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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America’s Continuing Toxic Legacy: Quantifying the Impact of PCBs

Carolina Rios, New York University

The Problem: Polychlorinated biphenyls (PCBs) are a legacy contaminant that pose a threat to human health. PCBs are classified as possible carcinogens and are known to affect neurological development and contribute to diabetes (Xue et. al 2014). Additionally, PCBs are known to alter liver function, impact immune and thyroid function and effect reproduction, as well as gastrointestinal and respiratory health (Hansen 1987). Humans are largely exposed to PCBs by consuming contaminated animal products, such as contaminated fish or dairy (Xue et. al 2014). Similarly, dolphins sampled near Brunswick, Georgia were found to have elevated levels of PCBs, likely due to the consumption of contaminated fish (Wirth et. al 2014). The hydrophobic properties of PCBs mean that they bioaccumulate and can be found in aquatic organisms in concentrations thousands of times greater than the surrounding environment (Nimmo et. al 1974). PCBs also biomagnify up trophic levels in the web, and can be found in even greater concentrations in predator species, as they consume contaminated prey. Thus, the effects of PCBs can be felt throughout the ecosystem.

As PCBs are still relevant contaminants, it is important that we are able to quantify injury associated with PCB levels found in the coastal environment. It is particularly difficult to assess this risk to benthic marine invertebrates (organisms that live in the interface between the bottom of the ocean and the sediment). Therefore, a model has been proposed that predict rates of injury to benthic marine invertebrates (Finkelstein. et al 2017). This model was created through an extensive literature search. However, the data collected as the basis of this mathematical model dates back to the 1970s. In order to verify this model, it is important that we generate new data to verify the accuracy of the model in predicting benthic marine invertebrate injury.

Biphenyl structure. PCBs consist of a biphenyl structure of varying degrees of chlorination. Created using Chemdraw

PCBs were produced for industrial use, such as dielectric fluids, hydraulic fluids, and heat transfer fluids. From 1929 to 1977, PCBs were produced by the Monsanto Corporation in the US, before being removed from production due to negative effects on human health and the environment. Of the 1.4 billion pounds of PCBs produced in the US, it is estimated that one third has entered the environment (Safe et. al 1987). Though they are no longer being produced, their stability and long half-life means that PCBs are still present and continue to pose a real threat to the environment.

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.

References

Finkelstein, K. & Beckvar, N. & Dillon, T. (2016). Benthic injury dose-response models for PCB-contaminated sediment using equilibrium partitioning. Environmental toxicology and chemistry, 36 (5), pp. 1311-1329. doi:10.1002/etc.3662.

Hansen, L. (1987). Polychlorinated Biphenyls: Environmental Occurrence and Analysis. In S. Safe (Ed.), Polychlorinated Biphenyls (PCBs): Mammalian and Environmental Toxicology, pp. 15-48. Berlin, Heidelberg: Springer Berlin Heidelberg.

Nimmo, D. & Forester, J. & Heitmuller, P & Cook, G. (1974). Accumulation of Aroclor 1254 in grass shrimp (Palaemonetes pugio) in laboratory and field exposures. Bulletin of environmental contamination and toxicology. 11 (4) pp. 303-308. 10.1007/bf01684932.

Safe S., & Safe, L., & Mullin, M. (1987). Environmental Toxicology of Polychlorinated Biphenyls. In S. Safe (Ed.), Polychlorinated Biphenyls (PCBs): Mammalian and Environmental Toxicology, pp. 1-13. Berlin, Heidelberg: Springer Berlin Heidelberg.

Wirth, E.F., & Pennington, P.L., & Cooksey, C., Schwake, L., & Hyland, J., & Fulton, M.H. (2014) Distribution and sources of PCBs (Aroclor 1268) in the Salepo Island National estuarine research reserve. Environmental Monitoring and Assessment. 186 (12) pp. 8717-8726. doi:10.1007/s10661-014-4039-4

Xue, J., & Liu, S., & Zartarian, V., & Geller, A., & Schultz, B. (2014). Analysis of NHANES measured blood PCBs in the general US population and application of SHEDS model to identify key exposure factors. Journal of Exposure Science and Environmental Epidemiology. 24 (6) pp. 615-621. doi: 10.1038/jes.2013.91