ABSTRACT
When we were young, most of us were told to wash our hands and face. Dirt (soil out of place) was something to be avoided. This was especially true when dirty objects were near the mouth and nose. In relatively recent times (beginning about 150 years ago), science showed that microorganisms living or surviving in the soil can cause human health problems. We now know that these organisms can be quite diverse and include viruses, bacteria, fungi, protozoa, and some nasty parasitic nematodes. Soil can be a major source for transmission of disease. It is not necessary for humans to physically eat soil to come into contact with infectious organisms. We accidentally ingest soil when we put our dirty ngers in our mouths or eat fruits or vegetables that have not been thoroughly washed and cooked. Preharvest contamination may occur in agricultural products subjected to irrigation with reclaimed wastewater, crop fertilization with sewage sludge, or fecal pollution in the soils in which they are grown (one needs to be especially careful where human feces are directly applied to soils). We may even swallow parasites in unltered water that has washed off or passed through contaminated soils. Soil particles may be picked up by the wind and inhaled. For some diseases (especially caused by worms), we need to avoid physical contact with soil to avoid the disease. Avoiding contact with soil, however, for many people is not feasible. We live upon soil, dig in soil, breath air that may be lled with soil, use soil to dispose of human and animal wastes, use soil to purify drinking water, grow foodstuffs in soil, and consume animals that live upon soil. Thus humans have developed a close relationship with soil and, in fact, we depend upon soil for our very existence.
