The chemical industry produces such things as petrochemicals, drugs, paint, and rubber.
It is especially worth noting that in the market, the price of organic food is at least twice that of food treated with chemicals.
A chemical is any substance that has a defined composition. In other words, a chemical is always made up of the same "stuff." Some chemicals occur in nature, such as water. Other chemicals are manufactured, such as chlorine (used for bleaching fabrics or in swimming pools). Chemicals are all around you: the food you eat, the clothes you wear. You, in fact, are made up of a wide variety of chemicals.

A chemical reaction refers to a change in a chemical. More generally, a chemical reaction can be understood as the process by which one or more substances change to produce one or more different substances. Chemical changes are different from physical changes, which don't result in a change in substances. One example of a physical change is when water freezes into ice. While ice may have different physical properties, it is still just water. Another example is when you dissolve salt into a cup of water. While the salt may appear to disappear into the water, you still have water and salt—no substance changed into a completely new substance.
While any of the above may be evidence of a chemical change, physical changes can have some of the same effects. One way to determine the difference between the two is to think about whether the new substance could be physically separated back into its original parts—in other words, if the matter could "go back" to how it originally was. If it cannot, then it's a chemical change.
A chemical is any mix of raw elements: hydrogen + oxygen produce the chemical water. Water is created by a change in the chemistry of hydrogen and oxygen atoms — a chemical change.

Be cautious of the negative reaction people have to chemical substances. Chemicals often bring to mind deadly substances, such as asbestos or deadly chemical weapons. But many chemicals are part of our everyday life. Our lives would be drastically different without chemical compounds — think of the infection that would result if we didn't have the chemical hydrogen peroxide for cleaning out cuts.
But no such humility marks the booming “weed killer” business of the present day, in which soaring sales and expanding uses mark the production of plant-killing chemicals.
Silent Spring by Rachel Carson
It would be unrealistic to suppose that all chemical carcinogens can or will be eliminated from the modern world.

His clothes and even his shoes had that chemical stink.

The poison might be a defense against being eaten, or it might just be one of the chemicals the fungus needs to do its work that happens to be toxic to humans.
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