If you live in a charming older home, near a busy street or near industrial sites, your garden soil could be making you sick. Lead and zinc are common soil contaminants in certain areas, and both of these heavy metals are toxic if we are exposed to them regularly and at excessive levels. While heavy metal poisoning is a valid concern, there are ways to make sure you and your plants stay healthy, even if your soil is not.
Lead Contamination in Your Garden
If you live in an older home or near a busy road, your soil may be contaminated with lead. Lead paint, common in homes built before the 1950s, flakes off siding, contaminating the soil around the home’s foundation. Within a few feet of a busy street, soil may be contaminated with lead from gasoline emissions (lead was added as an octane booster prior to being banned nationally in 1995). Not only is soil adjacent to the roadway a problem, but soil around your home and other structures may be contaminated as well, depending on prevailing wind patterns on your property. While lead isn’t as toxic as other heavy metals, it is still dangerous, and once in your soil, will be there indefinitely. According to soil scientist Garn Wallace, Ph.D. , lead is a bigger problem in some crops than others. “The highest lead content is in leafy greens and root crops. The lowest is in fruits and grains,” he says. Wallace notes that spinach is a “hyper-accumulator” of heavy metals such as lead.
Lead poisoning can result in permanent learning and behavioral problems, kidney damage and fertility problems. Inhaling lead dust after disturbing contaminated garden soil or eating food that has lead dust on it are two of the most common ways homeowners get lead poisoning.
Zinc Contamination in Your Garden
Zinc is a naturally-occurring metal in soil, but contamination is a problem near industrial areas, often a result of mining or smelting operations. Homeowners that have galvanized steel fencing or downspouts may also have elevated levels of zinc in their soil.
Plants grown in zinc-contaminated soil show clear signs of damage. “High zinc causes stunting, dieback and discoloration,” says Garn Wallace. “Older leaves turn a yellow orange and scorch. Tomatoes have early senescence. Vines fail before the fruit ripens.” Wallace also says that excess zinc interferes with root function, inhibiting the uptake vital nutrients such as nitrogen, phosphorus and potassium.
People are exposed to zinc most commonly through drinking well water from wells near current or former industrial sites or by eating vegetables grown in contaminated soil. Ingesting large amounts of zinc for a short period of time can cause nausea, cramps and vomiting. Prolonged exposure to zinc can cause nervous system disorders, damage to the pancreas, anemia and decreased levels of beneficial HDL cholesterol.
Gardening Safely in Contaminated Soil
To test for lead or zinc contamination, send soil samples to a professional soil testing lab for analysis. If the tests show high levels of lead or zinc in your soil, there are several ways to ensure both your family’s safety and good plant health:
- Wash produce well to remove lead dust.
- Grow in raised beds to avoid disturbing contaminated soil.
- Excavate the contaminated soil and replace it. This is best done by experts, as the contaminated soil will have to be disposed of properly and care must be taken to keep dust to a minimum.
- Grow in containers.
With a little care, analysis of your site and creative use of raised beds and containers, even those of us with lead or zinc contaminated soils can grow a healthy garden.