Microbiological contaminants include which of the following?

Microbiological contaminants are primarily biological organisms that can pose risks to health when present in water sources. This category includes living microorganisms such as bacteria, viruses, and protozoa, which can lead to various diseases and health issues if ingested through contaminated water.

Bacteria are single-celled organisms that can multiply rapidly and may cause illnesses such as gastroenteritis. Viruses, which are smaller than bacteria and require a host for replication, can lead to infections like hepatitis A. Protozoa are more complex organisms that often have a resistant stage, like cysts, allowing them to survive in challenging environments and can cause diseases such as giardiasis or cryptosporidiosis.

The other options consist of different types of contaminants that do not fall under the microbiological category. For instance, metals like lead, mercury, and arsenic are classified as chemical contaminants. Pesticides and herbicides also fall into the chemical contaminant category as they are synthetic compounds used in agriculture. Similarly, radionuclides and selenium represent inorganic contaminants rather than microbiological threats. Thus, the presence of bacteria, viruses, and protozoa is what makes the selected answer the correct one concerning microbiological contaminants.