appendix f: lead remediation
In the post-industrial Northampton Urban and Suburban Districts, there is a higher possibility of soil lead contamination in many areas due to historical uses. Therefore all sites, even in present-day residential areas, need to be tested before food cultivation. If lead is found, care should be taken with both crops and livestock to make sure the element does not accumulate in the tissues of edible plants, or in the eggs and flesh of animals raised for consumption. Many soils have naturally occurring lead levels between 15 to 40 parts per million (ppm), and all parts of crops and food from livestock such as eggs and meat are safe if produced on soil at these levels. For lead levels higher than 40 ppm, care should be taken, however. (University of Massachusetts Amherst Soil and Plant Tissue Testing Laboratory). Carl Rosen, a soil scientist with the University of Minnesota, finds that up to 300 ppm, “lead does not readily accumulate in the fruiting parts of vegetable and fruit crops” (Nordahl 33), suggesting that up to this level, it is safe to grow crops for their fruiting parts. He says that even in the plants’ vegetative parts, the danger of lead contamination is greater from accumulation on the plants’ surfaces than from accumulation. Thorough washing of fruits and vegetables can remove lead from plants’ surfaces. To avoid possible human health risks, however, crops cultivated in soils with these lead levels should be limited to those grown for their fruit. Eggs and meat from livestock should only be eaten if produced on soils containing up to the safe lead level of 40 ppm. Other sources, such as the University of Massachusetts, suggest that plants grown for their fruiting parts may still be consumed if cultivated in soils with lead levels up to 1000 ppm. In order to make contaminated sites suitable for production of vegetative crops, many sources suggest the importation of fresh soil to replace or sit on top of contaminated sites, whether by spreading or in raised planter beds. The only downsides to these solutions are that they are costly and involve high fossil fuel energy inputs. However, lead is a stable element that does not move easily through soil, so in tall-enough raised beds, plants grown for vegetative parts may be cultivated. Plants must sit in beds of uncontaminated soil high enough above the contaminated ground soil (~3 feet) so that plants’ roots are not able to grow deep enough to reach the contaminated areas. Lead also can be removed from soil by certain plants through phytoremediation, especially by plants in the Brassicaceae (mustards in particular) and Asteraceae (sunflowers in particular) families. Phytoremediation is the use of plants to remove contaminants by absorbing them through their roots.
Though this is an option, the only concern is that it simply re-locates the lead problem in the place in where plants are then disposed. If this practice is used, care must be taken, and a proper disposal plan must be in place (Randazzo).
low lead levels (-ppm):
1. Locate gardens away from old painted structures and heavily traveled roads. 2. Give planting preferences to fruiting crops (tomatoes, squash, peas, sunflowers, corn, etc.). 3. Incorporate organic materials such as finished compost, humus, and peat moss. 4. Lime soil as recommended by soil test (pH 6.5 minimizes lead availability). 5. Discard old and outer leaves before eating leafy vegetables. Peel root crops. Wash all produce. 6. Keep dust to a minimum by maintaining a mulched and/or moist soil surface.
medium lead levels (-ppm):
In addition to following LOW lead level recommendations, 1. It is recommended that the blood lead levels of children under six be tested. 2. Avoid growing leafy green vegetables and root crops if your children have above normal lead levels. 3. Give planting preference to fruiting crops.
high lead levels (-3ppm):
In addition to following LOW lead level recommendations, 1. It is strongly recommended that the blood lead levels of children under six be tested. 2. Grow only fruiting crops or limit gardening to flowers and ornamentals. 3. Replenish soil with clean topsoil; or create raised (or entrenched) beds lined in plastic and filled with clean topsoil to a depth of at least six inches.
very high lead levels (more than 3ppm):
Do not use this soil for vegetable gardening, and: 1. Be certain to test the blood lead levels of children under six. 2. Remove and replace soil; or grow only flowers and ornamental plants. 3. Containerize garden in pots with clean topsoil; or create raised (or entrenched) beds lined in plastic and filled with clean topsoil to a depth of at least six inches. Recommendations if lead is found in soils. University of Massachusetts-Amherst Soil and Plant Tissue Testing Laboratory. Soil Remediation: University of Massachusetts-Amherst Soil and Plant Tissue Testing Laboratory.
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