Ammonia


General Information:

Un-ionized ammonia (NH3) is a colorless gas at standard temperature and pressure. A pungent odor is detectable at levels above 50 ppm (NRC, 1979). Ammonia is very soluble in water at low (acidic) pH.

Ammonia levels in zero-salinity surface water increase with increasing pH and temperature (see Table 1). At low pH and temperature, ammonia combines with water to produce an ammonium ion (NH4+) and a hydroxide ion (OH-). The ammonium ion is non-toxic and not of concern to organisms. Above a pH of 9, un-ionized ammonia is the predominant species (Morgan et al., 1981). The un-ionized ammonia (NH3) can cross cell membranes more readily at higher pH values. The increased concentration that can enter the aquatic organism heightens the toxic effect (NRC, 1979).

Table 1. Percent total ammonia present in the toxic, un-ionized ammonia form in a zero salinity solution (USEPA, 1987).


Temp                              pH
(C)  6.0     6.5    7.0    7.5    8.0    8.5   9.0  9.5  10.0
 5   0.013   0.040  0.12   0.39   1.2    3.8   11   28   56 
10   0.019   0.059  0.19   0.59   1.8    5.6   16   37   65
15   0.027   0.087  0.27   0.86   2.7    8.0   21   46   73
20   0.040   0.13   0.40   1.2    3.8    11    28   56   80
25   0.057   0.18   0.57   1.8    5.4    15    36   64   85
30   0.080   0.25   0.80   2.5    7.5    20    45   72   89

Ammonia remains in the atmosphere only 5 - 10 days before being deposited or chemically altered. The fate of atmospheric ammonia is largely a function of global location and weather conditions. If ammonia is introduced into a pristine water system (neutral pH or slightly less), it is readily converted to nitrate by nitrification and becomes harmless to aquatic life (NRC, 1979). (For more information, refer to nitrification in the nitrate-nitrite section.)

Ammonia often serves as the primary or secondary source of nitrogen for plant life. While some plants prefer ammonia to other forms of nitrogen, other plants prefer nitrate but can assimilate gaseous ammonia if necessary (NRC, 1979).

Total Ammonia:

Total ammonia consists of the un-ionized (NH3) plus the ionized (NH4+) forms. Since most natural water is within the acceptable pH range of 6.5 - 8.5, a water quality manager must be primarily concerned with the toxicity of ammonia in this range to aquatic life, but the following tables (Tables 2-4) provide information on freshwater acute and chronic criteria for total ammonia. In freshwaters the concentration of un-ionized ammonia depends on the pH and temperature. In estuarine and marine waters in addition to pH and temperature, salinity influences the concentration of un-ionized ammonia (EPA. 1991c).

The Criterion Continuous Concentration (CCC), based on longer exposure times (four day average), is the chronic criteria. It is temperature and pH dependent, and in addition sets another more strict criteria for lower temperatures in the presence of early life stages of fish. At low temperatures the early life stages of fish are more sensitive to ammonia toxicity than adult or juvenile fish. This includes the beginning of spawning through the end of early life stages, which vary from species to species (EPA. 1999).

The Criterion Maximum Concentration (CMC), or acute criteria is based on short term exposure (one hour average). It is dependent on pH and fish species (salmonids or coldwater fish present, and the absence of salmonids) (EPA. 1999).

States should develop their own criteria as site specific criteria development is strongly encouraged by the EPA. Numeric criteria are suggested as opposed to narrative criteria for ease of implementation and use in TMDL programs and the National Pollutant Discharge Elimination System (NPDES). More strict criteria may be needed when dealing with waters that contain endangered or threatened species (EPA. 1999).

Ammonia toxicity levels are affected by dissolved oxygen concentrations, temperature, pH, previous acclimation to ammonia, carbon dioxide concentrations, and the presence of other toxic compounds (USEPA 1991c)

Numerical Categories:

     See Tables 2-4
   Acute (one-hour average)       0.233  mg/l
Chronic (four-day average)    0.035  mg/l 

   (EPA, 1989)


Table 2. pH-Dependent Values of the CMC (Acute Criterion)


CMC, mg N/L

pH

Salmonids
Present

Salmonids
Absent

6.5

32.6

48.8

6.6

31.3

46.8

6.7

29.8

44.6

6.8

28.1

42.0

6.9

26.2

39.1

7.0

24.1

36.1

7.1

22.0

32.8

7.2

19.7

29.5

7.3

17.5

26.2

7.4

15.4

23.0

7.5

13.3

19.9

7.6

11.4

17.0

7.7

9.65

14.4

7.8

8.11

12.1

7.9

6.77

10.1

8.0

5.62

8.40

8.1

4.64

6.95

8.2

3.83

5.72

8.3

3.15

4.71

8.4

2.59

3.88

8.5

2.14

3.20

8.6

1.77

2.65

8.7

1.47

2.20

8.8

1.23

1.84

8.9

1.04

1.56

9.0

0.885

1.32

(EPA, 199b)


