A weight of evidence approach (measure of the strength of data) relies on all available information. It recognizes that some tests have greater diagnostic precision than others in determining whether and at which exposure levels adverse effects will actually occur in living beings. Likewise, such an evaluation process assesses the consistency of data that supports a specific conclusion. A clear picture can only be obtained when all data are considered and weighed by importance. For example, observation of an adverse effect in an animal would have greater weight than the response of cells in isolation (in vitro).

Modern toxicology utilizes sensitive techniques that measure changes in biological processes at the cellular or sub-cellular level, often without the use of animals. Numerous test methods have been developed to assess the potential of substances to interact with components of the endocrine system. These tests cover a range of biological levels – from in vitro studies at the cellular level to whole animals.

To determine whether interactions with the endocrine system is how a substance causes adverse effects and the potential risks that may be posed by environmentally relevant levels of exposure, a weight of evidence evaluation is necessary, including:

• Laboratory toxicity studies, which typically follow internationally accepted test guidelines consisting of short- and long-term dosing, reproductive and developmental toxicity tests that define adverse effects in an animal, the doses at which effects are observed and the doses below which no effects are seen;
• Screening tests that identify potential interactions with components of the endocrine system (many can be performed in vitro with cell cultures or sub-cellular components);
• Data from studies aimed at identifying the mode of action underlying adverse effects and relevance to humans or wildlife;
• Data on environmentally relevant exposures and movement of a substance within a living being that characterizes concentrations at the active site in the being; and
• Use of objective evaluation criteria for assessing the quality and reliability of available studies, integration of data, understanding of the mode of action and knowledge of relevant exposures.

For more information about the Weight of Evidence Approach, click here.