550. An EPCRA section 313 covered facility maintains a Safety Data Sheet (SDS) for ammonium hydroxide (CAS number 1336-21-6). The SDS lists the concentration of total ammonia in the ammonium hydroxide at 29 percent. To assist covered facilities in calculating total ammonia in aqueous solutions, EPA has published a guidance document titled EPCRA section 313 Guidance for Reporting Aqueous Ammonia, which lists NH3 equivalent weight percentages for chemical sources of aqueous ammonia. Ammonium hydroxide is listed as a chemical source of aqueous ammonia consisting of 48.59 percent total aqueous ammonia. When calculating the weight of total aqueous ammonia from ammonium hydroxide, should a facility use the percentage on the SDS or the percentage in the Agency's guidance document? When calculating the weight of total aqueous ammonia in other solutions of aqueous ammonia, what percentage should a facility use if given the choice between EPA’s guidance document and solution-specific information?
The chemical ammonium hydroxide (NH4OH) is a misnomer. It is a common name used to describe a solution of ammonia in water (i.e., aqueous ammonia), typically a concentrated solution of 28 to 30 percent ammonia. EPA has consistently responded to questions regarding the reportability of these purported ammonium hydroxide solutions under the EPCRA section 313 ammonia listing by stating that these are 28 to 30 percent solutions of ammonia in water and that the solutions are reportable under the EPCRA section 313 ammonia listing. For a more detailed discussion, see page 34175 of the Federal Register final rule of June 30, 1995 (60 FR 34172).
Facilities should use the percent total ammonia specified on the label of ammonium hydroxide solutions they purchase to determine the total ammonia content in these solutions. Ammonium hydroxide has the chemical formula NH4OH; however, as mentioned above, strong evidence indicates that the species NH4OH does not exist. Bottles of concentrated aqueous ammonia purchased from chemical supply companies are almost always labeled ammonium hydroxide. These solutions primarily consist of molecules of NH3 dissolved in water (along with small amounts of ionized ammonia). The 48.59 percent listed for ammonium hydroxide is based on the ammonia weight of the chemical formula NH4OH, not the actual concentration of total ammonia in ammonium hydroxide solutions. The actual concentration may vary depending upon the amount of NH3 used to make the solution. Thus, this may not accurately reflect the actual weight of total aqueous ammonia in any given solution labeled ammonium hydroxide.
The percentages, reported in the document as NH3 equivalent weight percentages for chemical sources, are the precise percentages of total ammonia (expressed as NH3 equivalent weights) contained in each chemical listed based on the molecular formula for each chemical. Except for ammonium hydroxide, these numbers are exact for the pure chemical and do not vary. Facilities can use these numbers to calculate how much total ammonia will be in aqueous solutions made from these chemicals. If more specific information on the actual concentration of total ammonia in an aqueous solution is available from another source, such as an SDS label, or measurement, facilities can use this information rather than performing the calculations prescribed in the EPCRA Section 313 Guidance for Reporting Aqueous Ammonia.