01.08.2009 Environment

Toxic Overload

Pesticides may be getting safer but we're using more of them. And, warns environmental toxicologist Dr Peter Dingle, most of that use is indoors.

Pesticides are a major concern because despite our growing awareness we are using more every year. Many people incorrectly think that because these chemicals are available in the hardware shops or, in some cases even from chemists, they are safe. They are not. They are toxic products designed to kill insects. What big industry does not want you to know is that, in fact, insects and humans have a lot in common. This is especially apparent with the nervous system. Many insecticides that are designed to attach to the nervous system of flies and cockroaches also damage our nervous systems. The situation becomes worse when we use them in our homes because they stay in the air and we spend so much time at home so we, along with our kids, are continually inhaling these poisons. There are much safer techniques available (for example, sticky traps for cockroaches and ants).

Recent research suggests that up to 80 per cent of most people's exposure to airborne pesticides occurs indoors. Research in Australia in the mid 1980s identified that the organochlorine pesticides used for termite control were found in high levels in homes and, consequently, at high levels in the milk of breastfeeding mothers. My team's research also found that these chemicals could still be detected even 10 years after termite treatment.

While we have moved to less persistent pesticides, the currently used toxic chemicals can stay around for weeks, months and even years. The reason we overuse and abuse these chemicals is that we have often become fearful of insects and pests but, paradoxically, the pesticide is often more dangerous than the pest!

Pesticides are toxic. They are designed to kill and they affect the biology and biochemistry of humans in the same way they affect insects. A pesticide is any substance or mixture of substances intended for preventing, destroying, repelling or mitigating pests.

Pesticides cover several broad chemical categories. The major groups are the inorganic and organic chemicals. The inorganic category (those containing no carbon) includes substances that have been used as insecticides and fungicides since ancient times. Generally, they include minerals and heavy metals such as copper, zinc, boron, sulphur, arsenic, iron, cyanide, lead, mercury and sodium. During the 19th and 20th centuries, compounds of these substances were developed as pesticides. These included calcium arsenate, lead arsenate, hydrogen cyanide, lime sulphur, salts and various metals (copper sulphate, iron sulphate), organic mercurials and copper silicate. But like their predecessors, they were often toxic to mammals and were used in excessive quantities that left persistent residues in the environment.

The 1940s and 1950s saw the demise of these inorganic pesticides as the new breed of organic pesticides was researched and developed. These include the organochlorine (or chlorinated hydrocarbon), organophosphate, carbamate and synthetic pyrethroid pesticides.

This newer class of pesticides can cause a range of acute health effects (the result of a single heavy exposure) or chronic health effects that result from numerous low exposures over a period of time. Symptoms vary according to the pesticide used, the degree of exposure and the amount that gets into the body.

They are often non-specific and a number of diseases may produce similar symptoms. The most common classes of pesticides kill by damaging the nervous system and, in humans, can cause headaches, nausea, dizziness and poor coordination. Long-term exposure can cause a range of adverse effects on human health, including damage to the nervous system, reproductive dysfunction, immune and endocrine problems and some forms of cancer.

For several decades, the nervous system has been a target organ for pesticide toxicity. The brain and the nervous system are the two primary targets of pesticides. Depending on the individual and the type of exposure, typical symptoms include poor memory; inability to concentrate; paraesthesia (nerve tingling and numbness); anxiety; depression; hyperacusis (noises seem louder than they are); fatigue and ataxia (poor balance).

In addition to the neurologic signs and symptoms of acute intoxication, studies have shown that many of the pesticides directed at the nervous system may cause delayed polyneuropathy neurobehavioral effects. Other studies have shown a link between chronic exposure to pesticides and the development of Parkinson's disease and motor neuron disease. Parkinson's disease, a nervous system disorder, decreases muscle control and can eventually disable a person.

The ability of pesticides to damage the immune system and to cause hypersensitivity reactions is often overlooked. The age categories most at risk for immune system damage are infants and children under ten. This is true because their immune systems are very immature and at high risk for damage caused by pesticide exposure. Unfortunately, few epidemiological studies focusing on immune system damage have been conducted on human populations. But wildlife and animal studies provide us with substantial evidence that pesticides are indeed immunotoxic. More epidemiological studies on humans need to be conducted in this area of concern.

Exposure to pesticides can result in sterility, infertility and gene malformations. Over the past 50 years, measures of male fertility have decreased dramatically worldwide. It is hypothesised that synthetic oestrogens, also referred to as endocrine disrupters, are the reason behind this dramatic decrease in male sperm counts. Many endocrine disrupters are pesticides such as 2,4-D, atrazine, benomyl, carbaryl, endosulfan, parathion, and synthetic pyrethroids. A recent study found that male members of the Danish Organic Farmers' Association had sperm densities double those found in males who didn't consume organically grown food.

