Fluorescence spectroscopy for detection of toxic pesticides

A report by actionaid on the use of pesticide in Nepal. To learn more, click this cover of the UN report saying "catastrophic impact" of pesticide on human health and the envioronment.

Principal Investigator: Ashim Dhakal, PhD Photonic engineering.

Associated Investigator: Chintan Manandhar, MSc in Biology.

This project is intended to research a simple and cost effective method to measure pesticide residues in food (green vegetables, fruits, dairy and meat) so as to control the use of toxic materials in food. The targeted users of the technology are general farmers and consumers in Nepal, which benchmarks the intended user friendliness of the technology to be investigated. We envision a smartphone that will be equipped with small add-on hardware and an application that will allow determining toxic residues in food with a press of a button. Below we outline the context, and technology to be used in this project.

Pesticides are living organisms or chemicals used to kill, repel or control organisms that we do not want. According to FAO [1], pesticides include “ substances intended for use as insect or plant growth regulators; defoliants; desiccants; agents for setting, thinning or preventing the premature fall of fruit; and substances applied to crops either before or after harvest to protect the commodity from deterioration during storage and transport. The term also includes pesticide synergists and safeners, where they are integral to the satisfactory performance of the pesticide.” The use of pesticides adversely affects the ecosystems that are dependent on the target organism. Often due to lack of the specificity of the pesticide, untargeted organisms, and ecosystems that they are part of, are also affected seriously. Hence, the use of pesticides must be very carefully managed.

The current estimate [2] of average pesticide use in Nepal is an alarming 2560 g/ha in cotton farming, 2100 g/ha in tea farming and 1400 g/ha in vegetable farming. In urban areas, the use of pesticides can be expected to be much higher due to the need for higher yield, and need for preservation. Hence, not surprisingly, the pesticide-linked problems have been found in humans, fishes and wildlife. The problem is compounded by the heavy use of many primeval pesticides that are cheaper (because of expired patents), but more persistent, more toxic and less selective [3]. On the other hand, as high as 35% of food is lost annually due to improper pest management [4], coercing farmers for extensive use the pesticides. Inadequate resources, such as toxicology labs, instrumentation and staff, have been pinpointed as the most critical limitation to carry out the essential pesticide management [5].

World Health Organization estimates 240,000 people killed by unintentional poisonings in the developing countries, associated strongly with excessive exposure to, and inappropriate use of, toxic chemicals and pesticides present in occupational and/or domestic environments [6]. In context of Nepal, research has shown acute intoxication, and lower Erythrocyte Acetylcholinesterase (AChE) and lower hemoglobin levels among vegetable farmers [7]. In another study conducted in the soil sample of four major cities of Nepal (Kathmandu, Pokhara, Biratnagar, Birgunj), high levels of dangerous DDT and endosulfans were found, Biratnagar being the most vulnerable among the four sites [8].

Simple and user-friendly technologies for detection of pesticides allow the first hand measurement of the pesticide content in the food sample. With help from such technologies farmers and distributers can manage and control the use of the pesticides right at the production and distribution level. Regular measurements of the pesticide they use allow the farmers and the distributors correlate several hazards associated with the use of the toxic pesticides. This makes them more aware of the issue. On the one hand, this will make them more aware of the hazards associated with the use of excessive pesticides, which in turn minimize the unintentional and unnecessary use of the pesticides for food production and distribution, minimize the ecological hazards, and increase the productivity of the farmers. On the other hand, such techniques will also allow the consumers to determine any pesticide residues in the food they are planning to purchase or consume. Hence, a simple method to measure pesticide can lead to en masse decrease in the consumption of toxic produce, significant reduction in the pesticide use, leading to a significant positive impact in ecology and public health.

A technique similar to that we have envisioned has been recently reported by ITRI Taiwan. This technique uses absorption spectroscopy and can detect residues as low as 0.75 ppm. However, this technique is applicable only to certain types of pesticides, soluble to water. The techique needs sample preparation and is not applicable to vegetables and fruits "on the go" as we are investigating.
Read more on their webpage.

