Contamination and Remediation of Soil at a Former Orchard Site in Hamilton (June 2005)
Group or Institution
University of Waikato
Author(s)
Janine S. Sedgwick
Abstract
A national survey of agrichemical residues across New Zealand has identified a number of potentially contaminated sites associated with ex-horticultural properties. This study examines a former orchard property in Hamilton that was subjected to historical pesticide application that came to an end approximately 40 years ago. The persistence of these agrichemicals is of environmental concern because it has resulted in soils with higher-than-normal levels of contaminants such as heavy metals (e.g. Pb, Cu, Zn and Cd), metalloids (e.g. As), and DDT. It is also known that high concentrations of metals may inhibit the natural degradation of persistent organic pollutants in the soil and cause the contaminants of concern to remain in the soil for a prolonged period of time. To remove these contaminants from the soil several remediation techniques are possible; however, in situ remediation is considered to be the most environmentally friendly as it preserves the soil structure, requires little energy input and is aesthetically pleasing. The overall aim of this study was to investigate the efficacy of three different remediation techniques on an area of soil that was contaminated as a result of historical application of pesticides and to examine the remobilisation potential of contaminants from the soil into the soil pore water. It was found that the effects of two hyperaccumulator species; willow (Salix schwerinii) and poplar (Populus alba x glandulosa) on total heavy metalconcentrations were minimal and that it would require three years at least before a significant decrease (>5%) in total metal concentrations occurred. The effects of magnesium oxide application on the availability and movement of the contaminants was difficult to ascertain because pH measurements of the soil over time were not made. The distribution coefficients showed that the metals in the soil were not very mobile, each contaminant showing different trends down the soil profile. The relationship between soil and soil pore water concentrations was shown to be significant for some metals (Cd) under some treatments. The effects of different fungal strains on DDT concentrations showed no significant increase or decrease. However, the initial total concentration of DDT in the soil (~ 60 ppm) had decreased significantly to ~1 ppm by the end of the experiment. This decrease in total concentration was probably caused by either increased temperatures and/or the watering of the soil during the experiments.