Other hormonal disturbances can occur as a result of pesticide exposure. It has been demonstrated that synthetic chemicals such as pesticides, which are harmless on their own, may disrupt the female hormone system when they are combined with other chemicals.

A study published the journal Occupational and Environmental Medicine showed that children frequently exposed to insecticides used in the house, garden and in head lice shampoos run double the risk of developing childhood leukaemia. The latest study by France's National Institute for Medical Research showed that the risk of developing acute leukaemia was almost twice as likely in children whose mothers said that they had used insecticides in the home while pregnant and long after their children's birth. With rates of childhood leukaemia rising, most health professionals are trying to find new, great discoveries to cure it. We suggest the best strategy is to reduce your child's exposure to toxic chemicals.

Pesticides can pose a significantly greater threat to children than to adults. The reason is that in relation to their small body weight, children inhale or ingest a greater percentage of toxins than adults do. The playing habits of children such as somersaults on carpets, running barefoot on lawns, or digging through dirt give more direct contact with pesticide residues. Exposure of children to home-based pesticide residues (that is, after household items are treated with pest control products) is generally high as compared to adults since children tend to play in areas that have been sprayed. Research has shown that children living in areas where pesticides had been applied most heavily experienced elevated rates of acute respiratory diseases (including pneumonia), skin diseases, ear infections, tuberculosis, and dental caries.

Children receive four times greater exposure to pesticides than adults, because of their small body size and the large amount of fresh fruits and vegetables they consume. Hence children are much more susceptible to carcinogenic substances than adults. In early childhood, cells divide rapidly and this rapid division coupled with exposure to cancer-causing pesticides such as organochlorine increases the likelihood of cell mutations and the subsequent risk of cancer. Exposure to pesticides during preschool years could lead to cancer later in life.

It is found that half of a lifetime cancer risk from exposure to pesticides occurs during the first six years of life. This exposure also dramatically increases the risk of acute disease.

A pesticide profile

The organophosphate pesticide now used to control termites and ants, Chlorpyriphos, also persists in homes and continues to expose residents for months or, in some cases, even years. Chlorpyriphos affects the nervous system and is linked with a long list of adverse health effects.

Organophosphate pesticides to look out for are:

Diazinon;Dichlorvos; andChlorpyriphos.

Pyrethrum is derived from the dried flowers of Chrysanthemum cineraria folium. The term "pyrethrins" refers to the mixed active ingredients present in commercially available pyrethrum extracts, while "pyrethoids" refers to synthetic analogues of pyrethrin of similar structure to pyrethrums, hence their mode of action is the same.

Pyrethrins are acutely toxic to insects with a high degree of specificity that results from their relative rates of metabolism in insects compared with mammals. This fact has seen pyrethrins labelled as one of the safest and most ideal insecticides. The pyrethroids are metabolised very rapidly in mammals and, as a result, show only a low potential for bioaccumulation. The half-life of pyrethroids in adipose tissue was calculated at around two weeks. Concern has been raised about a link with the pyrethroids and allergies such as asthma.

Naphthalene is a white crystalline solid extracted from the petroleum refining process and coal tar distillation. The Environmental Protection Agency (EPA) classifies it as a Hazardous Substance, Hazardous Waste and Priority Toxic Pollutant. Despite its toxicity, it is a common product found in many homes. We most commonly come into contact with naphthalene through the use of mothballs.

Another toxic chemical commonly found in the home is arsenic. Arsenic has been used as a treatment for pine to prevent mould and termite attack. It is released into the environment from the timber, and children playing on arsenic-treated pine playgrounds will be exposed to some degree. Arsenic-treated pine is usually identifiable by the green colour of the logs or planks. Fortunately, CCA (copper chrome arsenic)-treated timber is now being phased out. Disposal of the logs is, however, a big problem as burning them creates a highly toxic gas and we shouldn't just dump wood impregnated with this toxic chemical.

Raising awareness of the prevalence and toxicity of such chemicals is an important step towards creating a safer environment, both within our homes and neighbourhoods.

Dr Peter Dingle is an environmental and nutritional toxicologist and Associate Professor in Health and the Environment at Murdoch University.

Peter Dingle

Dr Peter Dingle (PhD) has spent the past 30 years as a researcher, educator, author and advocate for a common sense approach to health and wellbeing. He has a PhD in the field of environmental toxicology and is not a medical doctor. He is Australia’s leading motivational health speaker and has 14 books in publication.