Tag Archives: agriculture; soil; food; sustainability

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.

Feeding the world with soil science?

The open-source journal SOIL of the European Geosciences Union is not just open source but also interactive. After a ‘traditional’ peer-review process is completed, scientific papers are posted on-line for the wider community to react to and comment on them. I was invited to contribute a piece about the contribution of soil science to achieving the UN Sustainable Development Goal 2 (SDG2): End hunger, achieve food security and improved nutrition and promote sustainable agriculture.  Euphemistically, the paper is entitled: Feeding the world with soil science: embracing sustainability, complexity and uncertainty. You are most welcome to have a look at it and leave your comments, questions and suggestions.

The paper revolves around the idea that feeding a growing and wealthier population, while providing other ecosystem services and meeting social and environmental goals, poses serious challenges to soil scientists of the 21st Century. In particular, three dimensions inherent to agricultural systems shape the current paradigm under which science has to contribute knowledge and innovations: sustainability, complexity and uncertainty. The current model of agricultural production, which is also often the source of inspiration to propose solutions for future challenges, fails at internalising these dimensions. It simply does not provide the necessary means to address sustainability, complexity or uncertainties. Part of the problem is that these are soft concepts, as opposed to hard goals, and so their definition and their translation into concrete actions is always subjective. In my view, in order to propose viable solutions to reach SDG2 soil science must contribute the necessary knowledge to:

(i) produce food where it is most needed;

(ii) decouple agricultural production from its dependence on non-renewable resources;

(iii) recycle and make efficient use of available resources;

(iv) reduce the risks associated with global change; and

(v) restore the capacity of degraded soils to provide ecosystem services.

This paper examines what the concepts of sustainability, complexity and uncertainty mean and imply for soil science, focusing on the five priorities enunciated above. It also summarizes and proposes new research challenges for soil scientists of the 21st Century.

Soil restoration

Particularly the last point, on the restoration of degraded soils (that occupy currently 25% of the land available for agriculture) is one of the key lines of action that I discuss in this paper.

The figure (click to enlarge) describes in a simple way the process of soil degradation, from left to right, and that of soil restoration, right to left. Restoration measures may result after time in soil conditions that are inferior to the original soil quality. The capacity of soil to restore its properties, or a management practices to facilitate that, is referred to as hysteresis of soil restoration (from Tittonell et al., 2016).