Large tsunamis are rare relative to other kinds of natural disasters, but when they do occur they can devastate coastal populations.
Climate change, rising food prices and a growing world population mean that GM crops are in the spotlight like never before, but few technologies are more controversial.
Acid rain is a classic example of an environmental threat that originates in one place and causes problems in another, often very far away.
Indoor air pollution is one of the great untold stories. It is responsible for more than a million premature deaths every year.
Outdoor air pollution – caused by industry, cars, fires and other factors – poses a range of health threats that can be felt far from their source.
Asbestos is a toxic mineral that has been banned in many Western nations but is widely used in developing countries, where it poses serious health threats to millions of people.
Bird flu, SARS and Ebola are just three of the many diseases to have crossed the species barrier from animals to humans recently.
People can carry on dying long after the last bullet in a war has been fired, thanks to the toxic legacy of military action.
Proponents of nanotechnology say it has many applications that could benefit society, while opponents say it could pose serious risks to people and the environment.
Toxic metals — often known as heavy metals — can persist in the environment and increase in concentration in the food-chain.