The role of expert judgement and conceptual approaches in setting OELs by the German MAK commission Institut für Angewandte Biowissenschaften, Lebensmittelchemie und Toxikologie DFG Senate Commission for the Investigation of Health Hazards of Chemical Compounds in the Work Area (MAK Commission) Chair: Prof. Dr. Andrea Hartwig, Karlsruhe Institute of Technology (KIT) 1 KIT Universität des Landes Baden-Württemberg Andrea Hartwig: und OEL setting by the MAK commission: Expert judgement and conceptual approaches nationales Forschungszentrum in der Helmholtz-Gemeinschaft www.kit.edu
Tasks of the MAK Commission Evaluation of chemical substances at the workplace (single substances) Conceptional work (criteria for risk assessment) 2
MAK and BAT values. derived by the DFG Commission for the Investigation of Health Hazards of Chemical Compounds in the Work Area (MAK Commission) based on scientific evidence, not technical or economic considerations published anually in the List of MAK and BAT values and documented in the Toxikologisch-arbeitsmedizinische Begründungen, available also in an English translation Since 2012: All lists and documentations available in open access at Wiley VCH: http://onlinelibrary.wiley.com/book/10.1002/3527600418... as well as original publications to selected aspects in international peer reviewed scientific journals... Prior to final publication: 6 months time for scientific comments 3
Structure of the MAK commission Currently 35 members, permanent guests, guests and ad hoc experts, covering the fields of Epidemiology Occupational medicine Toxicology Pathology Analytical chemistry Related disciplines Scientific secretariat 4
Working groups Establishment of MAK values (Hartwig) Skin and allergy (Schnuch) Evaluation of components of metalworking fluids, hydraulic fluids and lubricants (Fatasch) Establishment of threshold values for dusts (Hallier) Establishment of threshold values in biological material (Drexler) Air analyses (Hebisch) Analyses in biological material (Göen) 5
Ad hoc working groups Classification of carcinogens (Greim) Percutaneous absorption (Bader) Carcinogenicity of biopersistent granular dusts (Greim) MAK values and prenatal toxicity (Greim, Schriever- Schwemmer) Heavy metals (Hartwig) Nanoparticles (Hartwig) Genotoxic carcinogens (with SKLM) (Hartwig) Exposure limits for local effects (with AGS) (Brüning) 6
Hazard identification vs. risk assessment Hazard identification Risk assessment Toxicokinetic Acute toxicity (inhalative, dermal, oral) Subacute, chronic toxicity Irritation (skin, eye) Sensibilisation (skin, respiritory tract) Genotoxicity, Mutagenicity Carcinogenicity Reproductive toxicity Mode(s) of action Reversibility Dose-response relationships NOEL, NOAEL Derivation of threshold values if possible 7
Derivation of MAK values: Data base Data collection Published literature with respect to epidemiological data, occupational medical reports, toxicological properties other relevant information Company reports, if full study report available, handled confidentially Data evaluation relevance for current assessment validity of the studies (e.g., according to OECD guidelines if possible, otherwise expert judgement) 8
Derivation of MAK values: General approach Identification of the most sensitive parameter related to the exposure of a given substance, taking into account local effects (mucous membranes of respiratory tract and eyes) systemic effects Decision on adversity by expert judgement Identification of a no observed adverse effect level (NOAEL) for the most sensitive and relevant parameter for substances without genotoxic/ carcinogenic properties 9
Derivation of MAK values for substances without genotoxic/carcinogenic properties 10
Derivation of MAK values: Effects in humans Occupational medical and epidemiological studies Preferentially longitudinal studies with repeated determination and documentation of past and present external and internal exposure In case of good quality data MAK value is established at level of NOAEL (preferred value approach: 1,2,5 ppm or mg/m³ etc.) Human volunteer studies Exposed under controlled conditions Establishment of NOAEL and dose-effect relationship In case of good quality data MAK value is established at level of NOAEL after correction for higher breathing volume at work places in case of systemic effects; consideration of longer daily exposure at work places if not indicated otherwise by toxicokinetic data (preferred value approach) 11
Derivation of MAK values: Effects in animals Minimum requirements: Valid 90-day inhalation study for assessment of local and systemic effects, or Valid 90-day study with oral application for assessment of systemic effects, accompanied by information about the local effects of a substance, especially on the respiratory tract Establishment of NOAEL Assessment of potential differences in sensitivity of humans, considering especially toxicokinetic and toxicodynamic data If not suggested otherwise by these data, MAK value is established at level of half the extrapolated NOAEL, after consideration of species-specific toxicokinetic correction factors (preferred value approach) 12
Derivation of MAK values: Effects in animals In some cases, the MAK value is derived from the NOAEL of a 28- day study: if critical effect is irritation (e.g., SAR, Draize-test, ph-value); usually no time-extrapolation required unless structure-activityrelationship to other compounds indicate the time-dependence of irritation if critical effect is systemic and SAR data are available otherwise no MAK-value II b 13
