August 1992
ISOPROPYL
METHYLPHOSPHONIC
ACID
Health Advisory
Office of Water
U.S. Environmental Protection Agency
Washington, DC 20460

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Isopropyl Methylphosphonic Acid
(IMPA)
Health Advisory
Office of Water
U.S. Environmental Protection Agency
Washington, DC 20460
August 1992

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Health Advisory on Isopropyl Methylphosphonic Acid (IMPA)
Authors:
Joyce Morrisey Donohue, Ph.D.
Welford C. Roberts, Ph.D.
Project Officer:
Krishan Khanna, Ph.D.
Office of Water
U.S. Environmental Protection Agency
Washington, DC 20460
August 1992

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PREFACE
This report was prepared in accordance with the Memorandum of Understanding
between the Department of the Army, Deputy for Environmental Safety and
Occupational Health (OASA(ILSE)), and the U.S. Environmental Protection Agency
(EPA), Office of Water (OW) , Office of Science and Technology, for the purpose
of developing drinking water Health Advisories (HAs) for selected
environmental contaminants, as requested by the Army.
Health Advisories provide specific advice on the levels of contaminants in
drinking water at which adverse health effects would not be anticipated and
which include a margin of safety to protect the most sensitive members of the
population. A Health Advisory provides health effects guidelines and
analytical methods and recommends treatment techniques on a case-by-case
basis. These advisories are normally prepared for one-day, ten-day,
longer-term, and lifetime exposure periods where available toxicological data
permit. These advisories do not condone the presence of contaminants in
drinking water, nor are they legally enforceable standards. They are not
issued as official regulations and they may or may not lead to the issuance of
national standards or Maximum Contaminant Levels (MCLs).
This report is the product of the Health Advisory Development process.
Available toxicological data (as provided by the Army and as found in open
literature sources) on the munitions chemicals Sarin, diisopropyl
methylphosphonate (DIMP) and isopropyl methylphosphonic acid (IMPA) have been
reviewed, and relevant findings are presented in this report in a manner that
allows for evaluation of the data without continual reference to the primary
documents. This report has been submitted for critical internal and external
review by the EPA.
I would like to thank the authors who provided the extensive technical
knowledge required for the preparation of this report. I am grateful to the
members of the EPA Toxicology Review Panel who took time to review this report
and to provide their invaluable input, and I would like to thank Dr. Edward
Ohanian, Chief, Human Risk Assessment Branch, and Ms. Margaret Stasikowski,
Director, Health and Ecological Criteria Division, for providing me with the
opportunity and encouragement to be a part of this project.
The preparation of this Health Advisory was funded, in part, by Interagency
Agreement (IAG) 85-PP5869 between the U.S. EPA and the U.S. Army Medical
Research and Development Command (USAMRDC). This IAG was conducted with the
technical support of the U.S. Army Biomedical Research and Development
Laboratory (USABRDL), Dr. Howard T. Bausum, Project Manager.
Krishan Khanna, Project Officer
Office of Water

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TABLE OF CONTENTS
PAGE
LIST OF TABLES		iii
LIST OF APPENDICES		iii
EXECUTIVE SUMMARY 		ES-I
I.	INTRODUCTION 		1-1
II.	GENERAL INFORMATION AND PROPERTIES 		II-1
III.	OCCURRENCE 		III-l
IV.	ENVIRONMENTAL FATE 		IV-1
V.	TOXICOKINETICS 		V-l
A.	Absorption		V-l
B.	Distribution		V-l
C.	Metabolism		V-2
D.	Excretion 		V-3
VI.	HEALTH EFFECTS 		VI-1
A.	Health Effects in Humans		VI-1
1.	Short-term Exposure		VI-1
2.	Longer-term Exposure 		VI-1
B.	Health Effects in Animals 		VI-1
1.	Short-term Exposure		VI-1
a.	Skin and Eye Irritation 		VI-2
b.	Dermal Sensitization 		VI-2
2.	Longer-term Exposure		VI-4
3.	Reproductive Effects 		VI-4
4.	Developmental Effects 		VI-4
5.	Mutagenicity		VI-4
6.	Carcinogenicity		VI-5
VII.	HEALTH ADVISORY DEVELOPMENT		VII-1
A.	Quantification of Toxicological Effects 		VII-1
1.	One-day Health Advisory 		VII-1
2.	Ten-day Health Advisory 		VII-2
3.	Longer-term Health Advisory 		VII-2
4.	Lifetime Health Advisory 		VII-3
B.	Evaluation of Carcinogenic Potential 		VII-5
VIII.	OTHER CRITERIA, GUIDANCE AND STANDARDS 		VIII-1
IX.	ANALYTICAL METHODS 		IX-1
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Table of Contents - continued
PAGE
X.	TREATMENT TECHNOLOGIES 		X-l
XI.	CONCLUSIONS AND RECOMMENDATIONS		XI-1
XII.	REFERENCES 		XII-L
ii

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LIST OF TABLES
PAGE
II-l General Chemical and Physical Properties of
Isopropyl Methylphosphonic Acid		II-2
VI-1 Mortality in Rats and Mice Exposed to Acute Doses
of IMPA 		VI-3
LIST OF APPENDICES
Data Deficiencies/Problem Areas and Recommendations for
Additional Data Base Development for IMPA		Al-1
iii

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EXECUTIVE SUMMARY
Isopropyl methyl phosphonic acid (IMPA) is a degradation product of the nerve
gas isopropyl methylphosphonofluoridate (GB or Sarin). Isopropyl methyl-
phosphonic acid is a moderately strong acid (pKa - 2.38) which is most
commonly found in the environment in its ionized state; it is nonvolatile and
soluble in water. The resonance-stabilized IMPA ion is chemically stable with
a hydrolytic half-life of 1,900 years at pH 1 and longer at higher pH values.
Most bacterial species are not able to degrade IMPA; an exception is
Pseudomonas testosteroni. a species that is able to convert IMPA to methane,
isopropanol and phosphorous acid or phosphoric acid under anaerobic
conditions.
Some of the toxicokinetic and toxicological data that can be used in the
evaluation of IMPA come from studies of Sarin and diisopropyl methyl-
phosphonate (DIMP; a by-product produced during the manufacture of Sarin).
Since these compounds degrade to produce IMPA in living systems, the data are
applicable to IMPA.
Although there have been no absorption studies of IMPA, the systemic toxicity
that occurs following oral administration of this compound and the low
concentration of IMPA in the feces when DIMP is administered orally, indicate
that intestinal absorption does occur. After absorption, the IMPA is
distributed in the plasma to the tissues. There appears to be little or no
metabolic conversion of the IMPA to simpler compounds. The highest
concentrations of IMPA are found in the kidney, lungs and brain. A portion of
the IMPA in the brain becomes tissue-bound, particularly in the hypothalamus.
Unbound IMPA is excreted in the urine.
The oral LD50 values for rats and mice (5,500 to 7,700 mg/kg) are indicative
of low acute toxicity. Rabbits did not show any signs of toxicity or
irritation from IMPA (100 mg) applied to the eyes, but it was moderately
irritating to the skin at a dose of 2.0 mg/kg. Dermal application of a 0.1%
solution did not cause sensitization and IMPA was not mutagenic in the Ames
assay at concentrations of 0.5 to 5,000 /ig/plate. Compound-related adverse
effects did not develop in rats that were exposed to concentrations of 300 to
3,000 ppm (300-3,000 mg/L) IMPA in drinking water for 90 days. There are no
data on the reproductive or developmental toxicity of IMPA and no information
pertaining to its carcinogenic potential.
Since there are no other appropriate data, all of the HA values for IMPA were
derived from a 90-day study of rats exposed to concentrations of 0, 300, 1,000
or 3,000 ppm (0, 300, 1,000 or 3,000 mg/L, respectively) in drinking water,
despite the lack of any effects in this study. The highest concentration
tested (3,000 ppm) was determined to be the no-observable-adverse-effect-level
(NOAEL), based on observations of body weight, clinical signs, hematological
parameters, terminal blood chemistry values, and histopathology. (This
concentration is equivalent to a dose of 399.1 mg/kg/day for females and 278.5
mg/kg/day for males.) The longer-term HA for a 10-kg child calculated from a
NOAEL of 278.5 mg/kg/day is 30 mg/L. In the absence of available data to
ES-1

