A biocide is a chemical substance or microorganism which can deter, render harmless, or exert a controlling effect on any harmful organism by chemical or biological means. Biocides are commonly used in medicine, agriculture, forestry, and industry. Biocidal substances and products are also employed as anti-fouling agents or disinfectants under other circumstances: chlorine, for example, is used as a short-life biocide in industrial water treatment but as a disinfectant in swimming pools. Many biocides are synthetic, but a class of natural biocides, derived from e.g. bacteria and plants, includes brassica oleracea, brassica oleracea gemmifera, and clostridium botulinum bacteria.^{[citation needed][clarification needed]}

A biocide can be:

Biocide can also refer to the destruction of life, a form of omnicide that affects every living thing, not just humans; one who wishes that everything in the entire world, or universe, face extinction, is labeled a 'Biocidist', or having 'biocidal' ideologies.

Rachel Louise Carson (May 27, 1907 – April 14, 1964) was an American marine biologist and conservationist whose book Silent Spring and other writings are credited with advancing the global environmental movement.

Carson began her career as a biologist in the U.S. Bureau of Fisheries, and became a full-time nature writer in the 1950s. Her widely praised 1951 bestseller The Sea Around Us won her a U.S. National Book Award, recognition as a gifted writer, and financial security. Her next book, The Edge of the Sea, and the reissued version of her first book, Under the Sea Wind, were also bestsellers. That so-called sea trilogy explores the whole of ocean life from the shores to the surface to the depths.

Late in the 1950s Carson turned her attention to conservation, especially environmental problems she believed were caused by synthetic pesticides. The result was Silent Spring (1962), which brought environmental concerns to an unprecedented share of the American people. Although Silent Spring met with fierce opposition by chemical companies, it spurred a reversal in national pesticide policy, which led to a nationwide ban on DDT and other pesticides, and it inspired a grassroots environmental movement that led to the creation of the U.S. Environmental Protection Agency. Carson was posthumously awarded the Presidential Medal of Freedom by Jimmy Carter.