Insects and other arthropods are disappearing at an alarming rate all over Europe and pesticides play a major role. We interviewed the German Professor Dr. Carsten Brühl, specialist in ecotoxicology. His University Kaiserslautern-Landau recently published an alarming study in the journal “Scientific Reports”. Almost unbelievable but true, this was the first to examine pesticide contamination over the course of a year (1). They found a cocktail of pesticides not only during the spraying periods in the fields, but also throughout the year and in adjacent meadows.
The significant impact on the environment has hardly been investigated. The rapid loss of biodiversity is a disaster for our environment and jeopardises our food production, which depends on healthy and biodiverse ecosystems for pollination and fertile soil. The current EU pesticide regulation is failing, as was shown in our recent report ‘Licence to Kill’.
In this campaign, we will interview scientists, review new scientific research and highlight the importance of lesser-known arthropods. Our aim is to stimulate the discussion to achieve the urgent protection of the natural abundance on which our lives depend.
What is the role of arthropods in ecosystems?
Professor Dr. Carsten Brühl (CB): Insects and arthropods, including also crustaceans like that are present in terrestrial environments but also aquatic environments, play a big role in different processes in ecosystems like decomposition of organic matter or pollination of flowers. In general, they are the very base of food webs.
How big is the role of pesticides in the worldwide decline of insects?
CB: The good data set that triggered the discussion about 30-year decline comes from agricultural landscapes. That's very important and people have not seen such huge declines also in forest landscapes in central Europe, but in agricultural landscapes, so it means agriculture has to do something with it. If you look at the distribution of land area in Europe, roughly 50% is agriculture and a huge proportion, usually around 70% is dedicated to crop production. Most of it is conventional crop production and using therefore also pesticides. Even if you are not a biologist or ecologist, if you apply an insecticide on one third of the terrestrial land area of Europe and you do this again and again and again every year for 50 years. You don't need to be a genius to understand that an insecticide has an impact on insects. I therefore think that insecticides play a crucial role in the decline of insects.
What will happen if we continue like this?
CB: Where are we going if we continue to do this to apply pesticides in conventional agriculture as we currently do? I would say the main problem is that our ecosystem services pollination and decomposition, anything that has an impact on soil fertility will be disrupted. In the end we are about to reach a certain tipping point where there cannot be any recovery of the system.
Why is biodiversity not protected by pesticide regulation?
I guess the main misconception about the regulation of pesticides is that the regulation is always for one product alone. So there is a lot of information about what this one active ingredient the molecule that is responsible for the effect in the pesticide, what that does to the environment in humans. What we don't know is what a mixture does really.
A very important flaw of the system that in reality arthropods and anything that lives in agricultural landscapes is basically encountering a multitude of pesticides always in mixtures like 30 different pesticides. We don't know what this does to organisms. There is no information for this and this is not regulated and also this will never be regulated by the authorities
Another flaw in the regulation is the lack of indirect effects being assessed. Indirect effect means that a pesticides can as an example a herbicide has no toxicological effect. The bee is not dying. This is addressed in the risk assessment. However, the herbicide reduces plants that flowers in the landscape and therefore they indirectly affect bees because there is less food. Basically, this food chain effect is not addressed in the regulation. That's also very important.
What do you think of the concept of recovery?
CB: Anything that deals with mortality or recovery of populations only addresses one pesticide, so that's a flaw in itself. Therefore everything that will be developed will not help, because it's within this system where we assume that this insect will be only encountering one pesticide. That's entirely wrong.
The big question is why don't we use something similar as in the aquatic risk assessment where this so-called uncertainty factor is 100. So two orders of magnitude. To me at least it's very puzzling that we don't use a similar uncertainty factor in the risk assessment because I know the number for Germany. We have 30,000 insect species in Germany. In Europe must be quite a lot more. So I would think there is also a very large range of sensitivities towards an insecticide or any pesticide. And therefore the uncertainty factors should be high.
That's also something to take into account when a pesticide is regulated for and the companies carry out their test. It's the first time in an experimental situation where a field is treated with this specific pesticide. Once it's regulated and it's available in the market, this one pesticide is used by all the neighboring farmers as well. So it has an effect on landscape and this can be even very dramatic if you think of forecasting systems like we have for example for fungicides where basically every farmer gets a message by the organisation that does the forecasting. It says apply the fungicide now because it will be wet and warm and there's a risk for fungal infection and therefore all the farmers apply their product on a landscape scale. So we have an entirely different situation from that what we assume in the risk assessment, where we assume it's only a small area that is treated but that's not true. It is entire landscapes at once also within a very short period of time treated.
