Threshold of toxicological concern for chemical substances present in the diet: a practical tool for assessing the need for toxicity testing

The concentration of no toxicologic concern (CoNTC) and airborne mycotoxins

The threshold of toxicologic concern (TTC) concept was developed as a method to identify a chemical intake level that is predicted to be without adverse human health effects assuming daily intake over the course of a 70-yr life span. The TTC values are based on known structure-activity relationships and do not require chemical-specific toxicity data. This allows safety assessment (or prioritization for testing) of chemicals with known molecular structure but little or no toxicity data. Recently, the TTC concept was extended to inhaled substances by converting a TTC expressed in micrograms per person per day to an airborne concentration (ng/m(3)), making allowance for intake by routes in addition to inhalation and implicitly assuming 100% bioavailability of inhaled toxicants. The resulting concentration of no toxicologic concern (CoNTC), 30 ng/m(3), represents a generic airborne concentration that is expected to pose no hazard to humans exposed continuously throughout a 70-yr lifetime. Published data on the levels of mycotoxins in agricultural dusts or in fungal spores, along with measured levels of airborne mycotoxins, spores, or dust in various environments, were used to identify conditions under which mycotoxin exposures might reach the CoNTC. Data demonstrate that airborne concentrations of dusts and mold spores sometimes encountered in agricultural environments have the potential to produce mycotoxin concentrations greater than the CoNTC. On the other hand, these data suggest that common exposures to mycotoxins from airborne molds in daily life, including in the built indoor environment, are below the concentration of no toxicologic concern.

Determinants of whether or not mixtures of disinfection by-products are similar

Reactive chemicals have been used to disinfect drinking waters for over a century. In the 1970s, it was first observed that the reaction of these chemicals with the natural organic matter (NOM) in source waters results in the production of variable, complex mixtures of disinfection by-products (DBP). Because limited toxicological and epidemiological data are available to assess potential human health risks from complex DBP mixture exposures, methods are needed to determine when health effects data on a specific DBP mixture may be used as a surrogate for evaluating another environmental DBP mixture of interest. Before risk assessors attempt such efforts, a set of criteria needs to be in place to determine whether two or more DBP mixtures are similar in composition and toxicological potential. This study broadly characterizes the chemical and toxicological measures that may be used to evaluate similarities among DBP mixtures. Variables are discussed that affect qualitative and quantitative shifts in the types of DBP that are formed, including disinfectants used, their reactions with NOM and with bromide/iodide, pH, temperature, time, and changes in the water distribution system. The known toxicological activities of DBP mixtures and important single DBPs are also presented in light of their potential for producing similar toxicity. While DBP exposures are associated with a number of health effects, this study focuses on (1) mutagenic activity of DBP mixtures, (2) DBP cancer epidemiology, and (3) toxicology studies to evaluate similarity among DBP mixtures. Data suggest that further chemical characterization of DBP mixtures and more systematic study of DBP toxicology will improve the quality and usefulness of similarity criteria.

Application of mode-of-action considerations in human cancer risk assessment

The distinction between carcinogens with DNA-reactive and epigenetic modes of action and the application of mode-of-action considerations to risk assessment is reviewed. A bioindicator-based risk assessment strategy is described. This approach involves the use of mechanistic data to establish a "toxicologically insignificant daily intake".

The Threshold of Toxicological Concern (TTC) in risk assessment

The Threshold of Toxicological Concern (TTC) is a level of human intake or exposure that is considered to be of negligible risk, despite the absence of chemical-specific toxicity data. The TTC approach is a form of risk characterisation in which uncertainties arising from the use of data on other compounds are balanced against the low level of exposure. The approach was initially developed by the FDA for packaging migrants, and used a single threshold value of 1.5 microg/day (called the threshold of regulation). Subsequent analyses of chronic toxicity data resulted in the development of TTC values for three structural classes with different potentials for toxicity (1,800, 540 and 90 microg/day). These TTC values have been incorporated into the procedure that is used internationally for the evaluation of flavouring substances. Further developments included additional TTC values for certain structural alerts for genotoxicity (0.15 microg/day), and for the presence of an organophosphate group (18 microg/day). All of these TTC values were incorporated into an extended decision tree for chemicals, such as contaminants, which might be present in human foods. The TTC approach has been shown to have potential applications to risk assessments of cosmetic ingredients, household products and impurities in therapeutic drugs.

Thresholds for food allergens and their value to different stakeholders

Thresholds constitute a critical piece of information in assessing the risk from allergenic foods at both the individual and population levels. Knowledge of the minimum dose that can elicit a reaction is of great interest to all food allergy stakeholders. For allergic individuals and health professionals, individual threshold data can inform allergy management. Population thresholds can help both the food industry and regulatory authorities assess the public health risk and design appropriate food safety objectives to guide risk management. Considerable experience has been gained with the double-blind placebo-controlled food challenge (DBPCFC), but only recently has the technique been adapted to provide data on thresholds. Available data thus vary greatly in quality, with relatively few studies providing the best quality individual data, using the low-dose DBPCFC. Such high quality individual data also form the foundation for population thresholds, but these also require, in addition to an adequate sample size, a good characterization of the tested population in relation to the whole allergic population. Determination of thresholds at both an individual level and at a population level is influenced by many factors. This review describes a low-dose challenge protocol developed as part of the European Community-funded Integrated Project Europrevall, and strongly recommends its wider use so that data are generated that can readily increase the power of existing studies.

