By Salina Tewolde and Lou D’Amico, Ph.D.
The first thing that probably comes to your mind when I say “ammonia” is that household product you use to clean just about anything in your house. Besides being used as an all-purpose cleaner, ammonia also occurs naturally in air, soil, and water. As you’re reading this, you’re producing ammonia too – it’s used in nucleic acid and protein synthesis, and helps your body maintain its acid-base balance – all part of normal biological processes.
The largest and most significant use of ammonia is in agricultural fertilizers, which represents about 80% of commercially produced ammonia. Ammonia is also used in food products as an antimicrobial agent, in water purification, and in refrigeration systems. It’s also an important chemical intermediate in the production of pharmaceuticals and other chemicals, and is used to reduce nitrogen oxide emissions from combustion sources like some industrial boilers and diesel engines. Some major sources of ammonia gas come from leaks and spills during the production, storage, or processing stages of the chemical. Other sources include decaying manure from livestock, application of fertilizers in agricultural, and sewage or wastewater emissions in the environment. EPA’s Toxic Release Inventory reports that over 150 million pounds of ammonia was released from reporting facilities in 2014.
There are a number of ways that humans can be exposed to ammonia. The most common route of exposure is through breathing air that contains ammonia. Humans can be exposed to ammonia gas from household cleaning products or through direct skin contact via products that contain the chemical. Livestock and poultry farmers that work in animal feeding operations or confinement areas can be exposed to ammonia released from animal waste, and farmers can be exposed when applying ammonia-containing fertilizers to fields.
To characterize the potential health effects that humans can acquire from inhaling high concentrations of ammonia, EPA recently released an Integrated Risk Information System (IRIS) assessment that looks at the noncancer health hazards that may result from inhalation of ammonia.
EPA’s assessment evaluates chronic inhalation exposure to ammonia, observed at levels that exceed naturally-occurring ammonia concentrations. Human and animal studies showed that inhalation exposure had an effect on the respiratory tract in humans, which is the site of direct contact when ammonia is inhaled. This hazard determination was based on findings from multiple epidemiology studies in human populations exposed to ammonia in different settings (workers in industrial, cleaning and agricultural settings, volunteers exposed for up to 6 hours under controlled conditions, as well as case reports) and animals (short-term and subchronic studies in several species and across different exposure patterns). Short-term inhalation exposure to high levels of ammonia in humans can cause irritation and serious burns in the mouth, lungs, and eyes. Chronic exposure to airborne ammonia may increase the risk of respiratory irritation, cough, wheezing, tightness in the chest, and decreased lung function.
EPA’s IRIS assessment includes an estimate of the amount of ammonia that one can breathe every day for a lifetime that is likely to be without harmful health effects. This is known as an inhalation reference concentration, or RfC. The RfC was derived from an occupational study by Holness et al. (1989) that looked at the relationship between decreased lung function and long-term exposure to ammonia from workers at a soda ash plant. Ammonia was last evaluated by the IRIS Program in 1991, and as a result of the reevaluation posted this week, the RfC is five-fold higher (less stringent) than what was previously on the IRIS database. You can learn as much as you care to about ammonia inhalation toxicity through either reading the Toxicological Review on the IRIS Ammonia webpage, or getting the highlights through the accompanying IRIS Summary.
IRIS assessments go through rigorous review prior to finalization. This ammonia assessment was reviewed by EPA’s program offices and regions and other federal agencies, as well as external peer review by the Science Advisory Board Chemical Assessment Advisory Committee. The public also had opportunity to comment. All of this information is available on the IRIS chemical-specific page for ammonia, and demonstrates the IRIS Program’s commitment to transparency while providing high quality, publicly available information on the toxicity of chemicals to which the public might be exposed.
Reference: Holness, DL; Purdham, JT; Nethercott, JR. (1989). Acute and chronic respiratory effects of occupational exposure to ammonia. AIHA J 50: 646-650.
About the Authors: Salina Tewolde is a student contractor and writer working with the science communication team in EPA’s Office of Research and Development. Lou D’Amico is the Acting Communications Director for the National Center for Environmental Assessment, which houses the IRIS Program.