Contamination
Contamination is the presence of an unwanted constituent, contaminant or impurity in a material, physical body, natural environment, workplace, etc.
Sciences
"Contamination" has also more specific meanings in science:
In chemistry, the term usually describes a single constituent, but in specialized fields the term can also mean chemical mixtures, even up to the level of cellular materials. All chemicals contain some level of impurity. Contamination may be recognized or not and may become an issue if the impure chemical is mixed with other chemicals or mixtures and causes additional chemical reactions. The additional chemical reactions can sometimes be beneficial, in which case the label ‘contaminant’ is replaced with reactant or catalyst. If the additional reactions are detrimental, other terms are often applied such as toxin, poison or pollutant, depending on the type of molecule involved. A major fraction of chemistry is involved with identifying, isolating, and studying contaminants.