Current techniques used for detection of pesticides, such as rapid bioassay of pesticide residues [9], gas chromatograph and other techniques [10], require skilled technicians as well as sophisticated lab infrastructure. These techniques thus do not meet the requirement of a simple and user-friendly, yet effective technique. Hence our institute is currently investigating a technique based on natural light (called fluorescence) emitted by the plant and the pesticides, when exposed to a certain color of light. The emitted light can be detected using a CMOS camera embedded in almost every smartphones. The use of native light emitted by the target pesticide makes this method very simple, because no sophisticated methods of purification and separation of the chemicals is required. The sophistication and innovation of this technique lies at the hardware and software design, with which users are not concerned. We envision a technique that ideally allows users to scan the target samples and get the information with a simple user interface, which summarizes the result of the analysis done by the embedded hardware and software system.

The fluorescence spectroscopy technique we are investigating is a standard technique used in cellular and molecular investigations [11]. Feasibility of the quantitative and qualitative detection of pesticides and herbicides using fluorescence spectroscopy has already been scientifically established [13-14]. However, the technological challenges of optical hardware and software design are yet to overcome before the technology can be brought to the users. There are several key areas of innovations we are working to overcome these challenges. Our innovation is aimed to enhance the selectivity and sensitivity of this technique as required for a smartphone based technique [15]. We welcome you to contact us and visit our lab to know more about these innovations.

  1. Manual on the Development and Use of FAO and WHO Specifications for Pesticides
  2. Annual progress report, Pesticide Registration and Management Division (PR and MD), Dept. of Agriculture, Govt. of Nepal 2009
  3. Ecobichon, D.J., 2001. Pesticide use in developing countries. Toxicology, 160(1), pp.27-33
  4. Anual progress Report, Post-harvest Management Directorate, Dept. of Agriculture, Govt. of Nepal 2007.
  5. Advancement of pesticide regulatory management in Asia
  6. Goldman, L, Tran, N. Toxics and poverty: the impact of toxic substances on the poor in developing countries. Washington, DC, The World Bank, 2002.
  7. Neupane, D., J ø rs, E. and Brandt, L., 2014. Pesticide use, erythrocyteacetylcholinesterase level and self-reported acute intoxication symptoms among vegetable farmers in Nepal: a cross-sectional study. Environmental Health, 13(1), p.1.
  8. Yadav, I.C., Devi, N.L., Li, J., Zhang, G. and Shakya, P.R., 2016. Occurrence, profile and spatial distribution of organochlorines pesticides in soil of Nepal: Implication for source apportionment and health risk assessment. Science of The Total Environment.
  9. Chiu, C.S., Kao, C.H. and Cheng, E.Y., 1991. Rapid bioassay of pesticide residues (RBPR) on fruits and vegetables. Journal of Agricultural Research of China 中華農業研究, 40(2), pp.188-203.
  10. Jung, F., Gee, S.J., Harrison, R.O., Goodrow, M.H., Karu, A.E., Braun, A.L., Li, Q.X. and Hammock, B.D., 1989. Use of immunochemical techniques for the analysis of pesticides. Pesticide science, 26(3), pp.303-317.
  11. Sharma, A. and Schulman, S.G., 1999. Introduction to fluorescence spectroscopy (Vol. 13). Wiley-interscience.
  12. Obare, S.O., De, C., Guo, W., Haywood, T.L., Samuels, T.A., Adams, C.P., Masika, N.O., Murray, D.H., Anderson, G.A., Campbell, K. and Fletcher, K., 2010. Fluorescent chemosensors for toxic organophosphorus pesticides: A review. Sensors, 10(7), pp.7018-7043.
  13. Delattre, F., Cazier, F., Cazier, F. and Tine, A., 2009. Use a fluorescent molecular sensor for the detection of pesticides and herbicides in water. Current Analytical Chemistry, 5(1), pp.48-52.
  14. Viveros, L., Paliwal, S., McCrae, D., Wild, J. and Simonian, A., 2006. A fluorescence-based biosensor for the detection of organophosphate pesticides and chemical warfare agents. Sensors and Actuators B: Chemical, 115(1), pp.150-157.
  15. Mei, Q., Jing, H., Li, Y., Yisibashaer, W., Chen, J., Li, B.N. and Zhang, Y., 2016. Smartphone based visual and quantitative assays on upconversional paper sensor. Biosensors and Bioelectronics, 75, pp.427-432.