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determine One-day and Ten-day HAs, the Longer-term HA for a 10-kg child is
considered acceptable for these exposure durations. The Longer-term HA for an
adult is 100 mg/L.
The 90-day study in rats also serves as the basis for the Lifetime HA. The
Reference Dose (RfD), derived from the 90-day NOAEL of 278.5 mg/kg/day, is
0.1 mg/kg/day (100 Mg/kg/day). The Drinking Water Equivalent Level (DWEL)
derived from the RfD is 4 mg/L and the Lifetime HA is 0.7 mg/L (700 /ig/L),
assuming that 20% of the total exposure to IMPA comes from drinking water.
According to the EPA criteria for the classification of carcinogens, IMPA is
placed in Group D: Not classifiable as to human carcinogenicity. This
category is for chemicals with inadequate human and animal evidence of
carcinogenicity and for chemicals for which no data are available.
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I. INTRODUCTION
The Health Advisory (HA) Program, sponsored by the Office of Water (OW),
provides information on the health effects, analytical methodology and
treatment technology that would be useful in dealing with the contamination of
drinking water. Health Advisories describe nonregulatory concentrations of
drinking water contaminants at which adverse health effects would not be
anticipated to occur over specific exposure durations. Health Advisories
contain a margin of safety to protect sensitive members of the population.
Health Advisories serve as informal technical guidance to assist Federal,
State and local officials responsible for protecting public health when
emergency spills or contamination situations occur. They are not to be
construed as legally enforceable Federal standards. The HAs are subject to
change as new information becomes available.
Health Advisories are developed for one-day, ten-day, longer-term (approxi-
mately 7 years, or 10 percent of an individual's lifetime) and lifetime
exposures based on data describing noncarcinogenic end points of toxicity.
For those substances that are known or probable human carcinogens, according
to the Agency classification scheme (Group A or B), Lifetime HAs are not
recommended. The chemical concentration values for Group A or B carcinogens
are correlated with carcinogenic risk estimates by employing a cancer potency
(unit risk) value together with assumptions for lifetime exposure and the
consumption of drinking water. The cancer unit risk is usually derived from
the linearized multistage model with 95 percent upper confidence limits. This
provides a low-dose estimate of cancer risk to humans that is considered
unlikely to pose a carcinogenic risk in excess of the stated values. Excess
cancer risk estimates may also be calculated using the one-hit, Weibull, logit
or probit models. There is no current understanding of the biological
mechanisms involved in cancer to suggest that any one of these models is able
to predict risk more accurately than another. Because each model is based on
differing assumptions, the estimates that are derived can differ by several
orders of magnitude.
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II. GENERAL INFORMATION AND PROPERTIES
Isopropyl methylphosphonic acid (IMPA) is a hydrolytic degradation product of
the nerve gas isopropyl methylphosphonofluoridate (GB or Sarin) (Rosenblatt et
al., 1975a). Sarin was used as a chemical warfare agent.
Isopropyl methyl phosphonic acid can be prepared through the alkaline
hydrolysis of diisopropyl methylphosphonate (DIMP) or the hydrolysis of
isopropyl methylphosphonochloridate with cold aqueous acetone (Rosenblatt et
al., 1975b).
The pKg of the acid functional group is estimated to be about 2.38 (Bossle et
al., 1983). The anionic form of the molecule will, accordingly, exist at
neutral and alkaline pHs. Based on structure and chromatographic behavior
with an acetic acid/n-butanol/water solvent mixture (Hoskin, 1956), IMPA is
soluble in water and other polar solvents. Solubility in nonpolar solvents is
predicted to be limited. Based on a boiling point of 9798C at 0.08 torr and
its chemical structure, IMPA is expected to be relatively nonvolatile.
Chemically, IMPA is extremely stable due to resonance stabilization of the
alkyl-ester bond. Based on the rate of hydrolysis of IMPA in benzenesulfonic
acid, IMPA has a half-life of 1,900 years at pH 1 (Rosenblatt et al., 1975b).
At neutral and alkaline pHs the half-life of this compound is much longer.
Hydrolysis of the ester bond, when it does occur, produces methylphosphonic
acid (MPA) and isopropyl alcohol.
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TABLE II-1 General Chemical and Physical Properties of
Isopropyl Methylphosphonic Acid
CAS Number
Synonyms
Molecular Weight
Chemical Formula
Structure
Physical State
Boiling Point
Melting Point
Density
Vapor Pressure
Solubility
Octanol/Water Partition Coefficient
Lg K0W
Taste Threshold (Water)
Odor Threshold (Water)
Conversion Factor (in air)
1832-54-8
6838-93-3 (Sodium salt)
isopropyl methylphosphonate;
methyl phosphonic acid,
isopropyl ester; phosphonic
acid, methyl, monoisopropyl
ester; phosphonic acid,
methyl, mono(l-methylethyl)
ester
138.12
c4Hh03p
<
OH
(CH3)2CHO'
acid - liquid (oil)
sodium salt - solid
9798C (0.08 torr)
123125C (0.2 torr)
. .(a)
1.1091 (20"C)
1 ppm = 6 mg/m3
References: Beilstein Database, 1992; Rosenblatt et al., 1975b
(a) No data
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Ill. OCCURRENCE
Isopropyl methylphosphonic acid was introduced into the environment as a
degradation product of the nerve gas, Sarin. It is known to have contaminated
groundwater at, and adjacent to, its site of production. Its very low
volatility makes it an unlikely atmospheric contaminant. Isopropyl methyl-
phosphonic acid is not known to occur naturally.
Active production of Sarin was limited to the area of the Rocky Mountain
Arsenal (RMA) adjacent to the northern city limits of Denver, Colorado. This
area subsequently became a storage site for unused Sarin. Prior to 1956,
effluents from the manufacture of Sarin entered five unlined surface ponds
located on site at the RMA, with subsequent discharge into an asphalt-lined
reservoir at the same facility. Seepage from these ponds has contributed to
the contamination of the groundwater in the underlying aquifers (Robson, 1981;
PMRMA, 1991a). Between 1973 and 1981, the RMA was involved in the
detoxification of the previously-stored Sarin (Robson, 1981).
Actual levels of IMPA in groundwater during the years of active Sarin produc-
tion were not measured. However, a computer-simulation model based on
groundwater movement and solute transport, as described by Robson (1981), has
been used to estimate concentrations and movement of diisopropyl methyl-
phosphonate (DIMP), a by-product of Sarin synthesis, in the groundwater.
Since IMPA is formed from the degradation of DIMP, this same model can be used
to estimate the subsurface movement of IMPA at Rocky Mountain Arsenal. Based
on the Robson (1981) model, the movement of the groundwater through the
alluvial aquifer resulted in one contaminated area or plume reaching the South
Platte River, to the west of the arsenal, with the maximum rate of discharge
occurring between 1958 and 1960. Based on the rate of plume movement, this
particular contaminated area should have been essentially nonexistent by 1972,
according to the Robson (1981) model. Two additional contaminated areas, to
the south of the arsenal and to the north of the ponds and extending to the
surrounding area, are postulated to be relatively stable due to low
groundwater velocities. The northern plume has contaminated a creek, an
adjacent lake and its canal tributary. The diisopropyl methylphosphonate has
been detected in two samples from the lake (Robson, 1981). Rocky Mountain
arsenal area wells sampled in 1989 and 1991 had IMPA concentrations ranging
from less than 0.392 /ig/L to 26,236 /ig/L (PMRMA, 1991b).
The initial chemical analysis for DIMP, undertaken in 1974, revealed its
presence in the groundwater both at the arsenal and in the surrounding areas
to the north and west. Levels as high as 44,000 ng/L were detected near one
of the abandoned ponds (Robson, 1981), whereas wells at the arsenal contained
levels ranging from below the detection limit to 1,420 Mg/L (1.42 ppm). In
December 1974, analysis of off-post wells indicated concentrations of 75 ^g/L
(75 ppb) DIMP (Rosenblatt et al., 1975a). Trace concentrations have been
found in wells down-gradient from the ponds, generally north-northwest of the
arsenal, and within one mile of municipal water wells (Robson, 1981). More
recent measures of DIMP in groundwater at RMA ranged from 2.1 ng/L to
30,000 (ig/L in the first half of 1989, and from 0.445 //g/L to 37,200 ^g/L in
the fall of 1989 (PMRMA, 1991a,b). Monitoring data from 1991 show that DIMP
concentrations ranged from 0.43 ug/L to 21,000 Mg/L (PMRMA, 1991b).
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Computer-based predictions for distribution of DIMP indicate that without
remedial action or additional input of the contaminant, a steady decrease in
the concentration of DIMP in the groundwater in most of the area will occur as
a result of discharge to the South Platte River and dilution by uncontaminated
water, thereby posing no danger to municipal water supplies (Robson, 1981).
Levels of DIMP in the surface water of the lake act to recharge the aquifer.
Thus, the concentration of DIMP in the aquifer between the arsenal and the
contaminated lake will remain constant. Similar predictions apply to IMPA
since it will accompany DIMP in the environment. This estimate is based on
the assumption that the migration rate of IMPA in the aquifer is the same as
or is faster than the migration rate of DIMP.
Differences between IMPA and DIMP migration in soils and groundwater may exist
due to differences in chemical and physical properties. Diisopropyl
methylphosphonate is nonionic whereas isopropyl methylphosphonic acid is an
ionizable acid with a low pKg. The IMPA anion is expected to be more water
soluble than DIMP and more likely to bind to cationic soil surfaces.
Based on measured levels of DIMP in ground and surface waters 18 to 23 years
after active disposal of the effluent at the RMA, and considering IMPA's low
volatility, it appears likely that IMPA will remain in the water with little
or no volatilization into the atmosphere. The chemical stability of IMPA will
also contribute to its persistence in the environment.
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IV. ENVIRONMENTAL FATE
The available data suggest that little abiotic degradation of IMPA occurs in
the environment. Small amounts of the compound can be converted to methyl
phosphonic acid (MPA) particularly at low pHs. The half-life of IMPA at pH 1,
however, is 1,900 years and it is longer at higher pHs. Therefore, production
of MPA from IMPA is minimal in sterile media (Rosenblatt et al., 1975b).
Isopropyl methylphosphonic acid also appears to be stable to biotic
degradation under most circumstances. Cook et al. (1978) isolated one strain
of bacteria from sewage which appeared to metabolize IMPA, producing methane
as a by-product of IMPA degradation (Daughton et al., 1979a). This bacterium
was identified as a strain of Pseudomonas testosteroni. Thirteen other
bacterial strains from sewage had no effect on IMPA (Cook et al., 1978).
Detailed studies of the action of P. testosteroni on IMPA indicate that the
bacteria will utilize IMPA as a phosphorus source when other phosphorus
sources are limited (Daughton et al., 1979a). Under these conditions, the
phosphorus-carbon bond of IMPA is cleaved, resulting in a stoichiometric
release of methane under aerobic conditions. Some evidence exists that
hydrolysis of the ester bond occurs, releasing isopropanol and phosphorous
acid or phosphoric acid (Alexander et al., 1977).
Daughton et al. (1979b) studied the effect of soil binding and alternate
phosphate sources on IMPA metabolism by P. testosteroni. Isopropyl
methylphosphonic acid did not bind to the soils (pH 3.9; 35% organic matter)
and, therefore, remained available to the bacterial inoculum as a source of
phosphorus. The rate of degradation of IMPA was not affected by alternate
phosphate sources in the environment in this study.
Howells et al. (1973) examined the biotransformation of Sarin by wheat plants.
Isopropyl methylphosphonic acid was produced in the plants from the uptake of
Sarin from a hydroponic growth solution. There was no evidence that the IMPA
was further degraded to MPA in the 5-week period following 24-hour exposure of
the plants to Sarin. This study suggests that vascular plants lack the
ability to metabolize IMPA.
Wheat plants will also absorb Sarin from the vapor phase through leaf
surfaces. The Sarin is then metabolized to IMPA (Howells et al., 1976). In
this study, Sarin and IMPA were both detected in the exposed plants, but MPA
was not detected. These data confirm the stability of IMPA in tissues of the
wheat plant.
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V. TOXICOKINETICS
Although there have been no absorption studies of IMPA, the systemic toxicity
that occurs following oral administration of this compound and the low
concentration of IMPA in the feces when DIMP is administered orally indicate
that intestinal absorption does occur. After absorption, the IMPA is
distributed in the plasma to the tissues. There appears to be little or no
metabolic conversion of the IMPA to simpler compounds. The highest
concentrations of IMPA are found in the kidney, lungs and brain. A portion of
the IMPA in the brain becomes tissue-bound, particularly in the hypothalamus.
Unbound IMPA is excreted in the urine.
A.	Absorption
No data are available relating to the absorption of IMPA through the oral,
dermal or respiratory routes of exposure. However, based on effects that
occurred during oral LD5Q studies in rats and mice, it can be assumed that
IMPA is absorbed from the gastrointestinal tract.
B.	Distribution
No data are available describing the tissue distribution of IMPA following
oral exposure. The tissue disposition of Sarin, however, has been evaluated
following intravenous administration of a sublethal dose (80 A/g/kg) of
tritium-labeled material to mice (Little et al., 1986). Since IMPA is the
major degradation product of Sarin, Little et al. (1986) measured tissue
levels of IMPA as well as the parent compound. These data, accordingly,
provide information on the tissue distribution of IMPA, but they do not
indicate whether the label entered the cell as Sarin or IMPA. Since Sarin is
hydrolyzed to IMPA by a rat serum enzyme (Hoskin, 1956), it is postulated that
at least a portion of the tissue label enters the cell as IMPA.
Following intravenous administration of radiolabeled Sarin (80 ^g/kg, 70 ^Ci),
groups of five IRC outbred male mice were sacrificed at 1, 5, 15 or 30 minutes
and 1, 2,4, 8 or 24 hours. Blood was collected and tissues removed for
assay. Samples of brain, liver, lung, heart and kidney tissue, diaphragm fat,
and blood plasma were analyzed for Sarin, IMPA and MPA (Little et al., 1986).
In all cases, the concentration of IMPA in the tissues was greater than the
concentration of Sarin, suggesting a rapid metabolism of Sarin to IMPA (Little
et al., 1986). Isopropyl methylphosphonic acid concentration was 20 times
greater than the Sarin concentration in all tissues except the brain. A
smaller concentration difference occurred in the brain, IMPA concentration
being only 4 times greater than that of Sarin. Isopropyl methylphosphonic
acid concentration in the lungs, heart, kidneys and plasma declined by about
50% in the first 30 minutes after administration and more slowly after that.
At the end of 24 hours, free IMPA concentrations were highest in the lungs,
plasma and kidney. These organs also contained the highest concentrations of
bound IMPA. The high concentration of IMPA in the kidneys suggests that the
kidneys play a major role in Sarin detoxification and excretion. Liver levels
of free and bound IMPA were lower than the kidney levels at all time points.
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Residual bound IMPA in the brain exceeded the concentration of free IMPA in
the early, as well as most of the late, time periods suggesting rapid binding
of IMPA to brain proteins. After 24 hours, the levels of bound IMPA exceeded
the free IMPA in all tissues.
Additional studies have been conducted on the fate of Sarin in rat brain
tissues. Following intravenous administration of 60 fig/kg of P32-Sarin, IMPA
was bound to brain proteins (Fleisher et al., 1964). The administered dose
was equivalent to 1.5 times the LD5Q for Sarin.
In an attempt to study regional impacts of Sarin on the brain, Little et al.
(1988) injected tritium-labeled Sarin into the tail vein of groups of five
mice each. The animals were sacrificed at 10 minutes and at 6 or 24 hours
after injection. The brains were removed and carefully divided into seven
sections. Concentrations of Sarin, IMPA and MPA in each brain compartment
were measured. Sarin and its degradation products, IMPA and MPA were present
in the greatest concentration in the hypothalamus as compared to the
cerebellum, medulla, midbrain, striatum and cortex regions of the brain. The
level of IMPA in the hippocampus was also elevated compared to other brain
areas. The concentration of free IMPA declined with time in all brain
compartments whereas levels of bound IMPA increased in the period between 6
and 24 hours.
C. Metabolism
The biochemical stability of IMPA was studied by Hoskin (1956). Isopropyl
methylphosphonic acid was administered by an intraperitoneal injection of
56 mg to a single adult male Wistar rat. This is equivalent to a dose of
140 mg/kg, based on a body weight of 400 g for an adult male rat. Paper
chromatographic examination of urine collected over 48 hours indicated that
IMPA was excreted intact. No MPA was excreted, suggesting either that there
is little or no hydrolysis of the isopropyl-ester functional group or, if
hydrolysis does occur, the MPA produced is retained by the body.
Tissue retention of methyl phosphonic acid may well occur. In the Little et
al. (1986) study of tissue distribution of tritium-labeled Sarin, all tissues
except the kidney and plasma had relatively constant concentrations of
nonextractable label during the 24-hour period after compound administration.
The nonextractable radioactivity was presumed to be protein-bound MPA. Bound
MPA was also identified in the brain 24 hours after compound administration
(Little et al., 1988). However, conversion of Sarin to MPA has not been
demonstrated.
Hoskin (1956) also investigated the availability of the phosphate from IMPA to
form hexose phosphonate esters in the presence of active phosphorylase
enzymes. In vitro incubation of IMPA with phosphorylase, glycogen and
adenylic acid, followed by chromatographic analysis of the reaction product,
indicated that no hexose phosphonate esters were formed. When inorganic
phosphate was added to the same reaction medium, both glucose-1-phosphate and
glucose-6-phosphate were produced.
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D. Excretion
Isopropyl methylphosphonic acid appears to be excreted without metabolic
alteration. Hoskin (1956) found that 40% of the label from an intravenous
dose of 56 mg of P32-labeled IMPA was excreted in the urine over the first
48 hours following injection. The only label-containing compound found in a
chromatogram of the urine was the IMPA itself. There was no MPA excreted.
Isopropyl methylphosphonic acid is also an excretory metabolite for Sarin and
DIMP (Little et al., 1986; Ivie, 1980). Radioactive 14C-labeled DIMP was
given to a 357 kg lactating Jersey cow following 5 days of oral dosing with
10 mg/kg DIMP in gelatin capsules (Ivie, 1980). On the sixth day, the cow was
given radiolabeled compound. All excreta were collected. Analysis of the
excreta indicated that DIMP was stoichiometrically converted to IMPA which was
excreted primarily in the urine. Small amounts of IMPA and DIMP were also
identified in the feces.
After 96 hours, 84% of the label had been excreted in the urine and 7.4% in
the feces. Milk samples collected from the cow contained 0.08% of the label.
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VI. HEALTH EFFECTS
Isopropyl raethylphosphonic acid has a low degree of toxicity as demonstrated
by the lack of effects in animals during acute and subchronic studies (Mecler
and Dacre, 1982). Oral LD50 values for rats and mice demonstrated low acute
toxicity. Rabbits did not show any signs of toxicity or irritation from IMPA
applied to the eyes, but it was mildly irritating to the skin. Dermal
application did not cause sensitization, and IMPA was not mutagenic in the
Ames assay. Compound-related adverse effects did not develop in rats that
were exposed to IMPA in drinking water for 90 days.
A.	Health Effects in Humans
1.	Short-term Exposure
No information was found in the available literature regarding adverse health
effects associated with short-term exposure of humans to IMPA.
2.	Longer-term Exposure
No information was found in the available literature regarding adverse health
effects associated with long-term exposure of humans to IMPA.
B.	Health Effects in Animals
1. Short-Term Exposure
LD5Qs of IMPA have been evaluated in both the mouse and rat (Mecler, 1981).
In each study, IMPA was administered by gavage as a single dose. The animals
were observed for 14 days following treatment and weighed at 0, 7 and 14 days.
Appearance, behavior and clinical signs were monitored daily.
Male Charles River rats (56-67 days old, 5/sex/dose) were treated with doses
of 4,640, 6,810, 10,000 or 14,700 mg/kg 99% pure IMPA as the sodium salt
(Mecler, 1981). The females received doses of 3,160, 4,640, 6,810 or
10,000 mg/kg. The resulting mortality is summarized in Table VI-1. Loose
stools were observed in several animals at all dose levels. Reduced motor
activity and prostration were seen in some animals of both sexes at doses of
3,160 mg/kg or greater, while ataxia was observed in some animals at doses of
4,640 mg/kg or greater. The ataxia occurred in one female at the 4,640 mg/kg
level, three females at the 6,810 mg/kg level, and one male and one female at
the 10,000 mg/kg level.
In the necropsy studies, no gross organ or tissue abnormalities were observed
in the animals that survived until sacrifice. The animals that succumbed to
compound administration displayed red or mottled lungs and dark spots on the
thymus. Among rats that died, red or mottled lungs occurred in some of the
males at the 10,000 and 14,700 mg/kg levels and some females at the
6,810 mg/kg level, and one female at each of the 4,640 and 10,000 mg/kg
levels. The thymus spots were seen in females at 6,810 and 10,000 mg/kg
VI-1