The Dermal Sensitisation Threshold- a TTC approach for allergic contact dermatitis

The Threshold of Toxicological Concern (TTC) is a useful concept that is becoming of increasing interest as an addition to the arsenal of tools used for characterising the toxicological risk of human exposure to chemicals. Traditionally used for low level indirect additives, flavours and contaminants in foods, the TTC obviates the need for toxicological testing of chemicals where human exposure is low. Proposals have recently been made for the use of the TTC for low level ingredients in cosmetic and personal care products. However, use of the TTC is only protective for systemic toxicity endpoints, and cannot be used for local endpoints such as contact sensitisation. In this paper a probabilistic analysis of available sensitisation data, similar to that used in the development of the TTC, is presented. The incidence of sensitisers in the world of chemicals was estimated using the ELINCS (European List of Notified Chemical Substances) data set, and a distribution for sensitisation potency was established using a recently published compilation of Local Lymph Node Assay data. From the analysis of these data sets it is concluded that a Dermal Sensitisation Threshold (DST) can be established below which there is no appreciable risk of sensitisation, even for an untested ingredient. Use of a DST would preclude the need for sensitisation testing of ingredients where dermal exposure is sufficiently low.

Application of the threshold of toxicological concern (TTC) to the safety evaluation of cosmetic ingredients

The threshold of toxicological concern (TTC) has been used for the safety assessment of packaging migrants and flavouring agents that occur in food. The approach compares the estimated oral intake with a TTC value derived from chronic oral toxicity data for structurally-related compounds. Application of the TTC approach to cosmetic ingredients and impurities requires consideration of whether route-dependent differences in first-pass metabolism could affect the applicability of TTC values derived from oral data to the topical route. The physicochemical characteristics of the chemical and the pattern of cosmetic use would affect the long-term average internal dose that is compared with the relevant TTC value. Analysis has shown that the oral TTC values are valid for topical exposures and that the relationship between the external topical dose and the internal dose can be taken into account by conservative default adjustment factors. The TTC approach relates to systemic effects, and use of the proposed procedure would not provide an assessment of any local effects at the site of application. Overall the TTC approach provides a useful additional tool for the safety evaluation of cosmetic ingredients and impurities of known chemical structure in the absence of chemical-specific toxicology data.

The concentration of no toxicological concern (CoNTC): a risk assessment screening tool for air toxics

Although numerous chemicals might occur in ambient air as a result of natural or anthropogenic activity (primarily through vehicle exhaust and industrial emissions), not all are necessarily of concern for public health even if they are classified as hazardous. There are many minor components in emissions that are predicted to be present at small concentrations. For the majority of these chemicals a health-based guideline does not exist to facilitate risk assessment. Furthermore, there are no appropriate toxicological or health data to enable health-based guidelines to be established. Consequently in most risk assessments these substances are usually, and conveniently, ignored. The tacit justification is that concentrations in ambient air are small and thus insignificant. For many stakeholders this is an inadequate explanation, and the justifiable question of how it is known exposures are insignificant for health is often asked. The concept of a "concentration of no toxicological concern" (CoNTC) was developed for air toxics and can be applied as a risk assessment screening tool to legitimately dismiss substances whose ground-level concentrations are predicted to be trivial. The CoNTC helps define trivial and is grounded in regulatory and scientific deliberations of the U.S. Food and Drug Administration (FDA) and the European Commission for developing concentrations of no toxicological or regulatory concern for contaminants in food. The suggested conservative generic CoNTC value that can be applied to most organic chemicals in air is 0.03 microg/m3. The derivation of the CoNTC and its validation and limitations are discussed, and its utility as a screening tool is presented.

A proposed approach for the assessment of chemicals in indirect potable reuse schemes

The city of Perth in Western Australia is facing a future of compromised water supplies. In recent years, this urban region has been experiencing rapid population growth, coupled with drying climate, which has exacerbated water shortages. As part of the government strategy to secure water sustainability and to address an agenda focused on all elements of the water cycle, a target of 20% reuse of treated wastewater by 2012 was established. This includes a feasibility review of managed aquifer recharge for indirect potable reuse. A characterization of contaminants in wastewater after treatment and an assessment of the health implications are necessary to reassure both regulators and the public. To date, the commonly used approach involves a comparison of measured contaminant concentrations with the established drinking-water standards or other toxicological guidelines for the protection of human health. However, guidelines and standards have not been established for many contaminants in recycled water (unregulated chemicals). This article presents a three-tiered approach for the preliminary health risk assessment of chemicals in order to determine key contaminants that need to be monitored and managed. The proposed benchmark values for the calculation of risk quotients are health based, systematically defined, scientifically defensible, easy to apply, and clear to interpret. The proposed methodology is based on the derivation of health-based levels for unregulated contaminants with toxicity information and a "threshold of toxicological concern" for unregulated contaminants without toxicity data. The application of this approach will help policymakers set guidelines regarding unregulated chemicals in recycled water.

