CAS RN: 7664-41-7

Exposure Summary

Ammonia's production and use in fertilizers, as a component of household cleaners, as a refrigerant, in the manufacture of a various compounds and as a microbiocide for controlling algal, bacterial and fungal deposits in influent water systems may result in its release to the environment through various waste streams. The application of fertilizer to soil, as ammonia, ammonium compounds, or ammonia precursors (such as urea), is a major source of ammonia release to the atmosphere. Ammonia is released in exhaust emissions from automobiles and in tobacco smoke. Large amounts of ammonia are released to the atmosphere worldwide by domesticated farm animals. Natural sources of ammonia emissions to the atmosphere are volcanic eruptions, forest fires, and the decomposition of nitrogenous compounds arising from microbially-fixed nitrogen. If released to the atmosphere, a vapor pressure of 7500 mm Hg at 25 deg C indicates ammonia will exist solely as a gas in the atmosphere. Gas-phase ammonia will be degraded in the atmosphere by reaction with photochemically-produced hydroxyl radicals and nitrate radicals; the half-lives for these reactions in air are estimated to be 100 and 54 days respectively. Ammonia reacts rapidly in the atmosphere with both sulfuric and nitric acids to form fine particles. The formation of ammonium ions in air can result in incorporation into an aerosol or as part of the ionic mix found in cloud and raindrops. Ammonia itself can dissolve in the water in the atmosphere and form clouds or fog. The half-life for ammonia in the atmosphere has been estimated to be a few days. The reaction with acidic substances in the air results in the formation of ammonium aerosols that can be removed by wet or dry deposition. If released to soil, ammonia may either volatilize to the atmosphere, adsorb to particulate matter, or undergo microbial transformation to nitrate or nitrite anions. Uptake by plants can also be an important fate process. Ammonia at natural concentrations in soil is not believed to have a very long half-life. If ammonia is distributed to soil in large concentrations (such as following an ammonia-containing fertilizer application), the natural biological transformation processes can be overwhelmed, and the environmental fate of ammonia will become dependent upon the physical and chemical properties of ammonia, until the ammonia concentration returns to background levels. If released to water, ammonia may adsorb to sediments or suspended organic material. Transformation of ammonia in water occurs primarily by the microbial processes of nitrification (yielding nitrate and nitrite anions) and denitrification. Volatilization from water surfaces is expected to be an important fate process based upon this compound's Henry's Law constant of 1.61X10-5 atm-cu m/mole. In water, ammonia is in equilibrium with the ammonium ion (NH4+), and the ammonia-ammonium ion equilibrium is dependent on the pH. Occupational exposure to ammonia may occur through inhalation and dermal contact with this compound at workplaces where ammonia is produced or used. Farmers may be exposed during the application of ammonia-containing fertilizers, or manures high in ammonia content. The general population may be exposed to ammonia via inhalation of ambient air, ingestion of food and drinking water, and dermal contact with consumer products containing ammonia. Low levels of ammonia can occur naturally in food and water. Exposure to the general population can especially occur during use of ammonia-containing household cleaners. People living near farms, cattle feedlots, poultry confinement buildings, or other areas where animal populations are concentrated may also be exposed to ammonia. (SRC)
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