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levels and in males at the 10,000 and 14,700 nig/kg levels. The stomach tissue
was red and both the stomach and intestines were filled with fluid (Mecler,
1981) .
All of the highest-dose test animals (5/sex) died in the study, while none of
the lowest-dose animals died (Mecler, 1981). The LD50 value for the males was
7,650 mg/kg; for the females it was 6,070 mg/kg. Effects were seen at even
the lowest dose administered, thus, the lowest-observable-adverse-effect-level
(LOAEL) from this study is 3,160 mg/kg.
Male and female 9-week-old Charles River mice (5/sex/group) were given doses
of 3,160, 4,640, 6,810 or 10,000 mg/kg IMPA (Mecler, 1981). The observation
parameters for this study paralleled those for the rat study discussed above
with the resulting mortality summarized in Table VI-1. Soft liquid stools
were observed in some animals at all dose levels except the 3,160 mg/kg
females. Reduced motor activity and ataxia were seen in some animals at doses
of 3,160 mg/kg or greater, in all male mice at the 6,810 mg/kg level, and all
mice at the 10,000 mg/kg level that survived for 1 hour. Prostration occurred
in one female at 6,810 mg/kg and in two males and one female at 10,000 mg/kg.
Mottled or red lungs were observed in three females at the 10,000 mg/kg level
who died during the study; fluid-filled stomach and intestines appeared in all
mortalities. As described for rats, there were no mortalities in the low-dose
group. All animals in the high-dose group died before the end of the
observation period. Abnormal necropsy findings were not observed in any of
the mice that survived for 14 days. The LD5Q dose for male mice was
5,620 mg/kg and for female mice it was 6,550 mg/kg. Since some effects were
seen at all dose levels, the LOAEL is 3,160 mg/kg.
a.	Skin and Eve Irritation
A single dose of 2.0 mg/kg IMPA (sodium salt) was applied with an occluded
gauze pad to the prepared (hair removed) epidermis of six 16-week-old New
Zealand white rabbits for a 24-hour period (Mecler, 1981). An average of 65%
of the applied dose was absorbed as determined by pre- and post-dose weighing
of the gauze pad. In three rabbits, the epidermal surface was abraded prior
to compound administration, and the application site was observed daily for
14 days after testing. The animals were examined daily for gross signs of
systemic toxicity. All animals were sacrificed at the end of the 14-day
observation period.
Erythema was seen in all animals during the 1- to 5-day period after treatment
(Mecler, 1981). One animal had hair loss from the mid-dorsal cervical area;
another rabbit had a swollen left leg with a discharge. No mortality or signs
of systemic toxicity were noted in the rabbits and there were no visible
abnormalities noted at necropsy.
b.	Dermal Sensitization
In order to test for dermal sensitivity from IMPA, a 0.1% solution of the
sodium salt was injected intradermally in nine female guinea pigs (Mecler,
1981). Ten 0.1 mL injections were given over a 3-week period; 2 weeks later,
a 0.1 mL challenge injection was administered. Four guinea pigs were treated
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TABLE VI-1. Mortality in Rats and Mice Exposed to Acute Doses of IMPA(a)
Male rats
Female rats
Male mice
Female mice
Mortality
Dose
(mg/kg)
Number of Mortalities by
Day of death
0(b) 1 2 3 4 5-14
Total
Mortality
4,640
6,810
10,000
14,700
0/5(c)
1/5
5/5
5/5
3,160
4,640
6,810
10,000
0/5
1/5
3/5
5/5
3,760
4,640
6,810
10,000
0/5
1/5
4/5
5/5
3,160
4,640
6,810
10,000
0/5
1/5
2/5
5/5
(a)	Isopropyl methylphosphonic acid, sodium salt; administered by gavage in
distilled water
(b)	Day of death
(c)	Number dead/Total number in group
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with 2,4-dinitro-l-chlorobenzene as a positive control. There were no
indications of erythema during the sensitization period. A very slight
reaction to the challenge was noted during the 24 hours after injection. The
response of the exposed animals to IMPA was not significant when compared to
the response of the control animals exposed to 2,4-dinitro-1-chlorobenzene
(Mecler, 1981) .
Ocular irritation was studied by instilling 100 mg IMPA (sodium salt) into one
eye each of 6 female New Zealand white rabbits (Mecler, 1981). The eyes of
the treated rabbits were examined at intervals of 1, 24, 48, 72, 96 and
168 hours after treatment. No effects of exposure were noted in five of the
tested rabbits. One rabbit exhibited congestion and swelling of the iris and
redness of the conjunctiva at 24 hours. Isopropyl methylphosphonic acid was
judged not to be an eye irritant.
2.	Longer-term Exposure
Concentrations of 0, 300, 1,000 or 3,000 ppm IMPA (sodium salt) in drinking
water were given to groups of 20 male and 20 female Sprague-Dawley rats for a
period of 90 days (Mecler, 1981). Based on body weight and fluid consumption
data, the male rats were exposed to an average of 0, 25, 92.4 or
278.5 mg/kg/day; the female rats, to doses of 0, 34, 137.4 or 399.1 mg/kg/day.
The animals were observed for gross signs of toxicity twice daily. Food and
water intake and weight were noted on a weekly basis. Blood samples were
analyzed for standard hematological parameters at 4, 8 and 12 weeks, but blood
chemistry measurements were determined only at the end of the study. After
90 days the animals were sacrificed. All tissues for the control and
3,000 ppm groups were examined histologically and the weights of key body
organs were determined.
No statistically significant effects of exposure were noted in this study.
There was a slight decrease in the body weight of the 3,000 ppm dose group
when compared to the controls; however, the difference was not significant.
The decrease in body weight was less than 10% for both the males and females.
There is, accordingly, no LOAEL in this study. The NOAEL is based on
observations in the 3,000 ppm group. Based on fluid intake and body weights,
the NOAEL was 399.1 mg/kg/day for females and 278.5 mg/kg/day for males.
3.	Reproductive Effects
No information was found in the available literature regarding the repro-
ductive effects of IMPA.
4.	Developmental Effects
No information was found in the available literature regarding the develop-
mental effects of IMPA.
5.	Mutagenicity
Isopropyl methylphosphonic acid had negative mutagenicity results in five
strains of Salmonella tvphimurium when tested according to the Ames protocol,
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both with and without microsomal activation (Mecler, 1981). Concentrations
0.5, 1.0, 10, 100, 500, 1,000, 2,500 and 5,000 /ig/plate were tested. There
were signs of compound toxicity in some of the tested strains at doses of
2,500 jig/plate or greater.
6. Carcinogenicity
No information was found in the available literature regarding the
carcinogenic potential of IMPA.
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VII. HEALTH ADVISORY DEVELOPMENT
A. Quantification of Toxicological Effects
Health Advisories (HAs) are generally determined for one-day, ten-day,
longer-term and lifetime exposures if adequate data are available that
identify a sensitive noncarcinogenic end point of toxicity. The HAs for
noncarcinogenic toxicants are derived using the following formula:
HA	-
where:
NOAEL or LOAEL	=
BW	=
UF	~
L/day =
1. One-dav Health Advisory
There are no appropriate data for calculating a One-day Health Advisory. The
available animal data include LD5Q studies for rats and mice as well as
testing for dermal and ocular irritation and dermal sensitivity in animals.
LD50 data cannot be used, however, for quantification of toxicological
effects.
Some adverse effects other than death were noted in the LD5Q studies. Both
rats and mice experienced loose stools and reduced motor activity. Gross
observations of the organs following death or sacrifice revealed some
reddening and mottling of the lungs. Fluid was found in the stomach and
intestines. The combined observations of fluid in the gastrointestinal (GI)
tract and soft liquid stools suggest that body fluids may have been drawn to
this body compartment due to the high osmolality of GI contents; thus, these
effects are not related directly to the IMPA. The reddening of the lung
surface and motor abnormalities, on the other hand, may be directly related to
IMPA toxicity. The studies of Little et al. (1986, 1988) indicate that IMPA
has an affinity for both lung and brain tissues and will bind to proteins in
these tissues.
No suitable information was found in the available literature for determining
the One-day HA for IMPA. Accordingly, the Longer-term HA of 30 mg/L for a
child (calculated below) is recommended for use as a conservative estimate for
a one-day exposure.
(NOAEL or LOAEL) x (BW)	.. . . . _
	(UF) x ( L/day)	 - _ b/L (rounded to _ g/L)
No- or Lowest-Observed-Adverse-Effect Level in mg/kg bw/day.
assumed body weight of a child (10 kg) or an adult (70 kg).
uncertainty factor (10, 100, 1,000 or 10,000) in accordance
with NAS/EPA guidelines.
assumed daily water consumption of a child (1 L/day) or an
adult (2 L/day).
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2. Ten-dav Health Advisory
No suitable information was found in the available literature for determining
the Ten-day HA for IMPA. The Longer-term HA of 30 mg/L for a child (calcu-
lated below) is recommended for use as a conservative estimate for a ten-day
exposure.
3. Longer-term Health Advisory
The study by Mecler (1981) has been selected to serve as the basis for the
Longer-term HA since there are no other appropriate data. This is a 90-day
subchronic study of Charles River rats given concentrations of 0, 300, 1,000
or 3,000 ppm IMPA in drinking water. The animals were observed for gross
signs of toxicity twice daily. Food and water intake and weight were recorded
weekly. Blood samples were analyzed for hematological parameters at 4, 8 and
12 weeks. Blood chemistry measurements were all within the norms for the
species. There was a slight (<10%) decrease in the body weight of the
3,000 ppm dose group when compared to the controls. Thus, the 3,000 ppm dose
is the NOAEL for this study. Based on water intake and body weight records,
the 3,000 ppm concentration is equivalent to a dose of 399.1 mg/kg for the
females and 278.5 mg/kg for the males.
This study is the only multi-dose data available on IMPA; therefore, it is
used to provide a conservative HA estimate for both a child and an adult. The
278.5 mg/kg/day dose for the males is used as the NOAEL in the HA calculation.
The Longer-term HA for the 10-kg child is calculated as follows:
27.5 mg/L (:
30.0 mg/L or 30,000 Mg/L)
t	- u* (278.5 mg/kg/day) (10 kg)
Longer-term HA = 	(100) (1 L/day)	 =	(rounded to
where:
278.5 mg/kg/day = NOAEL, based on absence of an effect in male rats
exposed to IMPA via drinking water for 90 days.
10 kg = assumed weight of child.
100 = uncertainty factor; this uncertainty factor was chosen
in accordance with NAS/EPA guidelines in which a
NOAEL from an animal study is employed.
1 L/day = assumed water consumption by a 10-kg child.
The Longer-term HA for the 70-kg adult is calculated as follows:
Longer-term HA - (278^	) (70 kg) _
(100) <2 L/day)	1Q() ^ ^ ^ ^
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where:
278.5 mg/kg/day = NOAEL, based on absence of an effect in male rats
exposed to IMPA via drinking water for 90 days.
70 kg = assumed weight of adult.
100 = uncertainty factor; this uncertainty factor was chosen
in accordance with NAS/EPA guidelines in which a
NOAEL from an animal study is employed.
2 L/day = assumed water consumption by a 70-kg adult.
4. Lifetime Health Advisory
The Lifetime HA represents that portion of an individual's total exposure that
is attributed to drinking water and is considered protective of noncarcino-
genic adverse health effects over a lifetime exposure. The Lifetime HA is
derived in a three-step process. Step 1 determines the Reference Dose (RfD),
formerly called the Acceptable Daily Intake (ADI). The RfD is an estimate of
a daily exposure to the human population that is likely to be without appre-
ciable risk of deleterious effects over a lifetime, and is derived from the
NOAEL (or LOAEL), identified from a chronic (or subchronic) study, divided by
an uncertainty factor(s). From the RfD, a Drinking Water Equivalent Level
(DWEL) can be determined (Step 2). A DWEL is a medium-specific (i.e.,
drinking water) lifetime exposure level, assuming 100% exposure from that
medium, at which adverse, noncarcinogenic health effects would not be expected
to occur. The DWEL is derived from the multiplication of the RfD by the
assumed body weight of an adult and divided by the assumed daily water
consumption of an adult. The Lifetime HA is determined in Step 3 by factoring
in other sources of exposure, the relative source contribution (RSC). The RSC
from drinking water is based on actual exposure data or, if data are not
available, a value of 20% is assumed.
If the contaminant is classified as a known, probable or possible carcinogen,
according to the Agency's classification scheme of carcinogenic potential
(U.S. EPA, 1986), then caution must be exercised in making a decision on how
to deal with possible lifetime exposure to this substance. For human (A) or
probable human (B) carcinogens, a Lifetime HA is not recommended. For
possible human carcinogens (C), an additional 10-fold safety factor is used to
calculate the Lifetime HA. The risk manager must balance this assessment of
carcinogenic potential and the quality of the data against the likelihood of
occurrence and significance of health effects related to noncarcinogenic end
points of toxicity. To assist the risk manager in this process, drinking
water concentrations associated with estimated excess lifetime cancer risks
over the range of 1 in 10,000 to 1 in 1,000,000 for the 70-kg adult drinking
2 L of water/day are provided in the Evaluation of Carcinogenic Potential
section.
The study by Mecler (1981) has been selected to serve as the basis for the
Reference Dose because it is the only candidate study for this calculation.
An additional uncertainty factor of 10 is used because the study is a 90-day
VII- 3

