Ammonia: All You’ve Ever Wanted To Know
By Mark Hugdahl, Technical Director, ALS Environmental – Canada
The synthetic production of ammonia by the Haber-Bosch process has been called the most important invention of the 20th century. Fritz Haber received the Nobel prize in 1919 for pioneering the “fixation” of nitrogen, where nitrogen gas is converted to ammonia, a reactive form of nitrogen that can easily be taken up by plants. Nitrogen from synthetic fertilizers now provides more than half of the nutrients required by the world’s crops. Without the ammonia produced from the Haber-Bosch process, our planet could not feed seven billion people.
Ammonia plays a key role in the global nitrogen cycle, and is produced naturally through the decomposition of nitrogen-rich organic matter. However, it is also a very common environmental pollutant, and in 1990 was listed as the top priority on Environment Canada’s Canadian Chemical Spill Priority List. Outside the fertilizer industry, anthropogenic point sources of ammonia include the textile industry, household chemicals, explosives, the plastics industry, oil refineries, iron and steel mills, meat processing plants, and sewage treatment plants.
At low levels, ammonia in drinking water is not considered toxic to humans. It is produced naturally in the human body, and is efficiently targeted and detoxified by specific enzymes. However, ammonia is highly toxic to fish and amphibians at very low concentrations, since they lack these enzymes.
A Canadian Water Quality Guideline for the Protection of Freshwater Aquatic Life has been established for ammonia at 0.019 mg/L (CCME 2010; http://ceqg-rcqe.ccme.ca/download/en/141/). It is important to consider that this guideline applies only to un-ionized ammonia (NH3). Ionized ammonia (ammonium, NH4+) is much less toxic to aquatic life.
To understand this guideline, one must understand that the NH3 and NH4+ species co-exist in aqueous solution in an acid/base equilibrium that is controlled primarily by pH, and to a lesser extent by temperature (see chart). Ammonium (NH4+) is the principal species that exists under the pH and temperature conditions of most natural waters. The proportion of un-ionized ammonia, which exists in water as a dissolved gas, increases as the pH becomes more basic and as temperatures rise. Equations within the CCME guideline document permit the calculation of the fractions of NH3 and NH4+ that will exist in any water sample as a function of pH and temperature.
Water samples to be tested for ammonia should be preserved with H2SO4 immediately after collection in either glass or plastic bottles. Under acidic conditions, ammonia exists entirely as the ionic ammonium species, which is relatively stable when stored under refrigeration (recommended hold time limit is 28 days).
By convention, laboratory test results for ammonia are almost always reported as “Ammonia (as N)”, which refers to the sum of the un-ionized (NH3) and ionized (NH4+) ammonia species in the sample, expressed in units of milligrams of nitrogen per litre of sample.
To compare laboratory test results with the CCME water quality guideline, one needs to convert Ammonia (as N) results into the corresponding concentration of un-ionized ammonia in the water body (in mg/L of NH3), using the CCME equations and the field pH and temperature measurements (see examples that follow). Upon request, ALS can compute and report un-ionized ammonia concentrations if field pH and temperature are provided. Alternatively, one may compare “Ammonia (as N)” results against a table within the CCME guideline document that lists computed water quality guidelines for “Total Ammonia” (i.e. ionized plus un-ionized ammonia) at specified temperature and pH values. However, the values listed are “as NH3″ instead of “as N” (multiply by 0.8224 to convert to “as N”), and are only provided in 5°C temperature increments and 0.5 pH unit increments.
|Example Ammonia Species Calculations||Test Sample 1||Test Sample 2|
|Ammonia (as N) Lab Result (mg/L of N)||0.0500||0.200|
|Field Temperature (°C)||10.0||5.0|
|% Un-Ionized Ammonia (from CCME chart or calc)||0.186%||11.1%|
|Ionized Ammonia (mg/L of N)||0.0499||0.0178|
|Ionized Ammonia (mg/L of NH4+)||0.0643||0.229|
|Un-Ionized Ammonia (mg/L of N)||0.0000930||0.0222|
|Un-Ionized Ammonia (mg/L of NH3)||0.000113||0.0270|
|Comparison against CCME aquatic life guideline for un-ionized ammonia (0.019mg/L of NH3)||passes||fails|
Molecular Weight of Nitrogen (N) 14.01
Molecular Weight of Ammonia (NH3) 17.03
Molecular Weight of Ammonium (NH4) 18.04
Ammonia in Your Aquarium
Anyone who has kept pet fish should know that an imbalance in the nitrogen cycle is the most common cause of fish mortality in aquariums. Ammonia is produced rapidly in aquariums by the degradation of nitrogen-containing organic matter (fish waste and uneaten food). Healthy, established aquariums contain at least two bacterial strains that work together in a 2-step process to eliminate ammonia. Nitrosomonas bacteria first oxidize ammonia into nitrite (NO2), which is also highly toxic to fish. In the 2nd step, Nitrobacter bacteria convert nitrite into nitrate (NO3), which is tolerated by fish at much higher levels. Toxic levels of ammonia often build up quickly in newly established aquariums that don’t have established colonies of these two necessary bacterial strains, which is why fish often die in new aquariums. A common mistake people often make is to change out all the water on an established aquarium during tank cleanings – this can upset the balance of the nitrogen cycle, causing ammonia to accumulate, which could mean trouble for your fish.
For more information, visit http://www.alsglobal.com/environmental/services/north-america-environmental-services.aspx .