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Lead Contamination in the Garden

by Terry Logan    

Why You Should Worry About Lead

Lead is an extremely stable element categorized as a heavy metal. It is very toxic to humans and animals. Lead is a neurotoxin and lead poisoning is one of the most common pediatric health problems in the United States. In 1985 the Center for Disease Control (CDC) defined childhood lead poisoning as occurring at blood lead levels of greater than 25 ug/dL. This definition was revised down to 10 ug/dL due to new scientific evidence showing decreased intelligence and slower neurological development of children with blood levels as low as 10 ug/dL.

Children with elevated lead levels in their blood may show no symptoms, or show a progression of nonspecific symptoms, such as irritability, stomach aches, poor appetite, diarrhea, colic, distractibility and lethargy that often make diagnosis difficult. Most children show no symptoms. All children should be screened between the ages of 6 months and 6 years annually. Contact your family physician or clinic for lead testing referrals.

Lead naturally occurs in soils but is in relatively low concentrations - generally in the range of 15 to 40 parts lead to one million parts soil (ppm). Through the addition of industrial lead pollutants, such as lead particles and chips from lead-based paints, automobile emissions from leaded fuels, and other industrial sources, lead levels in contaminated soil range from 500 ppm to over 3,000 ppm. Soils near a heavily traveled roadway are typically 30-2,000 ppm higher than soils in a natural area. Soils adjacent to houses painted with exterior lead based paint may contain lead levels as high as 10,000 ppm. Once soil has become contaminated with lead, which is not biodegradable, it remains a long term source of lead exposure.

Areas Around Your Home You Should Be Concerned About

• Around the house foundation where lead paint chips and dust may be in the soil. If the house has been sand blasted the contaminated area will span out farther away from the house.
• If you live close to a heavily traveled roadway or close to a gas station.
• If you live in an industrial area.

A number of studies have established that the risk of lead poisoning is related to the presence of lead-based paints. Exterior lead-based house paint enters the soil by way of natural weathering, or removal of the paint by scraping or sand blasting prior to repainting, or the destruction of a building. In general, lead tends to remain in the top few inches of soil indefinitely.

If your house is made of wood or has wood trim and was built prior to the mid 1970s chances are that it has been painted with lead-based paint and the soil around the foundation could contain high lead levels. This soil should be kept in grass or a dense evergreen ground cover and mulched in order to reduce the amount of lead that will be brought into the house on people's shoes. Children should be discouraged from digging in this soil. Soil in close proximity to a roadway may contain high lead levels due to the past use of leaded gasoline. This soil should be tested prior to gardening or kept in grass or dense evergreen ground cover and mulched.

If you live near an industrial area, a busy roadway, or a lead painted structure, you should have multiple soil tests done, selecting samples from different locations in your yard.

What You Should Do to Protect Your Family and Pets

• Have your children screened for blood lead levels annually between the ages of 6 months to 6 years.
• Have your soil tested for lead, pH, and phosphorous levels. Select individual soil samples from several different locations where you will be disturbing the soil. These samples should not be combined and should be tested separately. Based on the information derived from the soil test determine gardening practices. Request a Lawn and Garden Soil Testing Kit and current prices from your county Extension office.

Send samples to:

Or send to a certified private soil testing laboratory

• Enforce a Clean Hands Policy. Children should wash their hands when they come in from playing outside. Teach your children to not put their fingers in their mouth.
• Monitor your child's playing habits while outdoors and discourage play in areas that may be contaminated with lead. It has been estimated that young children ingest up to 190 mg/day of soil under normal living conditions.
• Provide children with a covered sand box, located away from the areas where lead levels may be high, to discourage them from playing in the soil. Children eat soil - don't let them!
• Be aware of other potential sources of lead exposure at the daycare center, school, or friends' and relatives' homes.
• Follow the recommended cleaning practices used to eliminate lead contaminated dust in your home. See fact sheet HYG-5537-93 Lead in the Home.
• Follow the Good Gardening Practices.
• Brush pets often, outside.
• Children's diets should include low-fat foods that will provide at least 10 mg/day iron and 800 mg/day calcium to help decrease susceptibility to lead poisoning. See fact sheet HYG-5536-93 Nutrition and Childhood Lead Poisoning.

Interpreting Your Soil Test

The Soil and Plant Testing Laboratory at the University of Massachusetts, following several years of experience with the Suffolk County (MA) Lead Task Force and several other information sources, published the following classification of soil lead levels:

Good Gardening Practices Where Lead Levels are Less Than 500 ppm.

1. Locate gardens away from roads, driveways, old painted structures, and old garbage dump sites. Lay out gardens to keep leafy greens and other hard to wash vegetables far from the street.

2. Give planting preference to fruiting crops (tomatoes, peppers, squash, cucumbers, peas, beans, corn, etc.) rather than leafy vegetables, such as lettuce and spinach, and root crops, such as carrots and radishes.

3. Incorporate one-third by volume organic material such as peat moss, compost, and manure. For example, add three to four, 4-cubic-feet bales of peat moss to a 100 sq. ft. garden plot.

4. Lime the soil as recommended by your soil test to obtain a pH of 6.5. Phosphate has been shown to reduce pH availability.

5. Add super phosphate, to obtain a minimum of 1lb/100sq. ft. level in the soil.

6. Discard old and outer leaves of vegetables. Peel root crops before eating. Do Not Compost these Materials! Wash vegetables with a 1% vinegar in water solution (1 to 2 oz./gal. water) or soapy water (taking care to rinse the soap off prior to consumption).

7. Protect against air-borne lead (the finer the dust particle, the higher the lead load) by erecting a fence or planting a hedge between the street and your garden, and laying down mulch which should be discarded at the end of the season.

   If Lead Levels Are 500 ppm TO 1000 ppm - follow the good gardening practices and ...

8. Avoid growing leafy vegetables and root crops in this soil. Grow these crops in raised beds or containers with lead free soil.

   If Lead Levels Are Higher Than 1,000 ppm

9. Do not garden in this soil and contact your local Health Department. If lead levels are too high for gardening, install raised beds or try container gardening - you don't have to stop gardening.

Sources

Van Wijnen, J. H., Clausing, P., and Brunekreef, B., (1990). Estimated Soil Ingestion by Children, Environmental Research 51, 147-162.

Soil Lead Levels, (1990). University of Massachusetts.

Lead in the Soil, What You Can Do (1985). Suffolk County Cooperative Extension Service, University of Massachusetts.

Children, Gardens, and Lead (1992). Cornell Cooperative Extension.

Preventing Lead Poisoning in Young Children, (1991). U.S. Department of Health and Human Services/Public Health Service/Centers for Disease Control.

Strategic Plan for the Elimination of Childhood Lead Poisoning, (1991). U.S. Department of Health and Human Services/Public Health Service/Centers for Disease Control.

For More Information

Alliance to End Childhood Lead Poisoning. (1991). Childhood Lead Poisoning Prevention: A Resource Directory (2nd edition), Washington, D.C.: National Center for Education in Maternal and Child Health.