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study. An additional uncertainty factor of 3 is used because of the lack of
data on reproductive toxicity and teratogenicity and because of the lack of a
study in a second species. However, because IMPA is a metabolite of DIMP
(Little et al., 1986; Ivie, 1980; Hart, 1980), the DIMP data base can be used
to provide additional data on IMPA. In studies on DIMP conducted in rats,
mice, dogs, mink, quail and ducks, for periods ranging from 90 days to
26 weeks, and also in a three-generation reproduction study, DIMP was found to
be nontoxic to all species (U.S. EPA, 1989). The EPA concluded that no
significant adverse effect was observed in any species. Because DIMP is
rapidly and almost completely metabolized to IMPA, it is reasonable to assume
that the DIMP administered to mammals in these studies was metabolized to
IMPA; therefore, the absence of significant effects from DIMP supports the
observation of the absence of effects from IMPA in the Mecler study.
Using the Mecler (1981) study, the Lifetime HA is derived as follows:
Step 1. Determination of the Reference Dose (RfD)
RfD = (278-^mg/kg/day) _ 0 093 mg/kg/day (rounded to
0.1 mg/kg/day or 100 Mg/kg/day)
where:
278.5 mg/kg/day = NOAEL, based on absence of an effect in rats exposed to
IMPA via drinking water for 90 days.
3,000 = IAW NAS/EPA uncertainty factor. This uncertainty
factor includes a factor of 10 for interspecies
variation, a factor of 10 for intraspecies variation,
and a factor of 10 for use of a less - than-lifetime
study. An additional factor of 3 is applied for the
lack of reproductive and developmental toxicity
studies and lack of a study in a second species.
Step 2. Determination of the Drinking Water Equivalent Level (DWEL)
3.5 mg/L (rounded
4 mg/L or 4,000 Mg/L)
DUEL - "-1	k8> - 3.5 ng/L (rounded to
where:
0.1 mg/kg/day = RfD
70 kg = assumed weight of adult.
2 L/day = assumed water consumption by 70-kg adult.
Step 3. Determination of the Lifetime HA
Lifetime HA = (3.5 mg/L) (20%) = 0.7 mg/L (700 Mg/L)
VII -4

