In 2014, a Large Increase in a Chemical Called Microcystin

In 2014, a large increase in a chemical called microcystin, produced by bacteria in Lake Erie's water, prevented Toledo, Ohio, from using its drinking water for several days. Researchers are now conducting tests on how microcystin impacts the health of organisms living in the lake and of humans that consume it. This illustrates an example of

A) toxicology.
B) epidemiology.
C) environmental justice.
D) herd immunity.