Hazard index

{
  "id": "MLC-T-ENV-012890",
  "term": "Hazard index",
  "field": "Environment",
  "term_source": "Hazard Index",
  "definition": "1. The sum of more than one hazard quotient for multiple substances and/or multiple exposure pathways. The HI is calculated separately for chronic, subchronic, and shorter-duration exposures.\n\n2. The sum of more than one hazard quotient for multiple substances and/or multiple exposure pathways. The HI is calculated separately for chronic, subchronic, and shorter-term duration exposures.\n\n3. Potential noncarcinogenic (systemic) effects are characterized by comparing projected intakes of chemicals to toxicity values (i.e, reference doses). The numerical risk or hazard quotient estimate that results is a ratio. The ratio of the intake over the reference dose (hazard index) is compared to unity (1.0). If the quotient is less than 1, then the systemic effects are assumed not to be of concern; if the hazard quotient is greater than 1, then the systemic effects are assumed to be of concern. The hazard index is the sum of hazard quotients.\n\n4. The sum of hazard quotients for toxics that affect the same target organ or organ system. Because different air toxics can cause similar adverse health effects, combining hazard quotients from different toxics is often appropriate. A hazard index (HI) of 1 or lower means air toxics are unlikely to cause adverse noncancer health effects over a lifetime of exposure. However, an HI greater than 1 doesn't necessarily mean adverse effects are likely. Instead, EPA evaluates this on a case-by-case basis. Read more about hazard indexes in Section 6 of the AirToxScreen Technical Support Document.\n\n5. Sum of hazard quotients for substances that affect the same target organ or organ system. Because different pollutants (air toxics) can cause similar adverse health effects, combining hazard quotients associated with different substances is often appropriate. EPA has drafted revisions to the national guidelines on mixtures that support combining the effects of different substances in specific and limited ways. Ideally, hazard quotients should be combined for pollutants that cause adverse effects by the same toxic mechanism. Because detailed information on toxic mechanisms is not available for most of the substances in NATA, however, EPA aggregates the effects when they affect the same target organ regardless of the mechanism. The hazard index (HI) is only an approximation of the aggregate effect on the target organ (e.g., the lungs) because some of the substances might cause irritation by different (i.e., non-additive) mechanisms. As with the hazard quotient, aggregate exposures below an HI of 1.0 derived using target organ specific hazard quotients likely will not result in adverse non-cancer health effects over a lifetime of exposure and would ordinarily be considered acceptable. An HI equal to or greater than 1.0, however, does not necessarily suggest a likelihood of adverse effects. Because of the inherent conservatism of the reference concentration (RfC) methodology, the acceptability of exceedances must be evaluated on a case-by-case basis, considering such factors as the confidence level of the assessment, the size of the uncertainty factors used, the slope of the dose-response curve, the magnitude of the exceedance, and the number or types of people exposed at various levels above the RfC. Furthermore, the HI cannot be translated to a probability that adverse effects will occur, and it is not likely to be proportional to risk.\n\n6. The sum of hazard quotients for toxics that affect the same target organ or organ system. Because different air toxics can cause similar adverse health effects, combining hazard quotients from different toxics is often appropriate. A hazard index (HI) of 1 or lower means air toxics are unlikely to cause adverse noncancer health effects over a lifetime of exposure. However, an HI greater than 1 doesn't necessarily mean adverse effects are likely. Instead, EPA evaluates this on a case-by-case basis.",
  "abbreviation": "HI",
  "subject": "Outcomes",
  "references": [
    "Waste and Cleanup Risk Assessment Glossary",
    "EPA 2004; Thesaurus of Terms Used in Microbial Risk Assessment",
    "RAIS 2004; Thesaurus of Terms Used in Microbial Risk Assessment",
    "AirToxScreen Glossary of Terms",
    "National Air Toxics Assessment (NATA) Glossary"
  ],
  "url": "https://mlchart.com/terminology/environment/hazard-index/"
}