Scientists representing both sides of the Endocrine Disrupting Chemicals (EDCs) debate have agreed that thresholds for activity of EDCs may not exist. The conclusion is one of several reached during a recent meeting hosted by European Union (EU) chief scientific advisor Anne Glover in an attempt to identify areas of consensus and disagreement on the subject.
In the published minutes [PDF] of the meeting, the scientists say uncertainty about the existence of EDC activity thresholds—the exposure level or dose of a chemical above which toxicity or adverse health effects can occur—is due to experimental constraints and limited understanding of biological systems. They also agreed that defining EDC thresholds by in vivo experiments alone is not possible. Rather, establishing whether thresholds exist must be defined by better understanding “the mechanisms of action in a quantitative systems approach.”
The scientists also agreed with the World Health Organization’s 2002 definition of EDCs and that criteria for identifying endocrine disruptors need to consider the disturbance of homeostasis at different stages of development. In addition, they agreed that non-monotonic dose response effects exist for some EDCs, both in in vitro and in vivo tests. However, although reliable study designs to find non-monotonic effects are available, the scientists say that more dedicated methods are needed to evaluate possible effects of EDCs on humans. Furthermore, they noted that validated OECD guidelines for testing do not cover all adverse effects or modes of action of EDCs.
Meanwhile, the German Chemical Industry Association (VCI), which recently published its opinion on EDCs, believes that EDC thresholds do exist, despite uncertainty, and any discussion about setting regulatory limits on EDCs should be viewed in that context. Furthermore, the association argued that while in vitro tests can be used in order to inform the mode of action for EDCs, they should not be used to derive regulatory thresholds. In vivo testing should be used to test for endocrine disruption since it allows scientists to more meaningfully investigate the complex interactions in the hormone system.
VCI also criticized the group’s conclusions on testing as overly pessimistic, since OECD guidelines cover the most relevant endpoints for EDCs and provide a solid foundation to test chemicals for their estrogenic, androgenic and thyroid-endocrine properties.