Disposal of spent sheep dip wash straight onto the ground is not just an easy option - it might be a good option if a little preparation is put in first.

Diazinon has been found to have a short half-life in soil and leaves a relatively low pesticide load at the end of dipping.

"Our results suggest that good containment of spent dip wash in a dedicated disposal site prevents significant movement of diazinon residues, either down into the soil profile or laterally downhill of the disposal site," researcher, Dr Garry Levot, said.

Dr Levot, a NSW Department of Primary Industries’ principal research scientist, has been working to get some real data to indicate whether on-farm disposal of spent sheep dip washes is an environmentally acceptable practice.

Plunge and shower dipping of sheep in aqueous insecticide solutions for lice control are common practices on Australian sheep farms and mobile plunge dipping contractors are being increasingly relied upon to conduct these treatments.

Typically at the end of the process, more than 4000 litres of spent dip wash needs to be disposed of.

Dips cannot be moved full, so the volume must be pumped out or allowed to drain onto areas adjacent to the dipping site.

"Typically, wool producers make little or no site preparation and the opportunity exists for run-off to reach grazing areas or even enter farm dams and creeks before it is absorbed into the soil," Dr Levot said.

"The intention of on-ground disposal of effluent is to retain contaminants close to the soil surface, where biological and environmental processes can degrade the insecticides."

Dr Levot and his now retired colleague, Roger Lund, were concerned that on-farm disposal of spent sheep dip wash might pose a risk to livestock and the environment.

Dr Levot measured the concentrations of diazinon and diflubenzuron in soils within soil-bunded dip disposal sites.

"Diazinon was shown to breakdown to less than 0.1 parts per million within 56 days, whereas diflubenzuron residues greater than 6ppm were present a year later," he said.

"The difference between the depletion rates for these two common sheep dips was interesting but we did not have the whole story.

"Results of a recently completed trial have filled some of the knowledge gaps that remained - particularly movement of diazinon residues within soil."

In a second trial, on a co-operator’s central NSW farm, 3500 litres of spent dip wash with 59ppm diazinon was spread over a bunded area of 450 square metres, at the completion of annual dipping.

One day after disposal the average diazinon residue in the top seven centimetres of soil across the site was 2.3 ppm.

Diazinon concentration declined steadily, reaching 0.18ppm a month later and less than 0.1ppm after 56 days, which suggested a halflife of seven days.

Diazinon levels in the next seven centimetres of soil depth were low (maximum 0.8 ppm) or undetectable within two weeks of disposal.

There was no change to the negligible diazinon levels as a result of dip disposal in soil samples collected three metres downhill of the disposal site.

"With neither vertical nor lateral movement of diazinon away from the disposal site and with rapid degradation on the site itself, disposal of spent diazinon dip wash onto a contained area of ground looks to be a good option," Dr Levot said.

"Of course, given that soil characteristics vary, it is common sense to locate dipping sites away from obvious sensitive areas."

This research funded by Australian Wool Innovation will assist regulators develop clear guidelines for on-farm disposal of spent dip wash for wool producers.

Contact Dr Garry Levot, Camden, 02 4640 6376, garry.levot@dpi.nsw.gov.au.