Ammonia, anhydrous

Toxicological Summary

Workers - Hazard via inhalation route

Systemic effects

Long term exposure

Hazard assessment conclusion:

DNEL (Derived No Effect Level)

Value:

47.6 mg/m³

Most sensitive endpoint:

repeated dose toxicity

Route of original study:

Oral

DNEL related information

DNEL derivation method:

ECHA REACH Guidance

Overall assessment factor (AF):

10

Modified dose descriptor starting point:

NOAEC

Value:

476 mg/m³

Acute/short term exposure

Hazard assessment conclusion:

DNEL (Derived No Effect Level)

Value:

47.6 mg/m³

Most sensitive endpoint:

repeated dose toxicity

Route of original study:

Oral

DNEL related information

DNEL derivation method:

ECHA REACH Guidance

Overall assessment factor (AF):

10

Modified dose descriptor starting point:

NOAEC

Value:

476 mg/m³

Local effects

Long term exposure

Hazard assessment conclusion:

DNEL (Derived No Effect Level)

Value:

14 mg/m³

Most sensitive endpoint:

irritation (respiratory tract)

Acute/short term exposure

Hazard assessment conclusion:

DNEL (Derived No Effect Level)

Value:

36 mg/m³

Most sensitive endpoint:

irritation (respiratory tract)

DNEL related information

Workers - Hazard via dermal route

Systemic effects

Long term exposure

Hazard assessment conclusion:

DNEL (Derived No Effect Level)

Value:

6.8 mg/kg bw/day

Most sensitive endpoint:

repeated dose toxicity

Route of original study:

Oral

DNEL related information

DNEL derivation method:

ECHA REACH Guidance

Overall assessment factor (AF):

10

Modified dose descriptor starting point:

NOAEL

Value:

68 mg/kg bw/day

Acute/short term exposure

Hazard assessment conclusion:

DNEL (Derived No Effect Level)

Value:

6.8 mg/kg bw/day

Most sensitive endpoint:

repeated dose toxicity

Route of original study:

Oral

DNEL related information

DNEL derivation method:

ECHA REACH Guidance

Overall assessment factor (AF):

10

Modified dose descriptor starting point:

NOAEL

Value:

68 mg/kg bw/day

Local effects

Long term exposure

Hazard assessment conclusion:

medium hazard (no threshold derived)

Most sensitive endpoint:

skin irritation/corrosion

Acute/short term exposure

Hazard assessment conclusion:

medium hazard (no threshold derived)

Most sensitive endpoint:

skin irritation/corrosion

Workers - Hazard for the eyes

Local effects

Hazard assessment conclusion:

medium hazard (no threshold derived)

Additional information - workers

Overview

The substance is gaseous therefore the relevant route of exposure is by inhalation. Once inhaled, the substance will exist in the body in solution as aqueous ammonia / ammonium hydroxide with an equilibrium between NH4+ and NH3 strongly (>99.9%) in favour of NH4 +. Nevertheless the dossier includes studies performed by other exposure routes with aqueous ammonia and related water-soluble salts of ammonia. Anhydrous ammonia is classified as corrosive and studies using this substance identify local effects at the site of contact. Studies with other related compounds allow the elucidation of systemic toxicity, are therefore relevant and are included in this dossier.

 

Toxicokinetics

Absorption

Ammonia is generated by the bacterial flora of the gastrointestinal tract (~4 g/day) and as a very small water-soluble molecule, is likely to be rapidly and extensively absorbed. The results of a study in the rat (Schaerdel et al, 1983) indicate that the gaseous substance is absorbed into the bloodstream following inhalation exposure; this is consistent with the water solubility and small molecular size of the substance. Significant dermal absorption is not considered to be likely under exposure scenarios where the integrity of the skin barrier is maintained. If the skin is compromised (e.g. in cases involving burns), dermal absorption may be more extensive.

Distribution

Ammonia is distributed to all tissues in the body and is capable of crossing the blood-brain barrier.

Metabolism

No studies of metabolism are available, however the physiological role of ammonia as a product of normal metabolism (protein catabolism) is very well characterised. Ammonia is rapidly detoxified in the liver by the urea or glutamine cycle.

