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Chromium in the Garden

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Chromium is metal that occurs naturally in the environment, but can also exist at higher levels due to human activity. Chromium comes in different forms, the most common is the low-toxicity trivalent chromium (Cr+3). Hexavalent chromium (Cr+6) is less common but far more toxic at low levels. Summary for Gardeners » Cr+6 dissolves more easily in water than Cr+3, and so is more likely to be found in well water than garden soils. Chromium often shifts between these two forms, so there may be very small amounts of Cr+6 in soil. » Historical chromium inputs are less likely to be a cause for concern than current sources of chromium pollution. » Adding more organic matter (e.g. compost) can help convert chromium into the less-harmful Cr+3 form

Sources of Chromium Exposure

Chromium is not easily taken up by plants, so direct contact with contaminated soil is the most common exposure pathway in the garden. This can include breathing in or eating soil particles directly or from soil covered-produce, tracking soil inside the home, and breathing or eating the soil at a later time. Chromium exposure can occur in and outside the garden.

Industry nearby industry Industries producing steel, wood preservatives, paints, and
more can release chromium (Cr+6 specifically) into the air, water, and soil.
Well well water In some areas, well water is the most common source of Cr+6 exposure. Direct exposure can occur if a well is used for drinking water.
Plants in-garden sources Well water or nearby industry can contaminate garden soils, but exposure via soils or garden produce is a minor source, particularly for Cr+6.

Chromium

Making Sense of Regulatory Standards

No official standards have been established in North Carolina for acceptable levels of chromium in garden soils. For remediating soil at industrial sites, North Carolina uses EPA’s guideline of 24,000 ppm for Cr+3, and0.3 ppm for Cr+6. The guidelines below can help you contextualize the chromium levels in your garden soil.

Chart

Health Impacts of Chromium

Cr+3, the more common form, is a beneficial nutrient in small doses and is not easily absorbed into the body. Cr+6, however, is a known carcinogen when inhaled and therefore has no “safe” level of exposure.

Exposure to Cr+6 can increase your risk of developing breathing difficulty, asthma or allergy-like symptoms, stomach ulcers or irritation, anemia, lung cancer, and more. Long-term exposure to Cr+6 may affect the male reproductive system.
It is unknown whether children are more vulnerable to the effects of Cr+6 specifically, but it is still important to limit their contact with chromium.

Reduce Chromium Exposure in the Garden

  • Adding compost or other organic matter from a contaminant-free source may help convert Cr+6 into Cr+3. Check the NC Composting Council website to find STA or OMRI certified compost
  • Thoroughly wash produce grown in chromium-contaminated soil
  • Avoid growing root vegetables in soils with high levels of chromium, and peel root vegetables before eating to further minimize risk
  • If applicable, test well water sources for chromium, specifically Cr+6
  • Conduct a soil safety training to teach exposure reduction strategies to all garden users
  • Visit our website below for our factsheet on 10 Healthy Garden Habits

Testing Resources

water drop Well water testing for chromium
Hand holding soil and plant How to test your soil and interpret the results
Question mark Email questions about chromium soil testing

Email us at superfund@duke.edu

More Information

Print Chromium Factsheet

This work was supported through the National Institute of Environmental Health Sciences P42 Multiproject Center Grant program, grant number P42ES010356.