While all kinds of chemicals are made from the same set of chemical elements, not all chemicals are the same-- atoms can be hooked together in many different ways. This includes making molecules which are not found in nature but which can have profound impacts on natural systems, such as extra-strong analogs of biological hormones. Industry can also release greater concentrations of harmful atoms/ions/molecules, such as arsenic, which are normally found at low concentrations in ecosystems.
Work Step by Step
The key here is to see that biological molecules are only a subset of the possible chemicals which can be made, some non-natural ones being of great potential harm, and that the same is true for atoms/ions found in low concentrations in or near living things. Industry can greatly increase the concentrations, also potentially causing harm.