In order to study the effects of a chemical on the environment, including the organisms that inhabit it, an Ecological Risk Assessment (ERA) is undertaken. One of the tools of an ERA is the use of biomarkers, which are measurable changes in certain aspects of a cell, tissue, organ, or organism that can accurately and consistently indicate the presence and/or activity of a particular chemical pollutant (see figure 1). Although we disproportionately care more about large animals such as deer, bears, and fish, tiny organisms are the preferred indicators, because they are plentiful and easy to work with. In aquatic environments, we have traditionally exploited the water flea, Daphnia, and midge larvae of the family Chironomidae. However, the amphipod Hyalella azteca has been gaining traction due to its unique ecological niche. The fact that this species dwells at the soil-water interface makes it an ideal candidate to represent the toxicological conditions at this particular location.
Gott chose several chemicals that were classified as either metals (cadmium and copper) or organic pesticides (permethrin, DDT and imidacloprid). The first two were chosen due to the fact that man-made structures like refineries and power plants can concentrate them at levels much higher than those at a typical background level. The latter three were selected because insecticides are very widely used and can easily be distributed in bodies of water through pesticide drift. However, both toxin types can lead to a litany of cellular and physiological problems. After completing his experiments, Dr. Gott found some very interesting results during the analysis phase. Not only were there clearly observable changes in gene expression after chemical exposure, but several of the genes that responded to the metals also responded to the insecticides (see figure 3). Those genes whose expression was altered include cnc, which codes for a protein responsible for activating other proteins which handle stressors, Hsp90, a protein chaperone, and Mrp4, a transporter protein that moves molecules across the cell’s membrane.
About the author: Justin Rosenthal is a 4th year PhD. Candidate studying under Dr. Jian Wang, and is also in the Entomology Department at the UMD. He is using the Drosophila model system to uncover important signaling pathways involved in nervous system development, specifically at the level of the individual neuron.