Client Question: What Can Be Done About Heavy Metal Contamination In the Soil?
I was recently approached by a new community garden group interested in building a new community fruit and vegetable garden for their local residents. The location of this new community garden is in a moderate to heavily trafficked urban neighborhood. The members that reached out to me had concerns over Cadmium (Cd) and other heavy metal contamination in their new garden space. They wanted to know how to mitigate the contamination as well as what safety and other considerations they should take when both designing and choosing crops for their new garden.
Before I get into how I would approach & solve this problem, let me explain the negative health impacts of Cadmium contamination.
As per both the Centers for Disease Control (CDC) and the North Carolina State University (NCSU), “Cadmium is a heavy metal that has both natural and man-made sources. Cadmium is a byproduct of mining, fossil fuel emissions, and fertilizers. Cd is used in a variety of products including tires, batteries, metal coatings and pigments….”Cd and other heavy metal contamination is more likely in urban and suburban areas close to industrial manufacturing, and/or heavily trafficked roads. Emissions from vehicles and Cd from tires is a common contributor to Cd in the urban and suburban environments. Long-term low-level to moderate exposure to Cd through contaminated environment (water, soil, air) and produce can lead to kidney, lung and bone disease. Cd contaminated soil also prevents the uptake of other vital elements by plants thus inhibiting plant growth and limiting plant nutrition. So what can be done?
Here are my recommendations. Knowledge is power. Get your soil tested! Work with an expert from Soil Organic Solutions (SOS) to provide soil consulting services on all of the following steps. First step, observe your new potential garden space. Where is the garden most exposed to traffic emissions? How does the water and rain flow on your property? During a heavy rainfall does water flow from the street into the garden? and if so, where? By answering these questions you, or an expert designer from Soil Organic Solutions, can determine potential contaminated “hotspots” which will inform one’s soil sampling strategy. I would recommend getting 1 aggregate sample representing the entire garden space as well as samples from the potentially contaminated “hotspots” , and finally, 1 sample from the area of planting interest. After sampling, the Client will send their soil samples to a local university extension to get their soil tested from an elemental perspective. The results of this type of testing will come with levels of the elements present in your soil, how these levels compare to regulated safety levels and perhaps some recommendations or conclusions. These labs will provide you instructions on sampling your property. The lab will test only the samples you send to them which is why sampling strategy is so important. Your SOS expert can also perform biological analysis of your soil which looks at your soil under the microscope and determines the level of microbial life currently present in the soil. Beneficial soil microbes can aid in preventing the uptake of Cd by plants, so understanding the current state will help you determine the appropriate level of remediation needed moving forward. Once you understand the current state of the soil, this will help to inform the potential layout of your garden.
If there are side(s) of the garden that face the road, consider planting a hedgerow of native grasses or sunflowers. Using plants as a means of soil remediation is known as Phytoremediation. Phytoremediation is a green technology that uses plants to reduce, remove and eliminate the toxic metals from soil. Willows are an example of a tree that also can be used for Phytoremediation. Sunflowers will hold the Cd in their stalks, so at the end of the season, lob off the flowers and throw out the stalks.
Another approach to consider is to put a pathway or some raised beds on stilts, up off the ground. This approach has a couple of benefits:
it keeps the soil for gardening and the plants completely separate from the contaminated areas.
these standing-height raised beds provide an ergonomic option for gardeners of all ages.
In the areas with perhaps lower contamination levels, I may still recommend the use of raised beds so that you have direct control over the soil’s contents and health.
In addition to using plants to decontaminate the soil, I would also recommend applying compost to the soil within the garden. The microbes in the compost will help prevent the plants from Cd uptake as well as provide vital nutrients to the soil and plants to help them thrive.
In future blogs, I plan to address the use of biochar and manure in soil remediation activities.
So now that you have applied compost and designed your garden based upon your testing information, how do you maintain the health of your garden in the long term? SOS can test your soil to help advise as to when more compost or other decontamination soil amendments are necessary.
For more details or to work with an SOS expert, contact Soil Organic Solutions!
References:
https://www.cdc.gov/niosh/topics/cadmium/
https://www.mdpi.com/2227-9717/10/8/1627
https://www.mdpi.com/2073-4441/14/21/3432
https://www.sciencedirect.com/science/article/pii/S0147651320317231
https://www.tandfonline.com/doi/full/10.1080/10643389.2023.2210985?src=