Organophosphate
An organophosphate (OP) or phosphate ester is the general name for esters of phosphoric acid. Many of the most important biochemicals are organophosphates, including DNA and RNA, as well as many of the cofactors essential for life. Organophosphates are the basis of many insecticides, herbicides, and nerve agents. The United States Environmental Protection Agency lists organophosphates as very highly acutely toxic to bees, wildlife, and humans. Recent studies suggest a possible link to adverse effects in the neurobehavioral development of fetuses and children, even at very low levels of exposure. Organophosphates are widely used as solvents, plasticizers.
Source: www.wikki.com
Pesticides are a very important group of environmental pollutants used in intensive agriculture for protection against diseases and pests. The estimated annual application is more than 4 million tons, but only 1% of this reaches the target pests. Function wise they are divided into herbicides (protection against weeds), insecticides (against insects), fungicides (against fungi), and others. While their use improves the quantity of agricultural products it potentially affects their quality, as pesticides may enter human diet. This is a matter of major current concern.
Source: cdn.intechopen.com
Corn uptake and insecticide use in field
Source: http://i1.wp.com/sitn.hms.harvard.edu/wp-content/uploads/2016/08/fig2pesticides.png
Types of Organophosphorus compounds or organophosphates (OPs) group
On the basis of structural characteristics OPs are divided into at least 13 types including:
- Phosphates,
- Phosphonates,
- Phosphinates,
- Phosphorothioates (s=),
- Phosphonothioates (s=),
- Phosphorothioates (s substituted),
- Phosphonothioates (s substituted),
- Phosphorodithioates,
- Phosphorotrithioates,
- Phosphoramidothioates.
Source: http:// pdfs-wm/13231.pdf
OPs are the most widely used pesticides worldwide and their metabolites are widespread across different populations. The World Health Organization estimates that every year 3 million people experience acute poisoning by OPs, 200.000 people terminally. Humans are exposed to OPs via ingested food and drink and by breathing polluted air. The exposure of workers in closed areas and of agricultural workers or people living near farms is also very important. The primary mechanism of OPs toxicity is well studied – they function as inhibitors of the enzyme acetylcholinesterase (AcHE). Human exposure to Ops is most frequently assessed by measurement of decrease in AcHE activity. This method is relevant for professional exposure, where OP concentrations entering to body are relatively high. However, low OP concentrations, which are present continuously, do not cause significantly decreased AcHE activity. Exposure of wider populations must lean on assessment of OP metabolites, such as alkylphosphate in urine.
Source: http:// part02/2_5_theme_3_protecting_your_crop.html
Mechanisms of toxicity
Mechanism of Ops Toxicity
The toxicity of OPs depends on their chemical structure, metabolism in target organism, concentration (i.e. dose), mode of application, degree of decomposition, mode of entering organisms, etc. The best described OP toxic effects are the neurological symptoms following acute poisoning as a consequence of the primary target (AcHE). Potential secondary targets and toxic effects outside the nerve system have not been well studied, but are nevertheless very important for risk assessment. Unlike other man-made chemicals, OP pesticides can affect a large proportion of the human population, as a result theExposure through domestic use, proximity to agricultural activities and consumption of contaminated food and water.
Source: pdfs-wm/13231.pdf
Impact on Crop and Distribution pathways
To control the maggots, growers usually apply organophosphate insecticides, such as chlorpyrifos and diazinon, to the soil, but those chemicals don’t kill all of the destructive insects and may contaminate waterways.
Source: ANRnewsreleases index.cfm,
Root maggots are less than 1/3 of an inch and tunnel through the crop roots.
Consumption of organophosphate pesticides by various crops in the US
Source: http://images.slideplayer.com/22/6360779/slides/slide_61.jpg
Distribution Pathway for agricultural pesticides
Source: www.who.int
Organophosphorus pesticides are mainly used in crop protection
Source: http://grdc.com.au/reports/ar2013
Only parathion and Malathion can be shown separately from the other organophosphorus pesticides. The information is incomplete since, for example, the USA and some other countries and regions do not report figures for every year. However, comparison of the figures given on a yearly basis gives an idea of the magnitude of the consumption and distribution of the organophosphorus pesticides throughout the world. All organophosphorus pesticides are subject to degradation by hydrolysis yielding water-soluble products that are believed to be non-toxic at all practical concentrations. The toxic hazard is therefore essentially short-term in contrast to that of the persistent organochlorine pesticides, though the half-life at neutral pH may vary from a few hours for dichlorvos to weeks for parathion. At the pH of slightly acidic soils (pH 4 - 5), these half-lives will be extended many-fold. However, constituents of soil and of river water may themselves catalyse degradation.
Source: www.inchem.org
OPs in the environment
OPs tend not to persist or bioaccumulate in the environment. They do however figure in many official cause-for-concern priority lists because of their toxicity, especially to the aquatic environment. All OPs are part of the EU Black List, a priority list of the harmful chemicals set out in EU Directive 76/464/EEC which aims to protect the aquatic environment. The UK Department of the Environment classified Dichlorvos, Fenitrothion and Malathion as Red List substances in 1989. The use of these chemicals should be reduced in order to combat environmental pollution.
Source: http://ucanr.edu/blogs/
Conclusion
By the late 1970s, the use of OPs began to over-take the organochlorine insecticides which included DDT. While organochlorines were relatively safe to use, their problem was persistence in the environment and detection in the human food chain. OPs on the other hand are more acutely toxic, but, do not persist in the environment beyond a few months. So with the switch from organochlorines to OPs, it can be assumed that the consumer has benefited at the expense of the pesticide operator. In terms of sheep dips in the UK and OP use in developing countries, safer non-OP methods should be brought forward as a matter of urgency to reduce the risks to operators. There should be a moratorium on OPs until safer alternatives exist, and OP use should be severely restricted in developing countries where protective clothing cannot always be guaranteed.
Source: pestnews/Actives/organoph.htm