Persistent organochlorine contaminants in soil

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.

A significant proportion of problems with persistent organochlorine (OC) contaminants in animals are caused by consumption of contaminated soil.  The amount of soil consumed depends largely on the amount of grass cover and ranges from 20 to 1200 grams ingested per day.  Small amounts of contaminated soil can also be transferred to herbage by dust, rain-drop splash or flooding.

Flood rains transport OCs that are attached to soil particles from one property or paddock to another.  Farm water supplies are rarely the source of contamination because of the low solubility of OCs.

Soil sampling

Soil tests can be a useful tool in determining suspect contaminated areas.  The DPI&F Detector Dogs are another effective tool to assess any sites of concern for OC contaminants and are available on a fee-for-service basis.  For further information, please call the DPI&F Business Information Centre on 13 25 23 or follow the link at the bottom of this page.

Do OC soil levels accurately reflect levels in cattle?

No.  Soil sampling will not give a true indication of the OC levels in cattle grazing OC contaminated pasture.

What can cause OC contaminants in grazing cattle?

There are many variables involved in the uptake of OCs in cattle, including:

• OC hot spots in the sampling area - it is impossible to sample every square metre of a paddock. Highly contaminated areas from concentrated chemical spills may be missed
• pasture conditions - cattle grazing contaminated pasture with a good body of feed are less likely to ingest large quantities of contaminated soil. Cattle grazing pastures that are overstocked or pasture in a severe drought condition will allow more soil to be ingested as cattle search for feed
• cattle condition - samples from cattle in store condition will record a higher OC level when compared to samples of fat cattle grazing the same contaminated pasture
• adverse weather conditions - pastures that are subject to flooding may become contaminated from contaminated silt settling on them following flash flooding. 

What OC levels in paddock soil are considered ´low risk´ for cattle to graze?

All detections of OC contaminants in soil must be treated with caution, especially when the contamination is associated with an old dip site.  Dieldrin levels of 0.1 mg/kg found in treated yard posts have been shown to cause OC levels above MRL in cattle confined to the contaminated area.

A specific example of the variability of soil analysis results when compared to fat OC levels concerns a 5 ha paddock that collected drainage from surrounding treated cane paddocks.  A grossly overfat aged cow which had been grazing this paddock for more than five (5) years tested at 0.66 mg/kg dieldrin and 0.30 mg/kg BHC.  The paddock was not overstocked and had an average body of feed.  Heifers in forward store condition introduced and tested after 2 weeks showed dieldrin levels at 0.05 - 0.06 mg/kg.  A composite paddock soil sample tested at 0.08 mg/kg dieldrin.

As a rule of thumb if DDT (and its metabolites) levels in soil are below 0.1 mg/kg and dieldrin and BHC levels in soil are below 0.01 mg/kg, OC contaminants in cattle are unlikely to be above ERL unless animals are confined in the contaminated area for an extended period of time.  Many factors including length of exposure and whether the soil sample was collected from the most contaminated area can lead to exceptions to this rule.

Therefore, these soil levels are a guide only.  Fat biopsies should be performed to determine the actual OC concentration in cattle. 

Will detection of OC in soil affect my property´s OC status?

No, the detection of OC contaminants in soil samples will not affect a property´s OC status under the NORM program.  It will assist producers to identify hazard sites under their LPA risk assessment and to develop a residue plan to manage the suspect site.

For more information on the NORM program, follow the link at the bottom of this page.

What is the best method to collect samples?

1. Paddock samples are best collected to a depth of 10 to 15 mm.  Samples should be collected from 10 to 20 separate sites chosen at random while traversing the entire paddock.  Upon completion, the samples are thoroughly mixed together and a composite 500 gram sample should be submitted to the laboratory.
   
2. Each point source of contamination or hot spot (eg dip site, pump out area) requires more specific sampling.  Several surface soil samples each of  200-300 grams (about a trowel full) should be taken from each site, namely:

• pens immediately adjacent to a contaminated area - 5 soil samples are taken from spots evenly spaced around the pen. These samples are then combined into one container for each pen to give an average chemical contaminant level for that pen
• holding paddocks - the extent of soil contamination is assessed by taking samples from contour lines drawn 2, 4 and 8 metres from the contamination area.  Samples collected from five sites equally spaced along each contour line are combined into one container and repeated for each contour line.  One sample is submitted for each contour line.

Soil samples are submitted in a clean sealed glass jar or polythene bag along with details of the date of collection, location and the property name.  A map should also be submitted with the samples to illustrate the area sampled in relation to the potential contamination source.

Samples should not be contaminated with plant foliage or root material and each soil type should be sampled separately.  If a high level of OC is suspected the sample should also be marked with the words hot spot to avoid damage to sensitive laboratory measuring equipment.

Soil sampling methods are screening tests and will give indications of the concentration of OC contaminants at a site.  The results should not be taken as absolute statements of OC contamination or freedom, but as indicators for risk assessment and support for decision making on OC risk management.

What is the cost of sampling?

Testing costs for a soil sample ranges from $90.00 to $152.00 ex GST per sample plus freight costs. A list of National Association of Testing Authorities (NATA) accredited laboratories appears at the bottom of this page.

Management and remediation of OC positive sites

Your local DPI&F veterinary officer or biosecurity inspector will be able to assist you in the most suitable method of management or remediation of OC sites. 

Summary

Soil analysis results can be a useful tool in determining suspect contaminated sites.   Caution must be exercised when projecting positive soil results to probable levels in cattle. The DPI&F OC Detector Dog service offers an alternative way to identify OC contaminated sites on a property.

Further information

Contact your local DPI&F biosecurity inspector or veterinary officer.

DPI&F Business Information Centre

• National Organochlorine Residue Management (NORM) Program
• Persistent organochlorine (OC) contaminants in cattle
• Meat and Livestock Australia (MLA)

National Association of Testing Authorities (NATA)

Please refer to list below for contact details for laboratories approved in Queensland to test for organochlorines (OCs) in soil and/or fat.

Laboratory	Contact details	OC fat test	OC soil test
Amdel Limited	Brisbane Facility Unit 1 Smallwood PlaceMetroplex 07Gateway Murarrie QLD 4172 Phone: 07 3902 4600 Fax: 07 3902 4646	Not accredited	Accredited
SGS Environmental Services	Cairns Laboratory 2/53 Comport Street Cairns QLD 4870 Phone:  07 4035 5111 Fax:  07 4035 5122	Not accredited	Accredited
Symbio Alliance	44 Brandl Street Eight Mile Plains QLD 4113 Phone:  07 3340 5700 Fax:  07 3219 0333	Accredited	Not accredited
Qld Health Scientific Services	39 Kessels Road Coopers Plains  QLD  4108 Phone:  07 3274 9087 Fax:  07 3274 9186	Not tested	Accredited
Simmonds & Bristow Pty Ltd	Chemical Laboratory 40 Reginald Street Rocklea  QLD  4106 Phone:  07 3710 9100 Fax:  07 3710 9199	Not accredited	Accredited
Australian Laboratory Services Pty Ltd	Brisbane Laboratory 32 Shand Street Stafford  QLD  4053 Phone:  07 3243 7251 Fax:  07 3243 7218	Not accredited	Accredited

• List supplied by NATA - January 2007
• Please contact NATA if further information or advice is required on phone (07) 3870 3844, fax (07) 38483660.
• Please contact laboratories to confirm testing charges before sending samples