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where:
3.5 mg/L = Lifetime HA at 100% contribution from ingestion of
drinking water.
20% = Relative source contribution (RSC); percentage of
daily exposure contributed by ingestion of drinking
water.
B. Evaluation of Carcinogenic Potential
Applying the criteria described in EPA's guidelines for assessment of carcino-
genic risk (U.S. EPA, 1986), IMPA is classified in Group D: Not classifiable
as to human carcinogenicity. This category is for agents with inadequate
human and animal evidence of carcinogenicity and for those with no available
data.
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VIII. OTHER CRITERIA. GUIDANCE AND STANDARDS
In 1984, the U.S. Army Medical Bioengineering Research and Development
Laboratory (USAMBRDL) recommended water concentrations for IMPA of 16.75 mg/L
for ambient water quality and 16.80 mg/L for drinking water as an interim
criteria for the protection of human health (Dacre, 1984). No other guidance
or standards were available in the published literature.
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IX. ANALYTICAL METHODS
Analytical techniques that are appropriate for the identification and
quantification of IMPA utilize some form of ion exchange or liquid
chromatography. Chromatographic procedures are sometimes combined with mass
spectrometry or some other suitable technique to facilitate the identification
of the specific phosphonic acid present. The techniques discussed in the
following paragraphs apply to several methylphosphonic acids including
isopropyl methylphosphonic acid.
Schiff et al. (1977) developed a method using a Dionex Model 14 Ion Chromato-
graph for the separation and analysis of phosphonic acids. Both 3 x 150 mm
and 3 x 500 mm column sizes were used. Columns were connected in series.
Eluents were varied depending on the specific phosphonic acid to be eluted.
A 0.005 M borate eluent and flow rate of 138 mL/hr with a 650 mm total column
length provided effective separation of isopropyl methylphosphonic acid from
other phosphonates and competing inorganic anions. A detection limit of
0.1 mg/L was achieved.
The most effective separation of methyl phosphonic acid in the presence of
chloride ion was achieved with 0.01 M sodium hydroxide, a flow rate of
322 mL/hr and a 500 mm column length (Schiff et al., 1977). The detection
limit under these conditions was 1.26 mg/L. Alternatively, methyl phosphonic
acid separation could be achieved on a 650 mm column with a bicarbonate/
carbonate eluent (0.0024 M/0.0018 M) and a flow rate of 138 mL/hr. Although
the separation from chloride achieved was not as effective as that with the
sodium hydroxide, the detection limit of 0.1 mg/L for methyl phosphonic acid
was superior.
The major difficulty encountered in separating the alkyl phosphonic acids from
a medium that contains several members of this class of compounds using the
ion exchange chromatography method, is the similarity in the charges of the
anions. The various alkyl phosphonic acids have very similar pK0s and,
therefore, similar net ionic charges. Detection of the individual phosphonic
acids in the eluent is also difficult since, lacking a chromophore, the
individual compounds cannot be detected using a UV or fluorescent detector
(Bossle et al., 1983).
Esterification of the alkyl methylphosphonic acids with para-bromophenacyl
bromide (PBPB) has been proposed by Bossle et al. (1983) as a method for the
separation and quantification of alkyl phosphonates. After adding the
chromophore to the molecule, the modified methylphosphonic acids are separated
by high pressure liquid chromatography (HPLC). Using this technique, Bossle
et al. (1983) were able to separate ethyl, isopropyl, and phenacetyl
methylphosphonic acid and quantify the concentrations of these phosphonic
acids. The detection limits achieved with the ethyl, isopropyl, and
phenacetyl methylphosphonic acids were 43, 59 and 62 ng, respectively.
According to the Bossle et al. (1983) approach, the alkyl methylphosphonic
acids were first esterified with PBPB, 18-crown-6 catalyst, and potassium
bicarbonate in dry acetonitrile. The reaction product was sealed in a WISP
sample vial and applied to a 30 x 0.4 cm I.D. Bondapak C18 column for reverse
IX-1

