Bowdoin Science Journal

Marine Biology

Mercury, Contaminating Our Oceans and Your Food

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Mercury, you may know it as the solar system’s smallest planet or as the “red stuff” in old thermometers. You may have even heard of its toxic effects on people if exposure occurs. However, you may not know that mercury is significant outside of the realm of toxic thermometers and astronomy. The chemical element mercury is a contaminant that is being pumped into the atmosphere at an alarming rate and is poisoning aquatic environments. Mercury is becoming an increasingly common pollutant in our oceans and lakes and its toxic effects are causing harm to marine life and creating an imbalance in our marine ecosystems.

Before mercury can enter aquatic environments, it is released in large quantities by anthropogenic sources. Mercury can enter the atmosphere through natural sources such as volcanoes or forest fires, but it is primarily released through the burning of fossil fuels and small-scale gold mining (Montes 287). The release of mercury is problematic because it is very easily transported through the atmosphere. Mercury is a volatile element, which means that it evaporates at low temperatures (mercury can even evaporate at room temperature) and easily enters its gaseous state to be carried long distances through the air (Pollet 860).

After mercury is transported through the atmosphere and enters aquatic environments, it is transformed into its more toxic state, methylmercury (CH3Hg or MeHg). Mercury is transformed into methylmercury through the process of mercury methylation when Hg incorporates CH3, making it into CH3Hg (or MeHg). In the ocean, methylation of mercury is carried out by bacteria. Essentially, bacteria that are present in aquatic environments absorb mercury and perform the methylation reaction before releasing methylmercury back into the ecosystem (Poulain 1280-1281).

Once organisms ingest methylmercury, they experience detrimental effects on their function and, ultimately, their survival. For example, seabirds with more than 0.2 μg (micrograms) of mercury in their blood per gram of wet weight have observed negative effects on their bodies’ systems and their function. An approximately equivalent concentration can be represented by one person out of the entire state of Alabama, which has a population of 5.04 million. At this level or greater, birds experience detrimental effects on their nervous and reproductive systems as well as changes to their hormonal makeup and trouble with motor and behavioral skills (Pollet 860). 

Another interesting observation of mercury contamination is its differing distribution of concentrations among populations. The methylmercury concentration in seabirds was explored between 2013 and 2019 when egg and blood samples were taken of Leach’s storm petrels along with the GPS tracking of foraging petrels. By comparing measured mercury concentration in blood and eggs to ocean depth of foraging locations, a correlation was found. The study concluded that the water depth had a significant effect on the methylmercury levels measured in Leach’s storm petrels. Storm petrels who foraged in deep waters had higher methylmercury concentrations in their blood than storm petrels who forage in shallow or coastal waters. The positive correlation between ocean depth and mercury concentration is likely due to differences in diet based on foraging location. This could also be related to the fact that mercury methylation is most efficient in deep water (Pollet 860).

These negative effects on seabirds also have broad effects on the entire ecosystem that they are a part of. This is because methylmercury biomagnifies up the food web. As the methylmercury moves up trophic levels in a food chain, its concentration in a given organism increases. This increase in concentration is dramatic. In fact, measured mercury concentrations in predator species can be millions of times greater than the concentration observed in surface waters. The problem of biomagnification is even more dramatic in Maine because of its latitude. While the phenomenon is not entirely understood, ecosystems located at higher latitudes have been observed to be more susceptible to biomagnification than tropical regions (Lavoie 13385-13394). 

Other than affecting our Maine wildlife, mercury contamination could have a negative impact on human health. Mercury is not only a problem for seabirds, but fish are also just as susceptible to contamination. This can become a major problem for commercial fisheries because the seafood they produce for our consumption have the potential for mercury contamination. In fact, there was an incident in Japan in 1956 when people who consumed contaminated seafood became severely ill or died. Over the course of 36 years after the incident, 2252 people were infected 1034 people were killed in relation to the initial methylmercury contamination (Harada 1-24). While this level of contamination is an anomaly, a 2018 study projected that approximately 38% of countries experience some level of human exposure to mercury due to contaminated seafood consumption. There are steps that can be taken to prevent this. For example, setting stricter regulations on mercury content limits, applying proper culinary treatments, or updating fishing practices could all diminish the probability of mercury exposure to humans (Jinadasa 112710). 

