MEMORANDUM

To:	Erin Birgfeld

CC:	Margaret Sheppard

From:	Sarah Percy, Kara Altshuler, Nikki Maples, Mike Ragan, Meg McVey,
Mark Wagner 

Date:	January 19, 2004

Re:	nPB Aquatic Toxicity 

(EPA Contract Number 68-D-00-266, WA 3-05 Task 02)



Summary

	At EPA's request, ICF has prepared this memorandum to help inform a
decision regarding the acute ecotoxicity of n-propyl bromide (nPB). 
Based on the information presented in the following sections, it can be
concluded that nPB does not persist for long in the environment.  The
compound is not expected to bioconcentrate significantly in animals or
plants.  Further, its toxicity in indicator species suggests that it is
of low to medium concern for acute aquatic toxicity and would not be
listed in the Toxic Release Inventory (TRI) due to aquatic toxicity.

Fate and Transport in the Environment

n-propyl bromide's production and subsequent use as a solvent could
result in its release to the environment through various waste streams. 
If released to the atmosphere, nPB will exist solely in the vapor phase
based on its vapor pressure of 110.8 mm Hg.  It should react fairly
rapidly with hydroxyl radicals in the vapor phase with an estimated
half-life of 17.5 days.  Based on an estimated Koc (organic-carbon
partition coefficient) of 330, nPB has medium mobility in soil.  Given a
measured water solubility of 2450 mg/L, some leaching may be possible in
cases where nPB is present in soil.  In moist soils, hydrolysis should
occur; nPB has a measured hydrolysis half-life of 26 days at 25° C and
pH 7.  n-propyl bromide is expected to volatilize from moist soil
surfaces, based on an estimated Henry's Law constant of 7.32x10-3 atm
m3/mole. 

From dry soil surfaces, nPB should quickly volatilize due to its high
vapor pressure.  It is also expected to volatilize rapidly from water
surfaces based on its Henry's Law constant.  The volatilization
half-life from a model river was calculated as 3.4 hours, from a model
lake, 4.4 days.  This compound will also hydrolyze in water with a
measured half-life of 26 days.  Biodegradation may occur in soil. 
n-propyl bromide may biodegrade in water based upon a number of studies
using pure cultures that have indicated that nPB may be converted to
1-propanol.  The compound has a log Kow value of 2.10 and should not
bioconcentrate in aquatic organisms based on a bioconcentration factor
(BCF) of 23 (HSDB 2004).  Further, a similar BCF of 18 for freshwater
fish was calculated using structure-activity relationships for
environmental toxicants provided in Clements (1996).

Aquatic Toxicity

The following databases were queried regarding ecotoxicity of nPB:
ECOTOX database and the TOXNET database, which includes HSDB, IRIS,
GENE-TOX, CCRIS, Multi-Databases, TOXLINE, DART/ETIC, TRI, and
CHEMIDplus databases.  Only one relevant article was identified which
specifically addressed aquatic or terrestrial toxicity of nPB. Geiger et
al. (1988) reported 96-hour LC50 and EC50 values for nPB in 30-day old
fathead minnows.  Both the 96-hour LC50 and EC50 values were 67.3 mg/L. 
Affected fish reportedly lost schooling behavior and swam near the tank
surface.  In general, they were hypoactive, underreactive to external
stimuli, had increased respiration, and were darkly colored.  Fish lost
equilibrium prior to death. 

Estimated Ecotoxicity Values

	EPA has developed a methodology for estimating lethal concentrations
and exposure concentrations for effects on growth and reproduction in
aquatic, marine, and terrestrial indicator species (Clements 1996). 
This methodology utilizes structure-activity relationships of compounds
within general chemical classes, as well as certain physical-chemical
characteristics to predict these effective concentrations.  Equations
specific for neutral organics are used to predict ecotoxicity values for
alkyl halides such as nPB.  ICF has used the appropriate equations to
estimate these concentrations for acute exposures, as given below in
Table 1. 

Table 1: Predicted Ecotoxicity Values for nPB in Aquatic Speciesa 

Species	Endpoint	Estimated Concentration (mg/L)	Equation Used

Fish (freshwater)	96 hr LC50	73	log LC50 = 1.75 - 0.94log Kow

Fish (marine), sheepshead minnow	96 hr LC50	18	log LC50 = 0.69 - 0.73log
Kow

Daphnid (water flea)	48 hr LC50	79	log LC50 = 1.72 - 0.91log Kow

Lysid Shrimp	96 hr LC50 	19.7	log LC50 = 1.83 - 1.25log Kow

Green algae	96 hr EC50 (growth)	50	log EC50b = 1.466 - 0.885log Kow

a Values are determined using equations provided in Clements 1996;
concentrations are provided in mM/L and are converted to mg/L using the
molecular weight of nPB (122.99 g/mole), and log Kow = 2.1.

b  EC50= Exposure concentration that causes a change in the endpoint in
50% of the test species.

