Contamination is the presence of an unwanted foreign substance or material (a contaminant) in the body, food supply, physical environment or natural environment.  Contaminants range from toxins, pathogens and poisons to pollutants and radioactive waste.

In the natural environment, contamination can occur in land (groundwater), air (pollution) and sea.  In the body, pathogenic contaminants include viruses, bacteria, toxins, and radiation, etc.  (Photo: Shutterstock)