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Healthy Soil: Arsenic and Your Plants
What is Soil Contamination?
Mud, dirt, earth, ground….soil has a handful of different names. Whatever you call it–it’s undeniable that it plays an integral role in maintaining a healthy planet. However, industry, chemicals, and massive land-use changes all contribute to soil pollution and deterioration at an accelerating rate. As concrete jungles take over real ones, we see soil less and less in our daily lives. Unfortunately, this also means that dirt is often “out of sight, out of mind.”
We’re here to bring dirt back into the spotlight.
In our second installment of The Dirt on Soil, we take a look one of the more dangerous soil contamination concerns–arsenic.
Read on and find out:
What is Arsenic?
Arsenic can be found in all 50 U.S. states. Trace amounts of the naturally occurring metalloid are present in rock, water, air, and soil. This means that some arsenic exposure is inevitable. Unfortunately, human activity has increased arsenic concentrations in certain areas. These activities include:
Is Arsenic Harmful to My Health?
Arsenic cannot be destroyed in the environment, however it can combine with other elements to take on different forms–creating either organic or inorganic compounds. The different forms impact both the toxicity and the mobility of arsenic in the environment (eg. through your water or food). Organic arsenic compounds (such as those that bioaccumulate in seafood) are less harmful to human health than the highly toxic inorganic arsenic compounds, like those found in water.
The U.S. Environmental Protection Agency (EPA) categorizes arsenic as a Group-1 carcinogen and that poses a significant risk to human health.
The good news is, is that people who garden are unlikely to encounter high enough arsenic exposure to become suddenly ill. Although the rare case of acute toxic arsenic responses does exist, a bigger cause for concern is long-term (chronic) exposure.
Arsenic toxicity may impact metabolism and DNA repair. Arsenic’s toxic effects resulting from acute or chronic exposure may occur via ingestion, inhalation, and dermal absorption:
Abdominal pain, vomiting, muscle pain, flushing of the skin, numbness and tingling of the extremities, progressive deterioration in motor and sensory responses, or death.
Dermal lesions, including changes in pigment, peripheral neuropathy, and skin, bladder, and lung cancer.
While the EPA guideline for arsenic in drinking water is 10 parts per billion (ppb), the EPA has not established a national regulation for arsenic in soil. However, the soil screening level (SSL) for arsenic in soil is approximately 400 ppb. This means that - while your water supplier should be keeping arsenic levels below 10 ppb – no one is responsible for testing and treating your soil for arsenic. You might get where we’re going here–only you are responsible to test your soil.
How Can I Be Exposed to Arsenic From Soil?
In addition to arsenic exposure from drinking water, you can be exposed to arsenic by touching contaminated soil or eating plants grown in arsenic-rich soil.
Fortunately, arsenic is rarely present in topsoil in concentrations that are toxic to plants, making your risk of soil exposure unlikely. While concentrations of the heavy metal vary widely, the average concentration of arsenic in soil is between 1 and 40 ppm. However, soil near mining sites, hazardous waste sites, or where arsenic-containing pesticides have been applied in the past is much more likely to have elevated arsenic levels.
Arsenic concentrations within plants tend to rise as soil arsenic increases. The amount of arsenic a plant takes up varies based upon several criteria, usually stabilizing at some maximal value:
Once absorbed through their roots, arsenic disrupts plant metabolism. Subsequently, plants may exhibit symptoms that serve as indicators that you have an arsenic problem:
Arsenic Risk in Fruits & Veggies
As with most soil contaminants, arsenic tends to stay in the roots, with minimal transfer to leaves and fruit. This also means that root vegetables (carrots, potatoes, etc.) growing in arsenic contaminated soil are more likely to contain arsenic than fruiting plants (tomatoes, berries, etc.).
Perhaps the most famous crop affect by arsenic is rice. Not only does arsenic readily accumulate in rice, but because rice is grown in submerged conditions there is also the risk of it accumulating arsenic from the surrounding water. Arsenic has also been found in California wines.
Examples of other high, moderate, and low risk crops:
Highest risk of containing arsenic: turnips, radishes, potatoes, carrots
Moderate risk of containing arsenic: lettuce, collard greens, kale
Lowest risk of containing arsenic: tomatoes, peppers, peas, melons, strawberries, squash
What Can You Do About Arsenic in Your Soil?
The first thing you should do is test your soil.
If you find that it has an elevated-arsenic concentration, there is hope. A few steps you can take to decrease contamination risks to both you and your plants, include:
More questions on soil contaminants? Stay tuned for our evolving Dirt on Soil blog or send us a question at firstname.lastname@example.org!
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