Collins reagent (the complex of chromium(VI) oxide) are used for the oxidation of alcohols. Hazards Pyridine is a toxic, flammable liquid with a strong and unpleasant fishy odour. Its odour threshold of 0.04 to 20 ppm is close to its threshold limit of 5 ppm for adverse effects, thus most (but not all) adults will be able to tell when it is present at harmful levels. Pyridine easily dissolves in water and harms both animals and plants in aquatic systems. Fire Pyridine has a flash point of 20 °C and is therefore highly flammable. Combustion produces toxic fumes which can include bipyridines, nitrogen oxides, and carbon monoxide. Short-term exposure Pyridine can cause chemical burns on contact with the skin and its fumes may be irritating to the eyes or upon inhalation. Pyridine depresses the nervous system giving symptoms similar to intoxication with vapor concentrations of above 3600 ppm posing a greater health risk. The effects may have a delayed onset of several hours and include dizziness, headache, lack of coordination, nausea, salivation, and loss of appetite. They may progress into abdominal pain, pulmonary congestion and unconsciousness. The lowest known lethal dose (LDLo) for the ingestion of pyridine in humans is 500 mg·kg−1. Long-term exposure Prolonged exposure to pyridine may result in liver, heart and kidney damage. Evaluations as a possible carcinogenic agent showed that there is inadequate evidence in humans for the carcinogenicity of pyridine, although there is sufficient evidence in experimental animals. Therefore, IARC considers pyridine as possibly carcinogenic to humans (Group 2B). Occurrence Trace amounts of up to 16 µg·m−3 have been detected in tobacco smoke. Minor amounts of pyridine are released into environment from some industrial processes such as steel manufacture, processing of oil shale, coal gasification, coking plants and incinerators. The atmosphere at oil shale processing plants can contain pyridine concentrations of up to 13 µg·m−3, and 53 µg·m−3 levels were measured in the groundwater in the vicinity of a coal gasification plant. According to a study by the US National Institute for Occupational Safety and Health, about 43,000 Americans work in contact with pyridine. In foods Pyridine has historically been added to foods to give them a bitter flavour, although this practise is now banned in the U.S. It may still be added to ethanol to make it unsuitable for drinking. Metabolism Exposure to pyridine would normally lead to its inhalation and absorption in the