Pesticides – The Real Pests.

By Ceara Harper

Pesticides are defined as a substance to eliminate or control pests which cause harm or interfere with the production, processing, storage, transport or marketing of food, animal feedstuff, wood or agricultural commodities (Pesticides Act 2002). Pests include rodents, insects, bacteria, fungi, plants and larvae; which, for example, could reduce crop yields or the product quality (Ortiz-Hernandez et al., 2013). The spread of human vector-based diseases like malaria and schistosomiasis are also reduced by pesticides (Nicolopoulou-Stamati et al., 2016). However, whilst pesticides are lethal to their target organism, they are often toxic to the surrounding environment and to non-target animals, including humans. In order to ascertain correlations between the toxicity, degradation and structure of pesticides, pesticides are commonly classified based on their chemical composition (Ortiz-Hernandez et al., 2013). Some examples of pesticide groups include biological (viruses, microorganisms and their metabolic products), botanical (derived from plant products) and organosulphurs (which have sulphur as a central atom) but there are many others (Ortiz-Hernandez et al., 2002). These pesticide groups can be split between persistent and biodegradable. The persistent pesticides, such as organochlorides, are far more harmful to the environment and off-target organisms compared to biodegradable pesticides, because they can take months or even years to degrade. Organochlorines are particulary dangerous; they are soluble in lipids and thus accumulate in animals’ fatty tissue. In this way, they move through the food chain, where they can exert a toxic effect on a range of animals (Badii and Landeros, 2007). 

When it comes to humans, pesticides can enter the body via oral, respiratory and dermal entry (Nicolopoulou-Stamati et al., 2016). Depending on the type, concentration and amount of pesticide, the effects vary in severity. Detrimental side effects from the consumption of pesticides include gastrointestinal, neurological, carcinogenic disorders, reproductive disorders, chronic diseases, autoimmune diseases and birth defects (Sanborn et al., 2007; Bradberry, Proudfoot and Vale, 2004 and Mostafalou & Abdolahi, 2013). You may be wondering how pesticides elicit these toxic effects? Let’s look briefly at the mechanism of the widely used organophosphate, carbamate and organochlorine pesticides and their effects on the human body. Organophosphates and carbamates lead to symptoms of excessive cholinergic stimulation, as they have the ability to inhibit the acetylcholinesterase enzyme (Fukuto, 1990 and Kwong, 2002). Organochlorides are neurotoxins that cause repetitive firing of neurones by continual opening of sodium channels. All three of these pesticides cause cell toxicity and imbalance in metabolic function by disrupting mitochondria, which leads to cellular oxidative stress, thus causing a disturbance to hormonal and neuronal workings in the body (Karami-Mohajeri and Abdollahi, 2011). 

The chemical pollution brought about by pesticide use is not only dangerous to human health, but it is also extremely detrimental to natural ecosystems. One of the arguments for the use of pesticides is to ensure food security. However, contrastingly, pesticides jeopardise food security in the long term by acting as key drivers of insect decline (Brühl and Zaller, 2019), contributing to the extinction of 500,000 insect species in the coming years (IPBES, 2019). These insects are irreplaceable commodities, essential for pollinating crops and undertaking nutrient recycling, without which we cannot produce food. Furthermore, such extinction of insect species weakens and breaks-down ecological networks across the globe, greatly reducing biodiversity (Cardoso et al., 2020). A simple and clear example can be seen through bird and bee decline in areas with neonicotinoid pollution (Goulson, 2014). Overall, climate change, continued use of pesticides, harmful agricultural practices and loss of habitats threaten the collapse of ecosystems essential for human survival by pushing them beyond a point of recovery (Cardoso et al., 2020).

We must transform agriculture in order to move to a sustainable, greener, healthier and more robust food system by acting on solutions already available to us (Samways et al., 2020). Natural habitats need to be recovered and preserved, damaging agricultural practises need to be eliminated, over-exploitation of resources and careless use of toxic pesticides must be stopped. One solution to help positively transform agriculture lies in growing and buying organically, thus supporting an industry that meets a set of environmental requirements that develop a resilient natural landscape, increasing biodiversity by working with nature rather than against it (Samways et al., 2020). In order to sell under the ‘organic’ label, farms must use environmentally friendly methods of pest, weed and disease control (Šrůtek, 2008), meaning no synthetic fertilisers or pesticides are used whilst crop rotation, closed-loop nutrient cycles and soil fertility are focused on (Foley et al., 2011). Furthermore, old concerns that organic farming would not be sufficient to feed the world can be set aside as scientific research has found that organic farming has the potential to sustainably feed 9 billion by 2050 (Muller et al., 2017).

