  SEQ CHAPTER \h \r 1 

									February 5, 2007

MEMORANDUM

SUBJECT:		Science Chapter: Revised Environmental Fate Studies and
Environmental Fate Assessment of Propylene Glycol

FROM			A. Najm Shamim, Ph.D., Chemist

			Regulatory Management Branch II

			Antimicrobials Division (7510P)

TO:			Sanyvette Williams, D.V.M., Science Coordinator 

			Antimicrobials Division (7510P)

				And

			Michelle Centra, Chemical Review Manager

Diane Isbell, Acting Team Leader

Mark Hartman, Branch Chief

			Regulatory Management Branch II

			Antimicrobials Division (7510P)

	Environmental Fate Science Chapter and Fate Assessment on Propylene
Glycol is submitted for Reregistration Eligibility Decision (RED).

EXECUTIVE SUMMARY

	Environmental Fate Assessment:

	For the assessment of environmental health risks, the Agency has relied
on data and fate properties of propylene glycol obtained from published
literature.  Propylene glycol has a high vapor pressure (0.129 mm Hg at
25 oC) in the atmosphere, however, this poses no concern because it
degrades rapidly (estimated half-life of 32 hours) as a result of an
induced photochemical reaction with hydroxyl radicals.  This chemical
has a low absorptivity to sediment and is consequently very mobile in
soil.  Propylene glycol rapidly degrades to CO2 in soil within 4 days
under aerobic conditions and within 4-9 days under anaerobic conditions.
 Degradation does not appear to be dependent on high glycol
concentrations.  It is highly miscible in water and does not hydrolyze
due to the lack of a hydrolysable hydrogen within its structure, an
aliphatic trihydroxy chemical.  For these reasons, the Agency has
granted a data waiver from the requirement of an aquatic hydrolysis
study for propylene glycol.  The low octanol/water partition coefficient
(log KOW of -0.92) indicates that propylene glycol is not likely to
bioaccumulate in aquatic organisms such as fish and its low Henry’s
Law Constant (air/water partition coefficient (1.31 x 10-10 atm-cu
m/mole at 25 oC) limits the potential to partition from surface water to
air.  These data suggest that aquatic hydrolysis, oxidation,
volatilization, bioconcentration, and absorptivity to soil are not
expected to be significant fate processes for propylene glycol and
therefore, the presence of this chemical in the environment does not
pose a risk of concern.

	Environmental Fate Science Chapter For Propylene Glycol:

	Propylene Glycol is registered with OPP as an active product and is
used as a solvent in foods, pharmaceuticals, and cosmetics.  Propylene
glycol has a major use as a deicing fluid.  OPP has no data base on
environmental fate studies for propylene glycol as a solvent or deicing
fluid.  For the reregistration eligibility decision (RED) process the
Agency has relied on open literature and fate properties of Propylene
Glycol obtained from the open literature. The following fate properties
were obtained from an open literature search. 

	Vapor Pressure: 0.129 mm Hg at 25 oC (2)	

	Henry law Constant (air/water partition coefficient):1.31 x 10-10
atm-cu m/mole at 25 oC (1)

	KOC (organic carbon ratio in soil): 8 (3)(4) *

	Low absorptivity and therefore very high mobility in soil

	Log KOW (octanol/water partition coefficient):  - 0.92 (1)

	100% degradation in 4 days (aerobic conditions) and 4-9 days (anaerobic
conditions)(1)

	Miscible in water (1)

	Does not undergo direct air photolysis, but half life in air
(estimated) is 32 hours due to induced photochemical reaction of
atmospheric hydroxyl radical.  Physical removal of dipropylene glycol
from air by precipitation possible.(2)

	BCF < 1 (1)

*  The Koc of propylene glycol is estimated as 8 (SRC), using a log Kow
of -0.92 (3) and a regression-derived equation (4)  According to a
classification scheme (5), this estimated Koc value suggests that
propylene glycol is expected to have very high mobility in soil (SRC).

	

Aquatic hydrolysis, oxidation, vitalization, bioconcentration, and
absorption to sediment are not expected to be significant fate processes
for propylene glycol because of its high water solubility and lack of
hydrolyzable hydrogen.  Because of a low Henry Law Constant, it has a
low potential to partition from surface water to air.  Propylene glycol
has low Kd and therefore very high mobility in soil.  Propylene glycol
rapidly degrades to CO2 in soil without any lag time in 4 days (aerobic
conditions).  Degradation does not appear to depend on high glycol
concentrations.  The low KOW indicates that it is not likely to
bioaccumulate in aquatic organisms like fish.  With a vapor pressure of
0.129 mm Hg at 25 oC propylene glycol exists almost entirely in the
vapor phase in the atmosphere and can degrade rapidly by reaction with
photochemically produced hydroxyl radicals (half-life of 32 hours). 

	Surface Water and Ground Water Contamination:

Due to the use of propylene glycol as a deicing fluid there is a
scenario for ground water and surface water contamination.  Although,
propylene glycol is biodegradeable in aerobic soil and in water and
therefore has a low potential to migrate to ground water.

					

					BIBLIOGRAPHY

	Hazard Substances Databank (HSDB), A Database of the National Library
of Medicine’s    

TOXNET System.

	Environmental Fate Database.  A Database of the Syracuse Research
Corporation (SRC).

         Hansch C. et al; (1995). Exploring QWAR. Hysdrohobic,
Electronic, and Steric Constants.  ACS Prof Ref Book.  Heller SR,
consult. Ed., Washington, Dc: Amer Chem Soc p.7.

4.         Lyman, WJ et al; (1990). Handbook of Chemical Property
Estimation Methods. Washington, DC:  Amer Chem Soc. p. 4-9.

5. 	Swann, RL et al; (1983). Res Rev 85: 17-28.

