The Link between Pesticides and Parkinson’s Diseases
Pesticides have for many decades been used by farmers and other professionals in different activities to achieve various favorable goals. They have been responsible for the eradication of many pests, which has in turn had a positive effect on farming practices around the world. For many farmers, pesticides have been a necessity in farming as it has proven to be the most effective ways of dealing with pests. Pesticides have mainly been used in agriculture to protect crops against harmful pests. Pesticides have also been greatly used domestically, to guard against pests and insects. This has also proven useful through the last few decades. Pesticides however have been known to have a negative effect on human health. In recent years research has been conducted to investigate the effect of pesticides on human health and the extent to which a link between the two exists. This paper specifically addresses the link between pesticides and the causation of Parkinson’s diseases in human beings. The paper explores the various ways and settings in which pesticides are used and the involvement of human beings in that use.
Understanding Pesticides
Pesticides can generally be viewed as a possible set of interventions whose main goals is to eradicate or at least reduce the numbers of pests to manageable levels. Pesticide action is not just limited to insects, but extends to all kind of plant pests, pathogens and various weed populations. This means that pesticides contain in them insecticides, herbicides, fungicides and other forms of pest controlling chemicals. Pests around the world account for the destruction of about 40% of the world’s crops (Microsoft Encarta, 2007). This happens both when crops and in the fields and after they are harvested. Various kinds of insects, rodents, birds and various kinds of microorganisms are responsible for this damage and are the reason for the necessity of pesticide use. It is therefore easy to understand the popularity of pesticide use among farmers. It saves farming millions of dollars in losses resulting from crop destruction by pesticides. Some studies show that for every 1 million invested in pesticides, 4 million is saved in monetary returns (Microsoft Encarta, 2007 ). These savings in cash should however be weighed against the overall cost to human health brought about by the use of pesticides.
Understanding Parkinson’s disease(PD)
Parkinson Disease (PD) is a disorder of the nervous system. It mainly affects muscular control. The decreased integrity of the muscular system generally results in trembling of the arms and legs, muscular rigidity, and compromised balance. The disease progresses slowly overtime getting worse consistently until it has severely compromised all the main functionalities of a human being. It eventually makes some of the most basic activities impossible, including the ability to think. The disease does not have a cure but may be controlled through a variety of drug, therapy and surgical interventions. The drugs are majorly used to control some of the most difficult symptoms. Although the presentation of the disease as well as its progression is well known, the exact cause of it is still unclear. The National Parkinson Foundation based in Miami, Florida, estimates that 1.5 million people in the United States are affected with Parkinson disease, although estimates are difficult to make because symptoms of the disease are often mistaken for the normal effects of aging or are attributed to other diseases. People most commonly develop Parkinson disease around the age of 60, and the incidence rises with age. The term ‘parkinsonism’ refers to refers to a group of diseases whose symptoms mainly mimic those of Parkinson’s disease. The link between the development of these diseases and the use of pesticides are also of interest to this paper because of the connection to Parkinson’s diseases. Although Parkinsonism is often misdiagnosed as Parkinson’s disease they do not fully respond to similar interventions.
Causes of Parkinson’s
Genetic factors
Parkinson’s could be caused by several different factors. One of the causative factors is a genetic predisposition to the disease inherited from a parent or a close relative. Studies have shown that genetic predisposition may increase a person’s chances of developing Parkinson’s disease.15% of individuals with the disease have a close relative who also has it (Foltynie et al. 2002). Gene coding, which is somewhat similar in among family member may undergo mutation which may result in the degeneration of the cells which may lead to the development of Parkinson’s. Studies conducted with twins reveal that an identical twin is more likely to develop Parkinson’s disease if the other develops the disease. The case is not similar for fraternal twins who unlike identical twins do not have similar genetic makeup (Microsoft Encarta, 2007).
According to Foltynie ( 2002), in young onset of Pd, twin studies reveal high rates of concordance in monozygotic twins, suggesting that the development of PD in younger peplum may be influenced by genetic factor ( Tanner, 2003).
