Obviously it should come as no surprise that pesticides kill; it’s what they’re designed to do. However the range and quantities that are now being used means that many of these persistent chemicals are now impacting on organisms, including humans, that wasn’t envisaged when they first became available. So how do we, as humans, become consumers of pesticides and what effect do they have on not just our health, but the health of our future generation’s health?
A 1990 study by Dr Fenkse from Rutgers University (3) found that after treating rooms with the flea powder Dursban (chlorpyrifos), the air in a ventilated room was still more than twice over legal limits 5 hours after application. And it was 6 times over limits after 7 hours in an unventilated room. Of more concern was the residue still airborne at low levels (within the infant breathing zone). After 24 hours the pesticide level was still 3 times over the legal limits in an unventilated room. The researchers concluded; “Broadcast application and possibly total release/fogging applications of acutely toxic insecticides may result in dermal (skin) and respiratory exposures sufficient to cause measurable toxicological responses in infants.”
Pesticides are also now increasingly contaminating water supplies, with the European Union setting standards of 100 nanogrammes per litre of any individual pesticide. However there are no standards on the number or type of pesticides present. Contamination of water that we use for drinking, cooking and bathing is set to increase in the future as aquifers and other groundwater becomes contaminated through rainwater. Earlier this year in Switzerland, researchers discovered that rainwater laced with pesticides, such as atrazine and alochlor, at levels which would deem the rainwater unfit for human consumption (4). One sample contained the pesticide 2,4-dinitorphenol at a level of 4,000 nanogrammes per litre.
Other studies of rainwater have also shown the presence of pesticides, including a study undertaken by Charizopoules and Papadoppoplou-Mourkidou (5) who discovered at least one pesticide in 90% of samples taken in Greece.
With the air that we breathe and the water that we drink being contaminated, what can be found in the food that we eat?
In Britain, the Ministry of Agriculture, Fisheries and Food’s (MAFF) Working Party on Pesticide Residues (WPPR) has recently released its annual report for 1998 (6) and it contains some surprising reading:
+ 1998 saw the first time in many years that Lindane residues were NOT found in milk!
+ Excessive levels of pesticides were found on pears and there was even evidence that British farmers were using illegal pesticides on fruit. Putting profit before customers health.
But the worst examples were from UK winter lettuce, with almost half of all samples tested containing either pesticide residues higher than the maximum residue level (MRL) or, of more concern, non-approved pesticides. Exotic fruit and vegetables also tended to contain high levels of pesticides or non-approved pesticides. Contamination of non-approved pesticides is likely to increase over the coming years. Whilst action can be taken against British farmers for the use of dangerous chemicals on food, it is difficult to enforce standards in other countries.
The future world trade agreements will enable greater trade between nations and increase the risk of importation of contaminated food. Next time you go into your supermarket for fruit and vegetables check their country of origin. There’s a good chance that those French beans or tomatoes were grown in Africa or Asia.
What does this mean for the consumer? Well if you eat the recommended 5 portions of fruit and vegetables a day each year, you will most likely consume food containing excessive or illegal pesticides 24 time year or put another way, twice a month.
This constant battering of low levels of chemicals designed to kill, must eventually have an impact upon peoples lives. Evidence is now being found to suggest the use of chemicals to produce good looking, healthy and affordable produce is leading to cancer, infertility, genital deformations in males, increases in Attention Deficit Disorder, lowering of IQ and an increase in aggression, to name a few. But before we look at the health implications of these chemicals, what signs have we been given and still are being given over the negative aspects of pesticides?
Pesticides in the Wild:
The impacts of pesticides on birds was clearly and effectively described by Rachel Carson in her landmark book; Silent Spring (7). Fears of a future without wildlife led to people taking a closer look at the impacts of their actions on nature. Even now over 30 years later, nature is showing us warnings about indiscriminate and excessive use of chemicals.
Across the world conservationists and scientist have been looking for reasons why frog populations are crashing. Not only are frogs declining in number but also increasingly there are reports of strange deformities affecting frogs. Frogs and toads, breathing through their skin, can provide an extremely useful indicator of water pollution. As studies into their life cycle increase and a better understanding of their ecology evolves, the impacts of pesticides becomes clearer.