Framework for use of toxicity screening tools in context-based decision-making

One of the principal applications of toxicology data is to inform risk assessments and support risk management decisions that are protective of human health. Ideally, a risk assessor would have available all of the relevant information on (a) the toxicity profile of the agent of interest; (b) its interactions with living systems; and (c) the known or projected exposure scenarios: to whom, how much, by which route(s), and how often. In practice, however, complete information is seldom available. Nonetheless, decisions still must be made. Screening-level assays and tools can provide support for many aspects of the risk assessment process, as long as the limitations of the tools are understood and to the extent that the added uncertainty the tools introduce into the process can be characterized and managed. Use of these tools for decision-making may be an end in itself for risk assessment and decision-making or a preliminary step to more extensive data collection and evaluation before assessments are undertaken or completed and risk management decisions made. This paper describes a framework for the application of screening tools for human health decision-making, although with some modest modification, it could be made applicable to environmental settings as well. The framework consists of problem formulation, development of a screening strategy based on an assessment of critical data needs, and a data analysis phase that employs weight-of-evidence criteria and uncertainty analyses, and leads to context-based decisions. Criteria for determining the appropriate screening tool(s) have been identified. The choice and use of the tool(s) will depend on the question and the level of uncertainty that may be appropriate for the context in which the decision is being made. The framework is iterative, in that users may refine the question(s) as they proceed. Several case studies illustrate how the framework may be used effectively to address specific questions for any endpoint of toxicity.

Evaluation of acute inhalation toxicity for chemicals with limited toxicity information

A large reference database consisting of acute inhalation no-observed-adverse-effect levels (NOAELs) and acute lethality data for 97 chemicals was compiled to investigate two methods to derive health-protective concentrations for chemicals with limited toxicity data for the evaluation of one-hour intermittent inhalation exposure. One method is to determine threshold of concern (TOC) concentrations for acute toxicity potency categories and the other is to determine NOAEL-to-LC(50) ratios. In the TOC approach, 97 chemicals were classified based on the Globally Harmonized System of Classification and Labeling of Chemicals proposed by the United Nations into different acute toxicity categories (from most toxic to least toxic): Category 1, Category 2, Category 3, Category 4, and Category 5. The tenth percentile of the cumulative percentage distribution of NOAELs in each category was determined and divided by an uncertainty factor of 100 to derive the following health-protective TOC concentrations: 4microg/m(3) for chemicals classified in Category 1; 20microg/m(3) for Category 2; 125microg/m(3) for both Categories 3 and 4; and 1000microg/m(3) for Category 5. For the NOAEL-to-LC(50) ratio approach, 55 chemicals with NOAEL exposure durations < or = 24 hour were used to calculate NOAEL-to-LC(50) ratios. The tenth percentile of the cumulative percentage distribution of the ratios was calculated and divided by an uncertainty factor of 100 to produce a composite factor equal to 8.3x10(-5). For a chemical with limited toxicity information, this composite factor is multiplied by a 4-hour LC(50) value or other appropriate acute lethality data. Both approaches can be used to produce an estimate of a conservative threshold air concentration below which no appreciable risk to the general population would be expected to occur after a one-hour intermittent exposure.

Regulatorische, gesundheitliche und ästhetische Bewertung sogenannter Spurenstoffe im Trinkwasser unter besonderer Berücksichtigung von Arzneimitteln

More than 2500 chemically defined substances are approved as drugs in Germany. Unlike agricultural pesticides, these biologically active structures are not used in open environmental compartments and therefore their environmental toxicological data base is not nearly as complete. Nevertheless, some of them become environmental contaminants after their intended use. Therefore, from the viewpoint of environmental health protection, there are gaps in their health-related environmental risk assessment. Organic trace compounds that lack an adequate toxicological database, and their mixtures, in drinking water can be safely regulated and provisionally assessed by combining the "similar joint action" addition rule with the recommendation of the Federal Environment Agency of March 2003 "Assessing the presence of substances in drinking water without (adequate) toxicological database from the health point of view". The general precautionary value (Gesundheitlicher Orientierungswert GOW1=0.10 microg/l), which is a recommendation for weakly to not genotoxic compounds, re presents a workable compromise between preventive health protection, water management considerations and aesthetic quality claims (purity). Compliance with this value in the long term will only be possible if the chemical and biological degradation of pharmaceuticals and their metabolites in waste water and waste water treatment plants is effectively improved. Alternatively, there is the risk of drinking water degenerating into a sink for highly mobile, polar and persistent compounds. Their elimination at a stage as late as technical drinking water treatment would be neither close to the initial cause nor justifiable in terms of technical effectiveness. The risk assessment of their byproducts would give rise to further uncertainties. Possible conflicts with the therapeutic quality must be solved by developing substitute products which are environmentally sound.