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phase HPLC. Clear separation of the three alkyl methylphosphonic acids was
achieved. There was also a clear separation of the methylphosphonic acids
from excess PBPB reagent. Retention times for the methylphosphonic acids were
propor- tional to the size and lipophilicity of the alkyl side chains.
Wils and Hulst (1988) evaluated a different approach for the separation of
organophosphonic acids. Ion pairs of the phosphonic acids with ammonium
acetate or one of three tetraalkylammonium salts (methyl, ethyl, n-butyl) were
established. These ion pairs were then separated by liquid chromatography
(LC) on a Sep-Pac C18 column using methanol/water as an eluent. The column
was connected to a thermospray (TSP) interphase prior to analysis of the
eluent by a mass spectrometer with a TSP ion source. Although this approach
showed potential as an analytical technique for a wide variety of phosphonic
acids, a number of procedural difficulties were encountered. The experimental
conditions which favored effective separation of the short chain alkyl
phosphonates were not as effective for the longer chain alkyl derivatives and
vice versa. The method was not useful for separation and identification of
the diprotic methylphosphonic acid (MPA) which is formed when isopropyl
methylphosphonic acid degrades.
The creation of an ion pair between an alkyl methylphosphonic acid and an
ammonium compound is the first step in an additional analytical method which
can be used for isopropyl methylphosphonic acid and other alkyl phosphonic
acids (Tornes and Johnson, 1989). Samples of alkyl methylphosphonic acids
(10-100 mL) were separated on a column containing 100 mg of an aminopropyl ion
exchanger. The column was eluted with 300 pL of 0.1 M trimethylphenylammonium
hydroxide (TMPAH) in methanol. The eluent from the column was injected into a
Packard Model 438 gas chromatograph coupled to an LKB 2091 mass spectrometer.
The injector port temperature was set at 300C so that the alkyl methyl-
phosphonate would react with the TMPAH. In this reaction the acid functional
group was methylated, producing a volatile ester. The Tornes and Johnson
(1989) method was developed specifically for the identification of the alkyl
methylphosphonic acids produced during the degradation of the nerve agents
Sarin and Soman.
The TMPAH modification approach for identifying isopropyl methylphosphonic
acid from Sarin was evaluated by Tornes and Johnson (1989) under field
conditions. Sarin (1 mg) was first added to 5 mL samples of water or 10 g
samples of sand, soil or grass. All samples were held for 1 to 4 weeks under
the ambient temperature and humidity conditions. Prior to analysis, the sand,
soil and grass samples were extracted by shaking with 50 mL water for 1 minute
and filtered to obtain the supernatant.
The dissolved, unreacted (nonionic) Sarin was separated from isopropyl
methylphosphonic acid by passing the supernatant through a C18 column prior to
use of the aminopropyl ion exchange column. Sarin was identified in all the
1- and 2-week samples and in the 4-week water sample. Isopropyl methyl-
phosphonic acid was quantitatively identified in all samples except the 4-week
soil sample. The Tornes and Johnson (1989) method can be used in the field as
a method for verifying Sarin use, even several weeks after the initial release
of the nerve gas into the environment. Based on their field studies, the
authors suggested that reversing the arrangement of the C18 and ion exchange
IX-2

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columns so that the C18 column follows rather than precedes the ion exchange
column may improve the recovery of the degradation products from parent nerve
gas. There can be some retention of the degradation products by the C18
column.
IX-3

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X. TREATMENT TECHNOLOGIES
Mill and Gould (1979) reported that hydrogen peroxide (H202) combined with
oxygen and ultraviolet light degrades IMPA in aqueous solution. At pH 9, a
1 M solution of IMPA as its sodium salt was combined with 3.0 M hydrogen
peroxide and 2.11 mmol of oxygen and irradiated with 300 nm light for 2 hours
at 25C. At the end of 2 hours, irradiation was terminated for analysis of
intermediary oxidation products and then resumed with the addition of 3.0 M
hydrogen peroxide for another 2-hour period of irradiation. The reaction
cycle was then repeated with additional 3.0 M peroxide for a final 2-hour
irradiation period.
Analysis of the final solution after three 2-hour treatments with 3 M hydrogen
peroxide, oxygen and irradiation indicated that IMPA had been converted to
acetic acid (0.13 M), carbon dioxide (0.36 mmol), and phosphoric acid (Mill
and Gould, 1979). A small amount (0.07 mmol) of methyl phosphonate was also
detected. In the initial steps of the reaction, the isopropyl functional
group was converted to acetone and acetic acid while the methylphosphonate
group remained intact. Oxidation of the methylphosphonate continued during
the second and third oxidation periods. Further oxidation of the acetone
reduced it to carbon dioxide and acetic acid. Some carbon monoxide was formed
as a transient intermediate.
These data indicate that IMPA can be degraded by oxidation using peroxide and
oxygen as oxidizing agents under ultraviolet light. Elevated temperatures are
not needed for the reaction. Oxidation of isopropyl methylphosphonic acid to
acetic acid, carbon dioxide and phosphoric acid requires vigorous conditions of
oxidation (9 M H202/1 M IMPA; 6-hour irradiation). Less vigorous oxidation
(3 M H202/1 M IMPA; 2-hour irradiation) resulted in minimal oxidation of the
carbon-phosphorus bond, producing methyl phosphonic acid as a product of the
reaction. The isopropyl moiety of isopropyl methylphosphonic acid was oxidized
to acetone and acetic acid.
Accordingly, oxidation of water containing isopropyl methylphosphonic acid
using oxygen, hydrogen peroxide, and ultraviolet light is a potential
treatment option. Careful control of reaction conditions is important if
carbon dioxide and acetic acid are the desired end products and the use of
expensive oxidant is minimized. The solutions which were irradiated in the
study of Mill and Gould (1979) were initially at pH 9. The influence of pH on
the reaction was not determined. However, the use of other pH solutions could
influence the rate of reaction.
Data reported by Schiff et al. (1977) on the oxidation of DIMP by ozone and
ultraviolet light indicate that DIMP is first converted to IMPA which is then
oxidized to acetate, formate, and MPA. Only small amounts of MPA were
converted to free phosphate ion. A 3-hour reaction time was employed; the
other reaction conditions were not specified. These results, however, are in
general agreement with those of Mill and Gould (1979) and indicate that
oxidation of the carbon-phosphorus bond in MPA is difficult to achieve.
No additional information has been located in the literature on the use of
specific treatment technologies for the removal of IMPA from potable water.
X-l

