Sensitivity of different generations and developmental stages in studies on reproductive toxicity.

Numerous studies on reproductive toxicity are expected to be necessary under the EU program on Registration, Evaluation, Authorisation and Restriction of Chemicals (REACH). Therefore, it is important to analyse existing testing strategies including also the recently implemented extended one-generation reproduction toxicity study (EOGRTS, OECD guideline 443). For this purpose the responsiveness of the different generations and developmental stages in studies on reproductive toxicity is analysed and critical targets of reproductive toxicity are identified by using the Fraunhofer FeDTex database. The F1 generation is identified as most responsive generation in more than 50% of one-generation and multi-generation reproduction studies. Within the F1 generation the adult stage is mostly affected compared to the prenatal or postnatal stage. The target analysis in F1 has revealed alterations in body weight as highly sensitive for all developmental stages. Other important targets are the liver, kidney, testes, prostate, sperm parameters as well as developmental landmarks. The findings in the F2 generation have shown a higher responsiveness than F1 only in 3% of the studies. Although in 29 studies new effects are observed in F2 offspring compared to F1 irrespective of dose levels, overall no severe new effects have emerged that would change classification and labelling and justify an F1 mating. The presented data support the importance of F1 for risk assessment and demonstrate that the study design of the EOGRTS is a suitable alternative to two-generation studies. However, compared to a conventional one-generation study the EOGRTS may identify additional effects but will change risk assessment with respect to NOELs only in rare cases.

The Necessity of Developing New Criteria for Carcinogen Classification of Fibers by the Mak Commission.

The criteria for carcinogen classification of critical man-made mineral fibers (MMMF) by the MAK Commission are presently based on carcinogenicity and genotoxicity data. This classification is based on qualitative criteria. The MAK Commission considers all inorganic fibers and fibrous dust particles with a ratio of length to diameter greater than 3:1 and that are longer than 5 µm and have a diameter less than 3 µm to be potential carcinogens (category 3) (DFG, 1998; Creim, 1997). For chemicals in general, the MAK Commission has supplemented the three previously used categories "carcinogenic to humans," "carcinogenic to animals," and "suspected of having carcinogenic potential" with two additional categories. Chemicals that act primarily by nongenotoxic mechanisms and for which evaluation of low-dose exposure is possible are classified in category 4. Cenotoxic carcinogens for which risk at low doses can be assessed are classified in category 5. The essential feature of these two categories is that exposure at the workplace up to a given limit (MAK value) does not contribute significantly to the risk of cancer in humans. Thus, for classification of fibers into category 4 or 5, the evaluation of primary or secondary genotoxic effects is required. For the establishment of an MAK value for fibers, the identification of a no-observed-effect level (NOFL) representing a steady state of fiber uptake and elimination is necessary. Early inflammatory responses associated with changes in the parameters of bronchoalveolar lavage and cell proliferation in lung tissue are considered sensitive parameters for identifying the NOEL. Data on biopersistence under exposure conditions that prevent particle accumulation exceeding the steady-state conditions of the NOEL are required in order to consider the potential of fiber accumulation as an inherent fiber property including fiber dissolution and fiber disintegration. It is therefore necessary that the design of testing strategies to evaluate toxicity and carcinogenicity of fibers include dose-response studies to identify the NOEL of the most sensitive endpoint, such as by analysis of parameters of lung lavage, histopathol-ogy, and determination of biopersistence. Further, a basic understanding of the underlying genotoxic mechanisms is required for differentiation between primary and secondary mechanisms and their dose dependence.