All Shrimp Go To Heaven

Carolina Rios, New York University

The Approach: In my previous post, I discussed the negative impact that polychlorinated biphenyls (PCBs), long-lived chemical contaminants, can have on marine ecosystems and human health. Currently, I am working to verify a proposed model to estimate the impact that PCB contamination has on benthic marine invertebrates.

One of the issues with this proposed model is that it is based on data generated from the 1970s; and the analytical methods now available to scientists are much more sensitive and precise. To verify this model, we will generate contemporary data by running a series of short (acute) toxicity tests.

Testing

Test setup for grass shrimp (P. pugio)

In these acute toxicity tests, we measure the response of three species of marine invertebrates to PCBs. The three organisms that we are testing are grass shrimp (Palaemonetes pugio), amphipods (Leptocheirus plumulosus), and mysids (Mysidopsis bahia). We will be measuring mortality from PCB contamination. The standard tests that we are running consists of 6 concentrations, ranging from 6.25 ppb (parts per billion) to 420 ppb. It is important that we also have a control, so that we can understand the response of the organisms unaffected by PCBs. For the grass shrimp and amphipods, the test will run for 96 hours and we will renew the PCB solutions every 24 hours. Samples will be taken for chemical analysis at 0 hours, 24 hours, and 72 hours, so as to measure both the loss of PCBs over the 24 hour period, as well as the consistency of dosing. Loss of PCBs can be attributed to PCBs binding to the glassware and differences in dosing can be attributed to user variability. For the mysids, the test will also run for 96 hours, but the dosing solutions will not be renewed after the initial dosing. Samples will be taken at 0 hours, 48 hours, and 96 hours, so as to measure the loss of PCBs over the 96 hour period. For all tests, mortality will be recorded every 24 hours until the end of the test.

Analysis

Solid Phase Extraction apparatus. Dosed samples are within the large reservoirs at the top of the apparatus. PCBs will be isolated on the nonpolar solid phase, which consists of the smaller columns below the reservoirs.

The PCBs from the collected samples will be isolated through solid phase extraction. Solid phase extraction consists of a nonpolar solid phase and a polar liquid phase; similar to how oil cannot be mixed into vinegar, PCBs are not very soluble in water. As PCBs are nonpolar and hydrophobic, they will bind to the solid phase. The PCBs can then be lifted off of the column by running a nonpolar solvent (ethyl acetate) through the nonpolar solid phase. The sample is then analyzed using gas chromatography-mass spectrometry (GC-MS). The essential concept of GC-MS is that molecules will separate based on differences in size. This is how the amount of each individual PCB is determined, which can then be used to calculate an actual concentration. Analysis of the chromatograph can give more accurate concentrations, allowing us to understand how concentrations vary over time. This will give us a better understanding of the relationship between dose concentrations and the mortality response.

Acknowledgements

I would like to thank Dr. Ed Wirth and Brian Shaddrix for their continued guidance and support, as well as my co-mentor Dr. Paul Pennington. Supported by the Fort Johnson REU Program, NSF DBI-1757899.

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