Portland Soil Crisis Informs on Heavy Metals in the Garden | Civil Eats

What Portland’s Soil Crisis Can Teach Us About Heavy Metals in the Garden

As a city full of gardening enthusiasts reels from newly-discovered toxicity, it’s clear that Americans have more questions than answers about their backyard soil.

Person Picking Radishes in Backyard Garden

The news that toxic heavy metals have been detected at high levels around two glass factories located in residential neighborhoods has rattled the city of Portland, Oregon. These metals—primarily arsenic, cadmium, and chromium—are used to color glass and were found in moss samples collected around the city over the past few years and also in air sampling, the results of which were first made public early this year. (Update: New soil tests released this week show heavy metals generally low and garden soil and produce safe to eat, say Oregon health and environmental authorities. Thorough hand and produce washing are recommended and further test results will be forthcoming.)

A public furor has erupted over the potential effects of exposure to these metals, which are linked to diseases and health problems that include cancer, kidney, bone and nerve damage. Portland is a city filled with enthusiastic home gardeners and residents are asking: “Is my soil safe?” and “Can I eat the produce I grow?”

As testing around these factories continues, Oregon health and environmental authorities have admitted, “it is difficult to say for sure.” They’ve also recommended that people should avoid eating produce grown within a half-mile of the highest mapped metal concentrations until further notice.

While what’s happening in Portland has made national headlines and filled public meetings with concerned and angry families, home gardeners nationwide are asking questions about heavy metals in soil. Civil Eats spoke with several experts to find out what you need to know about keeping your garden safe.

Heavy metal soil contamination is “not uniquely an urban problem,” says Hannah Shayler, extension associate at Cornell University’s Waste Management Institute. But because cities have more concentrated human activity—buildings, vehicles, and industry—that does increase the likelihood of contamination, it’s worth taking steps to help ensure your soil is healthy. It’s also worth knowing something about how heavy metals behave and how these contaminants are regulated.

Do I need to get my soil tested?

Unfortunately, that’s a tough one to answer. Testing soil for heavy metals is costly and it’s likely that most urban soil will have some “background” level of these contaminants. There is also no single national standard to define acceptable levels of contaminants in soils. The U.S. Environmental Protection Agency (EPA) has guidelines for heavy metals cleanup at hazardous waste sites, but there is no equivalent for garden soils.

So, as the University of Vermont Extension has written, “It is not clear exactly what levels of heavy metals in soil are safe or unsafe.” As Tulane University School of Medicine research professor Howard Mielke notes, “We have a Clean Air Act and a Clean Water Act, but we don’t have a clean soil act.”

“We often work with gardeners with limited budgets and there’s often a tradeoff in how much money to put into testing,” says Cornell’s Shayler. Testing prices vary widely. In Portland, Oregon, for example, they range from $40 to $130 per sample. And most gardeners need more than one sample to get a good picture of what’s going on around their home and/or urban garden.

“I don’t think it is a cause for alarm for soil,” said Oregon Health Authority public toxicologist David Farrer of the glass factory emissions, explaining that the Department of Environmental Quality (DEQ) would soon be releasing results from additional testing of soil on public property. Many in the glass factories’ neighborhoods, however, feel otherwise.

What can I do to make my soil safer?

A number of official sources* recommend the following: Use raised beds deep enough to contain crop roots and maintain them with clean soil and fresh compost that’s free of pesticides or other hazardous chemicals. Keep the beds away from roof “drip lines” to avoid rainwater that may have picked up contaminants from roofing material. Make sure raised beds are not made with chemically treated wood–especially wood treated with heavy metals. If you’re concerned about contaminants in dust around garden beds, you can keep it down with hazardous chemical-free mulch, bark, stones, or wood chips.

“Container gardening, anything where you’re creating a barrier between potentially contaminated material” and bringing in clean material to grow in, is a basic healthy gardening method, says Shayler. And it’s “probably also more successful for getting a [good] yield,” she adds.

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Asked about sidewalk strip gardening and contaminants from traffic, Shayler says she’d “love to see some research,” on that.

What about heavy metals in soil and garden produce?

“In general, it’s very common to find metal concentrations inside vegetables,” says Farrer. But these levels, he says, are much lower than what might be in the soil because metals bind to biological material in the soil and make them less bioavailable to plants and to people. Because of this, the only way for metals that have become bound to soil to get into your body directly is by swallowing a bit of soil, he explains. These particles don’t get absorbed through the skin, and when combined with soil, formerly airborne metal particles are too big to get into the lungs, Farrer adds.

Basic good hygiene measures such as washing hands even if you’ve worn gloves, making sure kids aren’t getting soil in their mouths, and avoiding tracking it into the house, will all help safeguard against soil contaminants in food, note Shayler and other “healthy” gardening experts.

For the food itself, washing and peeling works really well for most produce, Shayler adds. “Some leafy greens are hard to wash off and some soil particles could be incorporated into the plant tissue.” But she also explains that fruit or plants that grow from flowers, like tomato or zucchini are less likely than leaves to have taken up any heavy metals. Roots, like carrots and potatoes, are closer to the source of contamination and are therefore likely to have higher levels of heavy metals.

Plants can take up heavy metals but predicting when that will happen in urban gardens isn’t easy, according to recent research conducted by Shayler and colleagues. Their study measured heavy metals–including cadmium and lead–in urban garden vegetables and found lead levels the most likely to exceed safety limits and the most likely plants to be contaminated, leafy vegetables, such as lettuce, spinach, and perennial herbs, such as mint or oregano.

What about the health effects?

Exposure to heavy metals presents serious health hazards and children are especially vulnerable, given their developing brains and bodies and their eagerness to taste and touch. Children, says Tulane’s Mielke, are “extraordinarily sensitive.” He says there’s not enough research into exposure to soil contaminants so available information is limited. “You get the runaround with people saying it’s probably safe,” when it may not be, he says.

