In Africa, they already do it.

Farmers feed insect larvae with household waste and sometimes even with animal droppings. Once the larvae are fully grown, they are then used as feed for fish, chickens or even pigs.

In the EU, this kind of thing is not allowed – and it makes insect production in Denmark and the rest of Europe far more expensive than it should be, explains PhD student at the Department of Animal and Veterinary Sciences, Ida Elisabeth Berggren.

- In the EU, you’re not allowed to feed insects with household waste if they are subsequently to be used to feed other animals. The legislators are worried that the insects absorb PFAS and pesticides from the waste, she says.

But in fact, no one knows whether the insects actually absorb PFAS and pesticides from the feed or not. Together with a number of colleagues, Ida Elisabeth Berggren therefore set out to answer that very question.

After extensive experiments with both mealworms and black soldier flies, two insects that are widely used as fodder, she discovered two things: That the insects absorb very small amounts of the pesticides from the feed, and that it is the opposite with PFAS, which accumulate in the insects.

- I would not say that pesticides pose a problem. We spiked the feed with high doses, and yet we found very small amounts in the insect larvae – especially in the black soldier fly. In other words they absorb almost nothing. The mealworms absorbed a little more, but we were able to reduce this by fasting the larvae afterwards, she says and continues:

- PFAS is a completely different story, but as far as I know, there is no PFAS in the household waste here in Denmark, as the substance is not allowed to be used in packaging.

Very few researchers have previously conducted experiments with insects and their ability to absorb pesticides and PFAS. Ida Elisabeth Berggren and her colleagues therefore had to develop a whole new method to test it. 

For this purpose, they used the institute's old rat laboratory.

- We devised a series of experiments that could determine whether the insect larvae absorb the toxins from the feed. In the old rat laboratory, we set up a number of insect boxes, filled some with larvae from the soldier fly, while we poured mealworms into others, she says.

The larvae starting crawling around, feeding in the boxes. All Ida Elisabeth Berggren and her colleagues had to do, was wait. But the feed in the boxes was not the usual insect feed. The researchers had spiked it with either PFAS or pesticides.

- We did a number of different experiments. In some boxes, the feed was spiked with four types of PFAS, in others with three different pesticides. In this way, we could investigate which substances the insects absorb and in what quantities, she says.

When Ida Elisabeth Berggren put the larvae in the boxes, they were only five days old and very small. Initially they weighed between 5 and 10 milligrams, but after eight days with the feed, they had grown to over 200 milligrams.

Now it was time to test whether the larvae had absorbed the toxic substances or not.

- First of all, we killed the larvae by freezing them. Then we sent both the larvae and the feed for analysis at the laboratory. This enabled us to spot any differences in the concentration of toxins in the feed and the larvae, and thus see how much they had absorbed, she says.

Ida Elisabeth Berggren's experiments show that insects absorb very small amounts of pesticides, even if their feed is packed with them. This suggests that it will not be a problem to feed them with household waste.

But more experiments are needed, before we know for certain, she emphasizes.

- We fed the larvae with chicken feed and not household waste. This means that we haven’t yet tested how many toxins insects on a diet of household waste absorb. But my prediction is that these insects will contain even less pesticides, because the level of toxins in the household waste is probably much lower than in the feed we gave them, she says.
With that said, she does not know the precise level of pesticides in household waste. That is why she believes that it needs to be tested, before politicians change the rules.

- The experiment should be repeated with real household waste. I’m pretty sure that it will contain some pesticide residues from, for example, citrus fruits. Whether there is PFAS in the waste, we do not know, but it is likely that PFAS, which comes from some types of pesticides, will be found in it as well, she says.

As it is now, according to EU rules, we are not allowed to use household waste for feeding insects. I hope that our results can pave the way for it to become possible in the future. To me, it would both be better for the climate and it would create a more valuable product from our waste. 

Ida Elisabeth Berggren

Scientists and the farming industry are interested in using insects as a source of protein for both humans and animals, because it’s a cheap and sustainable way to produce it. 

According to research from 2023, converting from soy-based feed to insect protein could reduce the climate impact from animal husbandry by between 40% and 97%. That is, if it is done in the right way. This requires that the larvae live on waste, and that the insect farms are heated with energy coming from sustainable sources like wind og solar power.

This is precisely why this form of production has great potential in Denmark, where green energy is abundant and cheap. But it requires that the legislation is changed, explains Ida Elisabeth Berggren.

- As it is now, according to EU rules, we are not allowed to use household waste for feeding insects. I hope that our results can pave the way for it to become possible in the future. To me, it would both be better for the climate and it would create a more valuable product from our waste. Today, most household waste is used for biogas, she concludes.

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Note: The results in this article come from a report commissioned by Danish authorities on insect breeding and the larvae's uptake of PFAS and pesticides. One of the researchers behind it, Ida Elisabeth Berggren, is working towards publishing the results as a research paper in a peer-reviewed journal later this year.