Which statement correctly matches the three classes of drinking water contaminants with an example of each?

• A. Inorganic contaminants (arsenic); Organic contaminants (pesticides); Microbial contaminants (bacteria such as E. coli).
• B. Inorganic contaminants (arsenic); Organic contaminants (lead); Microbial contaminants (bacteria such as E. coli).
• C. Inorganic contaminants (arsenic); Organic contaminants (DDT); Microbial contaminants (solids such as silt).
• D. Inorganic contaminants (carbon); Organic contaminants (solvents); Microbial contaminants (viruses).

Answer: (A)

Contaminants in drinking water are classified by chemical nature: inorganic contaminants are mineral or metal ions that do not contain carbon-hydrogen bonds; arsenic is a classic example. Organic contaminants are carbon-containing chemicals, such as pesticides and solvents. Microbial contaminants are living organisms, including bacteria, viruses, and protozoa. The combination of inorganic with arsenic, organic with pesticides, and microbial with E. coli fits this classification cleanly, since arsenic is inorganic, pesticides are organic, and E. coli is a microbe. The other options mix categories in ways that don’t match the chemistry or biology: metals like lead are not organic contaminants, silt is particulate matter rather than a microbe, and the inorganic carbon label doesn’t align with how these contaminant groups are usually defined.