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This article was published in 1988
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Pesticide Residues - Case Histories
P.D. KEMSLEY, Veterinary Inspector, WARIALDA
This report presents several beef cattle pesticide residue cases from Warialda Pastures Protection Board.
During the period August 1987 to March 1988 20 tracebacks were recorded, being 11 above the Maximum Residue Level (MRL) and 9 below MRL.
The majority of cases were due to dieldrin.
HISTORY OF ORGANOCHLORINE USE IN WARIALDA BOARD
The means by which stock are contaminated is a reflection of the history of chemical use on a property.
During the late 1950's and early 60's both DDT and Dieldrin were used for jetting sheep. At that time Warialda was a sheep area, so most properties have old sheep jetting race or dip effluent sites.
During the 1960's there was a major swing away from sheep to cropping. As a result old sheep yards were left standing or were bulldozed.
To store grain silos and grain storages were built. Organochlorines, particularly dieldrin became a common treatment both in and around grain storages for weevil control.
With the demise of grain farming during the 80's many producers have turned to cattle, and more recently, sheep.
As a reflection of this history most pesticide tracebacks in cattle are from either:
1. Dieldrin contamination from cattle grazing around old sheep yard sites.
2. Dieldrin contamination from cattle fed grain from treated storages or from entering or grazing around grain storages.
Generally residues from sheep jetting sites are at or below the MRL.
Residues from treated storages are usually above MRL. Residues resulting from cattle eating grain dust and scraps from the floor of treated storages can be at very high levels.
CASE 1.
a. In November 1986 a 0.19 mg/kg dieldrin and 0.42 mg/kg DDE was detected in a single heifer sold on an emergency tail tag. The owner had 2 cattle on as many acres. The heifer had spent her life around the house and in the neighbour's 'house' paddock. Both owner and neighbour denied having used dieldrin or DDT.
No samples were taken and the case was closed.
b. 12 months later the neighbour came up with a traceback. 0.40 mg/kg dieldrin and 0.66 mg/kg DDE in a 3 year old steer. No detention was issued as the steer was the only beast on the property.
The steer had been poddy reared and was kept in the 10 acre 'house paddock'. This paddock had an old sheep yard site and a shower dip. Soil analysis revealed 0.90 mg/kg dieldrin and 0.39 mg/kg total D.D.T. from around the sheep dip and 1.45 mg/kg dieldrin and 14.67 mg/kg total D.D.T. from the sheep yard site.
CASE 2.
A 0.80 mg/kg dieldrin in a steer.
The property of origin had a history of a dieldrin traceback 4 years before.
On that occasion the cattle had grazed a contaminated airstrip. Dieldrin had been handled and stored on the strip during the mid 70's for aerial spraying of sorghum for midge. As this was the only all-weather strip in the area, it was used heavily during wet summers.
However this traceback was not a repetition of the previous case.
A 3,000 tonne, concrete base, grain storage shed was found to be the source. It had been treated with dieldrin about 10 years before.
About 6 tonne of oats was stored in a corner of the shed for 4 months and then fed to 95 steers. Fortunately a further 300 steers on the property had not received grain.
In order to clear cattle for sale all 95 head were tested, some soon after the traceback, but most about 4 months later. Repeat testing on some confirmed 2½ - 3 months half life for dieldrin.
Test results, expressed on the following graph demonstrate a grain feeding pattern.
Dieldrin levels arranged into ascending order.
15/18 had detectable dieldrin residues.
10/18 had dieldrin residues over the MRL.
Average residue - 0.29 mg/kg, Range - <0.05 to 0.89 mg/kg when tested 2 months after commencement of grain feeding.
The grain tested at 1.1 mg/kg dieldrin.
Calculations
The following calculations were made to confirm the residue source.
Grain fed
- 6 tonne to 95 head
≃ 60 kg/head
Dieldrin ingested
- 60 kg grain/head, grain tested
1.1 mg/kg dieldrin
≃ 66 mg dieldrin/head
Total body fat
- Average steer body weight about 400 kg estimated body fat about 15% of body
weight
≃ 60 kg fat/head
Expected residue at time of feeding
- 66 mg dieldrin/head in 60 kg body fat/head
≃ 1.1 mg/kg dieldrin
Expected residue at time of testing
- Interval from feeding to testing = 2 months (about one half life)
≃ 0.55 mg/kg dieldrin.
Observed residue - average 0.29 mg/kg dieldrin.
Assumptions
1. Level in grain sampled the same as average level in grain fed.
2. Body fat (including nervous tissue) 15% of body weight.
3. All dieldrin ingested partitioned to body fat.
Conclusion
Observed residues in the same order as expected residue.
CASE 3
1.5 mg/kg dieldrin in a weaner heifer. The property of origin had no previous history of residue problems and had been purchased 3½ years before.
The heifer was from a mob of 77 mixed sex weaners, grazing a paddock of fodder oats.
The following sources were suspect -
1. Concrete based grain shed located in the oats paddock. Some weaners had access to the shed for a day, 3 months before. Grain dust and scraps off the floor were eaten. These tested at 3.75 mg/kg dieldrin.
