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The Toxicity of Methyl Mercury to Larval Teleost Fishes: A Mechanistic Examination of Teratogenicity, Reproductive and Developmental Toxicity

EPA Grant Number: F5D91351
Title: The Toxicity of Methyl Mercury to Larval Teleost Fishes: A Mechanistic Examination of Teratogenicity, Reproductive and Developmental Toxicity
Investigators: LANGSNER, MARY E.
Institution: University of California - Santa Cruz
EPA Project Officer: Willett, Stephanie H.
Project Period: September 1, 2005 through June 1, 2008
Project Amount: $107,252
RFA: GRO Graduate Fellowships (2005)
Research Category: Academic Fellowships

Description:

Objective:

The main objective of this project involves the idea that multixenobiotic resistance (MXR), a protective transport mechanism, exists in embryonic teleost fish and resists the cellular accumulation of methylmercury (MeHg), thereby preventing MeHg-associated toxicity.

The four primary objectives of this work are to

  1. Establish methods to detect and quantifiably assess MXR activity in larval teleost (bony) fish using the model aquatic vertebrate zebrafish (Danio rerio)
  2. Use these methods to assess whether MeHg is a substrate for MXR transport proteins, using the model laboratory species zebrafish
  3. Determine the relevance of MeHg exposure route on the ability of MXR to prevent MeHg accumulation (again using the model laboratory species zebrafish). (These experiments will address the transfer and bioavailablity of MeHg to embryonic Chinook salmon (Oncorhynchus tshawytscha) during environmental exposures.)
  4. Modify the zebrafish methods to quantifiably detect MXR in the native species of interest - Chinook salmon - and determine if a correlation exists between environmental MeHg concentrations and MXR activity, using wild populations of Chinook that spawn in various San Francisco Bay tributaries.

Approach:

The proposed research combines a multitude of approaches, primarily utilizing basic tools of molecular biology to assess protein activity and titer during a series of developmental periods in zebrafish (Danio rerio). The combination of approaches used in the proposed work will initially provide an in vivo qualitative detection of MXR as well as an in vitro quantitative measurement of MXR activity, at each stage of zebrafish embryo development. The development of these methods is critical in order to carry out experiments that first address the relevance of methylmercury (MeHg) exposure route on the ability of MXR to resist MeHg accumulation, and subsequently address the transfer and bioavailability of environmental MeHg to developing embryos. Nonetheless it is also imperative to demonstrate the applicability of the zebrafish MeHg studies to the phylogenetically equal but ecologically relevant native species of interest, Chinook salmon (Oncorhynchus tshawytscha), by also establishing MXR’s presence in embryonic salmon using the same combination of approaches. Therefore MXR in developing salmon will be evaluated at critical developmental periods analogous to the developmental periods studied in zebrafish, to detect and quantify MXR activity through early salmon development. Lastly, MXR activity in wild populations of spawning Chinook salmon (from various tributary streams of San Francisco Bay) will be used to evaluate the relationship between environmental MeHg and MXR activity, in the wild.

Rationale:

The proposed research relates to methylmercury (MeHg) toxicity in embryonic Chinook salmon (Oncorhynchus tshawytscha). Chinook home to certain tributary waters of San Francisco Bay which are contaminated with MeHg from various sources. As a consequence, embryonic salmon are plausibly exposed to MeHg via contaminated sediment and/or water during critical periods. It is important to evaluate potential routes of exposure when investigating mechanisms of protection from foreign compounds (xenobiotics). Multixenobiotic resistance (MXR) is a protective mechanism that exists in various organisms and resists the accumulation of xenobiotics, but little is known about MXR in embryonic fish. The crux hypothesis of this work involves the ability of MXR to resist MeHg accumulation in embryonic Chinook salmon, the target native species.

Expected Results:

  1. Develop methods to detect and quantify MXR activity in zebrafish (Danio rerio) embryos as well as Chinook salmon (Oncorhynchus tshawytscha) embryos
  2. It is anticipated that methylmercury (MeHg) is a substrate for MXR transport proteins, and that MXR activity (i.e. capacity to resist accumulating environmental MeHg) can be used to assess relevance among various routes of MeHg exposure. Lastly, that these principles can be used in field investigations that address larger-scale population issues.

Supplemental Keywords:

Multixenobiotic Resistance (MXR), Methylmercury (MeHg), teleost fish, Zebrafish (Danio rerio), Chinook salmon (Oncorhynchus tshawytscha), toxicity, development, , Water, Scientific Discipline, Mercury, Ecological Risk Assessment, Environmental Chemistry, Environmental Monitoring, fisheries, teratogenicity, aquatic, methylmercury, developmental toxicity, bioaccumulation, mechanisms of mercury formation, zebrafish, toxicology

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The perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.

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