Removal of Heavy Metals from Soil using Vegetation
by: Dawn Slack, Environmental Research Manager
Plants provide…
Food for people and animals, medicine, mitigate heavy rain, buffer wind and wave energy, protection from soil dehydration, beautiful meadows for pollinators, and the list goes on and on.
Plants have been used by Helping Nature Heal for over 23 years to help re-engage a healthy ecosystem triangle, slow overland flow and erosion processes, protect banks and cliffs along the ocean at the homeowner scale as well as larger community projects and Shore Up programs at municipalities throughout NS, NB and PEI. As our company has expanded over the years, we are researching and discovering new methods to help with environmental impacts and issues.
As I have started researching a new avenue for the importance of our plantings, I would like to share this blog article with you which will focus on an interesting method of implementing plant recipes on your property, one that you may or may not have heard of before known as phytoremediation.
What is phytoremediation?
In a nutshell, as described in Phytoremediation by Sigurdur Greipsson, it is the process of using “plants and associated soil microbes to reduce the concentrations or toxic effects of contaminants in the environment”.
This is such interesting research that has been increasingly studied for approximately four decades, so why isn’t it discussed more leisurely and at greater depth? The terminology and chemistry behind it are complicated!
For our purposes, we will focus on the sub-classification known as Phytoextraction.
Phytoextraction uses plants to uptake pollutants from the soil such as heavy metals (arsenic, cobalt, lead, zinc, iron) and store it within the plant roots and tissues. Not every plant is capable of this process, therefore specific plantings are required for specific contaminants you are trying to remove from the soil. There are many variables which must be met for this process to be effective such as the climate of the region with the contamination, the lifespan of the plants, protecting the areas from wildlife as well as harvesting and disposing of the plants.
Heavy Metals
Arsenic (As) is a naturally occurring element in the earth’s crust. Although it is naturally occurring, it can cause health problems when ingested in small doses over a period. Nova Scotia has an Arsenic Risk in Bedrock Water Wells map which Nova Scotian’s can refer to for relative risk in your area.
Garden vegetables that are grown in contaminated soils can be a method of accidentally ingesting it. It is also dangerous to inhale dust that contains arsenic. Health issues created by long-term exposure to arsenic can include various cancers.
Plants that can aid in removal of arsenic include Little Bluestem (Andropogon scoparium), Ribwort plantain (Plantago lanceolata), Crowberry (Empetrum nigrum), Tamarisk “saltcedar” (Tamarix parviflora).
Lead (Pb) is naturally occurring in the environment and has many uses in industry. It is a toxic contaminant which became significant during the industrial revolution in the 1920s. Lead was once a major ingredient in paint due to the ability to increase rates of drying and the long-life luster finish it provided.
Thankfully, Canada stopped using lead for indoor paints around 1992. Lead water pipes were also commonly installed in homes and industry until 1975.
Health issues caused by lead products in the home include anemia and nervous system damage especially in children. It is a cumulative poison accumulated within teeth and other bones. High exposure rates have reported symptoms of vomiting, convulsions and in most severe poisoning cases, death. For more information, visit the Nova Scotia Inspections, Compliance and Enforcement for Lead.
Plants that can aid in removal of lead include willow (Salix spp.), poplar (Populus spp.), mustard (Brassica juncea), and sunflowers (Helianthus annuus).
Cobalt (Co) is naturally occurring in the earth’s crust but is not found as a sole pure element. It is always combined with other elements; therefore, it must be chemically extracted.
Negative implications of cobalt on the environment include water pollution, landscape devastation such as agricultural contamination. Human health issues include asthma-like allergies, repeated exposure to cobalt dust can cause scarring of the lungs.
Vegetation that aids in the removal of cobalt includes canola (Brassica napus L.) and money plant (Epipremnum).
Zinc (Zn) is mined mainly in Canada; it can be dangerous to aquatic organisms as it stimulates oxidative stress in freshwater organisms.
Excessive levels of zinc are due to human impacts such as smelting, mining, tanning and sewage irrigation. High pH water levels (alkaline) can increase the absorption of zinc, therefore more acidic water limits the amount of zinc that can be detrimental to aquatic organisms.
Toxicity levels in humans are not life-threatening and very treatable. It can however cause fever, difficulty breathing, chest pain, nausea and cough.
Vegetation used to remove zinc from soil includes marigolds (Tagetes erecta) and sunflowers (Helianthus annuus).
Vegetation Removal and Discarding of Heavy Metals
A high level of responsibility must be met to remove and discard the post-phytoremediation vegetation without creating secondary sources of pollution. As indicated in Environmental Technology & Innovation Journal, the most environmentally friendly and popular method of vegetation destruction is heat treatment where products such as biochar, activated carbon and paper pulp can be produced.
Ongoing Research
There is great potential for Helping Nature Heal to offer our services using our tailored plant recipes to help mitigate contaminants from soil on your property. This is one broad topic I will continue to research so it can be tailored to individual properties.
