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Acute Exposure Guideline Levels for Selected Airborne Chemicals: Volume 7
predicted that the general population, including susceptible individuals, could experience notable discomfort, irritation, or certain asymptomatic, nonsensory effects. However, the effects are not disabling and are transient and reversible upon cessation of exposure.
AEGL-2 is the airborne concentration (expressed as ppm or mg/m³) of a substance above which it is predicted that the general population, including susceptible individuals, could experience irreversible or other serious, long-lasting adverse health effects or an impaired ability to escape.
AEGL-3 is the airborne concentration (expressed as ppm or mg/m³) of a substance above which it is predicted that the general population, including susceptible individuals, could experience life-threatening health effects or death.
Airborne concentrations below the AEGL-1 represent exposure levels that could produce mild and progressively increasing odor, taste, and sensory irritation or certain asymptomatic, nonsensory effects. With increasing airborne concentrations above each AEGL, there is a progressive increase in the likelihood of occurrence and the severity of effects described for each corresponding AEGL. Although the AEGL values represent threshold levels for the general public, including sensitive subpopulations, it is recognized that certain individuals, subject to idiosyncratic responses, could experience the effects described at concentrations below the corresponding AEGL.
Monochloroacetic acid (MCAA) is a colorless crystalline material, which is highly soluble in water and soluble in organic solvents. Its vapor pressure at room temperature is moderate with reported values between 0.2 hectopascals (hPa) (crystalline substance) and 10 hPa (solution in water). MCAA has a pungent odor.
MCAA is produced by chlorination of acetic acid or hydrolysis of trichloroethylene (also known as trichloroethene) using sulfuric acid. The world production capacity was estimated at 362,500 metric tons/year in 1987. MCAA or its sodium salt, sodium monochloroacetate, are used primarily in the industrial production of carboxymethyl-cellulose, herbicides, and thioglycolic acid as well as in the production of plastics, pharmaceuticals, flavors, cosmetics, and other organic chemicals.
MCAA is an acid (pKa, 2.85) and, therefore, can cause eye and skin irritation upon contact with a diluted MCAA solution and can cause skin corrosion and conjunctival burns upon contact with more concentrated solutions. The systemic toxicity of MCAA is caused by inhibition of enzymes of the glycolytic pathway and the tricarboxylic acid cycle. This metabolic blockage damages organs with a high-energy demand, such as heart, central nervous system (CNS), and muscles, and leads to metabolic acidosis due to the accumulation of lactic acid and citric acid in the body.