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IRIS

IRIS Public Science Meeting (Aug 2020)

Meeting Objective

At IRIS Public Science Meetings, the IRIS Program encourages the scientific community and the public to participate in discussions on IRIS draft assessment materials. The scientific information and perspectives from the meeting would be considered as this assessment progresses.

At this meeting, the IRIS Program invited public discussion on the following draft assessment material:

  • IRIS Assessment Plan for Oral Exposure to Vanadium and Compounds (Scoping and Problem Formulation Materials)

Dates

  • The meeting was held on August 19, 2020.

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Meeting Materials

Meeting Agenda

On August 19, 2019, EPA hosted a public webinar to provide an opportunity for the public to give input and participate in an open discussion regarding the IAP for Inorganic Mercury Salt. See the final agenda and meeting presentation materials:

Oral Exposure to Vanadium and Compounds Assessment Manager: Erin Yost

Key Science Topics

What is an IRIS Assessment Plan? An IRIS Assessment Plan (IAP) communicates the plan for assessing each individual chemical to the public.  It includes summary information on scoping and initial problem formulation, specific aims and objects for the assessment, identifies key areas of scientific complexity, and it includes the PECO (Populations, Exposures, Comparators, and Outcomes) criteria that outline the evidence considered most pertinent to the assessment. The PECO provides the framework for developing literature search strategies and inclusion/exclusion criteria, particularly with respect to evidence stream (i.e., human, animal, mechanistic), exposure measures and outcome measures.

The IRIS Program is seeking a discussion with the public aimed at improving or clarifying the IAP. Below are questions to facilitate the discussion of these science topics:

  • Are the assessment objectives and specific aims articulated clearly?
  • Does the background information and context that is provided support the objectives for the assessment presented in the plan? 
  • Does the proposed PECO (Populations, Exposures, Comparators, Outcomes) framework identify the most pertinent evidence to address the stated needs of the Agency programs and regions?

Science Topics

Key Topic 1. Consideration of potential toxicity and toxicokinetic differences across vanadium compounds. Differential absorption has been observed across inorganic vanadium compounds. For instance, as described earlier in this document, studies in progress by NTP preliminarily report that drinking water exposure to sodium metavanadate (+5) in rats led to higher levels of vanadium in plasma and urine as compared to vanadyl sulfate (+4) at similar vanadium exposure levels. This is consistent with reports that vanadate (+5) is absorbed more readily in the gastrointestinal tract compared to vanadyl (+4) (Treviño et al., 2019; Nielsen, 1995). Absorption may be correlated with toxicity, as the effects observed by NTP were more pronounced following exposure to sodium metavanadate compared to vanadyl sulfate. To address these apparent differences, in addition to more fully characterizing the toxicokinetic differences across compounds (including potential interconversion within the body), EPA plans to conduct separate toxicity evaluations for different vanadium compounds where the evidence supports such an analysis.

Key Topic 2. Consideration of vanadium speciation. Available information indicates that vanadium in solution can readily interconvert between oxidation states and will form different spectrums of species as a function of factors including pH, concentration, and redox potential. For instance, tetravalent vanadium in drinking water is stable at acidic pH but can convert to pentavalent species at neutral or basic pH (Mutlu et al., 2017). Given the apparent toxicokinetic (and, likely, toxicity) differences across vanadium compounds (see Key Science Issue #1), study evaluations will, to the extent possible, consider factors that could affect vanadium oxidation state and speciation in the available toxicity studies. Speciation of vanadium at low environmental concentrations will also be of particular interest.

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