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Author Topic: What is the degradation pathway of pesticides ?  (Read 1982 times)

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What is the degradation pathway of pesticides ?
« on: June 08, 2018, 10:52:52 PM »

My major is related to the climate and environment change, and have limited understanding of organic chemistry. Recently, our research on the pollution of agricultural activities to the soil has encountered some problems related to the pathway of pesticide degradation.
According to several studies I have read, the process of pesticide degradation I understand is like this:

Through the processes of ozonation and advanced oxidation processes (AOPs), such as Fenton oxidations, H2O2/UV or Photocatalysis, the active hydroxyl radical ·OH (like Fig. 1) will be generated. Of these hydroxyl radical reactions, the generated organic radicals (R·) can be oxidized further by molecular oxygen2. Finally, the pesticide will be completely mineralized to ammonia, nitrate, H2O, CO2 and some other inorganic substance.
In the natural environment, such processes could be regarded as follows: Environmental conditions such as soil temperature and humidity, oxygen concentration, as well as the presence of  some selected microorganisms bacteria promote oxidation processes of pesticides (the generation of hydroxyl radicals). Then, biodegradation with aerobic bacteria (anaerobic bacteria) and selected microorganisms could eventually mineralize the residual pesticides into environmentally harmless substances (in ideal conditions).
For example, malathion can generate diethyl malate through the degradation process (see Fig. 2.). Next, diethyl malate will be mineralized to H2O and CO2 with microorganisms or bacteria.

My questions are:
1. Am I somewhat on the right path with this understanding? Will the above degradation process really happen under the optimized reaction condition?
2. Is the degradation pathway in Fig. 2 generated by chemical and physical agents? Such chemical and physical agents (ferrous ion , ozone, H2O2/UV) In addition to producing ·OH, are there oxygen, ozone, ammonia or some other substances directly involved in the degradation process (not as catalysts)?
3. If diethyl malate could be mineralized, could the reaction equation gives:
C8H14O5 + 9O2  :rarrow: 8CO2 + 7H2O

Any help from you will be greatly appreciated!

My References:
1.    K. Ikehata, M. Gamal El-Din, Aqueous Pesticide Degradation by Ozonation and Ozone-Based Advanced Oxidation Processes: A Review (Part II). Ozone Sci. Eng. 27, 173–202 (2005).
2.    K. Ikehata, M. G. El-Din, Aqueous pesticide degradation by hydrogen peroxide/ultraviolet irradiation and Fenton-type advanced oxidation processes: a review. J. Environ. Eng. Sci. 5, 81–135 (2006).
3.    M. M. Ballesteros Martín, J. A. Sánchez Pérez, J. L. Casas López, I. Oller, S. Malato Rodríguez, Degradation of a four-pesticide mixture by combined photo-Fenton and biological oxidation. Water Res. 43, 653–660 (2009).
4.    M. Cheng et al., Hydroxyl radicals based advanced oxidation processes (AOPs) for remediation of soils contaminated with organic compounds: A review. Chem. Eng. J. 284, 582–598 (2016).
5.    T. N. Volgina, V. T. Novikov, D. S. Vorobiev, O. Y. Fedorova, Oxidative Detoxification of Organomercury Pesticides. Procedia Chem. 15, 115–119 (2015).


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Re: What is the degradation pathway of pesticides ?
« Reply #1 on: June 15, 2018, 07:43:53 PM »

1. Yes they will happen under the best conditions
2. Yes these molecules can degrade at the phosphorthioester via non-catalytic processes
3. gasoline doesn't burn by itself. One needs a spark i.e. an enzyme to catalyze the reactions

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