Ammonia In Polluted Water: Understanding Its Presence And Impact

Ammonia is a common pollutant in aquatic ecosystems, with human activities being a significant contributing factor. It is one of the several forms of nitrogen that exist in aquatic environments, and unlike other forms of nitrogen, ammonia has a direct toxic effect on aquatic life. Ammonia is present in water in various ways, including municipal effluent discharges, animal waste, and indirect means such as nitrogen fixation and air deposition. When present in high concentrations, ammonia can cause physical damage to fish, alter their behaviour, and even lead to death.

Ammonia is toxic to aquatic life

Ammonia is one of the several forms of nitrogen that exist in aquatic environments. Unlike other forms of nitrogen, which can cause nutrient over-enrichment of a water body at elevated concentrations and have indirect effects on aquatic life, ammonia has direct toxic effects on aquatic organisms. Ammonia is produced for commercial fertilizers and other industrial applications. Natural sources of ammonia include the decomposition or breakdown of organic waste matter, gas exchange with the atmosphere, forest fires, animal and human waste, and nitrogen fixation processes.

Ammonia can enter the aquatic environment through direct means such as municipal effluent discharges and the excretion of nitrogenous wastes from animals. It can also enter through indirect means such as nitrogen fixation, air deposition, and runoff from agricultural lands. The amount of ammonia in surface waters is influenced by many human activities in water bodies and their associated watersheds. The more extensive the relevant sources and activities, the more likely it is that ammonia will reach concentrations that can impair surface waters.

When ammonia is present in water at high enough levels, it is difficult for aquatic organisms to sufficiently excrete the toxicant, leading to a toxic buildup in internal tissues and blood, and potentially death. Environmental factors, such as pH and temperature, can affect ammonia toxicity to aquatic animals. The toxicity of ammonia is primarily attributed to the un-ionised NH3. Being a neutral molecule, un-ionised ammonia is able to cross the epithelial membranes of aquatic organisms more readily than the ammonium ion. However, the ammonium ion can also contribute significantly to ammonia toxicity under certain conditions. In general, more un-ionised ammonia exists at higher pH, and hence overall toxicity is greater, although the toxicity of the un-ionised form is less at a higher pH.

There have been many reviews of ammonia toxicity, with studies finding that ammonia is acutely toxic to freshwater organisms at concentrations ranging from 0.5 to 23 mg/L for invertebrate species and from 0.88 to 4.6 mg/L for fish species. Invertebrates are generally more tolerant to ammonia than fish, and phytoplankton and aquatic vascular plants are even more tolerant. Salmonid fish appear to be particularly sensitive to ammonia. Acute toxicity to fishes may cause loss of equilibrium, hyperexcitability, increased breathing rate, cardiac output and oxygen uptake, and, in extreme cases, convulsions, coma, and death. Chronic effects of ammonia include a reduction in hatching success, reduction in growth rate and morphological development, and pathological changes in gill, liver, and kidney tissue.

Human activities influence ammonia levels in waterbodies

Ammonia is one of the most common pollutants in aquatic environments. It is one of several forms of nitrogen that exist in such ecosystems. Unlike other forms of nitrogen, which can cause nutrient over-enrichment of a water body at elevated concentrations, ammonia directly harms aquatic life. It is toxic to aquatic organisms, causing a toxic buildup in internal tissues and blood, and potentially leading to death.

There are various natural sources of ammonia, including the decomposition of organic waste matter, gas exchange with the atmosphere, forest fires, animal and human waste, and nitrogen fixation processes. However, human activities also significantly influence ammonia levels in waterbodies. For instance, ammonia is produced for commercial fertilizers and other industrial applications. It can enter waterbodies through direct means such as municipal effluent discharges and the excretion of nitrogenous waste from animals.

Municipal waste treatment plants and public-owned treatment works (POTWs) process domestic waste and are designed to comply with permit limits to protect waterbodies from excess pollutants like ammonia. However, impoundment of water, or its storage in reservoirs, can contribute to elevated ammonia concentrations. The lack of turbulence and mixing in impoundments decrease the volatilization of ammonia, resulting in higher concentrations downstream. Thermal stratification in impoundments can further increase ammonia levels in the hypolimnion, which, combined with bottom-release dams, can lead to increased ammonia in downstream waters.

Additionally, human activities such as agriculture and industrial processes can contribute to ammonia pollution in waterbodies. Agricultural runoff, atmospheric deposition, and industrial effluent discharges are all indirect pathways for ammonia to enter aquatic ecosystems. These activities can have significant impacts on local ecosystems, as evidenced by studies showing the effects of ammonia pollution on fish behaviour and health in rivers in Spain.

