Respiratory tract toxicity phosgene

A) The Toxic Suffocants (or Lung Irritants). These include those gases which act principally on the respiratory tract chlorine, phosgene, chloropicrin, etc. 

Highly toxic perfluoroisobutylene (PFIB) poses a serious health hazard to the human respiratory tract. PFIB is a thermal decomposition of polytetrafluo-roethylene (PTFE), e.g., Teflon. PFIB is approximately lOx as toxic as phosgene. Inhalation of this gas can cause pulmonary edema, which can lead to death. PFIB is included in Schedule 2 of the Chemical Weapons Convention (CWC), the aim of the inclusion of chemicals such as PFIB was to cover those chemicals, which would pose a high risk to the CWC. 

The upper and lower respiratory tracts respond differently to the presence of toxicants. The upper respiratory tract is affected mostly by toxicants that are water soluble. These materials either react or dissolve in the mucus to form acids and bases. Toxicants in the lower respiratory tract affect the alveoli by physically blocking the transfer of gases (as with insoluble dusts) or reacting with the wall of the alveoli to produce corrosive or toxic substances. Phosgene gas, for example, reacts with the water on the alveoli wall to produce HC1 and carbon monoxide. 

Green Cross Gases. This includes substances with a high vapour tension and great toxic power on the respiratory tract phosgene, trichloromethyl chloroformate (diphosgene), chloro-picrin, etc. 

B. Less soiubie gases (eg, phosgene and nitrogen dioxide) are not rapidly adsorbed by the upper respiratory tract and can be inhaled deeply into the lower respiratory tract to produce delayed-onset pulmonary toxicity. 

GA, with the structure formula shown in Figure 2.3 — chemically known as ethyl N,N-dimethylphosphoroamidocyanidate — is a colorless to brownish liquid. Its vapor is also colorless. GA may have a faintly fruity odor when not pure. It is about 30 times as toxic as phosgene, which was used in WWI. Like other G-agents, it enters the body primarily through the respiratory tract. GA is approximately 20 times more persistent than GB, but not as stable in storage. At 20°C, its volatility is 328 mg/m, which increases to 858 mg/m when temperature changes to 30°C. 

Phosgene is manufactured from a reaction of carbon monoxide and chlorine gas in the presence of activated charcoal. Phosgene is used in the manufacture of isocyanates, polycarbonates, pesticides, dyes, and pharmaceuticals. Manufacture of phosgene in the United States is almost entirely captive in that more than 99% is used in the manufacture of other chemicals within a plant boundary (US EPA, 2003). The odor threshold is between 0.5 and 1.5 ppm (NIOSH, 1976) unfortunately, the odor threshold is inadequate to protect against toxic inhalant exposure because damage to the deep respiratory tract can take place at lower concentrations (Sidell et al., 1997). Phosgene has an odor safety classification rating of "E," which indicates that fewer than 10% of attentive persons can detect the Threshold Limit Value (TLV) (Amoore and Hautala, 1983). 

The use of phosgene gas by both sides continued for the rest of the war and caused the most fatalities from chemical warfare agents. Because of its lower water solubility compared with chlorine, phosgene was found to be more effective in producing a late onset of pulmonary oedema at lower concentrations. It was therefore more toxic than chlorine. It also caused immediate incapacitation due to its short latency upper respiratory tract actions ( irritant or choking ). 

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