Pyridines - Health Issues

Health Issues

Pyridine is harmful if inhaled, swallowed or absorbed through the skin. Effects of acute pyridine intoxication include dizziness, headache, lack of coordination, nausea, salivation and loss of appetite. They may progress into abdominal pain, pulmonary congestion and unconsciousness. One person died after accidental ingestion of half a cup of pyridine. The lowest known lethal dose (LD_Lo) for the ingestion of pyridine in humans is 500 mg·kg−1. In high doses pyridine has a narcotic effect and its vapor concentrations of above 3600 ppm pose a health risk. The oral LD₅₀ in rats is 891 mg·kg−1. Pyridine is flammable.

Evaluations as a possible carcinogenic agent showed there is inadequate evidence in humans for the carcinogenicity of pyridine, albeit there is limited evidence of carcinogenic effects on animals. Available data indicate that "exposure to pyridine in drinking-water led to reduction of sperm motility at all dose levels in mice and increased estrous cycle length at the highest dose level in rats".

Pyridine might also have minor neurotoxic, genotoxic and clastogenic effects. Exposure to pyridine would normally lead to its inhalation and absorption in the lungs and gastrointestinal tract, where it either remains unchanged or is metabolized. The major products of pyridine metabolism are N-methylpyridiniumhydroxide, which is formed by N-methyltransferases (e.g. pyridine N-methyltransferase), as well as pyridine-N oxide, and 2-, 3- and 4-hydroxypyridine, which are generated by the action of monooxygenase. In humans, pyridine is metabolized only into N-methylpyridiniumhydroxide. Pyridine is readily degraded by bacteria to ammonia and carbon dioxide. The unsubstituted pyridine ring degrades more rapidly than picoline, lutidine, chloropyridine, or aminopyridines, and a number of pyridine degraders have been shown to overproduce riboflavin in the presence of pyridine.

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.