DAll of the above.
The type of chemical, its concentration, and weather conditions where said chemical is introduced are factors that determine how harmful an introduced chemical will be in the environment.
Examples of chemicals that are harmful to our environment are:
1) organochlorines - compounds like polychlorinated biphenyl (PCBs) originally developed for use in electrical equipments as cooling agents. They are carcinogenic and capable of damaging the liver, nervous system, and the reproductive system in adults.
2) dioxins - by-product of the manufacturing, moulding, or burning off of organic chemicals and plastics that contain chlorine. An environmental and health hazard.
3) cadmium - used in batteries, plastics, pigments and metal coatings. Produced by mining and other industrial activities. Accumulation will lead to kidney and bone diseases.