Derivation of MAK values: Effects in animals If no NOAEL, but dose-response curve for critical effect available: Expert judgement - severity of effect - steepness of dose-response-curve Benchmark-dose calculation if data suitable otherwise no MAK-value II b 14
Other relevant aspects. Carcinogenicity Germ cell mutagenicity Pregnancy groups Sensitizing effects (skin, respiratory tract) Sa, Sh, Sah Danger of percutaneous absorption H Limitation of exposure peaks Biological Tolerance (BAT), exposure equivalents established for carcinogenic substances (EKA) and BLW values established in case of insufficient data for setting a BAT value Consideration of surveillance of respective exposure and development of methods for analyses in air and biological materials 15
Values in biological media 16
BAT values Definition Concentration of a chemical substance, its metabolites or an effect indicator o o in appropriate biological material at which the health of an employee is usually not affected (even after repeated or long-term exposure) BAT values are based on a relationship between external and o internal exposure or o the effect of the substance BAT value exceeded: average concentration, in one person, after several investigations BAT values are not established for carcinogenic substances! 17
Biological values for carcinogens EKA (Expositionsäquivalente für krebserzeugende Arbeitsstoffe; exposure equivalents for carcinogenic substances) BLW (Biologischer Leitwert; biological guidance value) BAR (Biologischer Arbeitsstoff-Referenzwert; biological reference value) 18
Future challenges for setting occupational exposure levels Due to more detailed knowledge inclusion of more sensitive endpoints, for example subtle neurotoxic effects Frequently very complex data, which require very detailed evaluation of the adversity of the effects Establishment of health-based exposure limits also for carcinogenic substances Consideration of modes of action and conceptional work required Consideration also of non-cancer effects of the respective substance Evaluations and classifications of groups of substances (e.g., Granular Biopersistent Dust (GBS), nanomaterials, metal ompounds) Conceptional work required 19
Carcinogenic substances 20
Genotoxic/ carcinogenic substances: Background Important question: Is there a carcinogenic potential relevant under realistic exposure conditions? What are the underlying mechanisms involved? Is it possible to define threshold values which protect from carcinogenicity? Hazard identification vs. risk estimation Health based exposure limits for carcinogens at workplaces also required by the german legislation ( Gefahrstoffverordnung ) 21
The problem of dose-response-relationships in case of carcinogenic compounds Tumor incidence Measured values Extrapolation Black Box??? LOEL? Dose 22
The problem of dose-response-relationships in case of carcinogenic compounds Tumor incidence Measured values Extrapolation Black Box??? LOEL? Dose 23
The problem of dose-response-relationships in case of carcinogenic compounds Tumor incidence Measured values Extrapolation Black Box??? LOEL Current approach for genotoxic carcinogens? Dose 24
Past and current approaches for workplace carcinogens TRK-Values (technical guidance concentration) Strictly based on technological considerations; valid until 2005 Since 2005: Requirement for setting health-based exposure limits also for carcinogens In Germany two different approaches: Exposure-Risk-Relationships (Expositions-Risiko-Beziehungen; ERB) established by Ausschuss für Gefahrstoffe (AGS): Tolerated or accepted risks: 4:1,000 (tolerated risk); 4:10,000 (accepted risk 2013); 4:100,000; accepted risk 2018 at the latest) MAK categories 4 and 5 (since 1998; similar approach by SCOEL since 2008) 25
MAK categories for genotoxic/ carcinogenic substances 1. Substances that cause cancer in humans and can be assumed to contribute to cancer risk (adaquate epidemiological evidence or limited epidemiological evidence and mode of action relevant to humans) No MAK or BAT value established 2. Substances that are considered to be carcinogenic in humans based on sufficient data from long-term animal studies or limited evidence from animal studies, substantiated by evidence from epidemiological studies and/or supported by mode of action (in vitro tests, short-term animal studies) No MAK or BAT value established 26
MAK categories for genotoxic/ carcinogenic substances 3. Substances that cause concern that they could be carcinogenic to humans but cannot be assessed conclusively because of lack of data. The classification in Category 3 is provisional. a. Substances for which the criteria for classification in category 4 or 5 are fulfilled but for which the database is insufficient for the establishment of a MAK or BAT value. b. Substances for which in vitro or animal studies have yielded evidence of carcinogenic effects, but not sufficient for classification of the substance in one of the other categories (further studies are required). A MAK or BAT value can be established in the absence of genotoxicity. 27
MAK categories for genotoxic/ carcinogenic substances 4. Substances that cause cancer in humans or animals... and for which a MAK value can be derived. A non-genotoxic mode of action is of prime importance; no contribution to human cancer risk is expected at exposure observing MAK and BAT values (mode of action well understood, related for example to increases in cellular proliferation, inhibition of apoptosis or disturbances in cellular differentiation) Example: Granular biopersistant dust (GBD or GBS) (inert dust without additional specific toxicity) 28
