Which of these contaminants is NOT classified as microbiological?

Selenium is classified as a chemical contaminant rather than a microbiological contaminant. Microbiological contaminants include organisms such as bacteria, viruses, and protozoa, which can cause illness and disease when present in water supplies.

Bacteria are single-celled organisms that can be pathogenic, meaning they have the potential to cause disease. Viruses are even smaller than bacteria and require living hosts to reproduce, often leading to viral infections. Protozoa are also microorganisms, larger than bacteria and capable of causing gastrointestinal diseases among other health issues.

In contrast, selenium is a trace element found in various minerals and is recognized as an inorganic contaminant when present in water. Its effects on health are associated with chemical exposure rather than infectious diseases caused by living organisms. Thus, the distinction between microbiological and chemical contaminants is crucial for understanding water quality and safety.