Pesticide and toxicity?

Traditional farming used a lots of pesticide to prevent, destroy, repel, or reduce the severity of pests.(1) Chemical pesticide are effective enough to control infestation of pest as they are capable to kill them instantly within seconds to hours.(1) However, pesticide can cause detrimental effect to health as it contains toxicity, such as methamidophos poisoning which can be lethal.(2, 3) Many pesticide are volatile enough and easily exposed with inhaling them or absorbing them through your skin which made you sick.(3, 4) Ecotoxicology research also shown that wildlife in aquatic and terrestrial environment are prone to toxicity of pesticide, which disrupt the food chain in the ecosystem and it is an important issue.(5, 6) Different pesticide has different toxicity in environment, the same pesticide has different strength of toxicity with varied particle size. (7)  

Different classes of chemical pesticide and fungicide
Chemical pesticide are varied in different classes, it mainly divided into inorganic ion form, organic compound and organometallic compound.(4) For inorganic ion pesticide, there are bouillie bordelaise which consist of copper sulphate and calcium hydroxide, aluminium phosphide.(8, 9) For organic compound, there are organochlorine insecticides such as DDT, Velum One from Bayer, permethrin etc, most of the pesticides are in this form.(10, 11) For organometallic compound, there are dimethylmercury etc.(12)

Organic compound pesticide tends to have bioaccumulation when compare to inorganic ion and organometallic compound due to lipophilicity, which tend to stay longer in organism by dissolving the pollutant into lipids within the organs, which cause significant damage to organism itself and its offspring.(13)

Different particle size of chemical pesticide and emergence of nanoparticle pesticide.
Nanoparticles are particles between 1 and 100 nanometres (nm) in size with a surrounding interfacial layer.(7) Imagine you are driver, you are driving your vehicle into a carpark and stop in front of the boom gate to press for hourly ticket/tag on your smart card (Octopus card in Hong Kong), while some children or animal like cats sneak through the boom gate and get in the carpark. This concept is also similar in cellular environment, the receptor on cell membrane play the role of boom gate to separate extracellular substance from entering the cell, thus bulky substance or metal ion need active transport to enter the cell, especially in situation which against concentration gradient with intracellular environment saturated with molecule while extracellular environment didn’t.(14) If the bulky molecule or metallic ion need to enter the cell, they need ligand which is the smart card/hourly ticket to activate the receptor to open a channel for the entry of substances.(14)

However, nanoparticles can enter the cell easily by sneak through the leak on cell membrance – fluid mosaic model due to its small size, which similar to the children and small animal that sneak through the boom gate.(7, 15) Those easy penetration properties of nanoparticles enable them to cause more damage within the cell when compare to bulk molecule due to the cell membrane cannot filter them.(7, 15)

Using silver nanoparticle pesticide as example, silver particle can easily penetrate the cell, cause DNA damage, inflammation of tissue and activate apoptosis of the cell at the end.(7) Silver nanoparticle can cause teratogenic effect in developing embryo, studies showed that zebra fish egg contaminated by silver nanoparticles turned newborn fish become defective monsters and lose most of their physiological functions.(7) Those nanoparticles cannot be remove easily by conventional sewage treatment, which pose the danger causing aquatic organism become teratogenic monster.(7)       

Mechanism of action for chemical pesticide cause detrimental effect to human and other organism.
Depends on the various chemical nature of those pesticide, there are various mechanism of action such as genotoxicity, neurotoxicity and endocrine disruption.(6, 16, 17)

For genotoxicity, the pollutant cause damage to the gene directly, which alter the cellular function and cause toxicity.(16) Teratogenecity is one of the sub effect of genotoxicity, which cause the embryo malformed instead of normally developed.(16) Carcinogenecity is one of the sub effect of genotoxicity, it initiate development of cancer after the gene are altered which pose danger to organisms.(16) 

For neurotoxicity, there are effects on the neuron structure and effects on the neurotransmission.(17, 18) For effects on neuron structure, toxicant altered the flow of Na⁺ and K⁺ across nerve membrane and disrupt the action potential process, this lead to the paralysis of organisms.(18) For effects on neurotransmission, toxicant altered the transmission of acetylcholine, which disrupt the parasympathetic nervous system and sympathetic nervous system, if the parasympathetic nervous system is over stimulate, the individual may suffer from vomiting, nausea, diarrhea, slower heartbeat etc.(17)

