How Widespread is the Problem?
When this was discovered, Environment Canada's National Water Research Institute (NWRI) began to investigate the extent of DDT contamination and the reasons for its persistence. Research scientist, Dr. Allan Crowe uncovered a good news – bad news story. The good news is that the soil contaminated by DDT at levels above the Canadian Soil Guidelines is confined to the former agricultural areas; the bad news is this is about one quarter of the land in Point Pelee National Park.
Because DDT has an extremely strong tendency to bind to organic matter, it is confined to the upper several centimetres of the soil profile. Unfortunately, this upper several centimeters is the biologically active zone, where many animals live, burrow, and obtain their food - insects, earthworms, and roots. This is why some of the amphibians, reptiles and birds within the Park have elevated levels of DDT and increased levels of mortality.
Is Water at Risk?
NWRI researchers were concerned that the DDT could be leaching from the soil downward to the water table, causing widespread contamination of the groundwater over the past 35 years. Contaminated groundwater would pose a threat to human health through the Park's water supply wells, and it could endanger the aquatic ecosystem via groundwater discharge to the marsh. Fortunately, groundwater analyses showed that concentrations of DDT are negligible – threat to drinking water or the marsh is very unlikely.
Taking Action – A New Remediation Technique
As well as the threat to wildlife from contaminated soil, there is also the risk of exposure to DDT for people hiking or working in the contaminated areas. Parks Canada has taken steps to eliminate the risk to people by closing hiking trails, picnic and camping facilities, and work areas in contaminated areas. However, researchers estimate that given the long half-life (the time it takes for half an initial amount to disintegrate) of DDT and the very high concentrations, it could take up to 700 years before levels degrade to below Canadian Soil Guidelines.
Dr. Crowe is working with Dr. James Smith and graduate students at McMaster University to develop a technique for remediating soil contaminated with DDT that causes minimal disruption of the ecosystem. Conventional methods of remediation involve excavating contaminated soil and disposing of it in a landfill, or aggressively and continually mixing the soil with chemical/nutrient additives. These approaches are not acceptable in many areas because they can destroy the local ecosystem and wildlife habitat, removing vegetation, soil and wildlife.
The new remediation technology applies a surfactant – an agent that acts like a detergent – at ground surface. The surfactant moves downward through the contaminated soil separating the DDT from the soil's organic matter, flushing it downward and away from the shallow soil or bioavailable zone, and thereby removing the risk of exposure to wildlife and people. The surfactant also enhances biodegradation – breaking down of the chemical by organisms in the environment – by increasing soil moisture and changing the state of the soil to an anaerobic (without oxygen) condition.
The NWRI/McMaster research team applied this technology at a test site at Point Pelee, and results show concentrations of DDT in shallow soil are decreasing very quickly, relative to the non-treated control sites. These results hold promise that an environmental hazard in one of Canada's richest site's of natural beauty and biodiversity will soon be a thing of the past.
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