Toxic:
Poisonous 

Toxic emissions:
poisonous chemicals discharged to air, water, or land. Cars and other motor vehicles can have toxic emissions.

Toxic sites:
land contaminated with toxic pollution, usually unsuitable for human habitation. Nuclear Waste toxic sites are generally uninhabitable for hundreds of years.

Toxic waste:
garbage or waste that can injure, poison, or harm living things, and is sometimes life-threatening.

Toxification:
poisoning of any living source 

Traffic calming:
designing streets to reduce vehicle speed and to make walking and bicycling easier and safer.

Tropical rain forest:
a large, dense forest in a hot, humid region (tropical or subtropical). Rainforests have an abundance of diverse plant and animal life, much of which is still unknown even today. 

Twilight zone:
The dark area of the ocean, extending from the bottom of the sunlight zone down to the very bottom of the ocean where plants cannot grow and where animals are less numerous and smaller