If you are exposed to heavy metals such as cadmium, hexavalent chromium and chemicals such as cyanide, nitrogen dioxide and sulfur dioxide (anoxic/hypoxic/histotoxic) over idlh's will it cause brain damage especially to the substantia nigra?

We are all exposed to trace amounts of many chemicals in air and water. Most of the compounds you listed are toxic, but health effects depend on the amount of chemical you may be exposed to. Exposure to car exhaust, with some of the compounds, in race car drivers has been associated with movement disorders.

We have knowledge of manganese miners developing Parkinson's disease, and now even air pollution appears to influence both dementias and movement disorders. Carbon disulfide is another known culprit, so not surprising if your list would likewise cause substantial problems, especially if hypoxia was caused by any of them. Contact a toxicologist, have a full evaluation and uncover hidden problems