Numbers of frogs and species of frogs can explode on farms that move away from chemicals and convert to organic methods. A Minnesota farm when it converted to organic growing saw a major expansion in its leopard frog populations and other species soon arrived at the farm (8). Again, this time in Sri Lanka, when tea growers stopped spraying with herbicide frog populations greatly increased (9).
Deformities of frogs have been discovered in ponds affected by pesticide pollution; In Canada on the St Lawrence River 12% of frogs and toads were found to have hind-limb deformity (10). Pesticides with retinoid characteristics, such as methoprene, are also thought to contribute to frog deformities.
Retinoids are potent hormones in the same family as vitamin A and control early embryo development. Retinoids have been found to contribute to birth defects in all vertebrates including human (11). The types of birth defects discovered in frogs have been wide ranging and includes:
+ missing legs
+ extra legs
+ misshapen legs
+ leg growth from wrong parts of the body
+ legs joined by webbing
+ fused legs
+ legs split in two
+ missing eyes
+ and eyes growing in the wrong place (12).
Unfortunately, simply looking for retinoid chemicals within a pesticide is not sufficient to ensure that the chemical is safe to use. S-methoprene is a common insecticide used in fly sprays, flea powders and farm treatments. It has always been considered a safe chemical for use. James La Clair and fellow scientists at the Scripps Research Institute discovered that when this pesticide was left in the sunlight for several hours, the ultra-violet light caused the chemicals to breakdown into several different retinoids (13). The researchers showed that the amount of flea powder used to treat the average 10-pound pet once could contaminate 110,000 litres of water sufficiently to lead to frog deformities.
Reproductive problems of wildlife are also a possible consequence of the over use of hormone-like pesticides. Tributylin, a compound used to keep seaweed and barnacles from the hulls of boats have caused problems in gastropods as this powerful hormone-like chemical changes the sex of male gastropods to females (14).
The endangered Florida panther is under great threat because of hormone disrupting chemicals. These are ingested by eating contaminated racoons that in turn receive their intake from fish swimming in contaminated lakes and rivers (14). A study between 1985 and 1990 recorded that 67% of male panther were born with cryptorchidism (undescended testicles) and many other were sterile or produced deformed sperm.
The same report also highlights that male hatchlings of fish eating birds were becoming feminised. And there was even a report of lactating male fruit bats.
Alligators living within pesticide contaminated lakes in Florida have been found to have penises so small that they are unable to reproduce (15).
The effects of hormone disrupting chemicals can also been seen in the feminisation of male birds. Dr Michael Fry at the University of California has studied gulls at Santa Barbara Island and he has noticed an increased in female-female bonding and nesting. Dr Fry believes that this could partly be attributed to feminisation of male bird sex organs and the resultant lack of interest in breeding, in effect chemical castration by DDT and other environmental pollutants (16).
During the mid-70s numbers of Canadian Atlantic salmon dropped sharply, now believed to be a result of hormone disrupting chemicals from the insecticide Matacil 1.8D (17), which was sprayed in the forests. In this particular case, however, it was not the active ingredient, aminocarb, that was the problem but the remaining 75% inert carrier called 4-nonylphenol (4-NP) which turned out to be the hormone disrupter. 4-NP appears to have interfered with the smoltification of the salmon. Smoulting is a process that enables young salmon to endure the move from fresh water to salt water. By interrupting this process up to 77% of the salmon was lost.
This obviously leads us into questions over the impacts of pesticides on our own lives. Are these hormone disrupters powerful enough to be able to cause problems in humans?
Impacts on humans
Evidence is mounting to suggest that previously safe levels are no longer safe and that there is still much to be learned about these poisons. In what has to be considered a classic modern statistical study in 1996, researchers from the US Environmental Protection Agency and the University of Minnesota looked at the relationship of births and pesticides in the state during 1989 and 1992 (18). The results of this study of 210,723 births were damming to pesticides:
· Children born to state registered pesticide applicators (49935 births) had significantly raised risks of general birth defects and particularly raised occurrences of defects to the circulatory/respiratory, musculoskeletal and urogenital systems.
