This report compares cancer classification systems, health risk assessment approaches, and procedures used for establishing occupational exposure limits (OELs), in various European countries and scientific organizations. The objectives were to highlight and compare key aspects of these processes and to identify the basis for differences in cancer classifications and OELs between various scientific organizations and countries. Differences in cancer classification exist in part due to differences in the ultimate purpose of classification and to the relative importance of different types of data (i.e., animal vs human data, mechanistic data, and data from benign vs malignant tumors). In general, the groups surveyed tend to agree on classification of chemicals with good evidence of carcinogenicity in humans, and agree less on classification of chemicals with positive evidence in animals and inadequate or limited evidence in humans. Most entities surveyed distinguish between genotoxic and nongenotoxic chemicals when conducting risk assessments. Although the risk assessment approach used for nongenotoxic chemicals is fairly similar among groups, risk assessment approaches for genotoxic carcinogens vary widely. In addition to risk assessment approaches, other factors which can affect OELs include selection of the critical effect, use of health-based vs technology-based exposure limits, and consideration of technological feasibility and socioeconomic factors.
"Today, the evaluations are more diversified and driven by mechanistic considerations and potency of carcinogens where possible (Bolt et al., 2004). This is reflected in the setting of OELs in Germany (Greim and Reuter, 2001) and TLVs in the US (Paustenbach, 2000; ACGIH, 2007), and more or less in several European countries (Seeley et al., 2001). "
[Show abstract][Hide abstract] ABSTRACT: The setting of occupational exposure limits (OELs) are founded in occupational medicine and the predictive toxicological testing, resulting in exposure-response relationships. For compounds where a No-Observed-Adverse-Effect-Level (NOAEL) can be established, health-based OELs are set by dividing the NOAEL of the critical effect by an overall uncertainty factor. Possibly, the approach may also be used for carcinogens if the mechanism is epigenetic or the genetic effect is secondary to effect from reactions with proteins such as topoisomerase inhibitors, and mitotic and meiotic spindle poisons. Additionally, the NOAEL approach may also be used for compounds with weak genotoxic effect, playing no or only a minor role in the development of tumours. No health-based OEL can be set for direct-acting genotoxic compounds where the life-time risks may be estimated from the low-dose linear non-threshold extrapolation, allowing a politically based exposure level to be set. OELs are set by several agencies in the US and Europe, but also in-house in major chemical and pharmaceutical companies. The benchmark dose approach may in the future be used where it has advantage over the NOAEL approach. Also, more attention should be devoted to sensitive groups, toxicological mechanisms and interactions as most workplace exposures are mixtures.
"The risk assessment approach for non-genotoxic chemicals is generally similar among diVerent regulatory bodies worldwide (Seeley et al. 2001). Therefore, OELs derived in this case of " true non-genotoxicants " , are considered by SCOEL " health-based exposure limits " . "
[Show abstract][Hide abstract] ABSTRACT: Setting standards, such as occupational exposure limits (OELs) for carcinogenic substances must consider modes of action. At the European Union level, the scientific committee on occupational exposure limits (SCOEL) has discussed a number of chemical carcinogens and has issued recommendations. For some carcinogens, health-based OELs were recommended, while quantitative assessments of carcinogenic risks were performed for others. For purposes of setting limits this led to the consideration of the following groups of carcinogens. (A) Non-threshold genotoxic carcinogens; for low-dose assessment of risk, the linear non-threshold (LNT) model appears appropriate. For these chemicals, regulations (risk management) may be based on the ALARA principle ("as low as reasonably achievable"), technical feasibility, and other socio-political considerations. (B) Genotoxic carcinogens, for which the existence of a threshold cannot be sufficiently supported at present. In these cases, the LNT model may be used as a default assumption, based on the scientific uncertainty. (C) Genotoxic carcinogens with a practical threshold, as supported by studies on mechanisms and/or toxicokinetics; health-based exposure limits may be based on an established NOAEL (no observed adverse effect level). (D) Non-genotoxic carcinogens and non-DNA-reactive carcinogens; for these compounds a true ("perfect") threshold is associated with a clearly founded NOAEL. The mechanisms shown by tumour promoters, spindle poisons, topoisomerase II poisons and hormones are typical examples of this category. Health-based OELs are derived for carcinogens of groups C and D, while a risk assessment is carried out for carcinogens of groups A and B. Substantial progress is currently being made in the incorporation of new types of mechanistic data into these regulatory procedures.
Archive für Toxikologie 02/2008; 82(1):61-4. DOI:10.1007/s00204-007-0260-z · 5.98 Impact Factor
"Insertion of an uncertainty (or safety) factor permits the derivation of permissible exposure levels at which no relevant human cancer risks are anticipated. The risk assessment approach for nongenotoxic chemicals is generally similar among different regulatory bodies worldwide (Seeley et al., 2001). For genotoxic carcinogens, Streffer et al. (2004) suggest several possibilities for assessing carcinogenic risk. "
[Show abstract][Hide abstract] ABSTRACT: There is growing recognition that carcinogenic risk extrapolation to low doses (and standard setting) should consider the mode of action of a given chemical. So far, there is agreement on distinguishing between genotoxic and nongenotoxic chemicals; yet, further differentiations seem appropriate. For genotoxic carcinogens, case studies of chemicals point to many possibilities for assessing carcinogenic risk. There are numerous, apparently genotoxic carcinogens where practical thresholds are a matter of discussion. For instance, positive data of chromosomal effects only, in the absence of mutagenicity, may support the characterization of a compound that produces carcinogenic effects only at high, toxic doses. There is a wide consensus that for non-DNA-reactive genotoxicants, such as aneugens, thresholds should be defined. Specific mechanisms of clastogenicity have been repeatedly addressed as also having thresholds, such as topoisomerase II poisons, or mechanisms based on reactive oxygen. These and other arguments together lead to the distinction of four groups of carcinogens, which have been introduced (C. Streffer et al., 2004, Springer-Verlag). There are nonthreshold genotoxic carcinogens (for low-dose risk assessment, the linear nonthreshold [LNT] model appears appropriate); genotoxic carcinogens, for which the existence of a threshold cannot be sufficiently supported (in these cases the LNT model is used as a default assumption, based on the scientific uncertainty and backed by the precautionary principle); genotoxic carcinogens for which a practical threshold is supported; and nongenotoxic carcinogens and non-DNA-reactive carcinogens (for these compounds a true [perfect] threshold is associated with a clearly founded no-observed-adverse-effect level).
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