Persistent organochlorine (OC) contaminants in cattle

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 following information is intended to provide advice to producers with potential problems associated with persistent contaminants in the environment impacting on their stock.  The discussion 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 the fat deposits of animals.  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 to 15.  The leaner the animal is, the less fat is available to dilute the chemical and the higher the resultant concentration in the fat.

The permissible levels of these chemicals in meat have set limits referred to as 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 this could result in the closure of these markets to Australia with obvious disastrous results for the meat industry.  The US market was temporarily closed in 1987 because of concerns over OC residues.

Table 1

Extraneous Residue Limits for OCs in animal commodities and stock feed.

Contaminant	ERL* Meat [mammalian] [in the fat]	ERL** (Animal Feeds)	Half life in soil	Half life in fat
Aldrin and dieldrin	0.2	0.01	2-8 years	6-12 weeks
BHC (other than the # isomer, lindane)	0.3	0.02	2-3 years	4-7 weeks
Chlordane (includes oxychlordane for animal commodities)	0.2	0.01	5-12 years	4-8 weeks
DDT (sum of p,p´-DDT; o,p´-DDT; p,p´-DDE and p,p´-DDD)	5	0.05	3-15 years	6-12 weeks
Endrin	none set (no contaminants in fat)	0.03	2-5 years	no contaminants in fat
HCB	1	0.01	7-15 years	10-13 weeks
Heptachlor (& metabolite heptachlor epoxide)	0.2	0.02	5-12 years	6-12 weeks
Lindane	2.0	0.1	1-3 years	7-10 days

*  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

Note:

• 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, in 12 weeks time that concentration generally will have fallen to about 0.1 mg/kg if that animal was grazing on non-contaminated pasture.  Faster growing animals will dilute the concentration of OCs at a faster rate with a resultant reduction in the time it takes for the contaminant to be 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 to 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 all 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?

Chart 1, under Resources below, shows the major sources of OC contamination identified in Queensland from 1995 to 2006.

Chart 2, under Resources below, shows the OC contaminants most often involved in violations from 1995 to 2006.

The tropical and subtropical climate of the coastal areas of Queensland ensures a high level of insect activity and resultant insecticide usage in crops and animals.  All sugar cane and most horticultural crops are grown on the coast.  Hence, persistent OC contaminants are likely to exist in coastal areas where sugar cane, 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, although some root crops (potato, turnip, beetroot etc.) can absorb and adsorb contaminants in the tubers or root growth.  Cucurbits (cucumber, zucchinis, etc) also have 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, however, cattle can consume between 20 to 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 can be obtained by following the link below.

National Organochlorine Residue Management (NORM) program

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

More information on the NORM program can be obtained by following the link below.