Heavy Metals

Lead and many other heavy metals exist in small quantities in most soils. Lead is a medical problem and an environmental problem when the concentration is raised, or the lead is in the atmosphere or in the foods that humans and animals eat in higher than normal levels.

Apparently Lead (Pb) can be leached away by adding dolomite or lime [Fanton, Mollison]. One advantage of this is, if your soil is highly acid then lime may increase the diversity in plants that you can grow, (humus will too but it will take a little longer). On the other hand, this leaching of lead may contaminate the ground water table.

The growing of food in containers with home made soil/compost would be the quickest and most responsible solution. Increasing the humus content in the upper layer of soil while also reduce the concentration of metals as long as there isn't a constantly renewed source of lead such as fall-out. If the lead is coming into the system daily, neither leaching or adding humus will lower the risk. Planting edibles under cover, in a greenhouse or beneath a good natural canopy, can reduce lead dust on delicate leafy crops. Plant filter hedges near roads to prevent additional lead from entering your system.

Strategies for Lead in soils: Lead is dangerous in the air and in food. The designer should plan a natural replacement of edible toxin-harbouring plants such as tubers with other less harmful crops, such as nut crops. Avoid removal of existing vegetation for fear of exposing the site to erosion and increasing chances of lead dust to the surrounding people and animals. Also, you cannot be sure that your new preferred vegetation will be as hardy in the circumstances/pollutive environment. You can plan to improve the diversity of crops with succession. (Succession is discussed in Section 9. Forests and Trees)

If the area has moderate exposure to lead fallout as the source of pollution then you could consider fruits that

1. Have firm, smooth, easily cleaned skins e.g. apples, pears, little tomatoes AVOID textured and soft skinned fruits i.e. mulberry, strawberry, persimmon.
2. Have removable outer part such as oranges, banana, guava, avocado, lychee, melon.
3. Usually grow under a cover of leaves e.g. kiwi fruit,

Cadmium (Cd) high levels result from the continued use of superphosphate.