Project Summary:
Trichloroethylene (TCE) and tetrachloroethylene (perchloroethylene; PERC) are two volatile organic compounds
(VOCs) that significantly contaminate the environment after a legacy of industrial use in the mid-twentieth
century. TCE and PERC are known or suspected carcinogens and are linked to congenital defects and
neurodegenerative disease. The US EPA regulates TCE and PERC in drinking water with a maximum
contaminant level of 5 ppb (parts per billion; µg/L); however, ground water levels can be greater than 300,000
ppb at Superfund sites. The proposed research seeks to address gaps in knowledge about the developmental,
delayed, multigenerational, and transgenerational toxicity of TCE and PERC though focused experiments using
the zebrafish (Danio rerio) model. A second goal is to determine how zebrafish metabolize these VOCs, as
species differences in metabolism represent an obstacle in modeling human health outcomes in laboratory
animals. The overarching hypothesis is that developmental exposure to VOCs like TCE and PERC causes acute,
delayed, and epigenetic toxicity that affects body system development and behavioral outcomes throughout the
zebrafish life-course and subsequent generations. It is further hypothesized that metabolism of TCE and PERC
is necessary for some of the toxic effects and the metabolites produced are dependent on the intrinsic metabolic
profile of the zebrafish model. The first aim of the proposed research will test the hypothesis that the VOCs TCE
and PERC cause acute toxicity in larvae and delayed toxicity in adult zebrafish after developmental exposure.
Developmental toxicity will be evaluated in larvae through acute toxicity assays, tests of behavior, and
morphologic measurements, while delayed toxicity will be assessed through reproductive, behavioral, and
morphologic endpoints. The second aim will test the hypothesis that TCE and PERC cause multi- and
transgenerational toxicity through the measuring of similar endpoints in F1 and F2 generation progeny and also
seeks to identify a mechanism of epigenetic toxicity through the evaluation of DNA methyltransferase expression
and global DNA methylation status in TCE exposed fish and their progeny. Finally, the third aim will test the
hypothesis that metabolites of TCE and PERC are partially responsible for toxicity and will characterize the
metabolism of TCE in zebrafish. The exposure water will be monitored via GC-MS and HPLC analysis to
determine the change in TCE concentration over time and the predominant metabolites excreted by zebrafish.
The developmental toxicity of major metabolites of TCE and PERC will be determined. Additionally, the gene
expression of common metabolic enzymes will be evaluated to determine how the expression of these enzymes
changes over time and after embryonic TCE exposure. The proposed studies would significantly address key
gaps in the VOC literature and inform toxicity modeling and regulatory efforts. Additionally, the proposed
experiments are designed to be approachable and intuitive to undergraduate, graduate, and professional
students, according to the goal of the R15 REAP grant program.