Table 3. Temperature and pH-Dependent Values of the CCC (Chronic Criterion) for Fish Early Life Stages Present

CCC for Fish Early Life Stages Present, mg N/L

Temperature, C

pH

0

14

16

18

20

22

24

26

28

30

6.5

6.67

6.67

6.06

5.33

4.68

4.12

3.62

3.18

2.80

2.46

6.6

6.57

6.57

5.97

5.25

4.61

4.05

3.56

3.13

2.75

2.42

6.7

6.44

6.44

5.86

5.15

4.52

3.98

3.50

3.07

2.70

2.37

6.8

6.29

6.29

5.72

5.03

4.42

3.89

3.42

3.00

2.64

2.32

6.9

6.12

6.12

5.56

4.89

4.30

3.78

3.32

2.92

2.57

2.25

7.0

5.91

5.91

5.37

4.72

4.15

3.65

3.21

2.82

2.48

2.18

7.1

5.67

5.67

5.15

4.53

3.98

3.50

3.08

2.70

2.38

2.09

7.2

5.39

5.39

4.90

4.31

3.78

3.33

2.92

2.57

2.26

1.99

7.3

5.08

5.08

4.61

4.06

3.57

3.13

2.76

2.42

2.13

1.87

7.4

4.73

4.73

4.30

3.78

3.32

2.92

2.57

2.26

1.98

1.74

7.5

4.36

4.36

3.97

3.49

3.06

2.69

2.37

2.08

1.83

1.61

7.6

3.98

3.98

3.61

3.18

2.79

2.45

2.16

1.90

1.67

1.47

7.7

3.58

3.58

3.25

2.86

2.51

2.21

1.94

1.71

1.50

1.32

7.8

3.18

3.18

2.89

2.54

2.23

1.96

1.73

1.52

1.33

1.17

7.9

2.80

2.80

2.54

2.24

1.96

1.73

1.52

1.33

1.17

1.03

8.0

2.43

2.43

2.21

1.94

1.71

1.50

1.32

1.16

1.02

0.897

8.1

2.10

2.10

1.91

1.68

1.47

1.29

1.14

1.00

0.879

0.773

8.2

1.79

1.79

1.63

1.43

1.26

1.11

0.973

0.855

0.752

0.661

8.3

1.52

1.52

1.39

1.22

1.07

0.941

0.827

0.727

0.639

0.562

8.4

1.29

1.29

1.17

1.03

0.906

0.796

0.700

0.615

0.541

0.475

8.5

1.09

1.09

0.990

0.870

0.765

0.672

0.591

0.520

0.457

0.401

8.6

0.920

0.920

0.836

0.735

0.646

0.568

0.499

0.439

0.386

0.339

8.7

0.778

0.778

0.707

0.622

0.547

0.480

0.422

0.371

0.326

0.287

8.8

0.661

0.661

0.601

0.528

0.464

0.408

0.359

0.315

0.277

0.244

8.9

0.565

0.565

0.513

0.451

0.397

0.349

0.306

0.269

0.237

0.208

9.0

0.486

0.486

0.442

0.389

0.342

0.300

0.264

0.232

0.204

0.179

(EPA, 1999b)


Table 4. Temperature and pH-Dependent Values of the CCC (Chronic Criterion) for Fish Early Life Stages Absent

