Animal bioassays remedy some of the weaknesses of epidemiological studies by allowing for greater control over the experiment and are deemed to be reliable measurement of toxic effects, although they require "high dose in animals-to low dose in humans" extrapolation. The selection of design parameters of animal bioassays is critically important in observing or missing an actual hazard. These parameters include: animal species selected for the experiment (rat, mouse); strain of the test species; age/sex of the test species; magnitude of exposure concentrations/doses applied or administered; number of dose levels studied; duration of exposure; controls selected; and route of exposure. Animal studies are characterized as acute (a single dose or exposures of short duration), chronic (exposures for full lifetimes of test species – about two years in rats/mice) and sub-chronic (usually 90 days) based on the exposure duration. In the hazard identification step, the following measures of toxicity are commonly compiled:
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LD
50
/LC
50
/EC
50 : The dose or concentration in a toxicity study at which causing 50 percent mortality in test species was observed. The EC
50 is the effective concentration causing adverse effects or impairment in 50% of the test species.
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NOAEL (No Observable Adverse Effect Level): The highest dose or concentration in a toxicity study at which no adverse effect was observed.
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LOAEL (Lowest Observable Adverse Effect Level): The lowest dose or concentration in a toxicity study at which an adverse effect was observed.
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MTD (Maximum Tolerated Dose): The largest dose a test animal can receive for most of its lifetime without demonstrating adverse health effects other than carcinogenicity.
Risk scientists rely on a number of reputable sources to gather, compile, and analyze hazard identification information to be able to perform weight of evidence analysis and to conclude whether a chemical may cause a health effect in humans. Some of these sources are:
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Hazardous Substances Data Bank (HSDB) maintained by the National Library of Medicine: This scientifically peer-reviewed data bank provides human and animal toxicity data for about 5,000 chemicals and can be accessed via
(External Link)
- ChemicIDplus Advanced database maintained by the National Library of Medicine: This database allows users to search the NLM ChemIDplus database of over 370,000 chemicals. Compound identifiers such as Chemical Name, CAS Registry Number, Molecular Formula, Classification Code, Locator Code, and Structure or Substructure can be entered to display toxicity data via
(External Link)
- National Toxicology Program (NTP) of the Department of Health and Human Services:
- Report of Carcinogens (RoC): The RoC is an informational scientific and public health document that identifies and discusses agents, substances, mixtures, or exposure circumstances that may pose a hazard to human health by virtue of their carcinogenicity. The RoC is published biennially and serves as a meaningful and useful compilation of data on: a) the carcinogenicity (ability to cause cancer), genotoxicity (ability to damage genes), and biologic mechanisms (modes of action in the body) of the listed substance in humans and/or animals; b) the potential for human exposure to these substances; and c) Federal regulations to limit exposures. The link to the most recent version of the RoC can be accessed via
(External Link)
- NTP Toxicity Testing Study Results and Research Areas: NTP tests chemicals for their toxicity in human and animal systems. The results of these toxicity testing studies along with current research areas can be obtained at:
(External Link)
- National Institute of Occupational and Safety Health (NIOSH) Hazard Identification Databases: The following NIOSH website houses a multitude of databases and information for chemicals and their hazards under a single umbrella, including NIOSH's "Pocket Guide to Chemical Hazards":
(External Link)
- Agency for Toxic Substances and Disease Registry (ATSDR) Toxicological Profiles and Public Health Statements: ATSDR produces "
toxicological profiles " for hazardous substances found at National Priorities List (NPL) Superfund sites. About 300 toxicological profiles have so far been published or are under development. The chemical-specific toxicological profiles can be accessed via
(External Link)
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World Health Organization (WHO) International Programme of Chemical Safety (IPCS): ICPS publishes "Environmental Health Criteria" (EHC) for chemical substances, which provide critical reviews on the effects of chemicals or combinations of chemicals and physical and biological agents on human health and the environment. The IPCS site can be accessed via
(External Link)
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Material Safety Data Sheets (MSDS): MSDS are invaluable resource to obtain compositional data for products and mixtures.