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Since this compound is not volatile, it would not be amenable to aeration.
Based on the low pK of the acid functional group, it should be amenable to
removal by ion exchange chromatography. Ion exchange processes are used as
analytical methods for IMPA (Bossle et al., 1979; Schiff et al., 1977).
Competition from other negative ions including the inorganic chloride and
fluoride ions can interfere with the ion exchange process (Bossle et al. ,
1979).
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XI. CONCLUSIONS AND RECOMMENDATIONS
Based on the available animal toxicity data, the HA for one-day, ten-day, and
longer-term exposures for a child is 30 mg/L. The Longer-term HA for the
adult is 100 mg/L and the Lifetime HA is 0.7 mg/L (700 Mg/L). These values
are considered protective against toxic effects for the most sensitive members
of the population. Currently, data are insufficient to assess the
carcinogenic risk for IMPA. Isopropyl methylphosphonic acid is classified in
Group D: Not classifiable as to human carcinogenicity.
A companion report, "Data Deficiencies/Problem Areas and Recommendations for
Additional Data Base Development for Isopropyl Methylphosphonic Acid"
(Appendix 1), summarizes the scope of existing data reviewed for this Health
Advisory. Recommendations are made for additional studies to assess the
lifetime toxicity, reproductive, teratological and carcinogenic risk, if any,
of isopropyl methylphosphonic acid.
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XII. REFERENCES
Alexander, M., A.M. Cook and C.G. Daughton (Cornell University). 1977.
Induction of microbial metabolism of organophosphorus compounds. Contractor
Report ARCSL-CR-78013. Aberdeen Proving Ground, MD: U.S. Army Armament
Research and Development Command, Chemical Systems Laboratory.
Beilstein Database. 1979. Data record for isopropyl methylphosphonic acid.
Scientific and Technical Information Network, Handbook of Organic Chemistry.
New York, NY. May 11, 1992.
Bossle, P.C., J.J. Martin, E.W. Sarver and H.Z. Sommer. 1983. High-
performance liquid chromatography analysis of alkyl methylphosphonic acids by
derivatization. J. Chromatogr. 267:209-212.
Cook, A.M., C.G. Daughton and M. Alexander. 1978. Phosphonate utilization by
bacteria. J. Bacteriol. 133(1):85-89.
Dacre, J.C. 1984. Recommended interim criteria for three environmental
polluting compounds of Rocky Mountain Arsenal. Technical Report 8302.
Frederick, MD: U.S. Army Medical Bioengineering Research and Development
Laboratory, Ft. Detrick. Available from NTIS, Alexandria, VA. Order No.
ADA 154826.
Daughton, C.G., A.M. Cook and M. Alexander. 1979a. Biodegradation of
phosphonate toxicants yields methane or ethane on cleavage of the C-P bond.
FEMS Microbiology Letters 5:91-93.
Daughton, C.G., A.M. Cook and M. Alexander. 1979b. Phosphate and soil
binding: Factors limiting bacterial degradation of ionic phosphorus-
containing pesticide metabolites. Appl. Environ. Microbiol. 37(3):605-609.
Fleisher, J.H., L.W. Harris, D.M. Murray and L.M. Braswell. 1964. Dealkyl-
ation as a mechanism for aging of rat-brain cholinesterase in vivo following
poisoning with GD or GB. Technical Report CRDLR 3243. Edgewood Arsenal, MD:
U.S. Army Edgewood Arsenal, Chemical Research and Development Laboratories.
Hart, E.R. 1980. Mammalian toxicology study of DIMP and DCPD. (Phase 2).
Kensington, MD: Litton Bionetics, Inc. Available from NTIS, Alexandria, VA.
Order No. AD-A058-323.
Hoskin, F.C.G. 1956. Some observations concerning the biochemical inertness
of methyl phosphonic and isopropyl methylphosphonic acids. Can. J. Biochem.
Physiol. 34:743-746.
Howells, D.J., J.L. Hambrook, D. Utley and J. Inoodage. 1973. Degradation of
phosphonates II: The influence of the 0-alkyl group on the breakdown of some
0-alkyl methylphosphonofluoridates in wheat plants. Pestic. Sci. 4:239-245.
Howells, D.J., J.L. Hambrook and E.A. Allenby. 1976. Uptake of some volatile
alkyl methylphosphonofluoridates from the vapor phase by wheat plants.
Pestic. Sci. 7:349-354.
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Ivie, G.W. 1980. Fate of diisopropyl methylphosphonate (DIMP) in a lactating
cow. Bull. Environ. Contam. Toxicol. 24:40-48.
Little, P.J., M.L. Reynolds, E.R. Bowman and B.R. Martin. 1986. Tissue
disposition of [3H]Sarin and its metabolites in mice. Toxicol. Appl.
Pharmacol. 83:412-419.
Little, P.J., J.A. Scimeca and B.R. Martin. 1988. Distribution of [3H]
diisopropylfluorophosphate, [3H]Soman, [3H]Sarin, and their metabolites in
mouse brain. Drug Metab. Dispos. 16(4):515-520.
Mecler, F.J. and J.C. Dacre. 1982. Toxicological assessment of isopropyl
methylphosphonic acid. The Toxicologist 2(1):35.
Mecler, F.J. 1981. Mammalian toxicological evaluation of DIMP and DCPD
(Phase 3-IMPA). Final Report. Litton Bionetics, Inc., Contract No. DAMD
17-77-C-7003. Frederick, MD: U.S. Army Medical Research and Development
Command, Ft. Detrick.
Mill, T. and C.W. Gould. 1979. Free-radical oxidation of organic phosphonic
acid salts in water using hydrogen peroxide, oxygen and ultraviolet light.
Environ. Sci. Technol. 13(2):205-208.
PMRMA. 1991a. Program Manager for Rocky Mountain Arsenal. Contract No.
DAAA 15-87-0095. Annual groundwater report for 1990. Final report.
Version 1.1. Commerce City, CO: U.S. Army Program Manager for Rocky Mountain
Arsenal.
PMRMA. 1991b. Program Manager for Rocky Mountain Arsenal. Comprehensive
monitoring program. Army complex disposal trenches reevaluation report (first
year), August 1991. Contract No. DAAA 15-88-D-0022. Commerce City, CO:
U.S. Army Program Manager for Rocky Mountain Arsenal.
Robson, S.G. 1981. Computer simulation of movement of DIMP-contaminated
groundwater near the Rocky Mountain Arsenal, Colorado. Permeability and
groundwater contaminant transport. ASTM Special Technical Publication
No. 746, pp. 209-220.
Rosenblatt, D.H., T.A. Miller, J.C. Dacre, I. Muul and D.R. Cogley. 1975a.
Problem definition studies on potential environmental pollutants I: Toxi-
cology and ecological hazards of 16 substances at Rocky Mountain Arsenal.
Technical Report 7508. Frederick, MD: U.S. Army Medical Bioengineering
Research and Development Laboratory, Fort Detrick. Available from NTIS,
Alexandria, VA. Order No. ADB039661L.
Rosenblatt, D.H., I. Muul, T.A. Miller, D.R. Cogley and J.C. Dacre. 1975b.
Problem definition studies on potential environmental pollutants II: Physical,
chemical, toxicological and biological properties of 16 substances. Technical
Report 7509. Frederick, MD: U.S. Army Medical Bioengineering Research and
Development Laboratory, Fort Detrick. Available from NTIS, Alexandria, VA.
Order No. ADA030428.
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Schiff, L.J., S.G. Pleva and E.W. Sarver. 1977. Analysis of phosphonic acids
by ion chromatography. Mulik, J.D. and E. Sawicki, eds. Ion chromatographic
analyses of environmental pollutants. Ann Arbor, MI: Ann Arbor Science
Publishers, Inc., pp. 329-344.
Tornes, J.A. and B.A. Johnson. 1989. Gas chromatographic determination of
methylphosphonic acids by methylation with trimethylphenylammonium hydroxide.
J. Chromatogr. 467:129-138.
U.S. EPA. 1986. U.S. Environmental Protection Agency. Guidelines for
carcinogen risk assessment. Fed. Reg. 51(185):33992-34003. September 24.
U.S. EPA. 1989. U.S. Environmental Protection Agency. Health advisory on
diisopropyl methylphosphonic acid (DIMP). Washington, DC: U.S. EPA, Office of
Water. Available from NTIS, Alexandria, VA. Order No. P1390273517.
Wils, E.R.J, and A.G. Hulst. 1988. Determination of organophosphorus acids
by thermospray liquid chromatography-mass spectrometry. J. Chromatogr.
454:261-272.
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APPENDIX I
Data Deficiencies/Problem Areas and Recommendations for
Additional Data Base Development for Isopropyl Methylphosphonic Acid

