Urban soils are often contaminated with heavy metals and other substances that are harmful to health. However, exposure to these contaminants is avoidable. Here we answer some common questions about exposure to lead and arsenic in soils.
What are the effects of exposure to lead and arsenic?
Lead:
This fact sheet from the Agency for Toxic Substances and Disease Registry answers the most frequently asked health questions about lead.
Arsenic:
This fact sheet from the Agency for Toxic Substances and Disease Registry answers the most frequently asked health questions about arsenic.
How could lead or arsenic be in soil?
Lead and arsenic can be in soil because of natural and industrial processes.
Lead and arsenic are chemical elements that occur naturally in the Earth’s crust. As a result, all soils contain at least some small amounts of lead and arsenic. This natural contribution of lead and arsenic to soil varies depending on the particular composition of the Earth’s crust (geology) in a given area.
Lead and arsenic can be present at larger amounts in soil because of industrial activities (like mining and smelting) and manufactured products that contain lead or arsenic (like lead-based paint, leaded gasoline, the pesticide lead arsenate, and the wood preservative chromated copper arsenate). Lead and arsenic do not break down over time, and past releases of lead and arsenic into the environment accumulate in soils.
Due to the intense past uses of lead in paint and gasoline, lead in soil and dust is a city-wide and world-wide issue. Arsenic is more localized and less widespread than lead.
How can people be exposed to lead or arsenic in soil?
People can be exposed to lead, arsenic, or other contaminants in soils through ingestion (eating) and inhalation (breathing).
Ingestion of soil and plants grown in soil:
- Hand-to-mouth activities, like putting hands or toys in in the mouth with dust or soil on them (this is normal for small children).
- Pica (eating non-food objects) is not uncommon for small children.
- Eating produce with soil stuck on the surface.
- Some plants can absorb lead or arsenic into the edible portion of the plant; however, this concern is generally secondary to soil physically stuck to the surface.
- It is important to know where your food comes from and how it is grown. For example, arsenic is present in rice and rice products. Read more about arsenic here.
- Swallowing dust or soil suspended in the air.
Inhalation of soil can happen from breathing in dust or soil suspended in the air.
Children are more likely to be exposed to contaminants in soil because of their closer proximity to the ground, normal hand-to-mouth activity that they exhibit, and pica activity (eating non-food objects, not uncommon).
How can we prevent exposure to contaminants?
We believe that a precautionary approach is the best way to deal with the potential of lead and arsenic in soil because there is no known amount of lead or arsenic that is safe in the human body.
Safety precautions for everyone
- Wash hands after being outdoors or whenever they are dusty or dirty.
- Keep shoes and gardening clothing and equipment outside so that soil and dust is not tracked into your house.
- Mop floors with a damp mop, and wipe down surfaces in your home regularly.
- Wash produce well to remove soil.
- Eat foods rich in calcium, iron, and vitamin C to minimize the absorption of lead into the body and mitigate its effects.
- Garden in tested soil, ideally in raised beds. Keep bare soil in gardens covered with mulch, straw, or plants.
- Cover bare soil in yards, along building driplines, or empty lots with thick vegetation like grass or with materials like landscape fabric, mulch, and gravel.
- Have children get blood lead testing at ages 1 and 2 years old.
- Establish play areas and gardens in areas away from building driplines and roads where lead is most likely to be found.
Actions for areas where lead or arsenic is detected
Along with the actions recommended above for everyone, the following additional actions can be taken in locations where lead or arsenic is detected:
- Relocate gardens or play areas away from these spots.
- Submit samples for further analysis in a laboratory.
- Conduct additional sampling and testing in the area.
- Establish barriers on top of soil and maintain them over time to prevent physical contact in the future:
- Yards and play areas: plant grass or other year-round ground-covering vegetation. Alternatively, use landscape fabric and build up a clean recreational surface with mulch, sand, pebbles, or other non-toxic materials.
- Gardens:
- Build layers of cardboard, compost, and new soil deep enough for plant roots.
- Maintain adequate levels of plant nutrients like calcium, nitrogen, potassium, magnesium and phosphorus in your soils by fertilizing regularly, not excessively.
- Organic matter can help reduce how much a vegetable takes up. Apply at least a layer of organic matter 2 to 3 inches thick on the garden area about 1 to 2 months before planting.
- Keep your soils near the near the neutral zone (6.5-7.5).
- Here is more guidance about gardening on lead-contaminated soils.
- Walking paths and building driplines: use landscape fabric or cardboard and add a thick layer of gravel or mulch.
- Parking areas: use landscape fabric and add a thick layer of gravel.
Major environmental actions
Lead and arsenic in soils is a city-wide and world-wide issue, resulting from industrial activities and the sale of unsafe products like leaded paint and gasoline. Research has shown that long-term changes in soil lead levels have a corresponding impact in lead blood levels in children. This means that communities can reduce children’s lead exposures as a whole by addressing contaminated soils on a community-wide basis.
Ultimately, resolving the issue of lead and arsenic in soil will require broader action and resources than we can muster as individuals. It will require collective action to call on government and regulatory agencies to (1) clean up past pollution and (2) curb the introduction of new sources of lead and arsenic into our soils.