In vitro effect of pesticides (dichlofluanid, endosulfan, simazine, tolylfluanid and triallate) on proliferative activity of animal derived cell cultures

In this study pesticides with different chemical structures (dichlofluanid, endosulfan, simazine, tolylfluanid and triallate) were examined for their potential cytotoxic effect on proliferative activity of cell cultures of mammalian origin. Cell lines Madin-Darby Bovine Kidney (MDBK), Rabbit Kidney (RK13), Porcine Kidney (PK15), and semicontinual line of Bovine Embryonic Pulmonary Cells (BEPC) were used in the study. From these cell cultures cell proliferative activity was suppressed most intensively in PK15 culture by endosulfan (10(-1) - 10(-6) M). The least effect on cell proliferation in all cell cultures tested, with the exception PK 15 (10(-1) - 10(-2) M), was recorded after simazine exposure. On the basis of IC50 values the cytotoxic effect was: dichlofluanid (IC50 = 10(-3.94) M) > tolylfluanid (IC50 = 10(-3.69) M) > endosulfan (IC50 = 10(-3.24) M) > triallate (IC50 = 10(-3.12) M) > simazine (IC50 = 10(-1.78) M). The comparison of average IC50 values of cell cultures revealed that the most sensitive cell lines were PK15 (IC50 = 10(-3.27) M) and RK13 (IC50 = 10(-3.21) M), whereas MDBK (IC50 = 10(-2.55) M) and BEPC (IC50 = 10(-2.52) M) were less sensitive to pesticide exposure.

Food Contamination with Organic Materials in Perspective: Packaging Materials as the Largest and Least Controlled Source? A View Focusing on the European Situation

The comparison of the various sources of food contamination with organic chemicals suggests that in the public, but also among experts, the perception of risk is often distorted. Firstly, neither pesticides nor environmental pollutants contribute the most; the amount of material migrating from food packaging into food may well be 100 times higher. Secondly, control of these large migrants is often lagging behind the standards set up for other sources, since many of the components (particularly those not being "starting materials") have not been identified and, thus, not toxicologically evaluated. Finally, attitudes towards different types of food contaminants are divergent, also reflected by the legal measures: for most sources of food contamination there are strict rules calling for minimization, whereas the European packaging industry has even requested a further increase in the tolerance to as close as possible to the limit set by the toxicologists. This paper calls for a more realistic perception and more coherent legal measures-and improvements in the control of migration from packaging material.

A rationale for determining, testing, and controlling specific impurities in pharmaceuticals that possess potential for genotoxicity

The synthesis of pharmaceutical products frequently involves the use of reactive reagents and the formation of intermediates and by-products. Low levels of some of these may be present in the final drug substance and drug product as impurities. Such chemically reactive impurities may have at the same time the potential for unwanted toxicities including genotoxicity and carcinogenicity and hence can have an impact on product risk assessment. This paper outlines a procedure for testing, classification, qualification, toxicological risk assessment, and control of impurities possessing genotoxic potential in pharmaceutical products. Referencing accepted principles of cancer risk assessment, this document proposes a staged threshold of toxicological concern (TTC) approach for the intake of genotoxic impurities over various periods of exposure. This staged TTC is based on knowledge about tumorigenic potency of a wide range of genotoxic carcinogens and can be used for genotoxic compounds, for which cancer data are limited or not available. The delineated acceptable daily intake values of between approximately 1.5 microg/day for approximately lifetime intake and approximately 120 microg/day for < or = 1 month are virtually safe doses. Based on sound scientific reasoning, these virtually safe intake values do not pose an unacceptable risk to either human volunteers or patients at any stage of clinical development and marketing of a pharmaceutical product. The intake levels are estimated to give an excess cancer risk of 1 in 100,000 to 1 in a million over a lifetime, and are extremely conservative given the current lifetime cancer risk in the population of over 1 in 4 (http://seer.cancer.gov/statfacts/html.all.html). The proposals in this document apply to all clinical routes of administration and to compounds at all stages of clinical development. It is important to note that certain types of products, such as those for life-threatening indications for which there are no safer alternatives, allow for special considerations using adaptations of the principles outlined in this paper.

Compositional GC-FID analysis of the additives to PVC, focusing on the gaskets of lids for glass jars

A gas chromatographic (FID) method is described which aims at the quantitative compositional analysis of the additives in plasticized PVC, particularly the plastisols used as gaskets for lids of glass jars. An extract of the PVC is analysed directly as well as after transesterification to ethyl esters. Transesterification enables the analysis of epoxidized soya bean and linseed oil (ESBO and ELO) as well as polyadipates. For most other additives, the shifts in the chromatogram resulting from transesterification is used to confirm the identifications made by direct analysis. In the gaskets of 69 lids from the European market used for packaging oily foods, a broad variety of plastisol compositions was found, many or possibly all of which do not comply with legal requirements. In 62% of these lids, ESBO was the principal plasticizer, whereas in 25% a phthalate had been used.