That being said, addressing the root of the problem is the only way to most effectively diminish mercury exposure for marine organisms and people. Mercury contamination is a problem that has a dramatic domino effect beginning in our atmosphere and ending in human consumption. It is an issue that is often forgotten in discussions of the environmental impact of burning fossil fuels. However, considering its impact on marine life and eventually human life, it is a byproduct that cannot be overlooked.

 

Works Cited

da Silva Montes, C., Ferreira, M. A. P., Giarrizzo, T., Amado, L. L., & Rocha, R. M. (2022). The
legacy of artisanal gold mining and its impact on fish health from Tapajós Amazonian
region: A multi-biomarker approach. Chemosphere, 287, 132263.

Harada, M. (1995). Minamata disease: methylmercury poisoning in Japan caused by
environmental pollution. Critical reviews in toxicology, 25(1), 1-24.

Jinadasa, B. K. K. K., Jayasinghe, G. D. T. M., Pohl, P., & Fowler, S. W. (2021). Mitigating the
impact of mercury contaminants in fish and other seafood—A review. Marine Pollution
Bulletin, 171, 112710.

Lavoie, R. A., Jardine, T. D., Chumchal, M. M., Kidd, K. A., & Campbell, L. M. (2013).
Biomagnification of mercury in aquatic food webs: a worldwide meta-analysis.
Environmental science & technology, 47(23), 13385-13394.

Pollet, I. L., McFarlane-Tranquilla, L., Burgess, N. M., Diamond, A. W., Gjerdrum, C., Hedd, A.,
… & Mallory, M. L. (2023). Factors influencing mercury levels in Leach’s storm-petrels at
northwest Atlantic colonies. Science of The Total Environment, 860, 160464.

Poulain, A. J., & Barkay, T. (2013). Cracking the mercury methylation code. Science, 339(6125),
1280-1281.

The Anti-cancer and Antimicrobial Activity Associated with Sea Sponge Extracts

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Toxic Negombata magnifica sponge at Shaab el Erg reef (Red Sea, Egypt) (Alexander Vasenin, 2010)

With an ever-increasing demand for novel drug therapies, scientists are turning to marine organisms as a source of bioactive chemicals, whose properties can be harnessed for medical development. One such organism is a rather unlikely candidate: the sea sponge (phylum Porifera). Lacking a brain and a central nervous system, sea sponges rely upon specialized cells to perform their required functions. As result of their structural simplicity and sedentary existence, these ancient creatures have evolved to protect themselves against predation by means of toxic chemicals, which can prove similarly lethal to cancer cells and microbes in humans (El-Naggar et. al., 2022). A study published in Applied Sciences examined the properties of two sponge species, Negombata magnifica (finger sponge) and Callyspongia siphonella (tube sponge). This drew from the scientists’ previous study, which had indicated that all eight extracts of finger-sponge and tube-sponge studied promoted the death and inhibited the growth of cells associated with liver, breast, and colorectal cancer (El-Naggar et.al., 2022).

Whereas the earlier study had used four different solvents in the production of sponge extracts, this newerstudy examined only the methanolic extracts of Negombata magnifica (NmE) and Callyspongia siphonella (CsE). Sponge specimens were collected from the Dahab region on the Sinai Peninsula and soaked with methanol to obtain NmE and CsE. One microliter of each extract was examined for its contents of bioactive compounds via a Gas Chromatography–Mass Spectrometer (GC–MS analysis). Out of the 117 chemical compounds revealed by GC­–MS analysis, 37 were determined to be bioactive. These compounds were tested against cultured liver, breast, and colorectal cancer cell lines and ten test microorganisms representing filamentous fungi, yeasts, and Gram-positive and Gram-negative bacteria (El-Naggar et.al., 2022).