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r
INTRODUCTION
The U.S. Environmental Protection Agency, Office of Water (U.S. EPA/OW), in
conjunction with the Department of the Army (DA), has reviewed the available
data on isopropyl methylphosphonic acid (IMPA) for the purpose of developing a
Health Advisory (HA) for this compound. The Health Advisory is designed to
provide data that are useful in selecting options for dealing with the
contamination of drinking water. The Health Advisory includes "state-of-the-
art" information on environmental fate, health effects, analytical methodology
and treatment options associated with IMPA.
OBJECTIVES
The objective of this appendix is to provide an evaluation of the data
deficiencies and/or problem areas encountered in the review process for IMPA,
and to make recommendations for additional data base development. An indepen-
dent analysis of the current status of IMPA technology, as it relates to
IMPA's possible presence in drinking water, is presented. This appendix also
includes a summary of the background information used in the development of
the HA. For greater detail on the toxicology of IMPA, the Health Advisory on
IMPA should be consulted.
BACKGROUND
Isopropyl methylphosphonic acid is a strong acid which is formed during
degradation of the nerve gas, isopropyl methylphosphonofluoridate (Sarin).
Isopropyl methylphosphonic acid is soluble in water and is present in
groundwater in the vicinity of the site of Sarin production near Denver,
Colorado (Rosenblatt et al., 1975a). Isopropyl methylphosphonic acid is a
chemically stable molecule. In the chemical decomposition of IMPA, hydrolysis
of the ester bond produces methylphosphonic acid (MPA) and isopropyl alcohol.
The rate of abiotic IMPA hydrolysis is slow, resulting in environmental
persistence (Rosenblatt et al., 1975b). One strain of bacterium found in
sewage, Pseudomonas testosteroni. is able to aerobically degrade IMPA,
releasing methane, isopropyl alcohol, and phosphoric acid or phosphorous
(Alexander et al., 1977). Isopropyl methylphosphonic acid found in either
ground or surface waters is expected to have a relatively long half-life
(1,900 years).
Isopropyl methylphosphonic acid is nonvolatile due to the polarity of the
nonionized molecule and its ionic state under most pH conditions. Therefore,
IMPA is not found as an atmospheric contaminant even in situations where it
occurs free in the environment.
Most of the data on the pharmacokinetics of IMPA are the result of studies of
the tissue distribution of Sarin. Sarin appears to be rapidly degraded to
IMPA by a serum enzyme (Hoskin, 1956). Subsequent de-esterification of IMPA
to produce MPA is minimal. Thus, IMPA is the principal metabolite of Sarin.
Distribution studies of tritium-labeled Sarin indicate that IMPA concentrates
in the kidney, lungs, liver and brain (Little et al., 1986). A portion of the
IMPA in all tissues becomes bound to cellular proteins. The concentration of
the bound IMPA increases with time (Little et al., 1986). Isopropyl
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methylphosphonic acid appears to be excreted without metabolic alteration. In
studies of the pharmacokinetics of P32-labeled IMPA, Hoskin (1956) found that
IMPA was the only labeled material that could be identified in the urine.
Data on the toxicity of IMPA are limited. Oral exposure data are available
from LDj0 studies in the mouse and rat and from a subchronic study in the rat.
The dermal and ocular toxicity and the dermal sensitizing effects of IMPA have
also been tested. There are no studies of the reproductive, teratogenic or
carcinogenic properties of this compound. All of the available data have been
produced from studies in animals; there are no data available which apply to
human exposures.
The LD50 values for IMPA in male mice and rats are 5,620 mg/kg and
7,650 mg/kg, respectively (Mecler, 1981). The values for female mice and rats
are 6,550 mg/kg and 6,070 mg/kg, respectively. In each of these LD50 studies,
the compound was administered orally as a single dose (ranging from
3,160 mg/kg to 114,700 mg/kg). The animals were observed for a period of
14 days following dosing; during this period both the mice and rats
demonstrated reduced motor activity and ataxia even at the lowest doses.
Loose stools also were seen in all animals. Postmortem examinations of the
treated animals revealed reddening of the lungs in both the mice and rats.
In addition, there were dark spots on the thymus in the rats. Fluid was found
in the stomach and intestines of the treated animals.
A single dose of 20 mg/kg sodium isopropyl methylphosphonic acid, applied to
either the intact or abraded dermal tissue of New Zealand white rabbits,
caused erythema in all exposed animals (Mecler, 1981). Studies of the ability
of IMPA to act as a sensitizing agent in female guinea pigs were negative
(Mecler, 1981). In tests of ocular irritation, only one of five tested
rabbits exhibited a response to 100 mg of IMPA instilled into the eyes
(Mecler, 1981).
When IMPA was administered orally to Sprague-Dawley rats for a period of
90 days, a nonsignificant decrease in the body weights of the high-dose
animals was the only noted effect of exposure (Mecler, 1981). Doses of 0,
300, 1,000 or 3,000 ppm were administered in drinking water. Food and fluid
consumption, body weight, hematological and blood chemistry parameters were
measured as indices of toxicity. The observed decrease in the weights of the
high-dose animals was less than 10% for both sexes. Thus, based on magnitude
of change and significance criteria, the observed weight loss cannot be
regarded as an adverse effect.
The animals were sacrificed at the end of the study and the tissues were
examined histologically; key organ weights also were recorded. No tissue
abnormalities were noted and the organ:body weight ratios were not affected by
exposure to IMPA. The 3,000 ppm dose is, accordingly, a NOAEL. Based on body
weight data and fluid consumption records, this 3,000 ppm exposure is
equivalent to a dose of 399.1 mg/kg for the females and 278.5 mg/kg for the
males.
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There have been no animal studies that focus on determining the carcino-
genicity of IMPA. The mutagenic potential of this compound has been evaluated
through the Ames assay (Mecler, 1981). The results of exposing five strains
of S. tvphimurium to concentrations of 0.5 to 5,000 Mg/plate indicate that
IMPA is not mutagenic. Doses of 2,500 and 5,000 /zg/plate were toxic to some
of the S. tvphimurium strains.
Based on the existing data, the HA value for one-day, ten-day, or longer-term
exposures for the 10-kg child is 30 mg/L. The longer-term exposure HA value
for the 70-kg adult was 100 mg/L.
In the absence of a lifetime study, subchronic data were used to calculate a
lifetime HA in order to provide a conservative estimate of a no-effect-
human-exposure level. Additional safety factors were used in calculating the
lifetime HA value to accommodate the less-than-chronic exposure duration of
the subchronic study, the lack of reproductive and teratogenicity data for
IMPA, and the fact that there is only one study of multiple-dose exposures to
IMPA. The resultant HA value is 0.7 mg/L (700 /zg/L) .
There are several methods available for identifying and quantifying the
concentration of IMPA in solution (Bossle et al., 1983; Schiff et al., 1977;
Tornes and Johnson, 1989; Wils and Hulst, 1988). Each of the available
methods uses either ion exchange or reverse phase liquid chromatography as the
initial separation technique. Prior modification of IMPA with a chromophore
or a detectable ion pair can be used to simplify the identification of this
compound after separation. Both mass spectrometry and gas chromatography are
useful as identification techniques.
Although no studies on ion exchange as a treatment technique were identified
in the literature, this method has the potential to be useful for the removal
of IMPA from contaminated water based on the data provided in the analytical
studies by Schiff et al. (1977). Oxidation with either ozone or hydrogen
peroxide under ultraviolet light has been tested under laboratory conditions
as a treatment technique for IMPA-contaminated water (Mill and Gould, 1979;
Schiff et al., 1977). However, reaction conditions must be carefully
controlled to allow for the complete decomposition of the IMPA to phosphate,
carbon dioxide and acetic acid. Methyl phosphonic acid and acetone are
produced as intermediates in the oxidation process and will be present in the
treated water under conditions where oxidation is incomplete. The decompo-
sition of the MPA under laboratory conditions requires the maintenance of an
oxidative environment for several hours. It is the most stable intermediate
in the oxidation reaction.
DISCUSSION
The pharmacokinetic data from intravenous administration of Sarin provide
considerable information concerning the distribution and excretion of IMPA in
the body. A study of the tissue distribution of IMPA when exposure occurs
through the oral route, would demonstrate the effect of route on the
toxicokinetics of the compound. A more detailed evaluation of the types of
interactions that influence the protein binding properties of IMPA and
identification of target proteins would be useful in evaluating the potential
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for this compound to produce functional impairment of either cellular
transport or metabolism following long-term exposure. The occurrence of
tissue protein binding suggests that a long-term chronic study of 1MPA should
be done. Either the LD50 data or a repeated subchronic study using higher
doses than those in the existing study should be used for selecting the doses
for a chronic study. The selection of parameters to be monitored should be
based on data from the protein binding studies. For example, the protein
binding data might suggest that specific enzymes be evaluated in the toxicity
screening. The fact that IMPA bonds to the brain tissue and the impact of
this compound on motor activity in the LD5Q studies suggest that neurological
toxicity end points should be evaluated in a chronic study.
The protein binding characteristics of IMPA also suggest that this compound
might have an impact on reproductive processes. At minimum, a two-generation
oral exposure study that includes teratogenic end points should be conducted.
CONCLUSIONS/RECOMMENDATIONS
Based on the preceding discussion, the following conclusions/recommendations
can be made:
	The HA values that have been calculated are conservative estimates
for humans. No studies or effects in humans were found in the
available literature; the data are limited to acute and subchronic
exposure studies in animals. Uncertainty factors were used in the
calculations because there are no studies of sufficient duration that
identify specific health effects resulting from exposures to IMPA and
there are no data on the effects of this compound on the reproductive
processes.
	The protein binding properties of IMPA should be studied to delineate
the mechanism of protein binding and target proteins. Information on
target proteins should be used to select the end points that will be
monitored during classical exposure studies.
	A chronic study of oral exposures to IMPA should be conducted and
should include tumorigenic end points in the evaluation criteria.
Neurological and enzymatic end points also should be considered for
monitoring in addition to the routine indices of chronic toxicity.
A battery of genotoxicity tests should be conducted prior to a cancer
assay.
	A two-generation reproductive study that incorporates teratogenicity
end points is recommended to evaluate the impact of IMPA on
reproductive performance.
No other studies of adverse health effects from exposure to IMPA, relative to
potable water, are recommended at this time.
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REFERENCES
Alexander, M., A.M. Cook and C.C. Daughton (Cornell University). 1977.
Induction of microbial metabolism of organophosphorus compounds. Report No.
ARCSL-CR-78013. Aberdeen Proving Ground, MD: U.S. Army Armament Research and
Development Command, Chemical Systems Laboratory.
Bossle, P.C., J.J. Martin, E.W. Sarver and H.Z. Sommer. 1983. High-
performance liquid chromatography analysis of alkyl methylphosphonic acids by
derivatization. J. Chromatogr. 267:209-212.
Hoskin, F.C.C. 1956. Some observations concerning the biochemical inertness
of methyl phosphonic and isopropyl methylphosphonic acids. Can. J. Biochem.
Physiol. 34:743-746.
Little, P.J., M.L. Reynolds, E.R. Bowman and B.R. Martin. 1986. Tissue
disposition of [3H]diisopropylfluorophosphate, [3H]Soman, [3H]Sarin and their
metabolites in mouse brain. Drug Metab. Dispos. 16(4):515-520.
Mecler, F.J. 1981. Mammalian toxicological evaluation of DIMP and DCPD
(Phase 3-IMPA). Final Report. Litton Bionetics, Inc., Contract No. DAMD
17-77-C-7003. Frederick, MD: U.S. Army Medical Research and Development
Command, Ft. Detrick.
Mill, T. and C.W. Gould. 1979. Free-radical oxidation of organic phosphonic
acid salts in water using hydrogen peroxide, oxygen and ultraviolet light.
Environ. Sci. Technol. 13(2):205-208.
Rosenblatt, D.H., T.A. Miller, J.C. Dacre, I. Muul and D.R. Cogley. 1975a.
Problem definition studies on potential environmental pollutants I:
Toxicology and ecological hazards of 16 substances at Rocky Mountain Arsenal.
Technical Report 7508. Frederick, MD: U. S. Army Medical Bioengineering
Research and Development Laboratory, Fort Detrick. Available from NTIS,
Alexandria, VA. Order No. ADB039661L.
Schiff, L.J., S.C. Pleva and E.W. Sarver. 1977. Analysis of phosphonic acids
by ion chromatography. Mulik, J.D. and E. Sawicki, eds. Ion chromatographic
analyses of environmental pollutants. Ann Arbor, MI: Ann Arbor Science
Publishers, Inc., pp. 329-344.
Tornes, J.A. and B.A. Johnson. 1989. Gas chromatographic determination of
methylphosphonic acids by methylation with trimethylphenylammonium hydroxide.
J. Chromatogr. 467:129-138.
Wils, E.R.J, and A.C. Hulst. 1988. Determination of organophosphorus acids
by thermospray liquid chromatography-mass spectrometry. J. Chromatogr.
454:261-272.
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