Synthetic chemical in the context of "Chemical reactor"

Silent Spring is an environmental science book by Rachel Carson. Published on September 27, 1962, the book documented the environmental harm caused by the indiscriminate use of DDT, a pesticide used by soldiers during World War II. Carson accused the chemical industry of spreading disinformation, and public officials of accepting the industry's marketing claims unquestioningly.

In the late 1950s, Carson began to work on environmental conservation, especially environmental problems that she believed were caused by synthetic pesticides. The result of her research was Silent Spring, which brought environmental concerns to the American public. The book was met with fierce opposition by chemical companies, but it swayed public opinion and led to a reversal in US pesticide policy, a nationwide ban on DDT for agricultural uses, and an environmental movement that led to the creation of the US Environmental Protection Agency.

A carcinogen (/kɑːrˈsɪnədʒən/) is any agent that promotes the development of cancer. Carcinogens can include synthetic chemicals, naturally occurring substances, physical agents such as ionizing and non-ionizing radiation, and biologic agents such as viruses and bacteria. Most carcinogens act by creating mutations in DNA that disrupt a cell's normal processes for regulating growth, leading to uncontrolled cellular proliferation. This occurs when the cell's DNA repair processes fail to identify DNA damage allowing the defect to be passed down to daughter cells. The damage accumulates over time. This is typically a multi-step process during which the regulatory mechanisms within the cell are gradually dismantled allowing for unchecked cellular division.

The specific mechanisms for carcinogenic activity is unique to each agent and cell type. Carcinogens can be broadly categorized, however, as activation-dependent and activation-independent which relate to the agent's ability to engage directly with DNA. Activation-dependent agents are relatively inert in their original form, but are bioactivated in the body into metabolites or intermediaries capable of damaging human DNA. These are also known as "indirect-acting" carcinogens. Examples of activation-dependent carcinogens include polycyclic aromatic hydrocarbons (PAHs), heterocyclic aromatic amines, and mycotoxins. Activation-independent carcinogens, or "direct-acting" carcinogens, are those that are capable of directly damaging DNA without any modification to their molecular structure. These agents typically include electrophilic groups that react readily with the net negative charge of DNA molecules. Examples of activation-independent carcinogens include ultraviolet light, ionizing radiation and alkylating agents.