Academic journal article The American Biology Teacher

Introducing Environmental Toxicology in Instructional Labs: The Use of a Modified Amphibian Developmental Toxicity Assay to Support Inquiry-Based Student Projects

Academic journal article The American Biology Teacher

Introducing Environmental Toxicology in Instructional Labs: The Use of a Modified Amphibian Developmental Toxicity Assay to Support Inquiry-Based Student Projects

Article excerpt

A current focus of instructional biology labs is to transition from traditional labs to inquiry-based formats that model the scientific process in which students formulate hypotheses, perform experiments, and analyze data. Environmental toxins and contamination generate concern and media coverage. Using a vertebrate developmental bioassay, students perform experiments investigating the environmental effects of toxins and contamination, encouraging interest in science. Experiments involving household chemicals such as cleaning agents, fertilizers, and pesticides give appreciation for their proper disposal.

The Frog Embryo Teratogenesis Assay-Xenopus (FETAX) assay is a widely used, validated vertebrate toxicity assay that uses the South African clawed frog Xenopus laevis (Bantle & Sabourin, 1991). Late-blastula embryos are incubated in control or test solutions under standardized conditions for 96 hours; then the 1-cm tadpoles are assessed for growth, malformations, and mortality (Nieuwkoop & Faber, 1975). Because fundamental developmental mechanisms are conserved, this model illustrates vertebrate embryonic development and is more relevant to humans than invertebrate models. Unlike most amphibians, Xenopus embryos are transparent, allowing easy observation of internal organs. The assay can be simplified to meet institutional constraints, provide valuable experiences in "hands on" science, and promote understanding of human environmental impacts. This assay is well suited for introductory college courses, AP Biology high school labs, and science fair projects.

* Learning Goals

Students will:

(1) Learn the scientific method, the process of science, by formulating hypothesizes about the effects of chemicals or samples on vertebrate development.

(2) Design and perform experiments using the developmental toxicology assay.

(3) Collect data, organize it into tables and graphs, analyze it with simple statistics, and interpret the meaning of their results.

(4) Present their results to the class, science fairs, or other venues, learning how to communicate scientific data.

* Materials & Methods

Instructors must follow all relevant institutional and government safety and disposal guidelines. Students must get the instructor's prior permission to bring in samples so that appropriate safety measures are taken. Animal care should be performed within the institution's regulations for animals in the classroom. Further information can be found at http://grants.nih.gov/grants/olaw/Guide-for-the-careand-use-of-Laboratory- animals.pdf (National Research Council, 2011).

Because frog embryos are aquatic, high-ionic-strength solutions may adversely affect development. Insoluble chemicals require carrier solvents that must be included in the controls. If highly acidic or basic chemicals are used, pH must be adjusted to 6.5-8.5 daily. As with any animal breeding studies, there can be variation in the number and quality of embryos.

Male and female X. laevis frogs (Xenopus One, Dexter, MI) are kept in separate aquaria (5 frogs per 10 gallons) to prevent spontaneous mating. The aquaria are kept at 22 [+ or -] 3[degrees]C with a 12:12 light:dark photoperiod and are best equipped with aerators and filters. Frogs are fed daily high-protein fishmeal pellets (Purina Aquamax Fish Pellets,1/4 inch). These standardized conditions (Bantle & Sabourin, 1991) for frog rearing ensure consistent and reproducible results for the assay.

* FETAX Solution

The FETAX solution below (pH 7.6-7.9) optimally supports embryonic growth and should be used for controls and all dilutions of toxicants (Dawson & Bantle, 1987).

Deionized/distilled water      10 L

NaCl                           6.25 g
NaHC[O.sub.3]                  0.96 g
KCl                            0.30 g
Ca[Cl.sub.2]                   0.15 g
CaS[O.sub.4] x 2 [H. … 
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