Application of the threshold of toxicological concern concept to pharmaceutical manufacturing operations

A scientific rationale is provided for estimating acceptable daily intake values (ADIs) for compounds with limited or no toxicity information to support pharmaceutical manufacturing operations. These ADIs are based on application of the "thresholds of toxicological concern" (TTC) principle, in which levels of human exposure are estimated that pose no appreciable risk to human health. The same concept has been used by the US Food and Drug Administration (FDA) to establish "thresholds of regulation" for indirect food additives and adopted by the Joint FAO/WHO Expert Committee on Food Additives for flavoring substances. In practice, these values are used as a statement of safety and indicate when no actions need to be taken in a given exposure situation. Pharmaceutical manufacturing relies on ADIs for cleaning validation of process equipment and atypical extraneous matter investigations. To provide practical guidance for handling situations where relatively unstudied compounds with limited or no toxicity data are encountered, recommendations are provided on ADI values that correspond to three categories of compounds: (1) compounds that are likely to be carcinogenic, (2) compounds that are likely to be potent or highly toxic, and (3) compounds that are not likely to be potent, highly toxic or carcinogenic. Corresponding ADIs for these categories of materials are 1, 10, and 100 microg/day, respectively.

The Threshold of Toxicological Concern Concept in Risk Assessment

The concept that "safe levels of exposure" for humans can be identified for individual chemicals is central to the risk assessment of compounds with known toxicological profiles. The Threshold of Toxicological Concern (TTC) is a concept that refers to the establishment of a level of exposure for all chemicals, whether or not there are chemical-specific toxicity data, below which there would be no appreciable risk to human health. The concept proposes that a low level of exposure with a negligible risk can be identified for many chemicals, including those of unknown toxicity, based on knowledge of their chemical structures. The present paper aims to describe the history of the TTC principle, its use to date, its potential future applications and the incorporation of the TTC principle in the Risk Assessment paradigm.

A procedure for the safety evaluation of natural flavor complexes used as ingredients in food: essential oils

A scientifically based guide has been developed to evaluate the safety of naturally occurring mixtures, particularly essential oils, for their intended use as flavor ingredients. The approach relies on the complete chemical characterization of the essential oil and the variability of the composition of the oil in the product intended for commerce. Being products of common plant biochemical pathways, the chemically identified constituents are organized according to a limited number of well-established chemical groups called congeneric groups. The safety of the intake of the each congeneric group from consumption of the essential oil is evaluated in the context of data on absorption, metabolism, and toxicology of members of the congeneric group. The intake of the group of unidentified constituents is evaluated in the context of the consumption of the essential oil as a food, a highly conservative toxicologic threshold, and toxicity data on the essential oil or an essential oil of similar chemotaxonomy. The flexibility of the guide is reflected in the fact that high intake of major congeneric groups of low toxicologic concern will be evaluated along with low intake of minor congeneric groups of significant toxicological concern (i.e., higher structural class). The guide also provides a comprehensive evaluation of all congeneric groups and constituents that account for the majority of the composition of the essential oil. The overall objective of the guide is to organize and prioritize the chemical constituents of an essential oil in order that no reasonably possible significant risk associated with the intake of essential oil goes unevaluated. The guide is, however, not intended to be a rigid checklist. The Flavor and Extract Manufacturers Association (FEMA) Expert Panel will continue to evaluate each essential oil on a case by case basis applying their scientific judgment to insure that each natural flavor complex is exhaustively evaluated.

Analysis of an interaction threshold in a mixture of drugs and/or chemicals

Increasingly, humans are exposed to drug/chemical mixtures. These exposures can result from therapeutic interventions or environmental sources. Of interest is the interaction that may occur among the components of these mixtures. Since interaction can be dose-dependent, it is important to determine exposure levels to either exploit the benefits of the interaction in a therapeutic application or to avoid the effect of the interaction in the case of an environmental risk assessment. We propose generalized linear models that permit the estimation of interaction threshold boundaries. The methods developed are applied to the combination of ethanol and chloral hydrate.

Structure-based thresholds of toxicological concern (TTC): guidance for application to substances present at low levels in the diet

