• What are organochlorines?
• Which OCs are banned?
• Why are OCs such a problem?
• How long do OC contaminants persist?
• What are some of the sources of contamination?
• What is the National Organochlorine Residue Management program?

What are organochlorines?

'Organochlorines' (OCs) is a generic term for pesticides containing chlorine; however, the term is commonly used to refer to the older persistent materials, including aldrin, BHC, chlordane, DDT, dieldrin, heptachlor, lindane or toxaphene. Most have now been deregistered or their use has been severely restricted. The banned OCs had widespread use in agriculture as insecticides and acaricides. Their persistence ensured they were very effective in some situations. However, this persistence in soil and animals led to trade concerns associated with OC residues in meat, milk and poultry products.

The information below gives producers advice about potential problems associated with persistent contaminants in the environment that could impact on their stock. It does not include currently registered OC compounds, such as endosulfan and dicofol.

Which OCs are banned?

• DDT
• Aldrin
• Endrin
• Chlordane/oxychlordane
• Heptachlor/heptachlor epoxide
• Dieldrin
• HCB
• Lindane
• Methoxychlor
• BHC

Why are OCs such a problem?

OCs are a problem because they persist in the environment and, when consumed, are stored in animals' fat deposits. This poses a risk of OC contamination in both meat and milk products of grazing animals, such as cattle. After exposure for some time, the concentration of the chemical in the fat of cattle becomes higher than in the feed, usually by a factor of 10-15. The leaner the animal is, the less fat they have to dilute the chemical and the higher the resultant concentration in the fat.

The permissible levels of these chemicals in meat have set limits called extraneous residue limits (ERLs) - see Table 1. An ERL refers to a contaminant arising from environmental sources (including former agricultural uses) other than the use of the pesticide directly or indirectly on the commodity. It is the maximum concentration of the contaminant legally permitted on a food and is expressed in milligrams of the chemical per kilogram of the food (mg/kg).

If OC contaminants above the ERL, or the levels set by major export markets, were detected in meat products, these markets to Australia could be closed with disastrous consequences for the meat industry. The US market was temporarily closed in 1987 because of concerns over OC residues.

* MRL Standard Maximum Residue Limits in Food and Animal Feedstuffs of Agricultural and Veterinary Chemicals and Associated Substances, Australian Government Publishing Service, Canberra, Table 1.

** MRL Standard Maximum Residue Limits in Food and Animal Feedstuffs of Agricultural and Veterinary Chemicals and Associated Substances, Australian Government Publishing Service, Canberra, Table 4.

Notes:

• DDT is metabolised in the animal or broken down in the environment to DDD and DDE.
• Aldrin is rapidly metabolised in the animal to dieldrin.
• Chlordane is rapidly metabolised in the animal to oxychlordane.
• Heptachlor is rapidly metabolised in the animal to heptachlor epoxide.
• HCB was used as a fungicide/seed protectant until 1970 but still poses a problem through its presence in some currently registered pesticides.

How long do OC contaminants persist?

The persistence of OCs in both animals and the environment is described by the term half-life. This is the time taken for the concentration of the chemical to reduce by half. For example, if an animal's test result was 0.2 mg/kg for dieldrin, that concentration generally would have fallen to about 0.1 mg/kg in 12 weeks if that animal was grazing on non-contaminated pasture. Faster growing animals dilute the concentration of OCs at a faster rate, reducing the time before the contaminant is no longer detectable in the animal.

In soil, half-lives are much longer and depend on the interaction of a complex range of factors. For example, in 2-8 years, the concentration of dieldrin generally falls to half its original concentration. This does not mean that the land will not be contaminated after one half-life - it depends on how high the OC concentration was in the first place. Half-lives for OCs in soil are extremely variable and the values appearing in the table above are offered as a guide only.

What are some of the sources of contamination?

The tropical and subtropical climate of the coastal areas of Queensland ensures a high level of insect activity and consequential insecticide usage in crops and animals. All sugarcane and most horticultural crops are grown on the coast. Hence, persistent OC contaminants are likely to exist in coastal areas where sugarcane, cotton, bananas, apples, pears or root crops are growing or have previously been grown. Old cattle and sheep dips, yards, fence posts, power/telephone poles and buildings treated for termites etc are also likely to contain OC contaminants.

Generally, there is little movement of OC contaminants from contaminated soil directly into pasture plants, though some root crops (potato, turnip, beetroot, etc) can absorb and adsorb contaminants in the tubers or root growth. Cucurbits (cucumber, zucchinis, etc) have also been shown to absorb OC contaminants.

A significant proportion of OC contamination in animals is acquired by consumption of contaminated soil. The amount of soil consumed depends largely on the amount of grass cover, though cattle can consume 20-1200 grams of soil per day. Small amounts of contaminated soil can also be transferred to herbage by dust, raindrop splash or flooding.

Runoff from contaminated soils to farm water supplies occurs, but significant contamination of cattle from this route is unlikely because of the high dilution factor and the fact that OC contaminants are tightly bound to sediment.

More information on the risks of contaminants from soil.

What is the National Organochlorine Residue Management program?

National Organochlorine Residue Management (NORM) program was established to address the issue of persistent chemicals being detected in beef products.

See more information on the NORM program.