ETL 1110-3-481
31 Mar 97
into the ground, fluorochemical surfactants may eventually reach
groundwater or flow out of the ground into surface water and
cause foaming and other undesirable effects.
Biodegradability
3.4
Biodegradability is a measure of the breakdown of chemicals by
bacteria in the same liquid environment. Bacteria use certain
chemicals as food, i.e., oxidizable carbon sources as well as
dissolved oxygen in the wastewater as it goes through its
metabolic life cycle. The biodegradability of a material is
typically determined by comparing the Chemical Oxygen Demand
(COD) of the material with it Biological Oxygen Demand (BOD).
The COD is determined by measuring the amount of a chemical
oxidant which is required to completely oxidize a known quantity
of the material. The BOD is determined by preparing a dilute
solution of a known quantity of the material, inoculating the
solution with a culture of bacteria from a sewage treatment plant
and measuring the oxygen uptake of the solution for a fixed
period of time. Results for both COD and BOD are reported in
milligrams of oxygen per liter (mg/l). It is generally accepted
that materials with a BOD/COD ratio greater than 0.5 are
biodegradable. Actual data reported in AFFF manufacturer's
literature shows ratios ranging from 0.60 to 0.99, thereby
qualifying AFFF solutions as being biodegradable.
Toxicity
3.5
AFFF solutions are reported to have a low degree of fish
toxicity, and varies widely with species. It has also been
reported that AFFF solution falls into the U.S. Fish and Wildlife
Service "Relatively Harmless" category and the USEPA "Practically
Non-Toxic" category for even the most sensitive species. There
is no published data on the phytotoxicity of AFFF solutions, but
there have been no published reports of plant kills resulting
from AFFF solution discharges.
General Concern
3.6
Even though AFFF solution is technically considered biodegradable
and practically non-toxic, the major concern is the large volume
of solution that can be produced from hangar fire protection
systems. If AFFF discharge is not contained and controlled,
relatively large volumes of AFFF discharge can flow into the
environment and have a negative impact to the environment, as
well as produce bad side effects, such as foaming. Because AFFF
is biodegradable, the breakdown of AFFF by bacteria consumes
oxygen. If enough AFFF is discharged. It can deprive aquatic
A-5
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