Gene-environment interactions in specific references to PD have not been exhaustively researched an d there exists a large possibility that interactions between certain kinds of genetic makeup with environmental influences such as pesticides could be responsible for the occurrence of PD (Kelada et al, 2006).
Free Radicals
Free radicals, naturally found in the body may also play a part in the development of the disease. They interfere with normal cell activities in the body, damaging cell organelles and eventually trigger cell death. This ultimately compromises body organs. Free radicals mainly flourish when inadequate amounts of antioxidants are unavailable in the body.
Environmental factors
Parkinson’s disease is mainly thought to have environmental factors that are the main cause of its development. Industrial chemicals and other artificially produced chemicals have been found to possess chemicals whose effect is detrimental and therefore a serious threat to human health. The increased number of patients diagnosed with the disease today may be related to the presence of an environmental toxin (poisonous chemical) released as a byproduct from machines and other technology. Scientists have identified a number of drugs, chemicals, and viruses that cause diseases that resemble Parkinson disease. The chemical MPTP for instance, a byproduct created in the synthesis of certain illicit drugs, is linked to the development of a disease in some drug abusers that closely resembles Parkinson disease. Individuals who are exposed for significant durations of time to certain pesticides seem to have a higher incidence of Parkinson disease, although a direct link between Parkinson disease and these chemicals has not yet been established.
Other environmental factors possible responsible for the development of PD include repeated head trauma and the extended use of neuroleptic drugs.managnese toxicity has also been thought to induce parkinsonism ( Addler, 1990).
It is worth noting that exposure to pesticides does not necessarily have to be through airborne ways, such as breathing it in. It may occur through interaction with contaminated water, soil and even the eating of contaminated food. Barbeau et Al ( xxxx) has suggested that there is a connection between development of Pd and the drinking of pesticide-contaminated water, based on the high prevalence of the disease in certain hydrographic regions in Canada which all seemed to have connections with farming and pesticide use. In one particular case, well water was found to be directly, positively and independently associated with PD development (Zorzon et al. ,2002).
The Link between Parkinson’s disease and Pesticide use.
A cause-and-effect relationship between environmental neurotoxins and Parkinson’s is difficult to prove. This is particularly difficult because it involves the study of different populations which present s difficulties in methodology of study. Moreover, other factors tend to come into play when studies involve many people and it is difficult to isolate required data that is uninfluenced by these other factors. It is therefore hard to authoritatively state that certain factors are the sole cause of PD. However, epidemiological and etiological research points to strong correlations between exposure to pesticides and the development of PD (Tanner et al., 2003).
Due the increasing incidence of exposure to pesticides with the development of Parkinson’s in individuals who are thus exposed, it is possible to conceive of a connection between the two. Scientists and other professionals have for a long time hypothesized about the existence of a connection between the two. In this regard many studies have been conducted in a bid to study the disease and its possible causative factors. Other studies have been conducted on the side effects of the use of pesticides on human beings. Others still have tried to connect the two. Research concerning the same is done mainly by testing the effect of suspect chemicals on animals and using the findings to establish the possible effects of the same chemicals on human beings. Other researchers study select populations who are significantly exposed to the suspect chemicals and compare their incidence rates of Parkinson’s to control populations of unexposed individuals. Many researchers over the last few years have established link between the two. Scientists have isolated 3 main types of chemicals that are suspected to trigger the development of PD. Each of these pesticide’s mechanisms of damage to cells are different.
Three ways have been suggested as to how pesticides may play a role in the development of Parkinson’s disease. The first is that pesticides are directly neurotoxic which cells cannot handle. ‘MPTP is the prototype Parkinson’s disease neurotoxin’ (Couteur et al, 1999).This toxicity interferes with the functioning of cell organelles, notably the mitochondrion. they also inhibit dopamine transmission between brain cells and this largely impairs cell functions. Secondly, pesticicides may cause PD through the induction or inhibition of certain important xenobiotic metabolizing enzymes. This then impairs metabolic activities, which ultimately leads to cell death. lastly, it is though that pesticides could be a conduit through which other naturally occurring neurotoxins are able to enter the body and cause Pd. In this theory it is not the pesticides themselves that result in Pd development but rather act as a host for Pd –causing neuro toxins. These neurotoxins maybe naturally occurring in farms or certain water sources ( Couteur et al ., 199).
Herbicides
These are generally chemicals designed to eradicate the development of weeds and other unwanted plants, mainly herbs, so as to ensure that they do not compete with the farmer’s crop for essential nutrients. Herbicides stop their growth and kill them. Paraquat is one such chemical whose main action is the destruction of broad leaf weeds. This chemical is thought to interfere with brain proteins and destroy brain cells, ultimately resulting in Parkinsonism ( ). Trifluralin is also a herbicide known to have similar effects. Organochloride and organophosphate containing pesticides are especially suspect for the causation of Pd.
Insecticides
As their name suggests, insecticides are designed to kill insects by the direct damage of their brain cells. Rotenone, which belongs in this class is particularly destructive to cell mitochondria and has been known to induce oxidative stress to the brain. It may also increase the production of certain brain chemicals, which lead to the ultimate destruction of brain cells.
Fungicides
These are chemicals that act against fungal organisms that pose a threat to crops and lead to plant diseases. Maneb and Benomyl are examples of fungicides that are thought to have a negative effect on brain cell mitochondrial functions. They also impair the ability of brain cells to repair themselves thus accelerating cell death.
Because of their different mechanisms of action, exposure to multiple types of pesticides poses an increased risk of PD development that the exposure to only one type. Research suggests a number of evidences that there is indeed a link between the two. Rotenone and paraquat are some of the major pesticides thought to play a part in the causation of Parkinson’s disease development.
Animal test evidences
The effect of pesticides on animal cells and structures has been known to trigger neurodegenerative processes in targeted pests. Research by scientists at the University of California Los Angeles revealed that the same effect that certain pesticides have on insects , rodent sand certain microorganisms also occur in human beings( ).certain chemicals work synergistically to from neurotoxic agents, although each of the chemicals used differently is relatively safe. Researchers at the University of Pennsylvania exposed a rat to rotenone, a common pesticide for a period of time. The rat gradually began to display symptoms of Parkinson’s disease. The mitochondrial inhibiting action of the chemical severely compromised the animal’s neurological functions and led to its parkinsonism ( ).Betarbet et al ( xxxx) similarly assert that ‘chronic administration of rotenone induces major symptoms of Parkinson’s disease in rats. Tests revealed that the exposure lead to the degeneration of animal brain tissue. This has led to the hypothesis that this particular chemical which is very widely used could actually be exposing its users to the risk of Parkinson’s disease development. The researchers however observed a difference in the level of vulnerability to rotenone among different populations, suggesting that there may also be other factors at apply, along with exposure to the pesticide such as genetic makeup. Pesticidal action has been observed to induce cell death in animals by initiating pathological processes which result in irreparable damage. The effects of this pesticide on animal brain cells can be used to suggest a link between the presence of certain pesticides and the occurrence of Parkinson’s especially where the incidence of the disease is high in regions where the chemical is present. The study can also be used to make inquiry into possible similar effect of other pesticides inhuman beings.
