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Threshold of toxicological concern

Increasing numbers of substances present at low and very low concentrations in food and feed are now detectable due to improved analytical methods. However, for many such substances there are little or no toxicological data available. There is an increased need to assess the potential health significance of these previously undetectable trace substances but it is not always possible to generate toxicological data on every single substance found in the diet.

The Threshold A dose or exposure below which adverse effects are not detected. of Toxicological Concern ( TTC The threshold of toxicological concern (TTC) is a screening tool that provides conservative exposure limits in the absence of sufficient chemical-specific toxicological data. It is a science-based approach for prioritising chemicals with low-level exposures that require more data over those that can be presumed to present no appreciable human health risk.) approach has been developed to qualitatively assess the risk of low-level substances in the diet. It can be used for an initial assessment of a substance to determine whether a comprehensive risk assessment  A specialised field of applied science that involves reviewing scientific data and studies in order to evaluate risks associated with certain hazards. It involves four steps: hazard identification, hazard characterisation, exposure assessment and risk characterisation. is required. It is an important science-based approach for prioritising assessment of those chemicals with low-level exposures that require more data over those that can be presumed to present no appreciable human health risk.


June 2019 – EFSA published new guidance on use of threshold of toxicological concern A screening tool that provides conservative  exposure limits in the absence of sufficient chemical-specific toxicological data. It is a science-based approach for prioritising chemicals with low-level exposures that require more data over those that can be presumed to present no appreciable human health risk. (TTC) approach in food safety assessment. The document takes into account the latest scientific developments in the field and was finalised following a public consultation with EFSA’s stakeholders. It is intended to help guide EFSA’s scientists in the use of the TTC approach as a screening and prioritisation tool for the safety assessment of chemicals, when hazard A substance or activity which has the potential to cause adverse effects to living organisms or environments. (toxicological) data are incomplete and human exposure can be estimated as low. Importantly, the TTC approach is not applicable where substance-specific data exist or where they are required under EU legislation.


If the chemical structure of a substance is known, it is likely health risk can be evaluated on the basis of generic human thresholds of exposure – “TTC values”. TTC values have been established for substances of similar chemical structure and likelihood of toxicity The potential of a substance to cause harm to a living organism., based on extensive published toxicological data. There are three broad categories of low, moderate or high toxicity. Substances are conservatively assessed by comparing the appropriate TTC value with reliable human exposure data. If human exposure to a substance is below the TTC value, the likelihood of adverse effects is considered to be very low.
The TTC approach is currently only used by EFSA on a regular basis for the evaluation of flavouring Ingredient added to foodstuffs to alter their flavour or odour. substances (according to assessment principles laid down in the EU regulation on flavourings) and of pesticide Substance used to kill or control pests, including disease-carrying organisms and undesirable insects, animals and plants. metabolites in groundwater. However, EFSA’s Scientific Committee has evaluated the relevance and reliability of the TTC approach in assessing possible human health risks from low levels of exposure to a wider range of substances present in food and feed. It has discussed using TTC for areas within EFSA’s remit including: food contact materials; impurities and breakdown/reaction products in food and feed additives; plant metabolites and degradates of pesticides; metabolites of feed additives; technological feed additives; and flavouring substances in feed.
The TTC approach is not a replacement for the risk assessment of regulated products such as pesticides or food and feed additives, where there is a legislative requirement for the submission of toxicological data. In addition, use of the TTC approach has been excluded for a number of categories of substances: high potency A measure of the capacity of a chemical substance to exert an effect, described in terms of the relationship between the dose used and the magnitude of the resulting effect. carcinogens (i.e. aflatoxin-like, azoxy- or N-nitroso-compounds), inorganic substances, metals and organometallics, proteins, steroids, substances that are known or predicted to bioaccumulate, nanomaterials, radioactive substances, and mixtures of substances containing both known and unknown chemical structures.
The TTC approach has been developed over the past 25 years by scientists specialising in chemical risk assessment, including many working for regulatory agencies. Some people and organisations feel that any chemical present in food or feed should be subjected to toxicity testing followed by risk assessment based on data from experiments on animals. However, public authorities have an obligation to use the accumulated scientific knowledge on toxicity of chemicals whilst still ensuring that public health is protected. This knowledge can allow scientists to give guidance to risk managers even when there are few toxicity data available. It also allows risk assessors to focus attention on those substances that are likely to pose a risk to health and can reduce the need for animal testing.
No. The TTC approach has been used by the U.S. Food and Drug Administration, JECFA (the Joint Expert Committee on Food Additives of the U.N.’s Food and Agriculture Organization and the World Health Organization), the former Scientific Committee on Food (SCF) of the European Commission and by the European Medicines Agency, among others.

EFSA’s Scientific Committee has carefully considered the applicability of the TTC approach to endocrine-active substances, including those that could have “low- dose The total amount of a substance (e.g. a chemical or nutrient) given to, consumed or absorbed by an individual organism, population or ecosystem. effects”. It concluded that:

  • If there are data showing that an endocrine-active substance has adverse effects, then the TTC approach should not be applied and a full risk assessment should be carried out based on these data.
  • If there are data showing that a substance has endocrine activity but the relevance to human health is unclear, then a decision should be made by risk assessors on a case-by-case basis whether or not to apply the TTC approach.
  • There is currently extensive work going on at an EU-level about how scientists should define and assess endocrine-active substances; once finalised, the impact of this work will need to be considered in relation to the use of the TTC approach.

EFSA has found that the TTC approach adequately protects infants and children. Broadly speaking, this is because the TTC values are expressed according to body weight and therefore take into account the lower body weights of infants and children.

EFSA also noted that in the first weeks of life young infants are capable of metabolising and eliminating substances, particularly when exposures are low, and that the differences between young infants and children or adults in this respect are small enough not to invalidate the use of the TTC approach.

However, EFSA does recommend that if the estimated exposure is in the range of the TTC value for young infants, additional considerations, such as predicted metabolism The total sum of physical and chemical processes that occur within living organisms., frequency and duration of exposure, need to be made, on a case-by-case basis, to determine whether the TTC approach can be relied on.

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