Leach downward through the soil. Broken down by microorganisms. Manures Most concern is over cadmium, lead, arsenic, zinc, copper, and nickel. These metals are usually bound to the soil particles and do not leach. These metals leach only in moderately to strongly acid soils.
Nitrates can contaminate groundwater supplies causing methemoglobinemia.
Most is fixed by interlayers of clays such as vermiculite. Plant uptake is slow in soils with fixing clays, but faster in tropical soils. Radon Gas a colorless, odorless gas that can cause lung cancer formed by radioactive decay of radium, a breakdown product of uranium. Methane can also be consumed by upland soils.