Tag Archives: pesticides

Non-toxic yesterday, but toxic today

In the 1940s a group of competent toxicologists led by William B. Deichmann conducted a number of thorough studies using state-of-the-art methods to conclude that the active ingredient dichloro-diphenyl-trichloroethane, or DDT, could be safely released to the environment for its use as insecticide. DDT was one of the first wide spread synthetic pesticides, and its widespread use led to resistance in many insect species.

ddt-good-for-me  ddt-recommended ddt-uses

As can be seen in the pictures, DDT was promoted to be used as insect repellent directly on human skin, to treat food products, or to impregnate the wall paper of your children’s room, so they won’t be bothered by mosquitoes. Tender images, such as a mother feeding a baby were used in commercial campaigns to basically sell poison. (*)

In the early 1970s, a scientific article authored by Deichmann (1972) himself and other studies provided enough evidence for the US Environmental Protection Agency to finally forbid the use of DDT as it became known to be toxic to humans, persistent in the environment, travel long distances in the upper atmosphere, and accumulate in fatty tissues of living organisms.


Rising evidence

What did actually happen between the 1940s and the 1970s? Why was DDT first considered innocuous or degradable and 30 years later banned and labelled as poisonous for humans, wildlife and the environment?There are several possible answers to these questions.

In the fist place, the ecotoxicity of certain chemicals when applied in small doses may only appear through cumulative effects (cf. http://www.efsa.europa.eu/fr/node/872721). Time is needed for problems to arise, or to become evident.

Second, and most importantly, the capacity of science to detect the adverse effects of a certain molecule released to the environment can progress substantially in 30 years.Problems that were overlooked or remained undetected in the past could be later on well understood and documented. (And the amount of scientific evidence that needs to be accumulated to be able to bend the arm of the chemical industry in court cases is not a minor detail).

The most skeptical opinions, in the third place, would argue that DDT was banned once the patent for exclusive production expired, and /or when the industry was ready to release a new product on the market. But these are just speculations.

Take home!

What’s important to take home is that examples such as this one should teach us about the long-term risk (uncertainty) associated with the widespread release of toxins into the environment, either as synthetic molecules or through toxin-producing plants (e.g., Cheeke et al., 2012). Alarming ideas such as the commercial release of genetically engineered microorganisms for soil amendment have been underway for a while (e.g. Viebahn et al., 2009), with unknown consequences for soils and the environment.

When it comes to releasing new technologies for food and agricultural production, I’d say it makes sense to follow precautionary principles. Releasing toxins into the environment: another case of organised irresponsibility…


(*) I believe that, nowadays, the baby in the early campaigns of DDT has been replaced by the term ‘sustainability’, which is also used in commercials and websites that advertise poison or toxin-producing plants.


Cheeke, T.E., Todd N. Rosenstiel, and Mitchell B. Cruzan. 2012. Evidence of reduced arbuscular mycorrhizal fungal colonization in multiple lines of Bt maize. American Journal of Botany 99, 700-707. DOI: 10.3732/ajb.1100529

Deichman, W.B., 1972. The debate on DDT. Arch. Toxikol. 29 (Springer), 1 – 27.

Viebahn, M., Smit, E., Glandorf, D.C.M., Wernars, K., Bakker, P.A.H.M., 2009. Effect of genetically modified bacteria on ecosystems and their potential benefits for bioremediation and biocontrol of plant diseases – a review. E. Lichtfouse (ed.) Sustainable Agriculture Reviews 2, Springer, p.45. doi 10.1007/978-90-481-2716-0_4.

Are there tipping points in pest management?

Tipping points are common in nature. When systems are disturbed beyond a certain point – a tipping point – they may undergo irreversible or hardly reversible changes that provoke shifts towards undesirable system states. It is often difficult to get systems back from this new ‘stable’ yet undesirable situation. Examples are many. A classical one comes from the work of Marten Scheffer in The Netherlands. He studied the dynamics of shallow lakes as they undergo phases of turbidity as influenced by nutrient loads or pollution. You can find out more about his work here.

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How about agricultural systems subject to high pesticide pressure? 

Synthetic pesticide applications are standard practice in conventional farming systems because they are simple to use, cheap, and usually effective in providing short-term reduction in pest densities. Yet, their effectiveness as a long-term sustainable pest management strategy is debated. This debate has been fuelled by the introduction of recent technologies, such as neonicotinoids seed coatings and herbicide tolerant GMO crops, with uncertain outcomes for biodiversity and resistance development.

Historic cases show that the use of pesticides can set off a positive feedback process whereby natural enemy populations are decimated and pesticides become the only pest management option left. The positive feedback between pesticide use and natural enemy mortality suggests the possibility of tipping point dynamics where the system can “tip” from a biocontrol dominated state to a pesticide dominated state. Tipping the system back from the pesticide dominated state to the biological control state could be challenging and require persistent efforts to allow a recovery process of natural enemy populations. Such transition may depend on landscape context and involve complex interactions between human actors and the agro-ecological environment.

The question remains: is there evidence for such tipping points? This will be the central question to be addressed during the debate that will bring Felix Bianchi, Dave Mortensen, Doug Landis and me together at a workshop organised by the PE&RC Graduate School of Wageningen University.

MORE INFORMATION: Poster-Tipping points in pest management