Chemical testing strategies for predicting health hazards to children

Tiered toxicity testing: evaluation of toxicity-based decision triggers for human health hazard characterization

A set of biologically-based toxicity testing decision triggers was developed and analyzed within a tiered testing and decision-making framework for evaluating potential human health hazards and risks associated with chemical exposures. The proposed three-tiered toxicity testing approach starts from a base set of toxicity studies (acute toxicity, in vitro genetic toxicity, in vitro cytogenetics, repeat dose/subchronic toxicity, developmental toxicity, reproductive toxicity) and then uses the toxicity triggers to identify which specific additional tests are needed to adequately characterize a substance's hazard potential. The toxicity triggers were initially evaluated using published information for eight chemicals, representing diverse classes. A retrospective validation study was then conducted using seven chemicals which had completed the USEPA's Voluntary Children's Chemical Evaluation Program (VCCEP). The toxicity triggers were shown to identify appropriate higher tier tests and to be reasonably predictive of the results expected in higher tiered tests. Employing these toxicity triggers within a tiered testing framework could lead to a reduction in the number of laboratory animals without diminishing the degree of scientific certainty necessary for hazard evaluations. The toxicity triggers appear to be suitable for identifying which specific endpoints and tests warrant further evaluation, and which do not, and for documenting the scientific basis for such decisions.

Risk Assessment of Endocrine Disrupters: The Role of Toxicological Studies

Endocrine disrupters (ED) represent a good challenge for experimental toxicology. In order to deal with several critical points relevant to risk assessment: (a) ED may induce long-term effects upon exposure in susceptible developmental phases, including postnatal life up to puberty; thus, efforts are required to refine testing strategies, for example, by supporting the two-generation rodent study with a comprehensive in vitro/in vivo screening battery; (b) due to the regulatory role of endocrine homeostasis, mechanisms of endocrine disruption may impact on immune, neurobehavioral, and reproductive development, as well as on susceptibility to cancer; (c) the potential multiple exposure to ED with common targets through diet and/or living environment calls for the development of models to understand mechanisms of interactions and effects of mixtures; and (d) last but not least, ED may interact with a number of factors related to differential vulnerability of individuals or population subgroups, including the intake of nutrients or bioactive food components. Besides reducing the chance for noxious chemicals to enter our life, toxicological research on mechanisms may also lead to the definition of possible biomarkers of exposure, effect, and susceptibility that may be further exploited in human health surveillance.

Implications of research in male-mediated developmental toxicity to clinical counsellors, regulators, and occupational safety officers

In closing, let me return to the somewhat irreverent question that I asked at the beginning: Apart from what we learn about fundamentally important biological processes, does male-mediated developmental toxicity make any practical difference? The answer is no, yes, and we don't know. No: The risk of serious birth defects in the future children of a man who is concerned about exposure to radiation or chemicals in the remote past does not appear to be measurably increased in comparison to the background. Yes: Male-mediated developmental toxicity may be of sufficient concern to restrict certain exposures in the population as a whole, but in order for male-mediated developmental toxicity to be determinative, these conditions will have to be otherwise non-toxic. To date, no exposures have been identified that produce substantial male-mediated developmental toxicity in the complete absence of other kinds of toxicity. We don't know how big a problem male-mediated developmental toxicity really is because we have not studied a large enough number and variety of exposures. We don't know if our perspective will change as we begin to understand the importance of individual susceptibility better. We don't know all of the mechanisms that may be involved in male-mediated developmental toxicity or their general biological importance. We don't know more than we do know about male-mediated developmental toxicity, and we are anxious to learn more.