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The Ministers of Environment and Health have released for final publication the assessment report for the priority substance Ammonia in the Aquatic Environment. Notice concerning the assessment of this substance and a summary of its assessment report was published in the Canada Gazette, Part 1 June 23, 2001.The synopsis of the report is provided below.

A draft of this Assessment Report was made available for a 60-day public comment period (May 13, 2000 - July 12, 2000). Following consideration of the comments received, the Assessment Report was revised as appropriate. A summary of the comments and their responses may also be accessed from this page.

For paper copies of the Full Assessment Report, please contact the Inquiry Centre at Environment Canada:

To obtain an electronic version of the Assessment Report in PDF, please request a copy from the following address: ESB.DSE@ec.gc.ca

Synopsis

Ammonia exists in two forms simultaneously, with the equilibrium between the two forms governed in large part by pH and temperature. The forms are NH₃ (un-ionized ammonia) and NH₄+ (ionized ammonia or ammonium). Together they are called total ammonia. It is the NH₃ form that is particularly harmful to aquatic organisms. The formation of NH3 is favoured at higher pHs but is also affected by temperature. This means that while the concentration of total ammonia may remain constant in a water body, the proportion of un-ionized ammonia fluctuates with temperature and pH. Significant formation of NH₃ can occur within a single day as water temperatures fluctuate.

Ammonia evaporates at temperatures above –33°C and will travel short distances (several kilometres) as a gas. It readily forms ammonium sulphate particles in air when in the presence of sulphur compounds; in this form, it can travel hundreds of kilometres.

In 1996, ammonia was ranked first by the National Pollutant Release Inventory in terms of amounts released by industry to the Canadian environment. Just over 32 000 tonnes were reported as released by industries across Canada to all media (air, water and land). Ammonia is also a naturally occurring compound required by most organisms for protein synthesis and a waste product of animal, fish and microbial metabolism. The primary human use of ammonia is as a nitrogen source in fertilizers, especially anhydrous ammonia and urea.

Ammonia is released into the environment by many industries and other human activities. The major quantifiable sources of ammonia released to aquatic ecosystems across Canada are municipal wastewater treatment plants (WWTPs). The amount of ammonia released to water via municipal WWTPs is estimated at 62 000 tonnes/year. Negative environmental impacts on some aquatic ecosystems are occurring from this source.

Agricultural releases of ammonia to water cannot be quantified because of the diffuse nature of agriculture in Canada and the difficulty in quantifying such releases. In general, only those intensive animal-rearing facilities (feedlots and dairies) with direct runoff to watercourses have the potential to significantly contaminate the water.

Industrial releases to water amount to 5972 tonnes/year. The major industries are pulp and paper mills, mines, food processing and fertilizer production.

The major industrial source of ammonia released to the atmosphere is the fertilizer industry, releasing some 12 000 tonnes/year. In contrast, the amount of ammonia released to air from agricultural operations is estimated at 474 000 tonnes/year. Through modelling and measuring ammonia deposition in areas influenced by agricultural emissions and studying the situation in Europe, it was determined that some areas of Canada, like the Lower Fraser Valley, are potential impact regions.

It was determined from reviewing toxicity and exposure data that freshwater organisms are most at risk from releases of ammonia in the aquatic environment. Rainbow trout, freshwater scud, walleye, mountain whitefish and fingernail clams are some of the most sensitive species. Aquatic insects and micro-crustaceans are more resistant to ammonia, although there is a large variation in sensitivity within aquatic insects.

The ecological impact of ammonia in aquatic ecosystems is likely to occur through chronic toxicity to fish and benthic invertebrate populations as a result of reduced reproductive capacity and reduced growth of young. These are subtle impacts that will likely not be noticed for some distance below an outfall. The zone of impact varies greatly with discharge conditions, river flow rate, temperature and pH. Under estimated average conditions, some municipal wastewater discharges could be harmful for 10–20 km. Severe disruption of the benthic flora and fauna has been noted below municipal wastewater discharges. Recovery may not occur for many (20–100) kilometres. It is not clear whether these impacts are solely from ammonia or from a combination of factors, but ammonia is a major, potentially harmful constituent of municipal wastewater effluents.

Owing to the interaction between receiving water pH and temperature, those waters most at risk from municipal wastewater-related ammonia are those that are routinely basic in pH with a relatively warm summer temperature combined with low flows. In Canada, winter temperatures, regardless of pH, are low enough to keep the formation of un-ionized ammonia below the toxic threshold. Potentially toxic conditions typically start in May and can continue through to early October, depending on the water system and the yearly variation in pH, dissolved oxygen and temperature. In general, waters potentially sensitive to ammonia from municipal WWTPs are found in southern areas of Alberta, Saskatchewan and Manitoba; southern Ontario; and the south shore of Quebec.

Ammonia is generally not problematic with respect to the eutrophication of fresh waters in Canada, as this is typically limited by phosphorus. There are a few exceptions to this, in particular the Qu’Appelle Lakes in Saskatchewan. Ammonia released by the Regina WWTP, coupled with phosphorus mobilization from sediments, seems to be contributing to the continued eutrophication of this lake system.

Conifer trees are sensitive to ammonia exposure from air, particularly in winter. They develop a reduction in winter hardiness due to an impaired ability to retain water. The beneficial mycorrhizal fungi that colonize many types of plant roots are particularly sensitive to ammonia. Reductions in mycorrhizal fungi on tree roots may be the reason for reduced water retention in conifers. Conifer forests and sphagnum bogs are particularly at risk if sufficient ammonia is added over time. Conifers may experience a form of eutrophication, and sphagnum cannot compete with grasses under increased ammonia conditions.

Ammonia is not involved in the formation of ground-level ozone, the depletion of stratospheric ozone or climate change.

Based on probabilistic risk assessments of three water bodies receiving ammonia from typical municipal wastewater discharges, it is concluded that ammonia is entering the aquatic environment in a quantity or concentration or under conditions that have or may have an immediate or long-term harmful effect on the environment or its biological diversity. Based on available data, it is concluded that ammonia is not entering the environment in a quantity or concentration or under conditions that constitute or may constitute a danger to the environment on which life depends. Therefore, ammonia is considered to be "toxic" as defined in Section 64 of the Canadian Environmental Protection Act, 1999 (CEPA 1999).

As the conclusion of this assessment is based on analyses of risks posed by releases of ammonia from municipal WWTPs, priority should be given to consideration of options to reduce exposure to ammonia from municipal wastewater systems taking into account site-specific conditions. Results of conservative screening-level assessments suggest that releases of ammonia from several other sources (e.g., runoff from manure-fertilized fields and intensive livestock operations) may also be causing environmental harm; however, available data were insufficient to establish the extent and magnitude of such harm. It is recommended that additional data be obtained to determine whether options to reduce exposure to ammonia from such sources should be undertaken.