspects in systems simulation.

Urgent need for action

All this would mean very big changes for the way ERA is carried out, but even larger changes in the way pesticides would be managed.

Instead of a black/white safe or unsafe classification, as is the case now, we would be able to determine an allowable volume of each group of pesticides tailored to the landscape in which they would be used.

It would be a much more dynamic situation, since monitoring could show that we should change the pesticide volume. Climate, agronomic or landscape changes may also change the capacity of the environment to withstand harm, also necessitating adjustment of the pesticide use.

Future pesticide management would be more integrative (multiple drivers and pesticides), spatially differentiated (different pesticide use approved for different places), include people by sharing information via monitoring, and be under continuous review.

There is an urgent need for action if we are to reduce the concern for the use of pesticides in the environment. Whilst the solutions suggested here cannot fix all ERA problems and will be difficult to implement, they would dramatically improve the current system.

Read this article in Danish at our Danish sister site Forskerzonen.