The threshold of toxicological concern (TTC) is a pragmatic risk assessment tool that is based on the principle of establishing a human exposure threshold value for all chemicals, below which there is a very low probability of an appreciable risk to human health. The concept that there are levels of exposure that do not cause adverse effects is inherent in setting acceptable daily intakes (ADIs) for chemicals with known toxicological profiles. The TTC principle extends this concept by proposing that a de minimis value can be identified for many chemicals, in the absence of a full toxicity database, based on their chemical structures and the known toxicity of chemicals which share similar structural characteristics. The establishment and application of widely accepted TTC values would benefit consumers, industry and regulators. By avoiding unnecessary toxicity testing and safety evaluations when human intakes are below such a threshold, application of the TTC approach would focus limited resources of time, cost, animal use and expertise on the testing and evaluation of substances with the greatest potential to pose risks to human health and thereby contribute to a reduction in the use of animals. An Expert Group of the European branch of the International Life Sciences Institute-ILSI Europe-has examined the TTC principle for its wider applicability in food safety evaluation. The Expert Group examined metabolism and accumulation, structural alerts, endocrine disrupting chemicals and specific endpoints, such as neurotoxicity, teratogenicity, developmental toxicity, allergenicity and immunotoxicity, and determined whether such properties or endpoints had to be taken into consideration specifically in a step-wise approach. The Expert Group concluded that the TTC principle can be applied for low concentrations in food of chemicals that lack toxicity data, provided that there is a sound intake estimate. The use of a decision tree to apply the TTC principle is proposed, and this paper describes the step-wise process in detail. Proteins, heavy metals and polyhalogenated-dibenzodioxins and related compounds were excluded from this approach. When assessing a chemical, a review of prior knowledge and context of use should always precede the use of the TTC decision tree. The initial step is the identification and evaluation of possible genotoxic and/or high potency carcinogens. Following this step, non-genotoxic substances are evaluated in a sequence of steps related to the concerns that would be associated with increasing intakes. For organophosphates a TTC of 18microg per person per day (0.3 microg/kg bw/day) is proposed, and when the compound is not an OP, the TTC values for the Cramer structural classes III, II and I, with their respective TTC levels (e.g. 1800, 540 and 90 microg per person per day; or 30, 9 and 1.5 microg/kg bw /day), would be applied sequentially. All other endpoints or properties were shown to have a distribution of no observed effect levels (NOELs) similar to the distribution of NOELs for general toxicity endpoints in Cramer classes I, II and III. The document was discussed with a wider audience during a workshop held in March 2003 (see list of workshop participants).

[Simulation of migration from internal can coatings]

Migration from can-coatings into retorted canned food simulants (canned oil and water, 121 degrees C, 30 min) was investigated through HPLC with a fluorescence detector and evaporative light scattering detector, and by measurements of residue on evaporation and consumption of potassium permanganate. HPLC analysis revealed that migration into the canned oil was hundreds of times more than that into n-heptane (25 degrees C, 60 min, the official test conditions according to the Japanese Food Sanitation Law), whereas it was similar to the migration into isooctane-butyl acetate mixtures (60 degrees C, 60 min), and that migration into the canned water was several times more than that into water (95 degrees C, 30 min, the official test conditions). Residue on evaporation for the n-heptane extract was several-fold lower than 30 ppm (the official limit), whereas that for the isooctane-butyl acetate mixtures exceeded 30 ppm. Consumption of potassium permanganate for the canned water was 30 times higher than that for the water extract (95 degrees C, 30 min). The official test conditions for can-coatings, in particular the use of n-heptane as an oil simulant, were suggested to lead to substantial underestimation of migration into canned food.

The applicability of in vitro-derived data in hazard identification and characterisation of chemicals

Toxicological hazard and risk assessments for chemicals presently are mainly based on highly standardised protocols for animal experimentation and exposure assessment. In this paper the possibilities are being discussed of developing systems in which the systemic (acute and chronic) toxicity of chemicals can be quantified, without the heavy reliance on animal experiments. On the basis of a chemical's structure, in vitro data on its toxicity, and biokinetic modelling a decision/flow scheme is presented. Key elements are the evaluation of chemical functionalities representing structural alerts for toxic actions, the construction of biokinetic models on the basis of non-animal data (e.g. tissue-blood partition coefficients (PCs), in vitro biotransformation parameters), tests or batteries of tests for determining basal cytotoxicity and more specific tests for evaluating tissue- or organ toxicity. It is concluded that such a flow chart is a useful tool for different steps in the toxicological hazard and risk assessment, especially for those forms of toxicity for which validated in vitro and other non-animal tests have already been developed.

Toxicological evaluation of chemical mixtures

This paper addresses major developments in the safety evaluation of chemical mixtures during the past 15 years, reviews today's state of the art of mixture toxicology, and discusses challenges ahead. Well-thought-out tailor-made mechanistic and empirical designs for studying the toxicity of mixtures have gradually substituted trial-and-error approaches, improving the insight into the testability of joint action and interaction of constituents of mixtures. The acquired knowledge has successfully been used to evaluate the safety of combined exposures and complex mixtures such as, for example, the atmosphere at hazardous waste sites, drinking water disinfection by-products, natural flavouring complexes, and the combined intake of food additives. To consolidate the scientific foundation of mixture toxicology, studies are in progress to revisit the biological concepts and mathematics underlying formulas for low-dose extrapolation and risk assessment of chemical mixtures. Conspicuous developments include the production of new computer programs applicable to mixture research (CombiTool, BioMol, Reaction Network Modelling), the application of functional genomics and proteomics to mixture studies, the use of nano-optochemical sensors for in vivo imaging of physiological processes in cells, and the application of optical sensor micro- and nano-arrays for complex sample analysis. Clearly, the input of theoretical biologists, biomathematicians and bioengineers in mixture toxicology is essential for the development of this challenging branch of toxicology into a scientific subdiscipline of full value.

Risk assessment of packaging materials

Risk assessment of packaging materials provides a unique challenge. Human exposure to packaging materials and/or their components occurs from migration into foods. There are various methods for determining migration into foods. Unlike most food additives, these exposures typically are very small. Because of this, and since complete toxicological data sets are not always available for packaging materials, the US Food and Drug Administration (FDA) has developed a process to make the evaluation of packaging materials more efficient, instead of the extensive review normally required for food additives. This process is used to determine 'when the likelihood or extent of migration to food of a substance used in a food-contact article is so trivial as not to require regulation of the substance as a food additive'. This trivial level, also known as the threshold of regulation, was based upon a large database of carcinogenic potencies and was determined to be 1.5 microg/person day(-1). This was determined to 'be low enough to ensure that the public health is protected, even in the event that a substance exempted from regulation as a food additive is later found to be a carcinogen'. Substances not having structural alerts, or that are not known carcinogens or potent toxins, based on existing toxicological information, and are below the threshold value, are considered by the FDA to be exempted from regulation as food additives. The threshold of regulation approach used by the FDA provides an excellent model by which to evaluate the majority of packaging materials.

Comprehensive analysis of migrates from food-packaging materials: a challenge

The premise is put forward that present European regulation of food-packaging materials does not provide the assessment for safety corresponding to the opinion of toxicologists that migrants ingested in amounts exceeding a threshold of 1.5 microg day(-1) should be identified and toxicologically evaluated. Many substances that migrate (the large majority of the components migrating from can coatings) are neither starting point materials, nor obvious derivatives therefrom, and are, therefore, not covered by existing systems based on positive lists. Safety presupposes the comprehensive analysis of the migrating substances, ultimately to the limits in terms of concentration and molecular weight considered to he of toxicological concern. This is a new analytical challenge. In this paper, expected problems are discussed, leading to the conclusion that it will be difficult to achieve comprehensive analysis down to the concentrations presently considered safe, but that systematic work should start to define the possibilities and limitations of analytical chemistry for a migrate-oriented coating legislation.

Polyethylene terephthalate recycling for food-contact applications: testing, safety and technologies: a global perspective

Studies were undertaken to determine the composition of five different types of post-consumer polyethylene terephthalate (PET) feedstreams to ascertain the relative amounts of food containers and non-food containers. Deposit post-consumer PET feedstreams contained approximately 100% food containers, whereas curbside feedstreams contained from 0.04 to 6% non-food containers. Analysis of the PET containers from the different type feedstreams after the containers were subjected to a commercial PET wash system and after processing with a proprietary decontamination technology was accomplished to determine the levels of compounds in the post-consumer PET after the various stages of processing. Comprehensive thermal desorption/GC/MS, purge and trap GC/MS purge and trap GC quantitation, PET dissolution and extraction GC analysis and PET dissolution HPLC analysis established the types and concentrations of compounds that absorb in the PET from the various types of postconsumer feedstreams. A total of 121 compounds were identified in the five different feedstreams. The concentration of absorbed compounds remaining in the deposit material and the non-food applications material after the commercial wash was 28 and 39mgkg(-1) respectively. Analysis of the feedstreams after subjecting the material to a proprietary decontamination process demonstrated the ability of removing all the absorbed compounds to a level below the level of the threshold of regulation. The safety of sourcing of post-consumer PET from food use applications verses non-food use applications of PET has been established.

Threshold of toxicological concern (TTC) in food safety assessment

The threshold of toxicological concern (TTC) is a principle which refers to the possibility of establishing a human exposure threshold value for all chemicals, below which there is no appreciable risk to human health. The concept that exposure thresholds can be identified for individual chemicals in the diet is already widely embodied in practice of many regulatory bodies in setting acceptable daily intakes (ADIs) for chemicals whose toxicological profile is known. However, the TTC concept goes further than this in proposing that a de minimis value can be identified for many chemicals, including those of unknown toxicity, taking the chemical structure into consideration. This concept forms the scientific basis of the US Food and Drug Administration (FDA) '1995 Threshold of Regulation' for indirect food additives. The TTC principle has also been adopted by the Joint FAO/WHO Expert Committee on Food Additives (JECFA) in its evaluations of flavouring substances. The establishment of a more widely accepted TTC would benefit consumers, industry and regulators. In precluding extensive toxicity testing and safety evaluations when human intakes are below such a threshold, TTC would focus limited resources of time, cost, animal use and expertise on the testing and evaluation of substances with greater potential to pose risks to human health and contribute to a reduction in the use of animals. An International Life Sciences Institute (ILSI)-Europe expert group has examined this TTC principle, which was based on general toxicity endpoints (including carcinogenicity), for its applicability in food safety evaluation. In addition, the group examined specific endpoints, such as neurotoxicity, immunotoxicity and developmental toxicity. The results of the expert group's considerations including the development of a guideline to apply the principle are discussed.