CCC for Fish Early Life Stages Absent, mg N/L

Temperature

pH

0-7

8

9

10

11

12

13

14

15*

16*

6.5

10.8

10.1

9.51

8.92

8.36

7.84

7.35

6.89

6.46

6.06

6.6

10.7

9.99

9.37

8.79

8.24

7.72

7.24

6.79

6.36

5.97

6.7

10.5

9.81

9.20

8.62

8.08

7.58

7.11

6.66

6.25

5.86

6.8

10.2

9.58

8.98

8.42

7.90

7.40

6.94

6.51

6.10

5.72

6.9

9.93

9.31

8.73

8.19

7.68

7.20

6.75

6.33

5.93

5.56

7.0

9.60

9.00

8.43

7.91

7.41

6.95

6.52

6.11

5.73

5.37

7.1

9.20

8.63

8.09

7.58

7.11

6.67

6.25

5.86

5.49

5.15

7.2

8.75

8.20

7.69

7.21

6.76

6.34

5.94

5.57

5.22

4.90

7.3

8.24

7.73

7.25

6.79

6.37

5.97

5.60

5.25

4.92

4.61

7.4

7.69

7.21

6.76

6.33

5.94

5.57

5.22

4.89

4.59

4.30

7.5

7.09

6.64

6.23

5.84

5.48

5.13

4.81

4.51

4.23

3.97

7.6

6.46

6.05

5.67

5.32

4.99

4.68

4.38

4.11

3.85

3.61

7.7

5.81

5.45

5.11

4.79

4.49

4.21

3.95

3.70

3.47

3.25

7.8

5.17

4.84

4.54

4.26

3.99

3.74

3.51

3.29

3.09

2.89

7.9

4.54

4.26

3.99

3.74

3.51

3.29

3.09

2.89

2.71

2.54

8.0

3.95

3.70

3.47

3.26

3.05

2.86

2.68

2.52

2.36

2.21

8.1

3.41

3.19

2.99

2.81

2.63

2.47

2.31

2.17

2.03

1.91

8.2

2.91

2.73

2.56

2.40

2.25

2.11

1.98

1.85

1.74

1.63

8.3

2.47

2.32

2.18

2.04

1.91

1.79

1.68

1.58

1.48

1.39

8.4

2.09

1.96

1.84

1.73

1.62

1.52

1.42

1.33

1.25

1.17

8.5

1.77

1.66

1.55

1.46

1.37

1.28

1.20

1.13

1.06

0.990

8.6

1.49

1.40

1.31

1.23

1.15

1.08

1.01

0.951

0.892

0.836

8.7

1.26

1.18

1.11

1.04

0.976

0.915

0.858

0.805

0.754

0.707

8.8

1.07

1.01

0.944

0.885

0.829

0.778

0.729

0.684

0.641

0.601

8.9

0.917

0.860

0.806

0.756

0.709

0.664

0.623

0.584

0.548

0.513

9.0

0.790

0.740

0.694

0.651

0.610

0.572

0.536

0.503

0.471

0.442

* At 15 C and above, the criterion for fish ELS absent is the same as the criterion for fish ELS present.
(EPA, 1999b)


Health Effects:

The ammonia molecule is a nutrient required for life. However, if excess ammonia is available, free ammonia may accumulate in the body and cause deleterious secondary effects, such as alteration of metabolism or increases in the body pH (NRC, 1979).

Ammonia is an irritant that often affects the eyes, nose, throat, and lungs. If ingested, ammonia will corrode the lining of the mouth, esophagus, and stomach (NRC, 1979).

Environmental Effects:

Ammonia levels in excess of the recommended limits may harm aquatic life. Although the ammonia molecule is a nutrient required for life, excess ammonia may accumulate in the organism and cause alteration of metabolism or increases in body pH (NRC, 1979). Fish may suffer a loss of equilibrium, hyperexcitability, increased respiratory activity and oxygen uptake, and increased heart rate. At extreme ammonia levels, fish may experience convulsions, coma, and death. Experiments have shown that the lethal concentration for a variety of fish species ranges from 0.2 to 2.0 mg/l. Trout appear to be most susceptible of these fish and carp the least (USEPA, 1987).

Slightly elevated ammonia levels falling within the acceptable range may adversely impact aquatic life. Fish may experience a reduction in hatching success; reduction in growth rate and morphological development; and injury to gill tissue, liver, and kidneys (USEPA, 1987). Experiments have shown that exposure to un-ionized ammonia concentrations as low as 0.002 mg/l for six weeks causes hyperplasia of gill lining in salmon fingerlings and may lead to bacterial gill disease (NRC, 1979).

Sources:

  1. Nonpoint source:
  2.  
  3. Point source: The following industrial processes produce ammonia emissions and effluent: conversion of coal to coke in coke plants, metallurgic operations, ceramic production, strip mining, chemical synthesis (nitric acid, synthetic monomers, and plastics), waste gas treatment, sewage treatment plants, ammonium nitrate explosive production, production of refrigeration equipment, production of household cleaners, oil refineries, and food processing (NRC, 1979).

Mode of Transport:

Ammonia can be transported to a surface water body by the following means:

  1. Overland flow after precipitation or irrigation event.
  2. Direct discharge in effluents from industry or sewage treatment plants.
  3. Deposition of airborne particulates.

Sampling techniques:

(APHA, 1992)

  1. Phenate Manual Colorimetric Technique: Reaction of hypochlorite, ammonia, and phenol catalyzed by a manganous salt produces the blue compound indophenol.
     
  2. Automated Phenate Method: Reaction of alkaline phenol and hypochlorite with ammonia reaction forms indophenol blue. the blue color can be intensified with sodium nitroprusside.
  1. Titration method with Preliminary Distillation:
  1. Nesslerization Colorimetric Technique: Direct and following distillation. Reaction forms a yellow to reddish-brown solution that indicates the ammonia concentration.

  1. Ammonia-Selective Electrode Method: