TAB G – Determining and Modeling Nerve and Mustard Agents’ General Population Limit and First Noticeable Effect Levels

The effect of a chemical warfare agent on a person depends on his or her cumulative dose—how much agent the body takes in or absorbs. Dose usually is expressed as milligrams of agent per kilogram (mg/kg) of body weight[105] but dose tends to be a scientific tool used in laboratory studies and is practically impossible to measure in the field.

Dosage, on the other hand, is possible to calculate in the field. Dosage is the cumulative exposure—the concentration of chemical warfare agent to which a person is exposed integrated over the time of exposure.[106] This translates as milligrams of agent per cubic meter of air (concentration) multiplied by the time of exposure. The units of dosage are milligram-minutes per cubic meter (mg-min/m3).

A. Militarily Significant Dosages

The military utilizes several dosages as a basis for comparing the effectiveness of chemical warfare agents. These dosages assume a 70-kilogram [154 pound] person engaging in very light activity with a breathing rate of 15 liters per minute. Three dosages of interest are:

Table G-1 shows the LCt50, ICt50 and FNE for sarin, cyclosarin, and mustard agent that were accepted standards during the Gulf War, as well as the latest guidelines. As the table shows, the amount of agent believed to cause lethal, incapacitating, or first noticeable effects is smaller than during the Gulf War (i.e., the agents are now considered more toxic). While the military has not yet officially approved reduced dosages, they have been published in numerous technical reports.

Table G-1. Various military significant dosages for mustard and nerve agents

 

Gulf War[109]

Current Estimates[110]

Sarin

Cyclo-sarin

Mustard

Sarin

Cyclosarin

Mustard

LCt50 100 mg-min/m3 (resting)
70 mg-min/m3 (mildly active)

None

1500 mg-min/m3

35 mg-min/m3 [111]

35 mg-min/m3 [112]

900 mg-min/m3 [113]

ICt50 75 mg-min/m3 (resting)
35 mg-min/m3 (mildly active)

None

150 mg-min/m3

None

None

None

FNE 1 mg-min/m3 (threshold-miosis)

None

100-200 mg-min/m3 (ECt50 – eye effects)*

1 mg-min/m3 [114]

0.50 mg-min/m3[115]

3.8 mg-min/m3 [116]

* ECt50 is an effective dosage.[117] For example, the FNE dosage for mustard agent is expressed as an ECt50, the dosage necessary to cause 50% of exposed, unprotected personnel to experience some type of eye effects.

As previously stated the FNE dosage represents the level at which exposed people could be expected to demonstrate noticeable effects of exposure. For nerve agent, this effect is miosis (constriction of the pupil of the eye). For sarin, miosis probably occurs between 0.5 and 2.0 mg-min/m3. The US Army Center for Health Promotion and Preventive Medicine (USACHPPM) has recommended our models use a value of 1.0 mg-min/m3 as sarin’s FNE dosage and 0.50 mg-min/m3as cyclosarin FNE dosage.[118] The mustard agent FNE currently is under review. Based on discussions with USACHPPM, we selected 3.8 mg-min/m3 as the mustard FNE dosage for our models.[119] Table G-1 reflects these values.

B. General Population Limit

Chemical warfare agents’ lethality, incapacitation, and threshold effects are immediate concerns in military operations. However, the long-term effects associated with exposure to nerve and mustard agent at concentrations below those needed to cause observable effects also are concerns. To gauge long-term, low-level effects, investigators focused on the general population limit (GPL) of nerve and mustard agents.

The GPL represents the limit below which any member of the general population could be exposed (e.g., inhale) seven days a week, every week, for a lifetime, without experiencing any adverse health effects. Scientists performed exposure testing and computed the GPL from the results of that testing as modified by uncertainty factors such as short-term to long-term exposure, average human to sensitive human population, etc.[120] According to USACHPPM, the GPL value is a 24-hour average established for the general population, including sensitive sub-populations, for lifetime exposure.[121]

Since exposures during the Gulf War from any possible chemical warfare agent release at Muhammadiyat would be one-time and short-term (i.e., individuals would be exposed for hours rather than a lifetime) we accepted the United States Army Center for Health Promotion and Preventive Medicine suggestion and removed the short-term to long term adjustment factor from the GPL calculation to better reflect the realities of any possible Gulf War exposure.[122] This change was done for sarin, cyclosarin, and mustard agent.

C. Summary

Since we are concerned about US forces’ low-level exposure, our modeling uses GPL dosages and the hazard areas our models produce reflect GPL limits. Figure G-1 graphically compares the various sarin dosages discussed above. We can similarly compare mustard agent and cyclosarin. Our analysis focuses on extremely small dosages—significantly less than those causing battlefield casualties or noticeable effects.

figG-1s.gif (3265 bytes)

Figure G-1. Comparison of Gulf-War standards of dosages for sarin

Table G-2 summarizes the FNE and GPL dosages we used to model the Muhammadiyat release. GPL dosages are obtained by multiplying concentration by length of exposure in minutes.

Table G-2. FNE and GPL dosages used to model the possible release at Muhammadiyat[123]

 

FNE

GPL

Agent

Time Period

Dosage

Time Period

Dosage

Sarin

10 minutes

1 mg-min/m3

24 hours

0.0432mg-min/m3

Cyclosarin

10 minutes

0.5 mg-min/m3

24 hours

0.0144mg-min/m3

Mustard

8 hours

3.8 mg-min/m3

24 hours

0.288mg-min/m3

The cited references specifically detail how we derived the numbers in Table 4. Briefly, based on USACHPPM’s recommendation, we chose 10 minutes, a duration USACHPPM believes is consistent with toxicological data contained in various studies, for determining nerve agents’ FNE dosage. Selecting a duration for mustard’s FNE dosage was more difficult because the issue is under review. We decided on 8 hours for mustard agent because, based on the latest Federal Register data, 8 hours would yield the biggest hazard area.


| First Page | Prev Page | Next Page |