It used to be considered a miracle material: blue asbestos can be woven and is a harmless, fire-resistant silicate rock. But its long fibres get caught in lung tissue where they trigger a chronic inflammation that can later cause cancer. Image: Raimond Spekking / CC BY-SA 4.0 (via Wikimedia Commons)

Under a scanning electron microscope, the fruiting bodies of mildew Aspergillus niger are beautiful. But mildew is also a pathogen and poisonous. The aflatoxin produced by the fungus is one of the most carcinogenic substances in existence. Image: Keystone / Science Photo Library / Thierry Berrod, Mona Lisa Production

The fumes of mercury, a heavy metal, swiftly enter the body where they remain for a long time in the fatty tissue. Among other things, mercury poisons the kidneys, the liver and the central nervous system. Image: Keystone / Science Photo Library

The clearfin lionfish (Pterois radiata) is common in the Red Sea and is attractive to divers, but the poison in its spines can kill off human tissue. Image: Keystone / Science Photo Library / Photostock-Israel

Lake Natron in northern Tanzania is impressive and oppressive in equal measure – not many living creatures can
withstand its extreme salt concentration and its highly alkaline pH level. These include flamingos and the
cyanobacteria that give the water its characteristic red colour. Image: Philippe Bourseiller / Getty Images