Excretion

Ammonia is rapidly detoxified in mammals by conversion to urea by the urea cycle in liver cells and is subsequently excreted (as urea) in urine following glomerular filtration. Ammonium ions (NH4 +) are also excreted by the kidney. Hepatic excretion of urea (15 -30% of that generated) results in the generation of ammonia by the gastrointestinal flora, and subsequent reabsorption.

 

Physiological production of ammonia and intake from other sources

Ammonia plays a key role in the nitrogen metabolism in all mammalian species. It is a product of both protein and nucleic acid catabolism, and a precursor for non-essential amino acids and other nitrogenous compounds. Approximately 4 g of ammonia are produced daily by intestinal bacteria. For comparison, the amounts of ammonia by daily intake through inhalation, ingestion (food and drink) and cigarette smoking have been estimated to be approximately 18 mg, <1 mg and <1 mg, respectively. Endogenously produced ammonia enters the portal circulation and is rapidly metabolized to urea and glutamine in the liver. Ammonia is primarily excreted as urea and urinary ammonium compounds through the kidney, however exhaled breath contains ammonia concentrations of 0.1 -2.2 mg/m³. These values, which are higher than those expected from equilibrium with ammonia levels in plasma and lung parenchyma, are most likely due to the synthesis of ammonia from salivary urea by oral microflora. Venous plasma levels of ammonia in healthy humans range from about 0.2 -0.9 mg/L in adults and children older than 1 month. In newborns, these intervals are 0.3-2.1 mg/L and 0.45 -1.1 mg/L for premature and mature babies, respectively. Congenital errors of metabolism (related to urea cycle enzymes) or other disease states (severe liver disease, e.g., cirrhosis) result in excess circulating ammonia levels (hyperammonaemia), which are associated with the clinical symptoms of hepatic encephalopathy in adults and decreased food intake, vomiting seizures, and lethargy in neonates and children. Correlating ammonia blood levels are 1.5 mg/L and 1.7 -2.6 mg/L, respectively. Comatose states are usually not present until ammonia levels reach >3 mg/L (Health Council of the Netherlands. Ammonia; Evaluation of the effects on reproduction, recommendation for classification. The Hague: Health Council of the Netherlands, 2009; publication no. 2009/01OSH). A health risk assessment of ammonium released from water filters was performed by EFSA (2012). The European Commission asked the European Food Safety Authority (EFSA) for scientific assistance regarding the possible impact on human health of exposure to ammonium released from water filter cartridges. Ammonia is a naturally occurring compound and an important source of nitrogen for mammals. Large amounts (3-4 g per day, 43-57 mg/kg body weight (bw) per day for a 70 kg adult) of ammonium are produced in the gut and excess ammonium is metabolised in the liver and excreted in urine. In healthy adults, the physiological ammonium levels in blood were reported below 35 µmol/L (corresponding to 0.67 mg/L), and most of the ammonium absorbed in the GI tract is metabolised in the liver and it has only limited influence upon the systemic levels of ammonium. E.g. transient increases in blood levels were observed 15 minutes after the oral administration of 44.4 mg/kg bw of ammonium chloride.

 

Irritation

According to Part 3 of Annex VI of the CLP Regulation 1272/2008/EC, anhydrous ammonia, has a harmonised classification for corrosive effects. It is classified for corrosivity as: Category 1B, H314 “Causes severe skin burns and eye damage” according to Annex VI of the CLP Regulation 1272/2008/EC. Waivers are therefore acceptable for skin and eye irritation. Nevertheless, the available data are reported. Prokop’evaet al(1973) report skin burns in rats exposed to anhydrous ammonia. Vernotet al(1977) report corrosive effects for a 20% aqueous solution but not for a 10% aqueous solution. No information is available on eye irritation, however can be assumed that the substance causes severe eye irritation. Animal data and human reports indicate that the substance is a respiratory irritant.

