SINGAPORE - The illegal dumping of toxic chemicals into a river in Pasir Gudang, Johor, has sickened more than 2,700 people, including hundreds of students.
Malaysia's Environment Minister Yeo Bee Yin said on Wednesday (March 13) that a number of chemicals have been ascertained from the samples taken.
They include benzene, acrolein, acrylonitrile, hydrogen chloride, methane, toluene, xylene, ethylbenzene and d-limonene.
What are these chemicals, where are they usually found, and what is their possible impact on humans?
What: Benzene is a chemical that has a sweet, aromatic, gasoline-like smell. Most people can begin to smell benzene in the air at 1.5 to 4.7 parts per million, according to the United States Centers for Disease Control and Prevention (CDC).
Where: Benzene can be found in crude oil, gasoline and cigarette smoke. It is also used to make some types of lubricants, rubbers, dyes and pesticides.
Impact: The International Agency for Research on Cancer has classified benzene as carcinogenic to humans. Human exposure to benzene has been associated with a range of acute and long-term adverse health effects and diseases, including narcosis - in which a person blacks out - and aplastic anaemia - which results in a drop in blood cell count - according to the World Health Organization.
Some symptoms of prolonged benzene exposure include headaches, dizziness, drowsiness, confusion, tremors and loss of consciousness.
What: Acrolein is a clear, colourless, or yellow liquid with a pungent, suffocating odour.
Where: The chemical has been used to control plant and algae growth in irrigation canals. It has also been used to manufacture other chemicals, as a warning agent in gases, as a test gas for gas masks, in military poison gases, for making colloidal metals, in leather tanning, and as a fixative in histology.
Impact: Inhaled acrolein is highly toxic and is irritating to the upper respiratory tract even at low concentrations, according to the US Agency for Toxic Substances and Disease Registry (ATSDR). Acrolein is severely irritating to the skin and eyes.
What: Acrylonitrile is a colourless, liquid, man-made chemical with a sharp, onion- or garlic-like odour.
Where: Acrylonitrile is used mostly to make plastics, acrylic fibres, and synthetic rubber. As acrylonitrile evaporates quickly, it is most likely to be found in the air around chemical plants where it is made, according to the ATSDR.
Impact: Exposure to large amounts of the chemical affects mainly the nervous system. Symptoms can include headaches and nausea, while exposure to higher concentrations may temporarily damage red blood cells and the liver.
Long-term exposure to acrylonitrile may increase the chances of getting cancer, according to the US Department of Health and Human Services.
4. HYDROGEN CHLORIDE
What: Hydrogen chloride has a strong irritating smell. The chemical's colour ranges from colourless to slightly yellow. Hydrogen chloride vapour is corrosive.