Even
at extremely low concentrations aquatic life will be harmed by ammonia.
 Ammonia occurs naturally in the environment. A small amount of
ammonia is generated when lightning strikes and reaches earth in
rainfall. But most ammonia is produced by bacteria in water and soil
as an end product of plant and animal waste decomposition. It is
found in relatively low nontoxic concentrations in soil, air, and
water and provides a source of nitrogen for plants.
In soils and water ammonia will go through many complex biochemical
transformations. These transformations constitute what is commonly
known as the nitrogen cycle. For a more in-depth discussion of the
nitrogen cycle see related links.
Ammonia in Water
Water reacts with ammonia to form ammonium and hydroxide ions.
Ammonia is often referred to as “unionized ammonia”. Ammonia is toxic
to aquatic organisms but ammonium is non-toxic. There
exists an equilibrium in water between the toxic ammonia and the
non-toxic ammonium. The equation shifts back and forth depending
upon existing or introduced environmental changes.
| NH3 (aq) + H2O (l) |
 |
NH3 · H2O (aq) |
|
NH4 + (aq) + OH - (aq) |
| (Ammonia in water) |
|
(ammonia+water) |
|
(ammonium + hydroxide ions) |
The dynamic equilibrium between NH3 and NH4 + is affected by water temperature and pH (acidity). At a pH of six
the ratio of ammonia to ammonium is 1 to 3000 but decreases to
1 to 30 when the pH rises to eight (becomes less acidic). Warm
water will contain more toxic ammonia then cooler water. When sampling
water for ammonia analysis both the temperature and the pH of the
surface water body must be measured at the same time the water
samples are collected. (See Ammonia,
pH and Temperature Calculator)
If ammonia is directly spilled into surface water or if water used
by a fire department to depress an ammonia vapor cloud is allowed
to reach surface water, aquatic life can be harmed. Even at a concentration
of 0.02 mg/L (48 hour LC50) unionized ammonia is lethal to some
sensitive freshwater fish. That equates to about ½ a cup of
unionized ammonia in one million gallons of water. Ammonia is also
highly toxic to freshwater invertebrates having a 48-hour LC50 of 0.66 mg/L for Daphnia magna . Again, water contaminated
with fertilizer ammonia should not be allowed to enter any storm
drains, rivers, drainage ditches, wetlands or lakes.
 Ammonia in Air and Soil
After a release of ammonia the vapors will
dissipate reacting with the moisture in the air to form ammonium
and eventually return to earth in rainfall. Ammonium then quickly
binds to the negatively charged soil organic matter and soil clays.
Ammonium rarely accumulates in soil because bacteria will rapidly
convert the ammonium that is not taken up by plant roots into nitrates
(nitrification). Nitrates can also be absorbed by roots or may
leach through the soil profile. Since ammonium is soil bound, unless
the soil is washed away by rainfall events the contamination will
likely stay put horizontally but leach vertically as nitrates through
the root zone.
If the fire department suppresses an ammonia vapor cloud with water
for a prolonged period of time the applied water may contaminate
soil. In this instance the soil may require some method of remediation
to prevent adverse environmental affects.
 Ammonia
Affecting Plants
Plants, trees and crops are mostly made up of water. If a large
release of ammonia occurs the vapor will likely burn the leaves of
nearby downwind vegetation. Ammonia will pull water from the leaves
but will not affect the roots so damaged plants will probably fully
recover although affected crops may suffer yield loss.
Ammonia Affecting Livestock
Be aware that ammonia vapors are toxic to livestock. Dairy, swine
and poultry livestock producers operating near to and downwind of
a release or potential release must be notified to take appropriate
action.
The Nitrogen Cycle in Soil from The Ohio State University
Extension Fact Sheet AEX-463-96
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