 

Repeated dose toxicity

The substance is a gas, therefore the oral route is not a relevant route of exposure. However studies with read-across compounds are available and have been evaluated as they provide useful information on the systemic toxicity of ammonia and its salts. A 4 -week screening study in the rat with diammonium phosphate (HLS, 2002) revealed only minor effects on weight gain and clinical chemistry parameters, with a NOAEL of 250 mg/kg bw/d can be determined for this study, equivalent to 68 mg/kg bw/ammonia. A 90 -day study in the rat with ammonium sulphate showed only minor effects at high dose levels (diarrhoea, renal pathology); a NOAEL of 886 mg/kg bw/d was determined, equivalent to 225 mg/kg bw/d ammonia (Tagaki et al, 1999). A NOAEL of 256 mg/kg bw/d (equivalent to 67 mg/kg bw/d) was determined for 1 -year and 2 -year studies by the same group (Otaet al, 2006).

No data are available for repeated dose toxicity by the dermal route. However the substance is classified as corrosive and it can be readily predicted that dermal effects will be dominated by local (site of contact) irritation and corrosion: significant systemic toxicity is not likely.A number of non-standard inhalation studies of varying duration that have been conducted in different species are available. The data indicate that the primary effect of exposure to inhaled anhydrous ammonia is local irritation of the respiratory tract. In a 5-week study in pigs, ammonia concentrations had a highly significant adverse effect upon feed consumption and average daily weight gain. However, there was no significant effect upon efficiency of food conversion. During both trials the high ammonia levels appeared to cause excessive nasal, lacrimal and mouth secretions. This was more pronounced at 100 and 150 ppm than at 50 ppm. Autopsies carried out on three animals showed no significant gross or microscopic differences related to ammonia level. Cultures of Corynebacterium and Pasteurella were obtained from swabs of the ethmoid turbinates from two animals removed from the compartment maintained at 150 ppm and one animal maintained at 100 ppm. There was no evidence of these bacteria in turbinate swabs from other animals (Stombaughet al,1969). Sherman and Fischer rats were exposed to environmental ammonia, derived from natural sources for 75 days, or to purified ammonia for 35 days. Rats were either inoculated intranasally with M. pulmonis prior to exposure, or left untreated. The average ammonia concentrations were 105 mg/m3 for 75 days and 175 mg/m³ for 35 days exposure. Ammonia exposure (from either source) significantly increased the severity of the rhinitis, otitis media, tracheitis and pneumonia (including bronchiectasis) characteristic of murine respiratory mycoplasmosis (rats infected with M. pulmonis). The prevalence of pneumonia showed a strong tendency to increase directly with environmental ammonia concentration (Broderson et al,1976). Twenty seven male rats, along with 27 age and weight matched controls, were exposed to atmospheric ammonia gas at a concentration of 350 mg/m³ for up to 8 weeks. The rats were sacrificed after different exposure times. Nasal irritation began on the fourth day. After 3 weeks continuous exposure exposed rats showed nasal irritation and inflammation of the upper respiratory tract. The number of pulmonary alveolar macrophages was similar to that in the controls. After 8 weeks none of the inflammatory lesions were present (Richard et al, 1978). Weatherby (1952) exposed twelve male guinea pigs (plus 6 controls) were exposed to anhydrous ammonia gas for up to 18 weeks (6 hours per day, 5 days per week). The average concentration in air was 119 mg/m³. Four experimental and 2 control animals were sacrificed at 6 week intervals throughout the study. There were no significant findings at necropsy after 6 and 12 weeks exposure. In animals sacrificed after 18 weeks, there was mild congestion of the liver spleen and kidneys, with degenerative changes in the adrenal glands, and hemosiderosis in the spleen indicating hematotoxicity. There was cloudy swelling in the epithelium of the proximal tubules of the kidney as well as albumin precipitation in the lumen with some casts. In a 50-day study (Stolpe & Sedlag, 1976), male Wistar rats were exposed to two concentrations of ammonia gas, continuously for 50 days. Concurrent controls remained untreated. There was no mortality at either concentration (35 or 63 mg/m³), and no treatment-related clinical effects were observed. Body weight gain and food intake, as compared to control values, was not significantly affected by ammonia exposure. At 63 mg/m³ rats showed increased haemoglobin and haematocrit levels compared to controls. The NOAEC for this study was 35 mg/m³.

 

DNEL derivation

No evidence of marked systemic toxicity has been seen in any study with ammonia or ammonium salts. Data from human patients with genetic defects or liver disease resulting in primary or secondary hyperammonemia, respectively, show that excess levels of ammonia in the blood have the potential to cause serious toxicity including hepatic encephalopathy. In normal individuals, however, blood levels of ammonia are closely regulated through the rapid breakdown of ammonia to urea via the high capacity urea cycle and also by other additional detoxification pathways. Humans are normally exposed to considerable levels of ammonia as a consequence of endogenous protein catabolism and also (~4 g/day) as a consequence of the breakdown of urea to ammonia by the gastrointestinal flora. It can therefore be concluded that the human body has the capacity for the rapid and effective detoxification of ammonia. The available data indicate that ammonia do not cause significant systemic toxicity, carcinogenicity, developmental or reproductive toxicity. The substance is classified as corrosive, therefore it is predictable that any effects of exposure will be limited to local effects at the site of contact (skin, respiratory tract). This hypothesis is supported by the results of the human volunteer studies which indicate a threshold for respiratory irritation of 25 ppm, whereas exposure to much (20x) higher levels of ammonia (500 ppm) were without effect on biochemical parameters. It is therefore concluded that protection against the local effects of ammonia will be significantly protective of any potential systemic effects.

 

Inhalation DNEL:

The critical inhalation effect is local irritation of the respiratory tract

For short-term exposures, ammonia at levels of 50 ppm (36 mg/m³) was tolerated without signs of definite irritation.

A NOAEL of 20 ppm (14mg/m³) for long-term exposure is derived from the weight of evidence from the human studies.

A DNEL for systemic effect is derived from the 4 -week toxicity and developmental toxicity screening test with diammonium phosphate (DAP). The NOAEL in this study of 250 mg/kg bw/day DAP is equivalent to 68 mg/kg bw/day ammonia. Assuming a bodyweight of 70 kg, this is equivalent to 4.76 g ammonia/day. It is notable that this level of exposure is less than the total amount of ammonia generated in the body and is approximately equal to the amount of ammonia produced by intestinal bacteria. Applying the standard assessment factors recommended under REACH would result in the generation of a DNEL value equivalent to a very small proportion (<1%) of the quantity of ammonia normally produced by the body’s metabolic processes and is considered to be excessively conservative. For this substance, therefore, an assessment factor of 10 is applied (6.8 mg/kg bw/d, equivalent to 476 mg ammonia/day). The maximum exposure to ammonia therefore represents approximately 10% of the quantities normally generated by the gastrointestinal tract bacteria.

The oral and inhalation absorption of ammonia is likely to be extensive. Dermal absorption is likely to be less extensive. However in the absence of specific information, dermal absorption is considered to be equivalent to oral absorption.

Assuming a breathing rate of 1.25 m³/hour and an exposure time of 8 hours/day, a long-term inhalation (systemic) DNEL of 47.6 mg/m³ is calculated. Given that this small additional exposure to ammonia is readily detoxified by normal homeostatic mechanisms, the same value of 47.6 mg/m³ is proposed for short-term inhalation (systemic) DNEL.

 

Dermal DNEL:

The substance is corrosive, therefore dermal exposure should be avoided by the use of PPE and engineering controls. A DNEL for local dermal effects is not quantifiable.

A dermal DNEL for systemic effects is derived from the 4-week toxicity and developmental toxicity screening test with DAP, in which a NOAEL of 250 mg/kg bw/day (68 mg/kg bw/day ammonia) was derived. Using the same logic as described above, a non-standard assessment factor of 10 is applied. 10% dermal absorption of ammonia is assumed for non-corrosive concentrations of ammonia (IPCS, 1990), however it is recognised that dermal penetration may be greater (worst case 100%) for higher (potentially corrosive) concentrations of ammonia used by workers. A short-term and long-term systemic dermal DNEL value of 6.8 mg/kg bw/d is therefore derived for workers (who may be exposed to corrosive concentrations), whereas a DNEL value of 68 mg/kg bw/day is appropriate for the general population who will only be exposed to lower (non-corrosive) concentrations. As noted above, the nature of the substance is such that local effects are predicted at exposure levels below those causing systemic effects by this route, and therefore the dermal DNEL for local effects will be protective.

General Population - Hazard via inhalation route

Systemic effects

Long term exposure

Hazard assessment conclusion:

DNEL (Derived No Effect Level)

Value:

23.8 mg/m³

Most sensitive endpoint:

repeated dose toxicity

Route of original study:

Oral

DNEL related information

DNEL derivation method:

ECHA REACH Guidance

Overall assessment factor (AF):

10

Acute/short term exposure

Hazard assessment conclusion:

DNEL (Derived No Effect Level)

Value:

23.8 mg/m³

Most sensitive endpoint:

repeated dose toxicity

Route of original study:

Oral

DNEL related information

DNEL derivation method:

ECHA REACH Guidance

Overall assessment factor (AF):

10

Modified dose descriptor starting point:

NOAEC

Local effects

Long term exposure

Hazard assessment conclusion:

DNEL (Derived No Effect Level)

Value:

2.8 mg/m³

Most sensitive endpoint:

irritation (respiratory tract)

DNEL related information

DNEL derivation method:

ECHA REACH Guidance

Overall assessment factor (AF):

5

Dose descriptor:

NOAEC

Acute/short term exposure

Hazard assessment conclusion:

DNEL (Derived No Effect Level)

Value:

7.2 mg/m³

Most sensitive endpoint:

irritation (respiratory tract)

DNEL related information

DNEL derivation method:

ECHA REACH Guidance

Overall assessment factor (AF):

5

Dose descriptor starting point:

NOAEC

General Population - Hazard via dermal route

Systemic effects

Long term exposure

Hazard assessment conclusion:

DNEL (Derived No Effect Level)

Value:

6.8 mg/kg bw/day

Most sensitive endpoint:

repeated dose toxicity

Route of original study:

Oral

DNEL related information

DNEL derivation method:

ECHA REACH Guidance

Overall assessment factor (AF):

10

Modified dose descriptor starting point:

NOAEL

Acute/short term exposure

Hazard assessment conclusion:

DNEL (Derived No Effect Level)

Value:

6.8 mg/kg bw/day

Most sensitive endpoint:

repeated dose toxicity

Route of original study:

Oral

DNEL related information

DNEL derivation method:

ECHA REACH Guidance

Overall assessment factor (AF):

10

Modified dose descriptor starting point:

NOAEL

Local effects

Long term exposure

Hazard assessment conclusion:

medium hazard (no threshold derived)

Most sensitive endpoint:

skin irritation/corrosion

Acute/short term exposure

Hazard assessment conclusion:

medium hazard (no threshold derived)

Most sensitive endpoint:

skin irritation/corrosion

General Population - Hazard via oral route

Systemic effects

Long term exposure

Hazard assessment conclusion:

DNEL (Derived No Effect Level)

Value:

6.8 mg/kg bw/day

Most sensitive endpoint:

repeated dose toxicity

Route of original study:

Oral

DNEL related information

DNEL derivation method:

ECHA REACH Guidance

Overall assessment factor (AF):

10

Modified dose descriptor starting point:

NOAEL

Acute/short term exposure

Hazard assessment conclusion:

DNEL (Derived No Effect Level)

Value:

6.8 mg/kg bw/day

Most sensitive endpoint:

repeated dose toxicity

Route of original study:

Oral

DNEL related information

DNEL derivation method:

ECHA REACH Guidance

Overall assessment factor (AF):

10

Modified dose descriptor starting point:

NOAEL

General Population - Hazard for the eyes

Local effects

Hazard assessment conclusion:

medium hazard (no threshold derived)

Additional information - General Population

DNEL derivation

No evidence of marked systemic toxicity has been seen in any study with ammonia or ammonium salts. Data from human patients with genetic defects or liver disease resulting in primary or secondary hyperammonemia, respectively, show that excess levels of ammonia in the blood have the potential to cause serious toxicity including hepatic encephalopathy. In normal individuals, however, blood levels of ammonia are closely regulated through the rapid breakdown of ammonia to urea via the high capacity urea cycle and also by other additional detoxification pathways. Humans are normally exposed to considerable levels of ammonia as a consequence of endogenous protein catabolism and also (~4 g/day) as a consequence of the breakdown of urea to ammonia by the gastrointestinal flora. It can therefore be concluded that the human body has the capacity for the rapid and effective detoxification of ammonia. The available data indicate that ammonia do not cause significant systemic toxicity, carcinogenicity, developmental or reproductive toxicity. The substance is classified as corrosive, therefore it is predictable that any effects of exposure will be limited to local effects at the site of contact (skin, respiratory tract). This hypothesis is supported by the results of the human volunteer studies which indicate a threshold for respiratory irritation of 25 ppm, whereas exposure to much (20x) higher levels of ammonia (500 ppm) were without effect on biochemical parameters. It is therefore concluded that protection against the local effects of ammonia will be significantly protective of any potential systemic effects.

 

Inhalation DNEL:

The critical inhalation effect is local irritation of the respiratory tract

For short-term exposures, ammonia at levels of 50 ppm (36 mg/m³) was tolerated without signs of definite irritation. Applying an assessment factor of 5 to cover intraspecies (general public) variation results in ashort-term inhalation (local) DNEL of 7.2 mg/m³.

A NOAEL of 20 ppm (14 mg/m³) for long-term exposure is derived from the weight of evidence from the human studies. Applying an assessment factor of 5 to cover intraspecies (general public) variation results in along-term inhalation (local) DNEL of 2.8 mg/m³.

A DNEL for systemic effects following inhalation is derived from the 4 -week toxicity and developmental toxicity screening test with diammonium phosphate (DAP). The NOAEL in this study of 250 mg/kg bw/d DAP is equivalent to 68 mg/kg bw/d ammonia. Assuming a bodyweight of 70 kg, this is equivalent to 4.76 g ammonia/day. It is notable that this level of exposure is less than the total amount of ammonia generated in the body (~20 g/day) and is approximately equal to the amount of ammonia produced by intestinal bacteria. Applying the standard assessment factors recommended under REACH would result in the generation of a DNEL value equivalent to a very small proportion (<1%) of the quantity of ammonia normally produced by the body’s metabolic processes and is considered to be excessively conservative. For this substance, therefore, an assessment factor of 10 is applied (6.8 mg/kg bw/d, equivalent to 476 mg/day). The maximum exposure to ammonia therefore represents approximately 10% of the quantities normally generated by the gastrointestinal tract bacteria.

Assuming a breathing rate of 20 m³/day a long-term inhalation (systemic) DNEL of 23.8 mg/m³ is calculated. Given that this small additional exposure to ammonia is readily detoxified by normal homeostatic mechanisms, the same value of 23.8 mg/m³ is proposed for short-term inhalation (systemic) DNEL.

 

Dermal DNEL:

The substance is corrosive, therefore dermal exposure should be avoided by the use of PPE and engineering controls. A DNEL for systemic effects is derived from the 4-week toxicity and developmental toxicity screening test with DAP, in which a NOAEL of 250 mg/kg bw/d (68 mg/kg bw/d ammonia) was derived. Using the same logic as described above, a non-standard assessment factor of 10 is applied. The dermal absorption of ammonia is likely to be very low (IPCS, 1990); a dermal absorption value of 10% is assumed for the purposes of DNEL derivation for the general population who will not be exposed to corrosive concentrations of ammonia. As described above, no additional (duration) factors are required for the derivation of a long-term dermal DNEL.

A short-term and long-term dermal DNEL value of 6.8 mg/kg bw/d is therefore derived. As noted above, the nature of the substance is such that local effects are predicted at exposure levels below those causing systemic effects by this route, and therefore the dermal DNEL for local effects will be protective.

 

Oral DNEL

The critical NOAEL is 250 mg/kg bw/d diammonium phosphate (equivalent to 68 mg/kg bw/d ammonia) from the 4-week toxicity and developmental toxicity screening test. Using the same logic as described above, a non-standard assessment factor of 10 is applied, resulting in a DNEL of 6.8 mg/kg bw/d.