Research Highlights

Provisional Advisory Levels (PALs) for Hazardous Agents

Provisional Advisory Levels support risk-based decision making

There is concern that hazardous substances released during a terrorist attack will contaminate people and the environment, but there are few health-based guidelines for temporary building or outdoor site re-entry or for resumed use of water resources, as might be needed after a large-scale disaster. To address these exposure knowledge gaps, EPA is,researching health-based provisional advisory levels (PALs) for high priority hazardous chemicals and chemical warfare agents in air and drinking water.

PALs are a tiered set of exposure values used to inform risk-based decision making during a response to environmental contamination involving hazardous chemicals. They are advisory levels for exposure to chemicals by the general public (including susceptible and sensitive sub-populations) and are developed for the following exposures to contaminated air and water:

Acute (24 hours)
Short-term (longer than one to 30 days)
Long-term (longer than 30 days to two years)

PAL Development Process

Figure: Characteritics of PAL severity levels.

The three health effect levels for defined exposure durations are PAL 1 (mild, transient, reversible effect), PAL 2 (serious, possibly irreversible effect), and PAL 3 (severe effect or lethality). The process for developing a PAL consists of the following steps:

Identify chemicals of interest and evaluate their environmental fate and persistence
- Conduct a comprehensive literature search of published and unpublished toxicity data
- Assess toxicokinetic data to identify target organs/systems and toxicodynamic information
Identify key studies (including supporting studies) along with their critical effects and point of departure values
Calculate air and water concentrations that correspond to adult and child target effect levels
Identify key uncertainties associated with toxicity information in order to apply appropriate uncertainty and modifying factors

The following are selected chemicals for which PALs have been determined:

Acrolein	Dimethyl phosphite	Methyl isocyanate
Acrylonitrile	Fluoroacetate salts	Methyl paraoxon
Aldicarb	Hydrazine	Methyl parathion
Ammonia	Hydrogen bromide	Mevinphos
Arsine	Hydrogen chloride	Oxamyl
Boron trifluoride	Hydrogen selenide	Phencyclidine
Carbonyl difluoride	Hydrogen sulfide	Phosgene
Chlorfenvinphos	Isopropyl methylphosphonic acid	Phosgene oxime
Chloropicrin	Methylphosphonic acid	Red phosphorus
Chlorpyrifos	Lewisite	Tetrafluoroethylene
Cyanide	Malathion	Titanium tetrachloride
Diborane	Dimethyl phosphite	Trimethyl phosphite
Dicrotophos	Methomyl

PALs Scientific Workgroup

EPA has established a scientific workgroup to provide a comprehensive review of data for the derivation of the PAL values and the rationale for their derivation. The workgroup, which includes scientists in academia, federal and state agencies, industry, and the private sector, meets quarterly to evaluate and approve developed PALs.

Availability of PALs