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Healthy Soil: Lead And Your Plants

TapScore’s The Dirt on Soil Is A Living Blog Written By Our Berkeley Team Of Scientists, Horticulturalists, and Plant Lovers. Our Goal Is To Provide You With Support And Professional Soil Testing Services So That You Can Improve Your Soil & Plant Health At Home.

Lead-Contaminated Soil

Soil–in its purest form, it’s a complex amalgamation of organic material, water, minerals, and living organisms. Unfortunately, humans have (often unintentionally) made dirt “dirty.” Soil contamination can impact both the environment’s health, but human health, as well.  

As the first part of our Dirt On Soil, we explore the impacts of lead-contaminated soil, including:

  • Means of exposure
  • What lead means for your plant’s health
  • What you can do about lead in your soil
  • What is Soil Contamination?

    There are a handful of nutrients (~17) that are absolutely essential for healthy plant growth. Just as for humans, balanced nutrition for plants is key. Both lack of nutrients and an overabundance of them can hinder a plant’s growth and even contaminate the soil.

    While contaminants can come in a variety of forms–microbial, radiological, chemical, etc.–we’re going to take a look at the impacts of lead contamination in soil.

    What is Lead?

    Element 82, lead is a bluish-silver metal that is fairly soft, highly malleable, and very resistant to corrosion. It is toxic to humans, animals, and most other lifeforms. While lead does occur naturally in the environment (albeit very rarely), most lead concentrations in nature are as a result of human activities. These activities include:

  • Leaded gasoline (which was popular until the 1970’s in the U.S.)
  • Lead-based paints (legal until 1978)
  • Solder
  • Lead-acid batteries
  • Why Care about Lead?

    When lead is released into the environment it can remain as dust particles (in the air, soil, and water) indefinitely.

    Humans can be affected by lead-contaminated soil by:

  • Accidentally ingesting it (especially children)
  • Inhaling contaminated soils (i.e. breathing in dust particles when gardening)
  • Eating lead-contaminated food
  • Lead and Plant Health

    It is possible for plants to grow in lead-contaminated soil. The downside, as you might expect, is that plants can take up some lead while they grow and develop. However, the good news is, is that lead does not readily accumulate in plants.

    So, how does lead impact plants?

    Factors that determine the amount of lead absorbed by a plant include: pH of soil, soil particle size, root surface area. When absorbed, lead tends to be held in the roots. There is minimal transfer from roots to shoots and fruits. This is why root vegetables potentially contain the most lead from contaminated soil. Leafy vegetables carry a lesser risk, and fruiting vegetables are the least likely to contained lead absorbed from contaminated soil.

    Examples of high, moderate, and low risk crops:

  • Highest risk of containing lead: carrots, sweet potatoes, turnips
  • Moderate risk of containing lead: lettuce, kale, swiss chard
  • Lowest risk of containing lead: tomatoes, peppers, eggplants
  • Note: These “risks of lead contamination” are in reference to the amount of lead that is accumulated within the plants as they grow. Plants that are not grown in lead soil would not be at risk.

    Lead by the Numbers

    For some perspective, the average lead concentration that occurs naturally in surface agricultural soils in the U.S. is about 10 ppm–with a range of 7 to 20 ppm. When soil has lead levels above this range, it is (generally) the result of lead contamination due to human activity.

    It is generally considered safe eat crops grown in soil with lead levels below 300 ppm. This is because low levels of lead accumulation mean the plant is not taking up these high lead levels. Even at lead concentrations in soil above 300 ppm, the more significant human health risk is due to contaminated soil or dust on the plants, rather than from uptake by the plant. If you have soils with this level of lead contamination, other exposures risks are more serious (e.g. children playing in the yard).

    What You Can Do About Lead in Your Soil?

    The first thing you should do is test your soil.

    If you find that it has an elevated-lead concentration, there is hope. A few steps you can take to decrease contamination risks to both you and your plants, include:

  • Add compost. Adding organic matter to contaminated soil will dilute the overall lead concentration in the soil. This subsequently reduces the amount of lead absorbed by your plants
  • Thoroughly wash your fruits and vegetables with clean (preferably tested) water. This reduces exposure to lead dust on the plants, but not any lead that as accumulated within them. Alternatively, you can peel off their skins or remove hard to clean areas
  • Maintain the optimal pH and nutritional conditions for the plants you are growing. Note: slightly alkaline soils hold more lead–so they may be preferable if you are concerned about lead leaching into your crops.
  • Opt for a raised-bed garden if your soil’s lead levels are higher than the recommended safety levels (> 300 ppm).
  • More questions on soil contaminants? Stay tuned for our evolving Dirt on Soil blog or send us a question at help@simplewater.us!

    It's hard to get trustworthy advice when it comes to your drinking water, so we made Tips for Taps to help answer your questions. Order a Tap Score Water Test and receive personalized support from professional engineers and scientists by phone, email and chat.