Soil the Pollutant Control
Another amazing feature of soil is the way it acts as a 'filter'
against many forms of harmful substances (pollutants).
Research by soil scientists has shown that soil can have a major
role in the transport of pollutants. Water in soil can transport
substances such as nitrate, phosphorus and pesticides to water
sources such as rivers, and whilst they are important to soil and
plant life, these materials are generally considered harmful to
humans and wildlife when they exceed certain quantities.
However, soils can also modify the impact of pollutants. For example,
in wet conditions in the soil nitrate is converted into nitrogen
gas, where it can be safely released into the atmosphere. Similarly,
pesticides can be broken down into harmless substances by certain
micro-organisms present in the soil. Phosphates are mostly filtered
naturally during drainage of water (percolation), as they become
tied to soil particles, and are trapped in the soil.
Soil is also effective at filtering ‘urban’ pollutants
like oil and metals. Oil in particular is an organic substance
which soil microbes can break down into carbon dioxide and water.
Metals such as lead from petrol however cannot be broken down in
such a manner, but the soil can often retain them until they can
be absorbed into plants, which can then be disposed of safely.