Threshold of Toxicological Concern (TTC)

Health risk assessments are ideally based on good quality, substance-specific toxicology data. The development of analytical chemistry however has far outstripped the resources available to the toxicologist, and as such many more compounds can now be detected and quantified than have ever been, or are ever likely to be, the subject of toxicological investigation. If the estimated human exposures are low, the means are fortunately now available to reach health precautionary conclusions of toxicological acceptability despite an absence of compound-specific toxicity data.

It is the concept of the threshold of toxicological concern (TTC) that has the potential to free the risk assessor from the analyst’s overly sensitive instrumentation; our scientists are experienced and comfortable in the appropriate use of the TTC approach. The premise is that the toxicological properties of the universe of tested compounds can reliably illuminate the likely toxicology of the much more expansive universe of compounds that have never been tested. Based on the statistical analysis of oral toxicity and carcinogenicity data bases, a number of default tolerable exposure levels can be defined (TTC values), below which an untested compound is considered very unlikely to pose an appreciable risk to human health. A chemical’s structure dictates the selection of the appropriate TTC value. The TTC has been embraced enthusiastically by the Joint FAO/WHO Expert Committee on Food Additives (JECFA), the European Food Safety Authority (EFSA), the European Medicines Agency (EMA), and a number of other regulatory bodies (and of course, by our own risk assessors). It is also a key part of the recently developed guidelines and draft guidelines from the Product Quality Research Institute (PQRI) on extractables and leachables in drug products, with which our risk assessors are familiar.

We apply the TTC approach to risk assessments covering
  • Food additives (including food flavourings)
  • Food contaminants (particularly migrating entities from packaging materials)
  • Impurities in pharmaceuticals
  • Extractable and leachables from medical devices, consumer products (including e-cigarette delivery devices) and pharmaceutical packaging
  • Inhaled substances (present, for example, in e-cigarette formulations)


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