Scientists elucidate the toxic effects of a common aquatic pollutant, the PAH Benzo[α]pyrene (BaP) on bay scallops

Polycyclic aromatic hydrocarbons (PAHs) are one of the most common pollutants released into the sea. They negatively affect aquatic ecosystem, but their impact on marine animals has not been sufficiently explored. Now, in a brand new study, researchers from Korea reveal that higher levels of benzo[α]pyrene (BaP), a carcinogenic PAH, can significantly dampen the immune and oxidative stress response of bay scallops. 

Rapid industrialization of coastal areas and a rise in sea transport continue to cause pollutants to be released into marine ecosystems. These contaminants pose a serious threat to marine life and habitat. For example, polycyclic aromatic hydrocarbons (PAHs, a common marine pollutant) disrupt a variety of biologic systems in marine creatures, including energy metabolism, growth, genetics, and reproduction. Exposure to these compounds causes toxicity not only in marine organisms, but also in humans who consume these organisms. Although the immunotoxicity of PAHs has been extensively studied in mammals and fish, its influence on shellfish has not been adequately investigated.

To fill this gap in knowledge, a group of researchers from South Korea, including Prof. Cheol Young Choi of Korea Maritime and Ocean University, evaluated the toxicological effects of PAHs on bay scallops. They selected a particular PAH―BaP―which is a known carcinogen.

“The effect of BaP on scallops,” says Prof. Choi, “was investigated by observing various immune- and oxidative stress-related parameters.” In their paper, which was made available online on 27 April 2022, and subsequently published in Volume 124 of Fish and Shellfish Immunology in May 2022, the researchers explain how they exposed the scallops to seawater containing four different concentrations of BaP (0.5, 1.0, 10, and 50 μg/L) for 72 hours, then measured five different parameters in these scallops: the nitric oxide (NO) levels in their hemolymph, and the mRNA ex-pression of peptidoglycan recognition proteins (PGRP), fibrinogen-domain-containing protein (FReDC1), metallothionein (MT), and heat shock protein (HSP) 70. While NO levels and the ex-pression of PGRP, FReDC1, and HSP70 indicate the scallops’ immune response to BaP toxicity, the ex-pression of MT is seen as a stress response in these organisms.

The study found that except for the BaP 0.5 μg/L group, NO and FReDC1 and MT mRNA ex-pression rose considerably with time in each BaP group. The ex-pression of PGRP and HSP70 mRNA in the BaP 50 μg/L group rose for 6-24 hours before declining. Moreover, at 72 hours, the BaP 50 μg/L group had greater MT mRNA ex-pression than the control group. “In conclusion,” says Prof. Choi, “All the parameters increased significantly over time at higher BaP concentrations.”

The researchers also used in situ hybridization, a special technique, to confirm the location of MT ex-pression in the cytoplasm of certain cells in these scallops―confirming that these organisms do, indeed, overexpress MT in the presence of PAHs.

From these observations, the researchers concluded that the BaP dampens the immune response of scallops and decreases their capacity to respond to oxidative stress, infection, inflammation, and tissue damage.

But how does this study matter in the practical world? Prof Choi says, “This study paves the way to develop new techniques to control the release of BaP into water bodies and its transfer to humans through the food chain.”

Reference

About National Korea Maritime & Ocean University 

South Korea’s most prestigious university for maritime studies, transportation science and engineering, the National Korea Maritime & Ocean University is located on an island in Busan. The university was established in 1945 and since then has merged with other universities to currently being the only post-secondary institution that specializes in maritime sciences and engineering. It has four colleges that offer both undergraduate and graduate courses.  

Website: http://www.kmou.ac.kr/english/main.do

About the author

Dr. Cheol Young Choi is a professor at Korea Maritime and Ocean University's Division of Marine Bioscience. His group is currently working on endocrine regulatory mechanisms of Cleanershrimp using the LED light wavelength, endocrine regulatory mechanisms of protandrous cinnamon clownfish gonadotropin-inhibitory hormone, and biomarker development for marine environmental risk assessment using ex-pression analysis of oxidative stress-related genes. He finished his postdoctoral training at Calgary University and the National Institutes of Health before joining Korea Maritime and Ocean University (NIH). Dr. Choi earned his doctorate in marine science and technology from Tokyo University of Marine Science and Technology.