While CsE showed no antiproliferative action against the cancer cells, NmE dose-dependently impeded their growth: it induced cell cycle arrest in the liver cancer lines by inhibiting the cell division protein CDK6. It also halted mitotic progress in all three cell types by inhibiting D1 and E1 cyclins, which regulate progression through the cell cycle (Alao, 2007). Furthermore, NmE activated reactive oxygen species (ROS) production in liver cancer cells and induced apoptosis in all cell lines, via Bax (a pro-apoptotic regulatory protein) and caspase-3 (a death protease that cleaves cellular proteins) increase and BCL2 (an anti-apoptotic regulatory protein) decrease (Blanco and García-Sáez, 2018) (Ponder and Boise, 2019; Youle and Strasser, 2002). Regarding antimicrobial activity, CsE was shown to be a superior antimicrobial agent by acting against six microbial strains, whereas NmE reacted favorably to only two strains (El Naggar et. al., 2022).

Looking forward, the anti-cancer properties of NmE indicate its potential for development as an anti-cancer drug, while CsE is a promising source for antimicrobial drug discovery. Additionally, several of the compounds’ bioactivity is neither anti-cancer nor antimicrobial—for instance, both fenretinide and ethyl iso-allocholate have been attributed to anti-COVID-19 activity (Orienti, et. al., 2020; Poochi et. al., 2020). Ultimately, given that approximately eighty of the compounds have yet to be attributed to anti-cancer or anti-microbial mechanisms, the study emphasizes the importance of looking to Earth’s oceans as potential sources of bioactive compounds and harnessing the biological potential of marine organisms in the development of novel drug therapies.

References:

Alao, J.P. The regulation of cyclin D1 degradation: roles in cancer development and the potential for therapeutic invention. Mol Cancer 6, 24 (2007). https://doi.org/10.1186/1476-4598-6-24

El-Naggar, H. A., Bashar, M. A. E., Rady, I., El-Wetidy, M. S., Suleiman, W. B., Al-Otibi, F. O., Al-Rashed, S. A., et al. (2022). Two Red Sea Sponge Extracts (Negombata magnifica and Callyspongia siphonella) Induced Anticancer and Antimicrobial Activity. Applied Sciences, 12(3), 1400. MDPI AG. Retrieved from http://dx.doi.org/10.3390/app12031400

Orienti, I.; Gentilomi, G.A.; Farruggia, G. Pulmonary Delivery of Fenretinide: A Possible Adjuvant Treatment in COVID-19. Int. J. Mol. Sci. 2020, 21, 3812.

Peña-Blanco, A., & García-Sáez, A. J. (2018). Bax, Bak and beyond – mitochondrial performance in apoptosis. The FEBS journal, 285(3), 416–431. https://doi.org/10.1111/febs.14186

Ponder, K.G., Boise, L.H. (2019). The prodomain of caspase-3 regulates its own removal and caspase activation. Cell Death Discovery 5, 56. https://doi.org/10.1038/s41420-019-0142-1

Poochi, S.P.; Easwaran, M.; Balasubramanian, B.; Anbuselvam, M.; Meyyazhagan, A.; Park, S.; Bhotla, H.K.; Anbuselvam, J.; Arumugam, V.A.; Keshavarao, S.; et al. Employing bioactive compounds derived from Ipomoea obscura (L.) to evaluate potential inhibitor for SARS-CoV-2 main protease and ACE2 protein. Food Front. 2020, 1, 168–179.

Youle, R., Strasser, A. (2008). The BCL-2 protein family: opposing activities that mediate cell death. Nat Rev Mol Cell Biol 9, 47–59. https://doi.org/10.1038/nrm2308