Post-Brexit trade deals are likely to lower pesticide standards in the UK, such that foods will be authorised to contain far higher levels of toxic pesticides than previously legal (PAN UK, Sustain and Lydgate, 2020). This is extremely harmful to the health of the human population as well as the environment. For example, grapes in the US are allowed to contain 1000 fold the quantity of propargite (an insecticide linked to infertility and miscarriages) than the current standard, whilst food containing residues of chlorpyrifos are permitted in the US and India – an insecticide linked to damage in the cognitive development of foetuses and young children (PAN UK, Sustain and Lydgate, 2020). Considering that imported food is likely to be cheaper post-Brexit due to lower health and safety standards, UK farmers will probably be outcompeted in the market. Therefore, UK customers should be alarmed and wary of the change in the market and the UK government should work to protect and improve upon current pesticide standards. For those able to afford Organic produce who don’t already purchase it, I hope you will consider doing so in the future. 

References:

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Bradberry, S.M., Proudfoot, A.T. and Vale, J.A. (2004). Glyphosate Poisoning. Toxicological Reviews, 23(3), pp.159–167.

Cardoso, P., Barton, P.S., Birkhofer, K., Chichorro, F., Deacon, C., Fartmann, T., Fukushima, C.S., Gaigher, R., Habel, J.C., Hallmann, C.A., Hill, M.J., Hochkirch, A., Kwak, M.L., Mammola, S., Ari Noriega, J., Orfinger, A.B., Pedraza, F., Pryke, J.S., Roque, F.O., Settele, J., Simaika, J.P., Stork, N.E., Suhling, F., Vorster, C. and Samways, M.J. (2020). Scientists’ warning to humanity on insect extinctions. Biological Conservation, 242, p.108426. 

Foley, J. A. et al. Solutions for a cultivated planet. Nature 478, 337–342 (2011).

Fukuto, TR . Mechanism of action of organophosphorus and carbamate insecticides. Environ Health Perspect 1990; 87: 245–254.

Goulson D. Ecology: pesticides linked to bird declines. Nature (2014) 511:295–6. 

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Kwong, TC . Organophosphate pesticides: biochemistry and clinical toxicology. Ther Drug Monit 2002; 24: 144–149.

Mostafalou S, Abdollahi M. Pesticides and human chronic diseases: evidences, mechanisms, and perspectives. Toxicol Appl Pharmacol (2013) 268:157–77. doi:10.1016/j.taap.2013.01.025

Muller, A., Schader, C., El-Hage Scialabba, N., Brüggemann, J., Isensee, A., Erb, K.-H., Smith, P., Klocke, P., Leiber, F., Stolze, M. and Niggli, U. (2017). Strategies for feeding the world more sustainably with organic agriculture. Nature Communications, 8(1).

Nicolopoulou-Stamati, P., Maipas, S., Kotampasi, C., Stamatis, P. and Hens, L. (2016). Chemical Pesticides and Human Health: The Urgent Need for a New Concept in Agriculture. Frontiers in Public Health.

Ortiz-Hernandez et al., 2002: Ortiz-Hernández ML. Biodegradación de plaguicidas organofosforados por nuevas bacterias aisladas del suelo. Thesis. Biotechnology PhD. Universidad Autónoma del Estado de Morelos.

Ortiz-Hernández, M.L., Sánchez-Salinas, E., Dantán-González, E. and Castrejón-Godínez, M.L. (2013). Pesticide Biodegradation: Mechanisms, Genetics and Strategies to Enhance the Process. Biodegradation – Life of Science. 

PAN UK, Sustain and Lydgate, E. (2020). Toxic Trade. [online] Pesticide Action Network UK. Available at: https://issuu.com/pan-uk/docs/toxic_trade_report_2020?fr=sM2MwNTExOTMxNQ.

Pesticides Act 2002, Kingdom of Tonga, http://www.fao.org. (n.d.). FAO.org : [online] Available at: http://www.fao.org/faolex/results/details/en/c/LEX-FAOC049091/ 

Samways M.J., Barton p., Birkhofer K., Chichorro F., Deacon C., Fartmann T., et al. Solutions for humanity on how to conserve insects Biol. Conserv. (2020)

Sanborn M, Kerr KJ, Sanin LH, Cole DC, Bassil KL, Vakil C. Non-cancer health effects of pesticides. Systematic review and implications for family doctors. Can Fam Physician (2007) 53:1712–20.

Šrůtek M., Urban J., in Encyclopedia of Ecology, 2008

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