Health criteria values (HCVs) are guidance levels set by expert groups. Combined with estimates of exposure, they can be used by assessors to determine the risk to human health, and to consider whether further investigation, assessment, and/or remediation is required. They are typically established by reviewing the evidence from occupational and epidemiological studies, laboratory animal studies, and also, where available, from an understanding of the chemical’s ADME and mechanism/mode-of-action.
HCVs may be expressed in different ways, depending on the organisation recommending them and their purpose. They cover different routes (notably oral and inhalation), durations (e.g. acute, lifetime), effects (e.g. systemic and local, cancer and non-cancer) and populations (e.g. workers, the general population and consumers). Oral values may represent a regular (generally daily) ingested dose of a substance that is anticipated to be acceptable or tolerable. Examples include the ADI (Acceptable Daily Intake), TDI (Tolerable Daily Intake) and RfD (Reference Dose). Inhalation values may represent an atmospheric concentration that is expected to be without appreciable risk to humans over a lifetime (24 hours/day for 70 years) or a “working lifetime” (8 hours/day, 5 days/week, for 40 years). Examples include the RfC (Reference Concentration), AQG (air quality guideline), DNEL/DMELs (Derived No/Minimal Effect Levels) and OELs (Occupational Exposure Levels).
Existing HCV Identification
Our in-house toxicological database, TRACE, is ideal for the speedy identification of existing HCVs derived by Expert Groups or industry, and provides a more reliable and efficient method of data searching and retrieval than some of the freely available databases (such as PubMed and those available via TOXNET). Our scientists have extensive experience of assessing and recording HCVs from a range of sources, comparing the values, and discussing the approach taken in their derivation. We are also frequently asked to identify and justify the most appropriate value for use in specific risk assessment scenarios (i.e. for a particular consumer use). Indeed, we often compare the critical HCVs to the (reasonable) worse-case exposure estimates as part of a risk assessment enabling us to discuss the safety-in-use of particular chemicals.
Our toxicologists are adept at analysing existing Expert Group reports and/or the primary literature in order to provide an external judgement on the following areas:
- identification of critical studies and points of departure (e.g. critical NOAELs, LOAECs)
- evaluation of the quality of the available toxicological dataset (e.g. Klimisch scoring)
- assessment of variability and vulnerability (e.g. elderly) within the population under consideration
- appropriate application of suitable safety/uncertainty/assessment factors
- objective analysis of the suitability of the HCVs (novel or existing) and their likely regulatory acceptability
Novel HCV Derivation
Where no appropriate HCV is identified, it is sometimes necessary to modify existing HCVs or to derive novel values from the available toxicological dataset. This latter option may involve applying, for example, ECHA guidance on DNEL calculation to propose new values from laboratory animal studies and, occasionally, studies in humans. In recent years, we have been commissioned to research and propose HCVs on behalf of Expert Groups, including the OECD, Health Canada and the UK Environment Agency. We have also proposed revised and novel HCVs for a large number of chemicals for companies from various industrial sectors (including REACH, electronic cigarettes, medical devices, E&L, consumer products).
Our team has an unrivalled level of expertise regarding the identification, compilation, evaluation and derivation of HCVs.
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