Granular biopersistent particles (GBP) Lung as critical target organ upon inhalation Carcinogenic in experimental animals on high-exposure conditions (particle overload) Proposed mechanism: chronic inflammation, macrophage activation, secondary genotoxicity MAK value (respirable fraction): 0,3 mg/m³ (density 1 mg/cm 3 ) MAK carcinogenicity category 4 NOAEL and thus MAK/OEL should protect from chronic inflammation 29
MAK categories for genotoxic/ carcinogenic substances 5. Substances that cause cancer in humans or animals... and for which a MAK value can be derived. A genotoxic mode of action is of prime importance but is considered to contribute only very slightly to human cancer risk, provided the MAK and BAT values are observed (must be supported by information on the mode of action, dose-dependence and toxicokinetic data pertinent to species comparison) Up to now only five substances listed: Acetaldehyde Ethanol Isoprene Styrene Dichloromethane (new) 30
Example Styrene (MAK Category 5) Metabolism of styrene and styrene-7,8-oxide DNA adducts 31
Metabolism of styrene and styrene-7,8-oxide Critical metabolite formed by mouse, rat and man Extent assessed by biochemical marker Hb-adducts: Mouse 1 Rat 1/2-1/3 Man 1/20-1/50 Carcinogenic risk calculation for systemic styrene exposure Based on the positive oral studies in mice (lung tumors) and one positive oral study with styrene oxide in rats Exposure at the workplace (40 years, 8 hrs per day, 5 days per week, 48 weeks per year) at 20 ppm results in an estimated risk of about 1 : 20 000, which is well below the risk of endogeneous epoxides (for example, ethylene oxide) Category 5, MAK 20 ppm 32
Example Ethanol (MAK Category 5) Human carcinogen; critical metabolite acetaldehyde Concentration of ethanol in blood over time determines the internal body burden of the critical metabolite acetaldehyde Humans are physiologically exposed to ethanol due to endogenous ethanol production amount and range of internal life-time body burden are known correlation of external ethanol concentration with ethanol concentration in blood is also known at an exposure of 500 ml ethanol/m 3 during the entire working life, the average life-time body burden of ethanol is still within the range of variation of the endogenous body burden 33
Example Ethanol (MAK Category 5) From: Seitz and Stickel, Genes Nutr (2010) 5: 121-128 34
Life-time body burden [mg/l * years] Life-time body burden of ethanol without and with occupational exposure 50 25 0 0 500 1000 Ethanol concentration at the workplace [ml/m 3 ] workplace exposure to concentrations up to 500 ml/m 3 would contribute only little to cancer risk 35
Current discussion Science-based threshold values also for genotoxic carcinogens? Must be evaluated on a case-by-case basis Required information: All types of DNA lesions induced Dose-response-relationship in the low dose range for DNA lesions Cellular consequences of respective DNA lesions Endogenous background frequency of the same or similar genotoxic compound or metabolite and/or DNA lesions Toxicokinetic data/modelling 36
Current status New analytical methods enable measurement of some DNA adducts also as background frequencies and in the low dose range Frequently linear increase of DNA adducts with dose within the low dose range However, in some cases increase in mutation frequencies nonlinear dose-response curve Significance of DNA adducts for mutagenicity and carcinogenicity? 37
Currently Working group on Genotoxic carcinogens (MAK/SKLM) Aim: development of concepts for integrating the manifold mechanisms of carcinogenicity including current knowledge of cell biology into risk assessment and classification of carcinogens 38
Risk assessment of nanomaterials... published in 2013 39
Distinction of nanomaterials for toxicological risk assessment Grouping of nanomaterials to establish general approaches for risk assessment: Granular biopersistant particles (GBP) with no or little additional chemical toxicity ( inert particles) Toxic or potentially toxic metal-based nanoparticles Coated nanoparticles, e.g. quantum dots Fibre-like nanomaterials, e.g. nanotubes Nanoparticles as delivery systems, e.g. drug delivery 40
Microscale vs. nanoscale granular biopersistent particles (GBP) GBP microscale GBP nanoscale Quantitative or qualitative differences in toxicity and mode of action? Differences in uptake/passage through biological membranes? Differences in toxicokinetics? Differences in receptor interactions? Additional target organs other than lung (cardiovascular system, brain)? Chronic inflammation most sensitive parameter? Critical effect also for carcinogenicity? Differences in genotoxicity (direct vs. indirect genotoxicity)? In case of primarily quantitative differences, which parameters are decisive for setting OELs (e.g., mass, surface area/reactivity, single particles, aggregates)? 41
Summary and conclusions Evaluation of chemical substances at the workplace MAK and BAT values derived by expert judgement Extrapolation factors based on toxicokinetic considerations and data quality Conceptional work Increasing significance with respect to More subtle toxicological relevant effects Groups of substances (e.g., particles, metals) Chemical carcinogens Identification of research needs 42
Thanks to all members, guests and ad hoc experts of the MAK commission the scientific secreteriat of the MAK commission the DFG for financial and other support 43