Workplace Chemical Monitoring - Occupational Health and Workplace Monitoring at Chemical Agent Disposal Facilities - page 13

ordinary facility activities, such as painting and weld-
ing, could be hazardous to workers. For instance, dur-
ing construction of the plant at Umatilla, there was an
incident in which a number of employees were treated
for respiratory distress and sent to the emergency de-
partment. The chemical substance(s) responsible could
not be identified, but this incident illustrates the poten-
tial for exposures to hazardous chemicals other than
agent.

Figure 2-3 shows the simplified hydrolysis of VX.
The two pathways correspond to initial hydrolysis of
(1) the P-SR bond, which produces 2-diisopropyl ethyl
mercaptoamine (DESH) and ethyl methylphosphonic
acid (EMPA), and (2) the P-OR bond, which produces
EA-2192 and ethanol. The upper path is favored at
pH > 10. EA-2192 hydrolyzes more slowly than VX and
is still very toxic (Munro et al., 1999). Further hydrolysis
of EA-2192 produces DESH and methylphosphonic
acid (MPA). The Army is currently working on ana-
lytical methods of quantifying low levels of VX in hy-
drolysate, but at this point an efficient, sensitive, rapid
method has not been developed and demonstrated
(NRC, 2000a). The Stockpile Committee has previ-
ously recommended that the Army increase its efforts
to develop innovative analytical techniques with suffi-
cient specificity, sensitivity, and speed for analyzing
VX and mustard hydrolysate matrices for process
monitoring under operational conditions (NRC,
2000a).
Figure 2-4 shows the major hydrolysis pathways for
mustard, which are complicated by the reversible reac-
tions of sulfonium ion and hemimustard with
thiodiglycol to produce sulfur mustard thiodiglycol
aggregate and hemimustard thiodiglycol aggregate. A
further complication is the related formation of poly-
meric sludge. The low solubility of mustard in water
and related high-molecular-weight compounds means
that hydrolysis may be mass-transfer limited and, there-
fore, may require effective mixing to proceed to
completion.
Currently, no monitoring program has been devel-
oped for agent degradation products. The assumption
has been that breakdown products from decontamina-
tion or other activities are either less toxic or less per-
sistent, or both. However, a recent evaluation prepared
by the Army's Center for Health Promotion and
Preventive Medicine and Oak Ridge National Labora-
tory has noted that a primary VX hydrolysis product,
EA-2192, is more stable in water and is nearly as toxic
as VX (Munro et al., 1999). Although EA-2192 may
primarily be a concern for operations at Newport
(where bulk VX will be destroyed by hydrolysis), it
may also be present at other facilities if it survives nor-
mal VX decontamination operations.
Sulfur mustard is a known human carcinogen, and
some of its degradation products may also be carcino-
genic (IOM, 1993). Sulfur mustard acts as a vesicant or
blister agent and shows acute systemic toxicity in addi-
tion to its effects on skin, eyes, and the respiratory tract.

AGENT BREAKDOWN PRODUCTS AND
CONTAMINANTS IN LIQUIDS

In addition to monitoring for mustard and VX that
may remain in the hydrolysates produced at Aberdeen
and Newport, respectively, monitoring must also mea-
sure the more toxic agent breakdown compounds that
remain after hydrolysis. Because hydrolysis by aque-
ous caustic or hypochlorite solution is the method used
for agent decontamination throughout the CSDP, all
sites should consider this possible exposure source.
Physical properties of the three most important agents
and their major hydrolysis products (listed below each
agent) are shown in Table 2-3, along with CAS (Chemi-
cal Abstracts Service) registry numbers, chemical for-
mulas, and molecular weights. As the table shows, the
hydrolysis products have lower molecular weights,
lower vapor pressures, and generally higher water solu-
bilities than the agent being hydrolyzed. The decreas-
ing lipophilicity (preference for oil over water) can be
seen in the more negative values of log K ow (where K ow
is the equilibrium constant for partitioning a species
between octanol and water) of the hydrolysis products.
A brief review of the chemistry of agent hydrolysis
is presented below based on information and figures
from The Sources, Fate, and Toxicity of Chemical
Warfare Agent Degradation Products (Munro et al.,
1999). Figure 2-1 shows a simplified scheme for the
hydrolysis of GB. The P-F bond is hydrolyzed more
rapidly than the P-OR bond; the P-C bond is much more
resistant to hydrolysis. The scheme is oversimplified
because most nerve agents are typically only 90 to
95 percent pure; they contain stabilizers, impurities
from manufacturing, and other compounds that have
formed during storage. For example, because GB is
sensitive to both hydrolysis and acid-catalyzed decom-
position, N-N

-diisopropyl carbodiimide and tributyl
amine have been added as stabilizers. The carbodiimide
reacts with water even more rapidly than GB, yielding
a urea, as shown in Figure 2-2.

′