October 2004 - Announcement of project for the re-evaluation of human and mammalian toxic equivalency factors (TEFs) of dioxins and dioxin-like compounds and request for information
Call for proposals on how to derive relative potency values - TEFs
The present method to derive TEF values for dioxin-like compounds based on expert judgement, results in point estimates without an indication of underlying uncertainties. This method has been applied by various governmental agencies during the last decades. In recent years, several individual scientists as well as organizations have suggested possible alternative approaches for deriving TEFs using different approaches, including distributional statistics.
To ensure the widest possible input, individuals and organisations are requested to provide information and proposals with a main focus on derivation of TEFs:
- Methods and approaches for the derivation of TEFs based on available literature. These can include quantitative (statistical) methods such as establishing an uncertainty range of available relative potency data and application of a specified cut-off value to derive TEF values; application of weighting factors to existing data, etc.
Information and data to address the following questions are also requested:
- Inclusion of mono-ortho PCBs in the present TEF concept: is this still justified, in light of new information that some studies with these mono-ortho PCBs may be compromised due to contamination with more potent dioxin-like compounds?
- Should other compounds be considered for inclusion in the TEF concept taking into consideration the prerequisites for inclusion outlined in Ahlborg et al 1990 and Van den Berg et al 1998?
- The current WHO-TEF values are applicable to direct intake e.g. through food and human milk. Application of TEF values is also frequently used for internal concentrations e.g. in plasma or adipose tissue. To what extent could/should internal (tissue/plasma) WHO-TEF factors be established in the future?
When providing information and proposals to WHO, it should be kept in mind that during the re-evaluation process studies that will be taken into consideration are only those that have been published in peer-reviewed literature or by recognized national science programmes such as the US National Toxicology Program.
Submissions of proposals and information are requested before 15 March 2005
and should be sent to:
Prof. Dr. Martin van den Berg
WHO Collaboration Centre for Environmental Health Risk Assessment
Institute for Risk Assessment Sciences, Utrecht University
PO Box 80176, 3508 TD Utrecht, The Netherlands.
with copy to:
Dr Angelika Tritscher
International Programme on Chemical Safety
World Health Organization
20, Avenue Appia, CH-1211 Geneva 27