As indicated in the data above, the estimated LC50 value for fish above,
73 mg/L, is very close to the experimental LC50 of 67 mg/L (Geiger et
al. 1988).  

Hazard Ranking for n-Propyl Bromide as an Environmental Toxicant

To determine whether there should be concern for aquatic toxicity of
nPB, ideally one would estimate possible surface water concentrations
under appropriate exposure scenarios (e.g., a spill) and compare those
to appropriate toxicity values.  However, EPA often must screen
chemicals for potential environmental hazards in the absence of
estimated environmental concentrations.  Different EPA programs have
established toxicity criteria by which to determine whether a chemical
might be considered of low, medium, or high concern based on the results
of various toxicity tests.  The criteria differ somewhat by risk
management context (e.g., a new chemical proposed for manufacture, an
existing chemical proposed for new uses, prioritizing chemicals for
additional toxicity testing).  

ICF examined how several different EPA hazard ranking systems would
categorize the level of concern for the acute aquatic toxicity of nPB
and found it to be of low-to-medium concern:

By the classification criteria for environmental toxicity and fate of
industrial chemicals developed by EPA’s Office of Pollution Prevention
and Toxics (OPPT), the acute aquatic toxicity of nPB of 67 mg/L
(identified experimentally) would be considered of medium concern (i.e.,
between 1 and 100 mg/L) (USEPA 1992a, Smrchek et al. 1993).  Chemicals
with LC50/EC50 values greater than 100 mg/L are considered of low
concern, while values less than or equal to 1 mg/L are considered of
high concern.  In general, that concern level triggers additional
toxicity testing (Tier II testing) if available data are limited.  

Those same criteria are used as aquatic toxicity scoring
“fencelines” for prioritizing chemicals for waste minimization
efforts under EPA’s Waste Minimization National Plan (USEPA 1997),
indicating that the acute aquatic toxicity of nPB can be considered
moderate (rather than low or high).  

In its hazard assessment guidelines for listing chemicals in the Toxic
Release Inventory (TRI), OPPT uses numerical screening criteria for
listing (USEPA 1992b).  In this program, an acute aquatic toxicity value
of greater than 10 ppm (mg/L) is considered “insufficient” for
listing; whereas an LC50 between 10 ppm and 0.1 ppm “may be
sufficient” for listing, and an LC50 less than or equal to 0.1 ppm
“is sufficient” for listing.  Thus, in this scheme, the available
data for nPB indicate that EPA would not list it on the TRI due to its
acute aquatic toxicity.

Note that these hazard ranking systems also consider bioconcentration
factors (BCFs) in combination with persistence in determining the
potential hazard of a chemical.  Chemicals with persistence in surface
water of less than two weeks and with a BCF of less than 100 are
considered of low concern.  The low estimated persistence of nPB in
surface waters (3.4 hours to 4.4 days), together with BCF values of 18
and 23 discussed above, represent low levels of concern for each
attribute, respectively (USEPA 1992a,b; 1997).  

References

Clements, R.G.  1996. Estimating Toxicity of Industrial Chemicals using
Structure-Activity Relationships. U.S. EPA.  Health and Environmental
Review Division.  OPPT.  

Geiger, D.L., Call, D.J., and Brooke, L.T.  1988.  Acute Toxicities of
Organic Chemicals to Fathead Minnows (Pimephales promelas), Vol. 4.  In:
Center for Lake Superior Environmental Stud., Univ.of
Wisconsin-Superior, Superior, WI I:355.

HSDB.  2004.  Hazardous Substances Databank File for 1-Bromopropane. 
Accessed 1/2004 from the World Wide Web at
http://toxnet.nlm.nih.gov/cgi-bin/sis/search/f?./temp/~dLwM9e:1

Smrchek, J., Clements, R., Morcock, R., and Rabert,W.  1993.  Assessing
ecological hazard under TSCA: methods and evaluation of data.  In:
Landis, W.G., Hughes, J.S., and Lewis, M.A. (eds.), Environmental
Toxicology and Risk Assessment, ASTM STP 1179.  Philadelphia, PA:
American Society for Testing and Materials, pp. 22-39.

USEPA (United States Environmental Protection Agency).  1992a. 
Classification Criteria for Environmental Toxicity and Fate of
Industrial Chemicals.  Washington, DC:  Office of Pollution, Prevention
and Toxics, Chemical Control Division.

USEPA (United States Environmental Protection Agency).  1992b.  Hazard
Assessment Guidelines for Listing Chemicals on the Toxic Release
Inventory, Revised Draft.  Washington, DC:  Office of Pollution,
Prevention and Toxics.

USEPA (United States Environmental Protection Agency).  1997.  Waste
Minimization Prioritization Tool, Beta Test Version 1.0: User’s Guide
and System Documentation.  Draft.  Washington, DC:  Offices of Solid
Waste and Emergency Response and Pollution Prevention and Toxics. 
EPA530-R-97-019.

***DRAFT (January 19, 2000) – DO NOT CITE OR QUOTE***

