powerlines, nuclear plants (yes, there's one 40 mins from where I live), asbestos, lead, check well water for chemicals, safety, under ground oil tanks, radon, mold, septic issues.

Does your question deal with a particular situation or location?

The question is so broad, and it seems like the general answer is something a broker would already know.  

Just wondering so that I could give you an answer that better met your needs...

No flooring inside the front door to prevent you from falling into the basement!! 

Mold, asbestos and in older homes lead. Radon can be an issue in some markets too.

Fuel oil barrels in the back yard, nuclear power plants nearby, and a few other things.

Ruth Mary Hansen Radon here.

Radon would be one to add to the list.

Lead, asbestos, meth, oil or fuel ground contamination, nearby leaking fuel tanks, old farm dumps or landfills, chemicals like creosote, pesticides, etc.

This is a long list. Lead paint and lead soldered pipes in the water system, radon, mold, USTs, asbestos, spilled hydrocarbons (gasoline, oil and so on), NORMs (naturally occurring radioactive materials), pesticides and herbicides, mercury contamination..the mind boggles!

Mold is of concern here  

underground oil tanks for one.... 

Left behind in a dark corner of the garage cabinet a rusty can of Chlordane.

Lead paint and asbestos still makes the rounds in the older homes.

Buried fuel tanks.

Gas stations, former rocket test sites and toxic waste dumping grounds (Rocketdyne Santa Susana out here), toxic waste lands due to fraking and natural gas leaks (search Porter Ranch).

One of the most common is a buried heating oil tank second only to a defective septic system.

Too many to list. Another good reason to use an experienced real estate agent.

There are many.  Consult an environment specialist, legal counsel and more.  Inspect the property.

There are many.  In California we have multiple advisories that are acknowledged by both the buyer and seller.  They include but are not limited to lead-based paint, power lines, radon, asbestos, earthquake fault zones, tsunami, liquefaction.....

there are many.

In old East Dallas lead.

Asbestos, lead paint, radon, former meth lab (hope that is not your problem!)

Lead, radon, asbestos, mold are only issues here in my area. But of course, power lines, even fwy that is closely, potentially harmful productions, etc. 

It all depends.  Termites?  Radon?  Spray painted grass?

There are all kinds of environmental hazards that need to be looked out for. This can range from mold, to lead based paint to something buried in the ground. 

asbestos

So many that could be pertinent and they will vary depending on your location.

Good answers already posted for you, especially asbestos, lead paint or radon.

 seismic

 flood zone

forest fire

undergroud toxic storage

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The contents of the comments are giving me the environmental hives.   Beware