Big, Green, Cleaning Machines

January 14, 2020

Plants are incredible. We may seem biased in saying so, but we figure if you’re reading this, you probably have an idea of this yourself. Over the last century, humans have caused a global pollution problem, releasing large amounts of chemicals and other toxic compounds into the biosphere. These include inorganic pollutants, such as heavy metals or arsenic, and organic pollutants, such as petroleum, fertilizers, and herbicides. There are 12,000 contaminated sites listed in the United States, close to a half-million contaminated sites in Western Europe, and thousands of others throughout the world.

Conventional remediation of these pollutants is often expensive and cause the problem to conveniently be relocated or buried deeper in the earth. However, new, environmentally responsible technologies have been emerging within the past decade that are less expensive and isolate and remove the contaminant. Enter our illustrious plants! That’s right, plants are leading the way as an option for remediating these contaminants on-site.

Growing up I heard about the sunflower and its sci-fi like ability to remove heavy metals from the ground through the process of phytoremediation. Like a snake oil salesman, “Plant your lead-ridden backyard with sunflowers and a year later you will have a bountiful, lead-free garden.” — What kind of plant magic was this? Little did I realize the extent to which plants can play a role in solving our human problems. Phytoremediation is the process by which living plants and their associated microorganisms detoxify contaminants in the soil, water, or air. Plants use photosynthesis and their natural processes to extract chemicals from the soil and naturally transform them into less toxic forms.

Where phytoremediation is really excelling is in the treatment of water. A natural wetland can be viewed as a living Brita filter. As water enters a wetland, it slows down and the contaminants within the water are removed through a series of physical and chemical processes. Wetland plants, or macrophytes, serve many functions within this wetland system. The roots and sometimes shoots cause suspended sediment to slow, become entangled, and settle or fall out of the water column. Some contaminants, especially nutrients including nitrogen and phosphorus, are taken up by plants or become inert. Wetland plants are even capable of promoting microbial colonies that transform or inactivate contaminants they contact. By understanding the importance of such a system, wetlands have offered a cost-effective and technologically feasible option for constructed replication and installation. The implementation of constructed wetlands, which mimic the filtration capacity of natural wetlands, are being installed more and more frequently to the point that it is one of the most robust and frequently applied use of plant systems to achieve remediation.

Plant scientists, landscape architects, and site designers share a toolbox of plants, soils, and water to build a lasting landscape that is both environmentally and socially responsible. These landscapes focus less on just the beauty of the plants and more on the unique characteristics of each plant selected to assist in the remediation process. Phytoremediation can be used for improvement and renewal, planning landscapes beyond the short-term to create longer visions of what our cities, natural lands, and waterways will look like tomorrow.

Want to try phytoremediation in your own backyard? Identify areas of water runoff from your roof or street and plant ornamental grasses or wetland plants. The root systems of these plants will both slow down the water and uptake the water along with its contaminants. You may even have some plants growing in your garden that are removing toxins from the soil without you realizing it. Hydrangeas can uptake aluminum. Kale, collards, and broccoli will remove lead from the soil. Willows accumulate heavy metals such as cadmium and nickel. So, step right up, “Plant your garden today with one of these amazing plants and remediate contaminants today.”