For endocrine disruption, there are estrogenic effect and androgenic effect.(6, 19) For estrogenic effect, the toxicant work as agonist and stimulate the female characteristic, female may experience early menstruation, early egg production which may not mature enough for fertilization and male may experience the female organ development with losing male characteristics.(6) For androgenic effect, male may experience early development of male sex organ with sex behavior like ejaculation, early production of sperm etc, female may develop male organ with losing female characteristics.(19) Those effects will altered the reproduction of organisms, which lead to the deadline of population at the end when the old generations are gone.(6, 19)       

The process of chemical pesticide damage wildlife
When organism has taken the chemicals, they experienced illness or death, which lead to the food chain problem.(20) The effect of toxicant is ranged from molecule to ecosystem, the process involved molecular, organelle, cell, individual, population, community and ecosystem depends on the strength and permeability of the toxin. (21) There are bioaccumulation of toxicant in organism, primary consumer consume the pollutant from producer, secondary consumer consume primary consumer, the highest level consumer in food chain will have the highest amount of pollutant in their body.(21) Organism with impaired reproductive ability from toxicant will experience population deadline at the long term.(21)

When pesticide are discharged into soil or water sources, they can cause damage to the environment due to persistency.(22) Many toxicants are known to have long degradation time, which indicate several generations of organism are prone to the damage of chemical pesticide and the degraded metabolites.(22)

Should we ban chemical pesticide or not?
Pesticide should not be banned completely because of its need in agriculture and the effect on the industry. If we ban pesticide completely and rely on organic farming, more efforts are need to compensate the lost of crops from disease and pests. If we completely cling to chemical pesticides, our health and ecology will be damaged. We have to preserve the balance between organic farming and use of chemical pesticide by stronger control and regulation, it can be done by random sampling of vegetables in the market and sampling of the soil in the farms with analytical chemistry. The control of pesticide can be enhanced by legal requirement for recording the amount of chemical pesticide/fungicide used each time in the field, include sowing chemical (Thiram+Metalaxyl) treated seeds




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8.     Mathew P, Austin R, Varghese S, Manojkumar A. Effect of copper-based fungicide (bordeaux mixture) spray on the total copper content of areca nut: Implications in increasing prevalence of oral submucous fibrosis. Journal of International Society of Preventive & Community Dentistry. 2015;5(4).

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11.   Cox C. Permethrin. Global Pesticide Campaigner. 1999;9(3):20.

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13.   Santos Á, Soares JX, Cravo S, Tiritan ME, Reis S, Afonso C, et al. Lipophilicity assessement in drug discovery: Experimental and theoretical methods applied to xanthone derivatives. Journal of Chromatography B. 2018;1072:182-92.

14.   Martenson JS, Yamasaki T, Chaudhury NH, Albrecht D, Tomita S. Assembly rules for GABAA receptor complexes in the brain. eLife. 2017;6.

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16.   Garry VF, Griffith J, Danzl TJ, Nelson RL, Whorton EB, Krueger LA, et al. Human Genotoxicity: Pesticide Applicators and Phosphine. Science. 1989;246(4927):251-5.

17.   Sharma S, Chadha P. Induction of neurotoxicity by organophosphate pesticide chlorpyrifos and modulating role of cow urine. SpringerPlus. 2016;5(1):1344.

18.   Garthwaite J, Garthwaite G, Hajós F. Amino acid neurotoxicity: Relationship to neuronal depolarization in rat cerebellar slices. Neuroscience. 1986;18(2):449-60.

19.   Hou J, Li L, Wu N, Su Y, Lin W, Li G, et al. Reproduction impairment and endocrine disruption in female zebrafish after long-term exposure to MC-LR: A life cycle assessment. Environmental Pollution. 2016;208:477-85.

20.   de Jong FMW, de Snoo GR, van de Zande JC. Estimated nationwide effects of pesticide spray drift on terrestrial habitats in the Netherlands. Journal of Environmental Management. 2008;86(4):721-30.

21.   Ghisi NddC. Relationship Between Biomarkers and Pesticide Exposure in Fishes: A Review. In: Soundararajan RP, editor. Pesticides - Advances in Chemical and Botanical Pesticides. Rijeka: InTech; 2012. p. Ch. 15.

22.   Helling CS, Kearney PC, Alexander M. Behavior of Pesticides in Soils. In: Brady NC, editor. Advances in Agronomy. 23: Academic Press; 1971. p. 147-240.

Figure 1: Movento pesticide from Bayer available in agriculture shop within Perth 

Figure 2: Different chemical pesticides availble in vegetable seeds shop within Hong Kong



Figure 3: Chlorpyrifos and Malathion available in vegetable seeds shop within Hong Kong, both are organophosphate pesticide which disrupt neurotransmission in the pest