Ammonia is produced for commercial fertilizers

Ammonia is a key ingredient in fertilizers, which are essential for food production. About 50% of the world's food production depends on mineral fertilizer application, and ammonia is a base material for fertilizers. It binds airborne nitrogen and makes nitrogen available for nitrogen fertilizer production. Nitrogen is the most important crop nutrient. As such, roughly 80% of the ammonia produced annually is used for fertilizer production.

However, the production of ammonia-based nitrogen fertilizers is highly concentrated and susceptible to price volatility and supply chain disruptions. The industry is responsible for about 1-2% of global carbon emissions, making it one of the dirtiest industries. The production process is energy-intensive and produces a lot of greenhouse gases.

To address this issue, there is a growing trend towards decentralized ammonia production, which has the advantage of not requiring conversion into an intermediate carrier like urea. Instead, ammonia fertilizers can be produced on-site in the form of anhydrous or aqueous ammonia, using small modular technologies such as electric Haber-Bosch or electrocatalytic reduction. Decentralized production could also reduce the risk of nitrogen losses along the supply chain.

In addition, there is increasing interest in "green" ammonia, which is produced using renewable energy sources such as wind and solar power. Green ammonia can be used not only as a fertilizer but also as a fuel for shipping and power production. It has the potential to significantly reduce the carbon footprint of agriculture and is predicted to have a vast new market in the future.

Ammonia can enter water via municipal effluent discharges

Ammonia is one of the forms of nitrogen that exist in aquatic environments. Unlike other forms of nitrogen, ammonia has direct toxic effects on aquatic life. It is produced for commercial fertilizers and other industrial applications. Natural sources of ammonia include the decomposition or breakdown of organic waste matter, gas exchange with the atmosphere, forest fires, animal and human waste, and nitrogen fixation processes.

Ammonia can enter the aquatic environment via direct means such as municipal effluent discharges. Municipal waste treatment plants and public-owned treatment works (POTWs) process domestic waste and are operated to comply with permit limits designed to protect receiving water bodies from excess inputs of pollutants such as ammonia. However, during storms, excess flow may be diverted into combined sewer overflows (CSOs) that deposit untreated municipal waste directly into streams and lakes. Treatment plant failures may also result in high ammonia releases into streams.

Ammonia from municipal effluent discharges can be introduced into aquatic systems via four main transport pathways (or transport-defined sources): stormwater runoff, leakage or leachate into groundwater sources, atmospheric emissions and deposition, or direct effluent discharges. Each of these transport-defined sources can lead to increased ammonia inputs into surface waters. In streams, ammonia may be dissolved in the water column or associated with sediments.

At non-toxic concentrations, ammonia acts as a nutrient and can stimulate microbial and plant production. Ammonia concentrations depend on the nitrogen cycle, or the transformation of nitrogen among different oxidation states. Environmental factors, such as pH and temperature, can affect ammonia toxicity to aquatic animals. When ammonia is present in water at high enough levels, it is difficult for aquatic organisms to sufficiently excrete the toxicant, leading to toxic buildup in internal tissues and blood, and potentially death.

Fish pre-exposed to ammonia suffer health consequences

Ammonia is a common pollutant in aquatic ecosystems, and it can have detrimental effects on fish, even leading to death. Fish that have been exposed to ammonia in polluted waters can suffer from various health issues and show signs of physical damage, altered behaviour, and increased physiological stress.

In one study, researchers analysed the effects of sublethal ammonia concentrations on the behaviour and oxidative stress of Barbus meridionalis, a species of freshwater fish. They compared fish from a polluted site (pre-exposed to ammonia) with fish from an unpolluted site (non-pre-exposed). The fish were exposed to different total ammonia concentrations (TAN) of 0, 1, 5, and 8 mg/L in a controlled experimental setting.

The results revealed that pre-exposed fish exhibited altered behaviour and oxidative stress responses, even at the control treatment level of 0 mg/L TAN. Pre-exposed fish also displayed reduced swimming activity, spending less time swimming and more time hiding. This behavioural change may be attributed to the previous damage caused by ammonia exposure in their natural habitat. Additionally, the pre-exposed fish had lower antioxidant defences, making them less tolerant of high ammonia concentrations.

Furthermore, the study found that the pre-exposed fish had a decreased appetite and were less voracious feeders compared to the non-pre-exposed fish. This suggests that the pre-exposed fish may have experienced a physiological cost to their health due to their adaptation to polluted waters. Even when transferred to purified waters, these fish did not recover their health, indicating that the survival of fish populations pre-exposed to ammonia pollution could be at risk.

The presence of ammonia in polluted water has a significant impact on fish health, and improving water quality alone may not guarantee the recovery of affected fish populations. Therefore, it is crucial to address the sources of ammonia pollution and implement measures to reduce its levels in aquatic ecosystems to protect and preserve the health and well-being of fish populations.

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