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Lead in Garden Soils
编辑:University of Rhode Island   出处:University of Rhode Island   时间:2011-1-13 14:39:07

Garden soils contaminated with lead can pose a health risk if vegetables and fruits from the garden are consumed. We don’t usually think of our gardens as dangerous or toxic, but unfortunately some garden soils do contain toxic levels of lead. We are familiar with the danger of lead in paint. Chipping or peeling paint around older structures will raise the lead level in the soils directly adjacent to the building. Even today when an old building is demolished, the soil can still become contaminated with lead from lead paint. In the 1950’s, restrictions were initially placed on lead in paint. Today, the lead content in paints has been reduced, however paint companies are allowed to mix up to 0.05% lead in paints. The lead content of commercial and artist’s paints are not restricted. Lead use has been reduced significantly, but not entirely eliminated.

Soil can be contaminated with lead from several other sources—industrial sites, industrial sludge with heavy metals, until recently from auto emissions, old lead plumbing pipes or even old orchard sites in production when lead arsenate was in use. From a gardener’s viewpoint, lead contamination is forever. Without remedial action, soil lead levels may never return to normal.

We do not require lead in our diet or environment. At very low levels that naturally occur in soils (15-40 ppm), no detrimental health effects have been noted. The effects of lead contamination can raise the lead level in the body and thus poses a substantial health risk. Young children under the age of six and pregnant women are at the greatest risk. The risk of lead poisoning is disconcerting to families since it is largely unseen. Physical symptoms, including headache and nausea, are frequently not present. Children exposed to lead tend to have lower IQs and may experience learning disabilities and behavioral disorders.

Test the Soil:

Testing for lead will help to evaluate the lead hazard level. See our GreenShare Factsheet on Soil Testing for information on submitting soil samples. Ultimately, the risk to you and your family is based on your exposure. Both private and some university soil test labs can determine lead levels in soil. Work at the University of Massachusetts soil testing lab and the experiences of the Suffolk County Massachusetts Lead Task Force has resulted in a classification system for soil lead levels. An increased soil lead level implies a greater hazard. The Massachusetts recommendations for limiting exposure to lead are based on the test results of soil lead levels. No legal regulations for soil lead levels are in effect, and no tests have linked health effects to high lead soil levels.

In fact, the classification system is a relative scale, designed to give the gardener an index of how much lead is in the soil and how to alter his gardening practices to reduce his exposure to the soil lead. When laboratories analyze lead in soil, the results will be returned listing the parts per million (ppm) of lead from either an extracted or total lead test. The values in Table 1 will help you to understand your test results:

Table 1. Soil Lead Levels
Relative Soil Lead Levels
Extracted Lead (ppm)
Total Lead (ppm)
Low 0-32 0-499
Medium 33-110 500-999
High 111-857 1000-3000
Very High above 857 above 3000

 

Soil samples should be taken from several areas to determine the location of the contamination. The greatest lead concentration is in the top one to two inches of the soil. Children’s play areas or vegetable gardens should be sampled separately. Avoid mixing several sites into one sample. Sample high-risk areas to locate potential problems.

Lowering the Risk:

Gardeners can use several methods to reduce the risk of lead poisoning from lead contaminated soils. Fruit and vegetable gardens should be located away from old painted buildings, heavy traffic and sites where sludge with heavy metals was applied. Vegetables and fruits can accumulate lead in their leafy green tissues, although lead accumulation will be lower in fruits. In high-risk lead areas, grow crops such as tomatoes, eggplants, peppers, squash, melons and cucumbers rather than leafy greens such as lettuce, chard, collards or spinach. Crops such as carrots, radishes, turnips, onions and potatoes can accumulate lead and should not be planted in heavily contaminated soils.

Direct ingestion of lead from contaminated soils is a risk. Soil clinging to the leaves, fruits or roots of crops can be directly ingested. Wash and peel fruits and vegetables to reduce this risk. A 1% vinegar solution (2.5 tablespoons per gallon) or soapy water is an effective way to remove soil. Discard the outer wrapper leaves of greens before washing. Wash off excess dirt from root crops outside the home, preferably at an outside hose bib to prevent bringing contaminated soil into the home.

The amount of lead absorbed by plants is affected by the pH, organic matter and phosphorus content of the soil. To reduce lead uptake by plants, lime the soil to a pH of 6.5 to 7.0. Add organic matter such as compost, leaf mold or grass clippings to the gardening site. Add phosphorus to the soil as recommended by a soil test.

To reduce the risk of bringing lead contaminated soil into the home, rinse and launder gardening clothing promptly. Young children, in particular, may directly ingest soil when playing. If possible do not allow children to play in contaminated soils. Hygiene is important, although understandably difficult, with young children. Frequent hand washing and rinsing outside toys will reduce the amount of soil ingested. Wash hands before eating meals or snacks. Do not let children eat soil or put their hands in their mouths. Mulch play areas with wood chips or other soft materials to reduce soil dust. Build a plastic-lined sand box for a clean area to play. Parents of children under six living in areas with contaminated soils should consult their pediatrician. A blood test to monitor lead levels may be recommended.

In heavily contaminated soils adjacent to a residence, plant trees, shrubs or perennials and mulch the area to minimize annual tilling and cultivation operations. When the soil lead level is over 5000 ppm total lead, the garden soil should be removed and replaced with clean topsoil. Direct ingestion of contaminated soils and the airborne soil dust can only be eliminated by removing the soil. Test the new topsoil before purchasing it. Test for soluble salts, pH and the standard nutrients (phosphorus, potassium and magnesium). Testing for lead and other heavy metals is recommended especially if the topsoil is from an urban area. No food crops should be grown in a soil that is heavily contaminated. Container gardening or construction of raised beds filled with purchased soil is an option for the avid vegetable gardener.


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