by National Korea Maritime & Ocean University
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 expression of peptidoglycan recognition proteins (PGRP), fibrinogen-domain-containing protein (FReDC1), metallothionein (MT), and heat shock protein (HSP) 70. While NO levels and the expression of PGRP, FReDC1, and HSP70 indicate the scallops’ immune response to BaP toxicity, the expression 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 expression rose considerably with time in each BaP group. The expression 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 expression 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 expression 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.”
Cheol Young Choi
National Korea Maritime & Ocean University
Jin Ah Song, Kang Hee Kho, Young-Su Park, Cheol Young Choi. 2022. Toxicity response to benzo[a]pyrene exposure: Modulation of immune parameters of the bay scallop, Argopecten irradians. Fish & Shellfish Immunology, Volume 124, 2022, Pages 505-512, ISSN 1050-4648, https://doi.org/10.1016/j.fsi.2022.04.044.