Investigating Ag Deposition/Distribution and Associations between Ag and Infectious Disease in Stranded Cetaceans
Abstract
Silver (Ag), such as silver nanoparticles (AgNPs), has been used in a variety of commercial products and may be released into environment.1,2 Cetaceans as apex predators of the ocean have been shown to have a relatively high level of Ag in their bodies accumulated through food chains.3,4,5,6 The aim of the present study was to comprehensively evaluate the negative health impact caused by Ag deposition. Ag distribution and the absence/presence of infectious diseases in stranded cetaceans with different Ag concentrations were systematically investigated. Tissue samples from 110 stranded cetaceans, including 38 Kogia spp., 22 Feresa attenuata, 13 Lagenodelphis hosei, 13 Stenella attenuata, 8 Steno bredanensis, 11 Tursiops truncatus, and 5 Grampus griseus, were collected. The Ag concentrations of the liver tissue from stranded cetaceans were estimated by cetacean histological Ag assay (CHAA), a regression model developed by using autometallography (AMG) on formalin-fixed paraffin-embedded (FFPE) tissues.6 The stranded cetaceans were classified into high and low Ag groups based on the Ag concentrations in the liver. The systemic distribution of Ag was investigated by AMG on various tissues including central nervous system, liver, kidney, heart, lung and adrenal glands of stranded cetaceans. Stranded cetaceans were classified in the infectious disease group by the presence of inflammatory diseases suspected to be associated with infectious agents such as bacteria, fungi, parasites and viruses. There was a significantly positive correlation between the presence of infectious disease and high Ag concentration. In the high Ag group, AMG positive signals were frequently found in hepatocytes, Kupffer cells, epithelial cells of proximal renal tubules, glial cells, pneumocytes, vascular endothelium of heart and brain, adrenocortical cells and chromaffin cells. Furthermore, the AMG positive signals were occasionally found in cardiomyocytes and neurons of some individuals. Compared with previous studies, the patterns of AMG positive signals in cetacean are different from those in laboratory rodents.7,8 This suggests that cetaceans may have a different silver metabolic pathway. On the other hand, the positive correlation between the presence of infectious disease and high Ag concentration suggested that the Ag may impair the immune function of affected cetaceans, thereby increasing their susceptibility to infectious diseases. Although previous studies have indicated the immunotoxic effects of environmental pollutants, such as polychlorinated biphenyls (PCBs), organochlorine pesticides, and heavy metals (especially mercury) in marine mammals9, no study on the interaction between Ag and the immune system of cetaceans has been reported. Environmental pollution of the ancient but emerging heavy metal, Ag, should not be overlooked. Further investigations, such as in vitro immunotoxic studies of Ag and/or AgNPs, are warranted.
Acknowledgements
The authors wish to thank the Taiwan Cetacean Stranding Network for sample collection and storage, including the Taiwan Cetacean Society, Taipei; the Cetacean Research Laboratory (Prof. Lien-Siang Chou), the Institute of Ecology and Evolutionary Biology, National Taiwan University, Taipei; the National Museum of Marine Biology and Aquarium (Dr. Chiou-Ju Yao), Taichung; and the Marine Biology & Cetacean Research Center, National Cheng-Kung University. This study is partially supported by the Ministry of Science & Technology, Taiwan under Grant MOST 106-2313-B-002-054-.
* Presenting author
+ Student presenter
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