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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:
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.
Adapted from Denise D. Sharp and David L. Clement, Maryland Cooperative Extension Service, 2001
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