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Matt Dodd: Sampling soil to protect human health

July 15, 2013
Matt Dodd

From Victoria to St. John’s, Matt Dodd is getting the dirt on the soil.

Since 2007, the School of Environment and Sustainability professor has been collecting and analyzing soil samples from across the country as part of the North American Soil Geochemical Landscapes Project in collaboration with Health Canada and Geological Survey Canada. The project is the first multi-national (Canada, U.S. and Mexico), multi-agency collaboration of its kind and will provide continent-wide data on natural variations in soil geochemistry to support risk assessment and management.

Certain levels of some metals in soil can be dangerous to human and environmental health, Dodd explains, so it’s important to know what you’re working with – and playing with – in any given area.

“When kids are playing in dirt they inadvertently eat some of it. High levels of some contaminants such as lead and arsenic in soil can be dangerous. Lead affects almost all organs in the body and affects human development especially for kids,” says Dodd, who has been teaching and researching at Royal Roads University since its inception. “Inorganic arsenic can be carcinogenic and therefore high levels in soil or dust is not good for human health.”

Chemical elements originating in the earth enter the air we breathe, the water we drink and the food we eat. While some elements are essential to our health (think iron and calcium) others, even in trace amounts, may be toxic. By determining the natural levels of metals in any given area, people working on contaminated sites can better compare the levels to environmental soil quality guidelines for cleanup. The Canadian arm of the program was supported by Natural Resources Canada and Health Canada, but the government withdrew its funding in 2011. Despite that, Dodd is dedicated to continuing his portion of the project, albeit on a smaller scale.

“I feel that it’s important that I continue,” says Dodd, who brings in grad students from across Canada to help with sample collection and testing. He has so far analyzed more than 500 samples from across Canada and plans on completing sampling and analysis in all the major cities with the hope of providing a data base of metal levels in soils from coast to coast.

After collecting soil samples, the next part of the study is determining total metals present in the sample and what percentage of each individual metal in the soil is harmful when ingested, which is called the bioavailability. Dodd does this at the Royal Roads lab through an in vitro bioaccessibility test, which involves extracting the soil sample using fluids and conditions that mimic human stomach and intestines to determine what portion of the contaminated metal is absorbed in the gut and could potentially get into tissue and blood.  

“You can have 1,000 parts per million of lead in a sample, but if that lead is not biologically available then the human health impact from exposure is minimal. That’s the very reason why you can touch a piece of solid metallic lead and it won’t have any impact on you because it’s not biologically available,” explains Dodd. “If you have the lead in a fine powdery compound form which is water soluble and you touch it, its effect would be very different. The bioavailability of the contaminant is therefore very important for human health risk assessment.”

Dodd is also exploring what can be added to soil to make metals less biologically available and is involving students in this work. Sometimes organic materials can react with metals to stabilize them, making the metals less bioavailable, Dodd explains. A Bachelor of Science in Environmental Science class has already tested bio-solids (the post-sewage treatment leftovers) and determined they were not very effective at stabilizing metals in samples of mine tailings and waste rock obtained from some mine sites in the Yukon. Dodd is also planning on testing clay obtained from a potable water filtration plant with another group of students.

Dodd often does bioavailability work for clients across Canada working on contaminated sites cleanup. He has also worked with the United States Environmental Protection Agency. The payment he receives is funneled back into his research. 

“The main objective of doing the bioavailability work is for policy development,” says Dodd who’s a member of the Bioaccessibility Research Canada working group.  “The soil quality guidelines are usually based on total metals using a default bioavailability of 100 per cent. We want to make sure that people doing contaminated sites cleanup have the scientific backing for incorporating bioavailability testing into their site specific human health risk assessment. The use of bioavailability data can result in a significant difference in the level of effort for a site which has a large amount of soil that requires remediation.”