Toolkit for Exposure Assessment: Beginners Start Here

How Does the Chemical Behave?

There are several important information elements that should be considered when determining exposure potential for a chemical product. These elements are listed below, with short explanations as to why they are relevant. It should be noted that a computer tool that includes a checklist approach to these elements (and other information) and generates a Word document report from the responses is included in the "Examples of Qualitative Exposure Assessment" section of the website.

  • Production volume(either by facility, by company, by country or globally): Although not a direct indication of exposure, a larger production volume value could indicate a potential for greater exposure, than would a small production volume value.
  • Physical form of chemical: Physical form is relevant because it impacts whether exposure is possible. For example, particle size will impact the ability of a chemical to pass through the skin or through nasal passages. So solids with large particle sizes would be expected to have less exposure potential than powders. Liquids and gases would be expected to have larger exposure potential.
  • Use pattern: Materials used directly on site under closed systems (non-isolated intermediate) have less exposure potential than materials that have widespread dispersive uses.
  • Function and application: Knowing what type of application the chemical is used in and what the function of the chemical within that application can provide insight as to potential exposure.
  • Natural sources: If there are natural sources of the chemical, that should be considered as part of the exposure characterization.
  • Potential exposure sources: Identify where exposure may occur in the workplace, through environmental releases or through consumer uses.
  • Certain physical and chemical characteristics will impact exposure potential, such as
    • a molecular weight of greater than 1,000. High molecular weight chemicals cannot cross the skin barrier and will result in negligible exposure via contact to the skin.
    • a permanent positive charge. A positively charged material has a reduced ability to cross the skin barrier and will result in negligible exposure via contact to the skin.
    • a log of octanol/water partition coefficient >5. Movement of substances with octanol/water partition coeffienct log of >5 across the dermal and gastric membranes is greatly reduced. Thus, contact via dermal or oral routes would result in negligible exposure.
    • a log of octanol/water partition coefficient <-1. Movement of substances with octanol/water partition coeffienct log of <-1 across the dermal and gastric membranes is greatly reduced. Thus, contact via dermal or oral routes would result in negligible exposure.
    • has a particle or aerosol size of >10 microns. Particles larger than 10 microns are too big to get into the lungs, thereby resulting in negligible exposure via inhalation route.
    • has a particle or aerosol size of >100 microns. Particles larger than 100 microns are too big to get through the nasal passages, thereby resulting in negligible exposure via inhalation route.
    • has a vapor pressure of <5000 Pa. A chemical with a low vapor pressure (<5000 PA) would have a low concentration in air and thus exposure to the chemical as a gas is negligible.
  • Workplace processes: The process type used (open or closed, heated or ambient, batch or continuous, spray or non-spray) will impact the exposure potential.
  • Sampling information: When and how sampling takes place can impact exposure potential for workers.
  • Material transfer: The system used to transfer material, and the packaging containers used will impact exposure potential. In general, larger containers can have a larger exposure potential for workers than smaller.
  • Number of sites and number of workers: Although not a direct correlation, the number of downstream sites using the chemical and the number of workers involved with the chemical within the sites could impact exposure potential.
  • Ventilation design: Certain ventilation designs can reduce exposure potential for workers.
  • Personal protective equipment (PPE): Use of PPE should be considered when discussing exposure potential.
  • Exposure limits: If the workplace adheres to regulatory or guideline exposure limits for the chemical, that should be addressed when considering exposure potential.
  • Vapor pressure: vapor pressure may be a good indication of volatility in air. Based on values from the National Technical Information Service (NTIS), a chemical with a vapor pressure of less than 1 mm HG would be expected to have low volatility in the air and a vapor pressure of greater than 100 mm HG would indicate a high volatility (Review of Exposure Assessment Guidelines, September 1996). A low volatility means that although the chemical would be found in the air for at least some length of time, it would be expected to partition primarily to other environmental compartments (e.g. soils and water).
  • Henry's Law constant: Henry's Law Constant (HLC) may be a good indicator as to whether a chemical is expected to evaporate from water. A lower HLC value would suggest that the substance will volatilize slowly and would more likely to have a greater partitioning into water. A greater HLC value suggests that it will evaporate from water at a significant rate. Based on information from NTIS ((Review of Exposure Assessment Guidelines, September 1996), typical ranges of HLCs are as follows:

    • H < 3 x 10-7 atm-m3/mole = essentially nonvolatile
    H - 10-7 to 10-5 atm-m3/mole = slow volatilization
    H > 10-5 to 10-3 atm-m3/mole = significant volatilization
    H > 10-3 atm-m3/mole = rapid volatilization

  • Log Koc: Log Koc can provide insight as to whether a material will cling to soils or sediments in water and whether they will desorb or be tightly bound. Based on information from NTIS ((Review of Exposure Assessment Guidelines, September 1996), approximate indications of relative soil absorption potential are as follows:

    • Low potential: Koc = 1 to 100, log Koc = 0 - 2
    Moderate potential: Koc = 100 to 10,000, log Koc = 2 - 4
    High potential: Koc = 10,000 to 10,000,000, log 4 - 7
    A high potential would indicate that a material would bind tightly to soils and sediments and thus, reduce overall exposure potential.

  • Incorporated into a matrix: Materials incorporated and bound into a matrix are generally less available for exposure
  • Half-life in air and half-life in water: Generally, a compound with a half-life in air < 2 days is considered to be degraded too quickly to undergo long range transport. Generally, a compound with a half-life in water < 2 months is considered to be degraded too quickly to undergo long range transport.

 

"...The starting point for understanding the exposure and subsequent risk associated with a chemical entity and its use is to understand both the innate characteristics of the entity (physical state, vapor pressure, boiling point, flash point, etc.) and its life cycle (how it is made, transported, used, and disposed of)..." (from "Hazard and Risk Assessment" chapter authored by Gad, S. C. Pages 577-638 in Product Safety Evaluation Handbook, second edition, edited by S. C. Gad. Marcel Dekker, Inc. (1999).

Key Resources:

  • The supplier(s) of a chemical.
  • Trade associations associated with a particular class of chemicals, e.g., the Soap & Detergent Association for surfactants.
  • Web sites containing chemical physical and chemical property information, e.g.:
    • ChemFinder at: http://www.chemfinder.com A Web-based search engine. Searching a chemical's name or CAS # provides links to and information from numerous Web sites. Includes physical properties.
    • Environmental Chemicals Data and Information Network (ECDIN) at: http://ecdin.etomep.net Searching a chemical's name or CAS # provides a document that includes information on physical-chemical properties.
    • (U.S.) National Library of Medicine's Hazardous Substances Data Bank (HSDB) at: http://toxnet.nlm.nih.gov/ Pick "HSDB" and then search for chemical of interest
  • Publications (books summarizing chemical and physical properties, and journal articles).
  • Software programs that can estimate chemical properties.

Identify key routes of exposure
If more than a qualitative screening level assessment is needed, exposure assessors can begin by identifying the key routes of exposure and the key receptors of that exposure. Key routes/receptors of exposure include:

  • Occupational , Community and Ecological exposures at industrial facilities where HPV chemicals are either manufactured, handled, or processed;
  • Product-related exposures where an HPV chemical is an ingredient. Consistent with the U. S. EPA's PMN framework, this includes sub-sets of industrial (e.g., a degreaser for cleaning machine tool parts.), commercial/institutional (e.g., janitorial products), or consumer (e.g., household products) applications;
  • Other exposures, such as when HPV chemicals are released to the environment from industrial facilities or product disposal in ways that may reach humans (e.g., via drinking water or food), or natural sources of a chemical.

Once the key routes and receptors of exposure are identified, the assessor can proceed in exposure evaluation framework to Assessing the magnitude of exposure. Use the Toolkit.

 

 
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