Chronic Effects

Exposure to pesticides has been linked with chronic illnesses and conditions, including cancers, reproductive problems and neurological effects, which may take many years to become manifest.

Pesticide Action Network UK, a non-government organisation, has compiled a list of pesticides that have been evaluated by national and international regulatory authorities as representing a carcinogenic hazard.

There are nearly 170 on the list.

Other potential health problems resulting from exposure to pesticides classified as persistent organic pollutants (POPs), organophosphates (OPs) and endocrine disruptors are discussed below.

The prediction of health impacts from pesticide exposure is complicated because people are exposed to numerous chemicals on a daily basis and the combined effect, or “cocktail” effect of such exposure is also discussed below.

Organophosphorous Pesticides (OPs)

Organophosphates emerged from wartime research on nerve gases.

Since then, OP compounds were found to have insecticidal properties and many compounds were commercialised for agricultural use.

OP pesticides in China are reported to be responsible for a high percentage of acute pesticide poisonings.

As a consequence of acute exposure to OP pesticides, long-term damage as well as short-term effects to the nervous system can occur.

Furthermore, long term (chronic) exposure to small repeated quantities of OPs may also result in long term damage to the nervous system.

Studies have also shown that OPs may also cause adverse effects to male reproduction.  

Endocrine Disrupting Chemicals

The endocrine (hormone) system of the body is vital for controlling growth, development and general health in humans and animals.

Many synthetic chemicals -- many of them used in pesticides -- can interfere with the endocrine system and interfere with the natural balance of hormones in the body.

Over the past 50 years there has been an increase in disorders of the male and female reproductive system throughout the world which could be linked to these chemicals.

They are also thought to be able to harm the development of babies in the womb and bodily functions.

Regulatory authorities agree that lindane, DDT, atrazine and tributyltin are endocrine disrupting chemicals.

Atrazine is one of the most widely used herbicides in the world and is registered for use in China.

Significant atrazine pollution has been found in the Liao-He and Yangtze rivers of China.

A recent survey of pesticide residues in food in China conducted by Greenpeace identified 8 potential endocrine disruptors in foods, namely, aldicarb, carbofuran, cypermethrin, DDT, deltamethrin, dicofol, endosulfan and lindane.

Persistent Organic Pollutants (POPs)

Persistent organic pollutants (POPs) are a group of chemicals which are very resistant to natural breakdown processes and are therefore extremely stable and long-lived.

Most do not occur in nature but are man-made.

Once released into the environment, many persist for years, even decades.

Many POPs are highly toxic and build up (bioaccumulate) in the fatty tissues of animals and humans.

These three properties – persistence, toxicity and potential to bioaccumulate, make them arguably the most problematic chemicals to which natural systems can be exposed.

Some POPs exert their toxic effects through endocrine disruption.

In recent decades, POPs have been produced worldwide and have become widespread pollutants in the environment and even contaminate regions remote from their source, such as the Arctic, deep oceans and mountain areas.

POPs are suspected to harm the immune system, nervous system and growth of babies in the womb.

Some chlorinated pesticides are POPs.

China has been a major producer and consumer of POPs pesticides.

DDT is still allowed to be used for control of malaria transmitting mosquitoes.

Chlordane and mirex are being produced and used for the control of termites.

HCB is not used as a pesticide in China but is being used as an intermediate for the production of other chlorinated substances.

A 2005 investigation in human breast milk in five regions, Guangzhou, Hong Kong, Beijing, Shenyang and Dalian, found that with the exception of Shenyang, levels of DDTs in milk in all other Chinese regions were among the highest concentrations found in other countries.

It was suggested that the high concentrations in Chinese human milk were largely due to past extensive use of DDT in agriculture.

Results also indicated that Guangzhou, Hong Kong and Beijing populations showed more recent exposures to DDT.

The “Cocktail” Effect

Humans and wildlife alike are exposed to a mixture or “cocktail” of numerous chemicals which pollute the environment including pesticides.

However, we know little about the health implications of the combined “cocktail” effect of this exposure.

Generally, in laboratory studies, the effects of exposure to chemicals are tested individually on a chemical by chemical basis.

There are few means to test the toxic impacts from exposure to chemical mixtures, especially when such chemical ‘cocktails’ run to tens or even hundreds of individual substances.

Theoretically, exposure to mixtures of chemicals/pesticides simultaneously, could result in an additive effect or even a synergistic effect whereby the effect of multiple chemical exposures is greater than the sum of the individual effects.

However, research on the toxicological impacts of mixtures of pesticides or other chemicals is limited and the “cocktail” effect is not usually addressed by regulatory authorities.

Some research has shown that pesticides can act additively or synergistically when in combination.