The weaners also spent a lot of time camping and grazing around the shed. Soil from this site tested 0.19 mg/kg dieldrin.
2. Hay stored in a shed previously treated with 15 times concentration dieldrin formice.
Weaners had access to shed and surrounding yard for one night only.
3. Old sheep yard site located in the oats paddock.
Soil from this site tested at 0.42 mg/kg dieldrin. The 52 remaining weaners were all fat biopsied with the following results -
The residue affected cattle fall into two groups -
1. The 7 head with levels over 0.40 mg/kg were probably contaminated from eating grain from the treated shed.
2. The 17 head with levels less than 0.30 mg/kg contaminated from grazing around the grain shed and the old sheep yard site. To confirm that the suspect sources were capable of producing the residues observed the following calculations were made:
e.g. 1. Grain from floor of treated shed -
Body weight ≃ 300kg
Estimated body fat ≃ 30kg
Residue found 5.0 mg/kg
Total dieldrin in
body fat ≃ 150 mg dieldrin
Level in suspect material - 3.75 mg/kg grain
Total suspect material required to produce residue found 40 kg
e.g. 2. Soil from sheep yard site
Body weight - 300 kg
Estimated body fat - 30 kg
Residue found - 0.10 mg/kg
Total dieldrin in
body fat - 3 mg dieldrin
Level in soil detected - 0.42 mg/kg soil
Total soil required to produce residue found ≃ 17 kg.
NOTE - As sampling technique involves pooling in a number of samples, dieldrin levels at some sites may be higher than the level detected.
CASE 4
a. A vealer with 0.14 mg/kg dieldrin. The calf was from a 6 acre property close to town.
The owner, a Council worker had owned the property for many years and claimed to have not used dieldrin.
Grazing history of the calf included 2 months on the common.
Analysis of treated seed wheat fed to the calf revealed no dieldrin.
The case was closed.
b. One month later another traceback vealer was detected from the
same town. Being -
0.61 mg/kg dieldrin (MRL 0.20 mg/kg)
0.04 mg/kg oxychlordane (MRL 0.05 mg/kg)
and 0.20 mg/kg heptachlor epoxide (MRL 0.20 mg/kg).
The owner, a retired Council worker grazed the vealer and its mother on a small piece of common next to a sewerage pumping station.
The cow was fat biopsied and had 0.45 mg/kg dieldrin and 0.12 mg/kg heptachlor epoxide.
The cattle had been fed grass clippings from nearby house blocks and from the pumping station enclosure.
The clippings sampled contained 1.2 mg/kg dieldrin.
From the history a 'common' source for both cases was suspected.
The owner of the traceback from the previous month was questioned further. His calf had also grazed on common land next to another pumping station. It had also been fed grass clippings, from grass mown within the pumping station enclosure. The enclosure had been treated with dieldrin to control ants. The other pumping station enclosure had also been sprayed.
CASE 5
Another unusual case was that of 2 steers in a consignment of 17, with dieldrin residues of 1.70 and 1.04 mg/kg. The other 15 carcases tested clean.
Property history was of dieldrin being used on ant mounds in one of the paddocks, around the yards for white ants, and as a seed dressing.
On property fat testing revealed only 2/26 head with trace dieldrin levels.
The source?
On the eve of being sold the steers were fed with grain. The grain was known to be free from residues, having been sampled and tested at the owner's initiative some months before.
However the grain had been carried over from the shed in an old seed grain sack.
The season before the traceback, seed grain was treated with dieldrin in a cement mixer.
The dieldrin solution, grain dust and commercial seed dressing formed a slurry in the mixer. When the seed was returned to the bags this slurry settled and adhered to the bottom of the bags in lumps.
I strongly suspect that the 2 steers were unlucky enough to have eaten a lump of dried slurry dislodged from the bottom of the bag. The remaining steers of course nust have missed out.
The old seed grain bag involved (minus the lumps) tested' at 1,700 mg/kg dieldrin.
CASE 6
The final case 'history, is that of a friesian steer detected with 0.48 mg/kg dieldrin.
The steer ran with the milkers around the house paddocks and cattle yards.
The steer had access to several sites and feeds which were sampled.
1. The shower dip effluent site soil tested 10.7 mg/kg dieldrin.
2. A work shed sprayed 3 or 4 years before with dieldrin for mice soil tested 120.0 mg/kg dieldrin.
3. Hay stored on the floor of that shed had been fed to the milkers mob. Hay scraps tested 19.5 mg/kg dieldrin.
4. An old pig sty, soil tested 0.10 mg/kg dieldrin.
5. An old dump had soil tested 0.05 mg/kg dieldrin.
6. Around the base of free standing silo the soil tested 11.5 mg/kg dieldrin.
7. Grain oats fed regularly to the mob tested 0.018 mg/kg dieldrin.
The 6 head remaining from the milkers mob had the following fat biopsy results -
Dieldrin levels arranged in ascending order.
The cattle from his beef herd had no significant residues.
The milkers mob were moved to another paddock and fed grain from another storage.
Unfortunately when this grain was tested it was found to have 0.01 mg/kg dieldrin.
Another storage on the property is also now known to be contaminated and the owner is planning to have all storages tested before next harvest.