· Pesticide applicators in areas with the highest reported use of 2,4-D herbicides also gave birth to only half as many children as the general public, confirming previous studies that this herbicide is toxic to sperm.
· Children born in agricultural regions were statistically more likely to be born with defects than children born in non-rural areas. The risks increased for children conceived during the spring when more pesticides were used.
· Rural areas with high use of chlorophenoxy herbicides (2,4-D and MCPA) saw an 86% increase in the rates of birth defects affecting the central nervous, circulatory/respiratory, urogenital and musculoskeletal systems compared to low use areas. Areas that used these chlorophenoxy herbicides also witnessed a further 30% increase in defects to infants conceived during the spring months.
· Male infants seem to be more affected by the impacts of pesticides. The sex ratio for live births is generally around 104 males to 100 females, however the sex ratio of births with defects was 138 males to 100 females.
Birth defects affecting just males include an increase in the occurrence of hypospadias between the late 1960’s and early 1990’s. This increase was seen in both the United States and Europe (19). Hypospadia is a condition that effects male embryos between 9 and 12 weeks old and results in the penis not developing correctly.
Another way, in which pesticides are having an impact on males, is the increasing rates of infertility. Decreasing sperm counts and low sperm quality are clearly being recorded across the world where pesticides are in use. And again, it is thought that actions of toxins may be mimicking hormones during foetal life or childhood, the stages of life when low level chemicals can have devastating effects (20).
These effects are thought to have led to a loss of 50% in sperm count during the last 40 years (21). In Europe the quality of sperm donors is now so reduced that Danish fertility doctors have to recruit 10 potential sperm donors to find one with adequate sperm quality (21). A 1990 study in Denmark found that 84% of men had sperm quality standards below that set by the World Health Organisation (21).
Fertility Treatment Clinics in the United States have also found it increasingly difficult to find sperm donors even among young medical students (21). The report in the New Yorker even suggested that the average hamster now produces more normal sperm than the average human male! (21). The New Yorker article also high-lighted a study by Scottish researcher Stewart Irvine in which a Scottish male born in the 1940’s had a sperm count of 128 million while for those born in the late 1960’s it was 75 million, a drop of 40% in one generation. Difficulty in conceiving occurs at 20 million or less.
Lifestyle changes have been attributed to this reduction in sperm quantity and quality, unfortunately there are many cases of wildlife also being effected in the same way and they haven’t changed their way of life. Reduction in sperm quality has also be found in Belgium (22) where the amount of normal shaped sperm had dropped to less than 28% in 1994 from 40% in 1977. The amount of sperm with strong movement ability had also dropped from 53% in 1977 to less than 33% in 1994.
Toxins, predominantly pesticides, particularly those with estrogenic action, are thought to be the cause of some male reproductive problems. With the effects taking place before birth or very shortly after birth, the future could be bleak. As MRC researcher, Richard Sharpe, in Edinburgh points out, ‘Changes in life style won’t help men whose sperm-producing capacity has been crippled at birth.’
There is little doubt that pesticides can be found in the amniotic fluid of pregnant women (23, 24). And they can be found at levels that are similar to natural hormones. Animal experimentation has also found that pesticides can affect the functioning and structure of the testes resulting in reduced fertility (25).
Most people associate pesticides with cancer and there is an increasing body of evidence that suggest that a number of specific cancers can be attributed to pesticide use. Occupational groups that are involved with pesticide applications are showing higher occurrences of non-Hodgkin’s lymphoma, brain cancer, prostrate cancer and leukaemia (26, 27, 28, 29, 30).
There is ample evidence in the literature to link phenoxy herbicides to non-Hodgkin’s lymphoma (a study has shown that farmers using 2,4-D pesticide have 6 times the occurrence of lymphatic cancer than the general population (31, 32). We should remember that phenoxy herbicides are not restricted to agricultural use and many lawn treatments and garden plant treatments can provide a source of damaging chemicals.
A study undertaken by Giga-Talamanca (28) found pesticide applicators had up to 3 times the occurrence of brain cancer than the general population. The Aschengrau study (29) discovered a 7 times higher occurrence of astrocytoma type brain cancers among people living closer than 2600 feet of active agricultural land. Prostrate cancer was found to be 3 times the expected level for golf course superintendents together with over double the brain cancer death rate and over double the non-Hodgkin’s lymphoma rate (30). There is also ample laboratory evidence that pesticides affect animals leading to cancer (33).
