6 August 2002
Research Underway To Remediate Sheep Dip Sites
Landowners concerned about contamination from old sheep dip sites may soon learn more about a solution to their problem
from HortResearch.
In the first step to address remediation, HortResearch is carrying out a trial using plants to degrade dieldrin, a
persistent pollutant, still found on many sheep dip sites. The work is being carried out in the Waikato region and
Environment Waikato's Environmental Initiatives Fund has contributed $10,000 towards it.
The trial began in September 2001 on a disused sheep dip site where willows were planted to restrict leachate. Willows
remove water from the site and also help degrade contaminants in the soil. In late June this year, the site was
interplanted with poplars to enhance further site remediation. The HortResearch-bred willow and poplar clones used in
the trial have been shown to dry out soils more than pasture species.
As part of the trial, trees are also being grown at HortResearch, in soil collected from the sheep dip site, in an
experiment to determine the tree rootzone degradation of dieldrin.
Results so far indicate that willows greatly enhance the microbiological activity in the soil, and thereby enhance the
degradation of dieldrin in the rootzone. Over a five-month period, the dieldrin concentration in the root-zone of the
willows was 20 percent lower than before the treatment.
Over the next four months the full impact of phytoremediation on the site will be assessed, and a 'whole system' model
developed that details contaminant immobilisation and degradation over time under various scenarios.
Until the early 1990s all sheep farmers in New Zealand were required by legislation to dip sheep. As a consequence,
sheep dips were often emptied into nearby creeks and directly on to soil. During the dipping process residue may have
contaminated the surrounding area and wet sheep standing in a holding paddock have also contaminated the soil.
The half-life of dieldrin is about three years, meaning its concentration degrades by half only every three years. At
many sites, therefore, the dieldrin is still present, and a threat to the environment and public health. It may also
leach into groundwater.
Dieldrin is on the "dirty dozen" list of the Stockholm Accord.
Ends