Can you tell more about specific findings from your research?
CB: One study that we did, for example, was with a herbicide and a moth caterpillar. The idea what we could show was the herbicide changes the biochemistry of the plant so to say because it's inducing in the plant, most likely a defense system and regulating its plant defense. It's regulating that up making the leaves of the plant less palatable for the insects. And so the moth that feeds on the plants that were only treated with very low concentrations of the herbicides. So the plant itself was not dead at all. It only started to synthesize something that was not beneficial for the insect. it basically decreased the food quality of these leaves for the insects, and it resulted in very small caterpillars that either did not hatch or they hatched into smaller moth species. So, generally, in insect size is also related to reproduction, and you could assume that these smaller individuals reproduce less and therefore in the long run, if we repeat this again and again we have again a population decline or even extinction of that specific species. But this was not a direct effect and it was also only a low dose effect that worked indirectly through the plant on the insect.
So it was not the herbicide that had the negative effect. It was something else that was triggered by the herbicide. So things can become very complex and the question is, do we really address this complexity? What we measure in risk assessments is generally acute mortality. In most cases, this is the called endpoint. You measure when 50% of your caterpillars or some organisms that you intend to study are dead. What you do not really measure or what is not addressed is the reproduction. What we would need is multiple cycles of exposure to see that we still have even after five generations no impact on the reproduction. But this would be a very complicated test.
We once also suggested to use Drosophila, the fruit fly, which is an organism that you can keep in laboratories and where we have an enormous amount of information on all kinds of biological aspects. So some people just started to use drosophila as a screening model for pesticides and they could show that there are tremendous effects also on reproduction. You could do life cycle tests for multiple life cycles. You could do mixture studies with drosophila. So I think that would be an ideal system to do something with it. Unfortunately, this was not taken up as a suggestion.
How far do pesticides spread from the fields?
My current research actually focuses more on measurements of realistic pesticide exposure in agricultural landscapes. And what we see there is that pesticides do not stay in fields. They are distributed over larger scales. I'm not talking about 100 meters.
I'm more talking about 20 kilometers. That's the scale I'm thinking of. Within 20 kilometers, everything from an agricultural field, most areas of Europe are covered. So, you can imagine that from any field that is under conventional agriculture, pesticides are emitted so they are volatized and they are distributed in landscapes and they reach other areas. We find their pesticides at low concentrations, but we always find mixtures and what we also did with an annual study, where we basically measured pesticides every month, we could also show that this is a pattern that is chronic.
For example, in agricultural soils we find 20 different pesticides every month throughout the year. Therefore, that was basically the starting point of this interview. I think this mixture is a real problem. We don't know what this mixture does. We have indications from now a new study on Drosophila that mixtures at low concentrations have impacts on reproduction. We can assume that this is also relevant for other organisms and therefore it should be addressed also in the regulation somehow.
What do you think of the concept of ecosystem disservice?
CB: The main point and the important point for everybody is that ecosystem services means there is for example, pollination of some crops. It doesn't matter, and that's the important point, if this is done by one species or by 20,000. For the concept of ecosystem services, biodiversity is not entirely necessarily until it's specifically mentioned. If you include the biodiversity in the ecosystem services, then things are getting more interesting.
Otherwise, you should be aware that maybe the reduction of species is entirely fine with the concept of ecosystem services.
Probably you can argue quite a lot with the ecosystem services. it's diffusion basically I would say there is not something like a disservice. This idea is entirely anthropocentric. We know now there was huge discussions about certain invasive species and all of a sudden if you study them for a longer time you realize that they provide flower and nectar for some species and it might be actually a beneficial addition to the flora and you can't do anything about it anyway. So yeah, I'm very critical about that kind of concept.
How can we protect biodiversity?
CB: So I mean it will not help to develop guidelines. The entire system is absolutely flawed. It is not representing reality and the only solution that I can see currently is really to reduce pesticides. That's the only solution.
if we want to protect insects, we need to stop using or reducing pesticides on larger scales. I'm talking about landscapes because we don't have another 30 years to see another 70% decline of the remaining 30% because then we are down to nothing. And yeah, unfortunately it's the climate crisis like any other crisises we live in currently and we need to act.
Full Interview with Prof. Dr. Carsten Brühl
Notes:
(1) Exposure of insects to current use pesticide residues in soil and vegetation along spatial and temporal distribution in agricultural sites - Carolina Honert, Ken Mauser, Ursel Jäger & Carsten A. Brühl , Januari 202