We have already seen the way in which hormone-like pesticides can affect the development and fertility of males. These same hormone-like actions, particularly of those chemicals that have estrogenic properties, are also implicated in the increasing rates of breast cancers among women.
A recent study by Wolff (34) has shown that women with blood levels of DDE (a breakdown product of DDT) over 20 billionth of a gram per millilitre of blood had a 4 times greater risk of breast cancer. A further study by Falck et al, (35) demonstrated that breast tissues of those with cancer had elevated levels of DDT, DDE and PCBs compared to the breast tissue of woman without cancerous breast disease. The impacts of these estrogenic chemicals, however, could be more subtle than a direct action on breast tissues.
Evidence is beginning to mount that, just as with males, pesticides are having their impacts while the foetus is still in the womb. The age of puberty in females has been reducing during recent decades (36, 37) and it is not unusual now for puberty to begin at 7. This is increasing the time range that the female body is being subjected to estrogens during the ovulation cycle. Increasingly pesticides and PCBs are being implicated in this phenomenon. Studies within this field is at a very early stage, however, it is expected that exposure to environmental chemicals will be the leading protagonist.
A major concern to most people is the impacts of these chemicals on their children. Foetuses and young children are particularly susceptible to the smallest quantities of chemicals and links are now being made associating pesticides to childhood illnesses.
A review of 31 studies looking at pesticides and cancer concluded ‘…results from leukaemia studies suggest that no-pest strips and frequent use of pesticides in the home may be strongly associated with childhood leukaemia…'(38). The review also highlighted a number of other results;
· If the father was exposed to pesticides during the mother’s pregnancy then there was an increased rate of brain cancer, leukaemia, Wilms’ tumour and other childhood cancers.
· Children living on farms were more susceptible to brain cancer, non-Hodgkin’s lymphoma, neuroblastoma and retinoblastoma.
· Exposure as a child or while the mother is pregnant to professional pest extermination practises led to increases in rates of brain cancer and leukaemia being found.
Flea treatments in particular tended to result in an increase in brain cancer among children (39). Further evidence showing that home use of pesticides, such has flea collars and dog flea shampoos, led to increases in brain cancers was demonstrated by Davis et al (40). Household use of pesticides has also been demonstrated to lead to a 4 fold increase in the rate of childhood leukaemia, the rates increased to 6.5 times greater if pesticides were also used in the garden (41).
As we live in an ever-increasing hygienic society, childhood illnesses are bound to continue to increase. Pesticides can now be found in such a wide range of household products including anti-mould and anti-fungal paints and disinfectants that it is difficult for children to avoid the risks.
Apart from physical illness and defects, there is a growing awareness that very low levels of pesticides may be having a neurological effect on our children. Attention Deficit Disorder and hyperactivity is becoming increasingly prevalent and little is known about the cause, but pesticides are slowly becoming implicated.
It is thought that low levels of pesticides can affect the levels of thyroid hormone leading to greater aggressiveness and irritability. This has been shown in the lab with animals (42, 43) and increasingly with human studies in the field. A study of Mexican 4 and 5 year olds noted an increase in aggressive behaviour and reduction in mental ability in those children living in an area exposed to pesticides compared to those living in upland areas with low to no exposure to pesticides (44). Exposed children were more likely to be violent to siblings and became upset and angry at even minor corrective comments by parents. This behaviour was not noted in upland non-exposed children.
We need to accept that unless we are willing to reduce our reliance on pesticides and particularly those based on chlorine compounds, we are condemning our future generations to physical and mental disabilities. With the increasing power of multi-national companies and the willingness of big supermarkets to buy goods from countries with low environmental and health standards the risks of pesticide overload through our food and other products increases.
While it can take twenty years or more for these impacts to work its way through to illness in adults, children do not have that luxury and we see the results every day in hospitals and various media appeals for treatments and organ transplants. Are the consequences of killing that fly with a spray rather than a rolled up newspaper really worth it?
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