health surveillance and/or diagnosis.
Relationship of occupational toxicology to other disciplines relating to workplace chemicals
As is apparent from the preceding sections, the overall management of workplace chemicals requires input from various disciplines. These include occupational toxicology, hygiene, medicine and epidemiology. All are specialities in their own right but each is required for satisfactory attention to this important endeavour. For this reason individual chapters have been included on each of these aspects. The practising occupational toxicologist must have an appreciation of these other areas to make the most meaningful input into the overall deliberations on issues involving occupational exposure to chemicals. As alluded to above, the need to consider information emanating from each of these fields is particularly apparent during the standard’s setting process for chemical exposures and during resolution of workplace problems involving chemicals.
Future directions and challenges for occupational toxicology
Continued vigilance and improvement in the safety of chemical products should be a goal for those of us working in the area of occupational toxicology. There are some particular issues that are deserving of and will receive increasing attention over the coming years.
Some are issues relating to toxicology in general while others are more specific to occupational toxicology.
The ethical issues associated with animal testing and the dilemma faced in trying to balance this with protecting human health continue today and will continue for some time yet. This matter was addressed by Purchase (1999) whereby he used a recent development in toxicology—endocrine disrupters—to illustrate this dichotomy.
The continued development of in vitro tests should be a priority because this will have both humane (as in the previous paragraph) and economic benefits once successfully established. It will also allow a more rapid procedure for assessing the toxicity of chemicals. While there have already been some considerable achievements in the area of in vitro toxicology (Tyson and Stacey 1992) it must be appreciated that there is much work to be done and that human health must not be compromised. In the years since the first edition of this textbook, it is the opinion of the authors that progress has been slow in this important area, especially with regard to the use of in vitro data in risk assessment.
The toxicity of mixtures remains an issue as it is appreciated that people are exposed to many chemicals simultaneously and that the vast majority of toxicological data are on the individual chemicals. This presents a massive problem, as it would not be possible to test all permutations and combinations of chemicals to which humans may be exposed.
Here there may be a role for in vitro systems as a screen for likely problem mixtures, although this is still to be realised. It does seem, however, that calculation of the toxicity of mixtures based on their individual ingredients is becoming used and accepted more often and that, usually, the calculated value has been found to be consistent with the toxicity when this has actually been determined.
The greater application of molecular biological tools to aid toxicological assessment continues to emerge. One example is the use of transgenic mice so that genotoxic chemicals can be identified in multiple organs, with all body systems interacting so that a more reliable indication of likely applicability to the human can be obtained. A second application, which has had an impact on toxicological matters relating to the workplace, is found with the identification of adducts to cellular macromolecules as indicators of carcinogen exposure. These adducts, especially those to DNA—the genetic material—are thought to reflect exposure at the critical site of action of the chemical. The promise continues to emerge of being able to monitor workers for exposures at a site where differences in disposition and interaction at the molecular target and repair mechanisms in that individual are no longer an unaccounted for entity.
There will also be increasing attention to the detection of toxicity that may have been unappreciated in the past due to inadequate measurement techniques. Examples of these can be found with investigations into neurobehavioural effects of solvents, and perhaps insecticides, and greater emphasis on immunological alterations induced by chemicals and the relevance of such changes to the organism as a whole. For example, improvement of cognitive test regimens may well assist in more reliably predicting the neurotoxic effects of chemicals in humans (Slikker et al. 2000). Another example is the
improvement in monitoring in recent years, such as the measurement of serum bile acids to reflect possible subtle hepatic effects of solvents (Driscoll et al. 1992; Franco 1991;
Neghab and Stacey 2000).
It might also be anticipated that with the passage of time there will be an improvement in data used for hazard assessment for occupational chemicals. Toxicology in general would also benefit substantially from improvements in models used for hazard assessment. This is exemplified by the increasing use of the pharmacokinetic modelling approach in recent times (Andersen 1995). However, it must be remembered that substantial amounts of data are required in the first instance to allow the successful application of such models.
Three final issues deserve special mention because of their importance, and because they are not really the province of the occupational toxicologist but impinge greatly on our efforts.
■ Firstly, it is apparent that even the existing toxicological knowledge is not always transmitted and disseminated as well as it should be. Efforts to improve this should be continued.
■ Secondly, it would seem that chemical-related injury in the workplace may be reduced by invoking programs to change attitudes with regard to exposure to occupational chemicals. It seems as if even when the knowledge is there it is sometimes ignored for questionable reasons.
■ Thirdly, it will be difficult to evaluate the benefits of such programs because our baseline knowledge of the extent of workplace chemical-related injury is unknown.
While it should be appreciated that this is a difficult problem, it will be essential to have such knowledge in the future to determine the areas where resources should be concentrated. Finally, while there have been some advances since the first edition of this textbook, it is the opinion of the author that it has been slow moving. While the reasons for this would be manifold, the expression of will by government, industry and the scientific community has to be regarded as a contributing factor.
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