By: Marcus Ramos-Pearson, Scott Weir
Abstract
Gibberellic acid (GA3) is a plant hormone commonly used in the agricultural industry to increase crop yield. Gibberellic acid is considered a crop additive and thus has been tested for acute toxicity by the US EPA as required by law. The EPA concluded that it was not hazardous to aquatic invertebrates because the LC50 concentration was above environmentally relevant levels. However, their conclusion came from an acute LC50 concentration of one aquatic invertebrate species (Daphnia magna). The purpose of this study is to expand upon their research due to the lack of data their report provides. This study used a modified EPA protocol for acute testing of crop additives on aquatic invertebrates. Buffered and unbuffered gibberellic acid solutions were used to determine if acidity was causing toxicity. Daphnia pulex were used alongside D. magna as a comparison to determine if they have different sensitivities to gibberellic acid. A chronic study was done as well using only D. magna. There was no statistical difference in LC50 concentration between the buffered and unbuffered solution for D. magna. This suggests that the toxicity of gibberellic acid comes from the structure itself and not from its acidity. There is also no statistical difference between the two species tested; although, the data suggest that D. pulex may be more tolerant to the compound. The mean number of offspring per replicate decreased in the three highest concentrations in the buffered acute D. pulex. Sub-lethal effects could possibly be seen at environmentally relevant levels.