The two fundamental issues raised by Castleman and Ziem [ 19881 concern the scientific validity of the evidence on which threshold limit values (TLVs) are based and the process by which a given value is selected.
The climate of social opinion has changed since the TLV committee was first established. Assuming that no rebuttal is received, then the events recorded by Castleman and Ziem, do not provide confidence in present practices. Due process of openness and freedom from vested interests must be demonstrated in order to reassure the scientific community and to protect independent members of the committee from calumny. To an extent, they are victims of their own success. The Guidelines have been of great practical benefit, and volunteer members, many of whom have no vested interest, have contributed valuable work. However, despite a carefully written warning in the introduction, the values have been used for legislative purposes in a number of countries and are widely misquoted as distinguishing safe from non-safe conditions.
The problem is to determine how concerns about the issue can best be channeled into productive effort. The TLV proposals have filled a vacuum created by the inability of other agencies to cope with the massive effort required to produce critical reviews of epidemiology and toxicology pertaining to major industrial chemicals. Estimates of risk and serious evaluation of claims of "no hazard in our experience" appear to be valid scientific areas that can and should be critically reviewed by appropriate experts. In many areas this process is almost certain to rely heavily on information and interpretation supplied by industry. Some mechanism needs to be developed so that this can be obtained in a way that guarantees confidentiality.
The choice of a specific TLV is a political issue, since it is based on the concept that some health risk will be borne by workers. It is inappropriate for international teams to assume this responsibility. It will be important to ensure that input on behalf of those at the receiving end is from individuals who actually work in plants where the substances are used.
Bias is a difficult issue in the politics of occupational health. Financial or political commitment is easily understood, but even the vested interest generated by maintaining the normal courtesies of friendly relations can be potent. For this reason, some form of anonymous voting in the final evaluation of risk estimates may have advantages. The method facilitates discussion but eliminates pressures on individuals.