Mielke calls the soil information gap “enormous.”

Are healthy gardening practices enough? Except in cases where contamination is very likely, no one seems prepared to say for sure. Also unanswered is the question of who should pay for this testing in response to identifiable industrial pollution sources.

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Oregon DEQ says the next test results for will be available the second week in March and in early April.


*Cornell University, Johns Hopkins University, the New York State Department of Health and Oregon’s Health Authority among others.




Elizabeth Grossman was a senior reporter for Civil Eats from 2014 to 2017, where she focused on environmental and science issues. She is the author of Chasing Molecules, High Tech Trash, Watershed and other books. Her work appeared in a variety of publications, including National Geographic News, The Guardian, The Intercept, Scientific American, Environmental Health Perspectives, Yale e360, Ensia, High Country News, The Washington Post, Salon, The Nation, and Mother Jones. She passed away in July 2017, leaving behind a legacy of dedication to her mission of journalism that supports and protects people and the planet. Read more >

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  1. Jerry Kubal
    That the metals are showing up in urban soils should come as no surprise. One thing you failed to cover in the article: How many backyard gardeners use any old hose to water? Unless specifically labelled save for drinking, the hose will generally say something about not drinking the water. This is because the hoses contain heavy metals, which is doubly problematic because they usually sit out and the temperature of the first flush is like boiling. All those metals leached from the hose end up sprinkled on the soil and taken up by the plants.
  2. Elizabeth Grossman
    Good point about garden hoses – something that none of the "healthy" gardening guidelines mention. But here is a 2013 report on heavy metals and other chemicals in garden hoses from the Ecology Center in Ann Arbor, Michigan and HealthyStuff.org:
  3. Bruce Gruber
    The insulation from liability that corporations afford management and shareholders who profit PALES in contrast to what our depleted uranium munitions do to our fellow humans across the globe.

    BUT ... the devolution of mankind will prove a measurable concomitant of our reptilian greed - if we survive long enough to recognize and categorize our individualistic self-importance. At present, mankind, as a species, proves the theory underlying the Peter Principle.
  4. Ray Kinney
    Gardening in urban soils is very risky if not done VERY carefully. Like Howard Mielke said, there are very important questions that have not been adequately asked or answered. He is an expert in lead toxicology in house dusts and soils and realizes how lead adversely affects numerous physiologic pathways once it enters the body. Toxic metal air pollution drifting through Portland does not just fall on garden soils, with subsequent risk of inhalation and uptake through the lungs, it also collects on roofs and pavement. Cars can stir the dusts up repeatedly and breezes can transport toxic metal pollutants through the air to lungs again. Not all of these particulates are too large to be taken up and into cells in the body.
  5. Ray Kinney
    Often, home gardeners do not know much of anything about the contamination history that the garden soils have as a legacy, assumptions are dangerous. Any organic grower should feel very uncomfortable in not knowing. The costs of metals analysis is really very small compared to the risks involved. If chemicals that are chealators have contaminated the soil, metals can be transported to places that they would not normally get to, perhaps more readily into plants. Metals acute toxic effects are usually the focus of most public health assessment, yet that is only the tip of the iceberg when chronic low dose effects pathogenesis is taken into account. Test your soils, and bring in cleaner soil.
  6. Ray Kinney
    Contrary to common belief, even common belief among toxicologists, is that there is significant research of up-take of lead through the skin. Lead, entering through skin, however loses its affinity to associate to red blood cells and as a result does not get detected in the blood lead test that is the major screening method. It needs clarification, where it goes and what damage it does, but there is a lot of research that it is probably doing damage wherever it is in the body... even bone lead can remobilize to be toxic to the fetus when pregnancy need for calcium draws it out. Washing it off hands with common soaps can also increase transport through skin. Best to wear gloves around lead sources, including urban garden soils.IMHO
  7. charles graf
    I wonder what the glass makers would say if there batch of molten glass was contaminated with unwanted metals at the same rate that they say is safe for the garden?
  8. Phil
    Testing soil only tells one what is in the soil.
    It does not tell how bioavailable the metals are.

    A more meaningful test is to determine the levels of metals in food grown in "contaminated" soil. Then if they are high, determine the levels of metals in the blood of the gardeners, which would then be compared to background levels in nongardeners. And if similar to background, no meaningful risk is present and the scare would be over.

    Relevant to the subject is that in NJ there are substantial areas in the coastal plains area of the state with naturally occurring very high levels of arsenic and farming has not been banned in those areas. Google: Selected Sites with Potentially Naturally Occurring Elevated Background Arsenic and/or Beryllium Levels
    • Ray Kinney
      There should be a caution about trying to determine toxic metals accumulative body burden by only monitoring levels in the blood. Blood lead levels are only accurate very temporarily (a matter of a couple of months), thus not saying much about body accumulation over time in bones and teeth. As we age, or become physiologically stressed with conditions where they body is seeking additional calcium to deal with the stress, this body pool of calcium is used to supply the need. Lead comes out with the calcium to circulate in soft tissues once again, before gradually being put back into the bones. The timing for blood lead assessment is rarely correct for catching these risks, and can effectively mask the risks from being accurately assessed.
  9. AgSci
    Think about how you will build your raised beds. It is amusing that many of the radical anti-pesticide crowd will use pressure-treated lumber or railroad ties in their gardens. Both of these are impregnated with pesticides to prevent rot. These chemicals eventually leach out of the wood and into the soil. CCA pressure treated lumber contains chromium, copper, and arsenic. Creosote is a mixture of a number persistent chemicals/pesticides. Modern, low-persistent pesticides are much safer!!!
  10. dr .taha
    valuable article,thank you

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