Study reveals the toxic effects of a common aquatic pollutant, the PAH Benzo[α]pyrene (BaP), on bay scallops
A new study from South Korea has found that higher levels of benzo[α]pyrene (BaP), a carcinogenic polycyclic aromatic hydrocarbon, 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. Polycyclic aromatic hydrocarbons (PAHs) are one of the most common pollutants released into the sea. They negatively affect aquatic ecosystems, but their impact on marine animals has not been sufficiently explored.
For example, PAHs disrupt a variety of biological 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 knowledge gap, a group of researchers from South Korea evaluated the toxicological effects of PAHs on bay scallops. They selected a particular polycyclic aromatic hydrocarbon (BaP), which is a known carcinogen.
“The effect of BaP on scallops was investigated by observing various immune- and oxidative stress-related parameters,” said Dr. Cheol Young Choi, professor at Korea Maritime and Ocean University’s Division of Marine Bioscience.
The researchers exposed the scallops to seawater containing four different concentrations of BaP (0.5, 1.0, 10, and 50 μg/L) for 72 hours, and 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,” wrote the research team in a press release.
The study, which was recently published in Fish and Shellfish Immunology, 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.
“All the parameters increased significantly over time at higher BaP concentrations,” said Choi.
The researchers also used a special in situ hybridization 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.
“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,” said Choi.
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