Service learning in the Ecuadorian Amazon: Developing an inexpensive and easily interpretable plant bioassay for monitoring bioamendment mediated reductions in soil toxicity

Background/Question/Methods

Service-learning is a method by which students learn through active participation in organized service that is conducted in and meets the needs of a community. Environmental education combined with service learning can foster civic responsibility and strengthen proficiency with field ecological methods. We organized and conducted service-learning courses in an oil-contaminated region of the Ecuadorian Amazon. Students from numerous universities and local villages conducted ecological research on the impact of oil pollution on biodiversity and community health. Students generated original hypotheses and designed experiments for testing their predictions. Students cultured microbes and plants within a petroleum pollution gradient and conducted multi-factorial experiments with microbial inoculant for remediating petroleum-contaminated soil. Students developed a plant bioassay for documenting the effectiveness of these inoculants for detoxifying contaminated soil. Our students performed plant inhibition bioassays by planting seeds and measuring germination frequencies across a range of petroleum contaminated soils between 0.0% vol./vol and 80% vol./vol. petroleum. These plant performance bioassays measured the efficacy of the microbial inoculants at decreasing soil toxicity. Seedling shoot height (mm), and above-ground biomass yield (grams) were recorded. In addition, total recoverable petroleum hydrocarbon analyses were conducted for quantifying the effectiveness of this bioassay.

Results/Conclusions

In order to determine the appropriate model organism for the bioassay, students experimented with several plant species within a range of petroleum-contaminated soils. Seeds of Lolium perenne and Lycopersicon esculentum demonstrated between 40% and 60% yield reduction and germination at 2.5% vol./vol. petroleum contaminated soil. Lolium perenne and L. esculentum seeds were planted in control and contaminated soils treated with bacterial and/or fungal inoculants. All of the fungal treatments demonstrated a significant increase in above ground plant yield in both L. esculentum and L. perenne. In addition, the combined effect of fungal and bacterial treatments demonstrated a strongly significant increase in L. perenne above-ground shoot height (mm). Soils without microbial inoculants had significantly higher total petroleum hydrocarbons (TRPH) than soils with added inoculant. However only the combined effect of the fungal and bacterial treatments showed a more significant reduction in TRPH than either the fungal treatment or the bacterial treatment alone. The costly TRPH test could be avoided with the use of this student-developed plant bioassay in the Ecuadorian Amazon.  This plant bioassay is an inexpensive and easily interpretable metric encouraging citizen scientists to build data sets for determining the effectiveness of the inoculant-mediated decreases in soil toxicity.