Organochlorines (OCs) include pesticides such as DDT, dieldrin and heptachlor, which were used in towns and rural areas of Western Australia from around the 1940s until phased out in the 1980s. Organochlorines do not break down easily and persist in the soil for decades.
In WA, organochlorines may be found in old:
- potato crops
- backyard vegetable patches
- termite protection
- timber houses and fences
- firewood piles
- areas of Perth and surrounding suburbs treated during the Argentine ant eradication campaign (see map below)
- areas developed before 1987.
Poultry kept on these areas may develop OC residues.
Chickens and OCs
Chickens are efficient scavengers and soil scratchers and can consume enough dirt to accumulate OC residues in both their meat and eggs if kept on land that has been treated with OCs. OCs attach to the fatty components of animals - in the case of chickens to the fat and to the egg yolks. Minimal deposits are found in lean chicken meat and are totally absent from egg whites.
OC-affected soil can contaminate chicken feed as the soil will attach itself to organic matter. Dry, dusty soil, a common feature of backyard chicken pens, is easily disturbed and compounds the problem. Feed grown on OC-treated land will have low levels of residues but can have higher levels if contaminated by soil.
Chickens produced in cages or on a deep litter are unlikely to consume OC-affected soil.
Note: Products sold in shops from commercial chicken and egg producers are tested under the National Residue Survey system to ensure harmful residues do not enter the food chain.
Managing chickens on OC-affected land
Anyone who runs or intends to run free-range chickens in any area of WA that was developed before 1987 (when OCs were banned) should arrange testing of the soil where the chicken coop is sited and where the chickens will be allowed to roam.
To have soil tested, contact a commercial laboratory.
Chickens run on OC-affected soil will begin to show residue levels in the eggs within a few weeks. If you consume the meat and eggs, then samples of these should also be tested at a commercial laboratory.
DPIRD recommends that affected birds should be humanely destroyed as levels will not reduce below the minimum acceptable levels in the lifetime of the bird. Egg production (as long as they are not eaten) from chickens scratching clean land will result in a decrease in residues but it is slow and not recommended. It is better to start again with clean birds on clean land.
Fence off any contaminated areas and bring in new birds to scratch areas that have tested clean. If the whole area is contaminated or there is no alternative location for the run, one solution is to pave and put clean sand, soil or sawdust over the contaminated area. A 30-centimetre deep layer of sand, soil or sawdust will isolate the contamination.
Testing chickens and eggs for OCs
If you run free-range chickens for either commercial or domestic consumption, you should be aware of the possibility of OC contamination. If you suspect your land has been treated with OCs, then you should arrange for your soil or eggs to be tested by a commercial laboratory. If you find your land does contain residues, then you will need to make the management changes outlined above.
OCs residue limits
Land with a soil OC level of 0.1 parts per million (ppm) or more is regarded as a risk and can result in residues in grazing animals and a higher risk for chickens. Levels above 0.06 ppm are considered a risk for chickens, as they ingest contaminated soil feeding.
The Western Australian Department of Health provides a guide to organochlorine pesticide residues in home garden soils, which includes information about testing. The maximum residue limits for dieldrin in eggs is set at 0.10ppm.
For human health enquiries related to OCs, please contact the WA Department of Health - Environmental Health Directorate.
Using OC-contaminated land
DPIRD places restrictions on the use of land contaminated with OC levels likely to result in agricultural produce above the maximum residue level. To use this land, the owner must obtain written permission from the Department of Primary Industries and Regional Development.
Approval will be given if the landowner can demonstrate that produce from the area will not exceed maximum residue levels. This will usually require an audited property management plan that will indicate the products produced are below the maximum residue level.
Areas affected by the Argentine ant eradication spray program
OCs were used in the Perth metropolitan area during the Argentine ant eradication program in the 1970s. The following map details approximate areas that were part of the spray program throughout WA at that time. There may be areas that were treated by private contractors and these are not listed. The map is only a guide to whether poultry may have a higher residue risk via soil ingestion in treated areas.