Mathematical modelling and quantitative methods

The present review reports on the mathematical methods and statistical techniques presently available for hazard characterisation. The state of the art of mathematical modelling and quantitative methods used currently for regulatory decision-making in Europe and additional potential methods for risk assessment of chemicals in food and diet are described. Existing practices of JECFA, FDA, EPA, etc., are examined for their similarities and differences. A framework is established for the development of new and improved quantitative methodologies. Areas for refinement, improvement and increase of efficiency of each method are identified in a gap analysis. Based on this critical evaluation, needs for future research are defined. It is concluded from our work that mathematical modelling of the dose-response relationship would improve the risk assessment process. An adequate characterisation of the dose-response relationship by mathematical modelling clearly requires the use of a sufficient number of dose groups to achieve a range of different response levels. This need not necessarily lead to an increase in the total number of animals in the study if an appropriate design is used. Chemical-specific data relating to the mode or mechanism of action and/or the toxicokinetics of the chemical should be used for dose-response characterisation whenever possible. It is concluded that a single method of hazard characterisation would not be suitable for all kinds of risk assessments, and that a range of different approaches is necessary so that the method used is the most appropriate for the data available and for the risk characterisation issue. Future refinements to dose-response characterisation should incorporate more clearly the extent of uncertainty and variability in the resulting output.

Assessment of intake from the diet

Exposure assessment is one of the key parts of the risk assessment process. Only intake of toxicologically significant amounts can lead to adverse health effects even for a relatively toxic substance. In the case of chemicals in foods this is based on three major aspects: (i) how to determine quantitatively the presence of a chemical in individual foods and diets, including its fate during the processes within the food production chain; (ii) how to determine the consumption patterns of the individual foods containing the relevant chemicals; (iii) how to integrate both the likelihood of consumers eating large amounts of the given foods and of the relevant chemical being present in these foods at high levels. The techniques used for the evaluation of these three aspects have been critically reviewed in this paper to determine those areas where the current approaches provide a solid basis for assessments and those areas where improvements are needed or desirable. For those latter areas, options for improvements are being suggested, including, for example, the development of a pan-European food composition database, activities to understand better effects of processing on individual food chemicals, harmonisation of food consumption survey methods with the option of a regular pan-European survey, evaluation of probabilistic models and the development of models to assess exposure to food allergens. In all three areas, the limitations of the approaches currently used lead to uncertainties which can either cause an over- or underestimation of real intakes and thus risks. Given these imprecisions, risk assessors tend to build in additional uncertainty factors to avoid health-relevant underestimates. This is partly done by using screening methods designed to look for "worst case" situations. Such worse case assumptions lead to intake estimates that are higher than reality. These screening methods are used to screen all those chemicals with a safe intake distribution. For chemicals with a potential risk, more information is needed to allow more refined screening or even the most accurate estimation. More information and more refined methods however, require more resources. The ultimate aims are: (1) to obtain appropriate estimations for the presence and quantity of a given chemical in a food and in the diet in general; (2) to assess the consumption patterns for the foods containing these substances, including especially those parts of the population with high consumption and thus potentially high intakes; and (3) to develop and apply tools to predict reliably the likelihood of high end consumption with the presence of high levels of the relevant substances. It has thus been demonstrated that a tiered approach at all three steps can be helpful to optimise the use of the available resources: if relatively crude tools - designed to provide a "worst case" estimate - do not suggest a toxicologically significant exposure (or a relevant deficit of a particular nutrient) it may not be necessary to use more sophisticated tools. These will be needed if initially high intakes are indicated for at least parts of the population. Existing pragmatic approaches are a first crude step to model food chemical intake. It is recommended to extend, refine and validate this approach in the near future. This has to result in a cost-effective exposure assessment system to be used for existing and potential categories of chemicals. This system of knowledge (with information on sensitivities, accuracy, etc.) will guide future data collection.

Hazard characterisation of chemicals in food and diet. dose response, mechanisms and extrapolation issues

Hazard characterisation of low molecular weight chemicals in food and diet generally use a no-observed-adverse-effect level (NOAEL) or a benchmark dose as the starting point. For hazards that are considered not to have thresholds for their mode of action, low-dose extrapolation and other modelling approaches may be applied. The default position is that rodents are good models for humans. However, some chemicals cause species-specific toxicity syndromes. Information on quantitative species differences is used to modify the default uncertainty factors applied to extrapolate from experimental animals to humans. A central theme for extrapolation is unravelling the mode of action for the critical effects observed. Food can be considered as an extremely complex and variable chemical mixture. Interactions among low molecular weight chemicals are expected to be rare given that the exposure levels generally are far below their NOAELs. Hazard characterisation of micronutrients must consider that adverse effects may arise from intakes that are too low (deficiency) as well as too high (toxicity). Interactions between different nutrients may complicate such hazard characterisations. The principle of substantial equivalence can be applied to guide the hazard identification and hazard characterisation of macronutrients and whole foods. Macronutrients and whole foods must be evaluated on a case-by-case basis and cannot follow a routine assessment protocol.