Mechanistic evidence
Another way in which it is possible to draw evidence that there exists a link between pesticides and the development of Parkinson’s disease is in the cell functions. Individuals experiencing the disease are known to have certain symptoms in their cells. The cell mitochondrion which converts cell nutrients into energy is usually fairly destroyed. In other cells, oxidative stress which often causes cell self-destruction often occurs. By investigating the prior presence of chemicals (pesticides) known to have this effect on animal cells, researchers are able to conclude that a connection exists. Control populations of individuals from the same region are also considerd.Using statistical methods; researchers are able to draw meaningful conclusions. Such a study was conducted and revealed that the incidence of Parkinson’s disease was 2.5 times more likely in individuals who had been exposed to toxic pesticides than those who had not. There is a significant association of the use of certain groups of pesticides which contain substances that disrupt mitochondrial activities or cause oxidative stress with the occurrence of Parkinson’s. Research by the National Institute of Health indicates that individuals who are exposed to either rotenone or paraquat over significant periods of time usually have a two and a half more chance of developing Parkinson’s than those who have not, all other factors being constant (Tanner et al, 2011). In joint study by the National Institute of Environmental Health Sciences (NIEHS) and the Parkinson’s Institute and Clinical Center in California, 110 people with PD, along with 358 control individuals were studied to determine the influence of pesticides on PD development. This was part of a larger study where 90,000 farmers and their spouses were interviewed to assess the life-long effects of pesticide use was on them. Findings revealed increased incidences and severity of PD among individuals more often exposed to the pesticides both infrequency and in quantities. Control populations revealed less incidences of PD (Tanner et al, 2011 ).
Proximity evidences
There is a correlation between the occurrence of PD in individuals and their proximity areas where pesticides are available or in use. As early as in the seventies epidemiologists noticed an increased incidence of Pd development in individuals who had grown up in rural areas where they were more likely to be exposed to farm pesticides. This was even more true for individuals who had grown up on farms. The role of pesticides in the possible cause of Pd was suggested. Further research has been conducted in recent years where individuals living or working in areas where they are likely to be exposed over a long duration of time to pesticides are examined for PD as compared to those who are not. Research reveal that such individuals report two and a half times more case of PD as compared to the control populations(Tanner et al, 2011).Some studies have geographically linked pesticide usage to the occurrence of PD( Couteur et al, 199).Many studies reveal a positive correlation between the duration of exposure to harmful pesticides and the development of PD. The same studies also suggest a similar correlation with increased quantities of exposure. The likelihood of PD development is though to increase if exposure to harmful pesticides occurred in an individual’s youth and teenage years other than later in life ( Nelson, 2000).Thy fact that farming, rural living and consumption of well water have been found to be closely linked with many PD patient suggests that pesticides, which is a factor that is related with all the three is a causative factor of Pd ( Brown et al., 2006).
Other studies also show that continued contact with certain domestic pesticides can also expose individuals to the same fate as those exposed to industrial herbicides and farm pesticides. In 2009, UCLA published a report linking Parkinson’s to exposure of both farm and domestic pesticides.
Drug use evidences
There are some substances that have been known to induce Parkinson- like symptoms. Such substances have been used in research to establish whether a link between Parkinson’s and Pd exists. The chemicals in the substances are compared to chemicals found in pesticides to gauge whether he same substances could be responsible for Parkinson’s.
Certain types of drugs have been known to induce Parkinson-like tremors. Heroin for instance has a chemical in it that causes individuals to tremble involuntarily. This makes heroin addicts of particular interest in scientific studies. Investigations into whether similar chemicals found in heroin are found in some pesticides have been done with positive results in some pesticides. Methamphetamines have been known to also induce temporary Parkinsonism in some of its users ( ). The toxicant 1-methyl-4-phenyl-1,2,3,6-
tetrahydropyridine (MPTP) usually found in certain quantities in some drug substances taken by human beings has been known to induce parkinsonism in its patients , causing symptoms that pathologically and biochemical present like those in a Parkinson’s patient. This has been true foe some drug addicts however and not for all of them. Pesticides which therefore bear a similar structural or molecular make up as that in MPTP are therefore thought to be risk factors for PD development. These include pesticides like rotenone and Paraquat (Goldman & Tanner, 1998).
Conclusion
Although there are numerous gaps in research done about the connection between PD and pesticide use mainly due to methodological inadequacies, it is possible with the amount of data already gathered to suggest that there is indeed a strong link between the two.
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