Why do herbicides affect animals?

Maanantai 17.10.2022 klo 16.50 - Mikko Nikinmaa

The development of herbicides has long concentrated on finding molecules that affect biochemical pathways not present in animals. As a consequence, it has been considered that they do not cause harm to insects and vertebrates. Studies on animal cells have usually confirmed this supposition: since the biochemical pathway is not present, the compound is not toxic to animals.

Because of this, the increasing number of findings suggesting that herbicides have toxic effects on animal populations have largely been labelled as trash. This conclusion does not, however, take into account that the animal body has more microbes than body’s own cells. The animal’s microbiome, as it is called, influences nutrition, humoral and immune functions, metabolism and even neural behaviour. Many microbes in our body have the biochemical pathways targeted by the herbicide molecules. Consequently, herbicides affect the species distribution of microbiome, whereby the functions affected by the microbiome can also be influenced in animal body, and the herbicide be toxic to animal.

In recent review by Ruuskanen et al. in Trends in Ecology and Evolution (doi.org/10.1016/j.tree.2022.09.009) give a detailed description of the role of microbiomes in shaping the responses of non-target organisms to herbicides. An important point to note is that the sensitivities of organisms that are susceptible vary markedly. Also, the speed by which resistance is developed is highly variable. Further, the fact that different conclusions are reached if animal cells or whole animals are used in the studies casts significant doubt on the animal protection thesis that instead of intact animals, cell cultures should be used in toxicological studies.

Microbiota and environmental pollution

Sunnuntai 26.11.2017 klo 17.40 - Mikko Nikinmaa

All animals contain microbes, often billions of them.The symbiosis between the host and its microbes is essential for the well-being of the animal. Two examples of this show how important it is. If one is eating antibiotics, the gut microflora becomes disturbed, and, e.g., diarrhea can be the result. Ruminants utilize bacteria for digesting grass. Because of the fact that microbes are affected by completely different toxins than their animal hosts, surprising effects of environmental pollutants can be observed. For example, some herbicides may affect the necessary microbes of man, and because of this, although the effective compound does not exert any toxicity on the animal itself, by disturbing the microbial community of the animal, it may influence its well being. Effects of environmental pollution on the microbiota of animals is so far poorly studied - and is undoubtedly one area, which will receive important attention in the future.

Poorly known addditives may be more harmful than glyphosate itself

Torstai 22.6.2017 klo 10.31 - Mikko Nikinmaa

With the discussion about the harmful effects of glyphosate on tends to forget that the additives in the different commercial formulations may be more harmful to non-target species than the main toxic ingredient. It is undoubtedly true that the persistence of glyphosate in soil in different climatic zones is poorly known, and because of the antibiotic properties of the compound, knowing this would be necessary to be able to estimate the effects of the toxin on the community functions of soil micro-organisms.

However, for animals the additives in the commercial formulations are the real problem. The additives are a commercial secrecy, but an example of their importance in mediating at least acute toxic effects in non-target animals comes from a recent study: pure glyphosate and one commercial formulation showed negligible toxic effects, whereas another formulation was acutely highly toxic. Since the additives are a secrecy, the properties of the compounds used cannot be studied, since the compounds in question are not known.

Two things should generally be noted about glyphosate and its formulations. First: because glyphosate is affecting pathways specific to autotrophic organisms, it has not been considered important that the effects of its commercial formulations are studied with non-target animals. And because the additives are a secrecy, even if the effects on non-target animals are studied, one does not know the toxic compound. Second: the chronic effects of the main toxic ingredient and additives have not been investigated at all on non-target animals. Because of this, there are wild, and completely unsubstantiated, rumours about the harmful effects caused.