The U.S. Environmental Protection Agency (USEPA) is validating an assay for use in determining the adverse consequences of exposure to endocrine-active substances on the development and reproduction of amphibians. The assay involves exposing Silurana (Xenopus) tropicalis to low levels of chemicals from embryonic development through reproductive maturity. Histopathology is a core endpoint in this test. However, little technical guidance exists describing the collection, fixation, and processing of tissues, or the potential diagnostic criteria and approaches to grading the severity of lesions. Therefore, in an effort to optimize repeatability and reduce bias in the assay, the USEPA is seeking expert guidance for developing protocols for processing tissues, the general histological assessment of tissues, approaches to reading histological studies, determining appropriate diagnostic criteria and severity grading schemes for the criteria, potential interpretive difficulties, and data reporting and analysis.

EPA is identifying qualified pathologists for potential future consultation to develop this guidance. The pathologists ideally shall possess a majority of the following experience/proficiencies/qualifications:

• General practices of toxicologic pathology
• Reading toxicologic pathology studies performed on amphibians
• Familiar with normal amphibian histology and physiology
• Familiar with general responses of amphibian tissues to toxicologic insult
• Preferably board certified (e.g., American College of Veterinary Pathologists, the European College of Veterinary Pathologists, or other certifying organizations), however if not possible, he/she must have obtained sufficient experience with, and knowledge of, amphibian histology and toxicologic pathology.

Battelle, a private contractor, is supporting the USEPA to identify candidate amphibian pathologists and submit their names and qualifications to the USEPA. At some time in the future, the USEPA is expected to select those pathologists that will participate in a workshop for developing the guidance document.