Although the effect of natural organic matter (NOM) on nanoparticles (NPs) in the food chain is unexplored, studies have found that NOM present in aquatic environments affects the toxicity and behavior of NPs.
Study: Effect of organic matter on the trophic transfer of silver nanoparticles in an aquatic food chain. Image Credit: Tim7914/Shutterstock.com
In an article recently published in the Journal of Hazardous Materials, researchers chose Escherichia coli (E. coli) bacterial species and Tetrahymena thermophila (T. thermophila) protozoa to investigate the influence of NOM on trophic transfer, toxicity, and bioaccumulation of silver nanoparticles (Ag NPs).
The results revealed that NOM reduced the toxicity of Ag NPs on T. thermophila and E. coli via influence mechanisms like reduction in the accumulation of Ag NPs or formation of Ag+ ion complex, which were specific to the type of organisms and NOM. The biomagnification of Ag NPs on T. thermophila was via trophic transfer.
Three typical NOMs showed an approximately two-fold increase in Ag NP’s trophic transfer factor (TTF), wherein NOM reduced the capacity of T. thermophila to expel the Ag during exocytosis. The present study gave an insight into the influence of NOM in interrupting the ecological disturbances caused by Ag NPs that enter the food chain.
Applications of NPs and their Effect on Food Chain
NPs have widespread use in various fields. Thus, it is critical to monitor the risks posed to ecological and human health due to the excess presence of these NPs. The extensive use of Ag NPs and their consequent large production resulted in their accumulation in water bodies causing pollution in aquatic systems. Moreover, Ag NPs found on the surface of water bodies could be ingested by various microorganisms and aquatic organisms, causing toxic effects.
The consumption of Ag NPs in contaminated food or water causes their bioaccumulation in living systems. Moreover, previous reports mentioned that trophic transfer is the primary pathway for the of NPs uptake by predators. Furthermore, bio amplification of NPs by the trophic transfer via food chains can affect high trophic level organisms.
Various factors affect the NP’s trophic transfer, and the impact of NOM is of primary concern due to its ubiquitous existence in the aquatic environment. Moreover, NOM is adsorbed on the surface of NPs to form a coating, which significantly affects the transformation, environmental behavior, and bioavailability of NPs. One of the previous reports mentioned the reduction of toxic effects caused by Ag NPs due to their complexation with NOM, forming a water-soluble Ag-NOM complex.
Effect of NOM on the Trophic Transfer of Ag NPs Aquatic Food Chain
In the present study, the researchers established a food chain model with E. coli bacteria and the T. thermophila protozoa that belonged to two different trophic levels and investigated the impact of NOM on the trophic transfer of Ag NPs. Transmission electron microscope (TEM) images showed that the Ag NPs had a mean particle diameter of 23.61 ± 0.20 nanometers, and the hydrodynamic diameters were 50.98 and 59.95 nanometers in a concentration of 0.1 and 1 milligram per liter of artificial freshwater, respectively.
NOM constitutes a wide range of complex organic compounds like polysaccharides, proteins, humic acid (HA), and lipids. Hence, bovine serum albumin (BSA), sodium alginate (SA), and HA were used as representative elements of previously mentioned complex organic compounds present in NOM. The presence of BSA and SA did not influence the Ag NP’s hydrodynamic diameter. However, HA promoted agglomeration of the NPs, resulting in a higher hydrodynamic diameter.
Consequently, polyvinyl pyrrolidone (PVP) was used as a surface coating agent on Ag NPs as it can control the morphology of Ag NPs and prevent their agglomeration. Investigations on the bioaccumulation of Ag NPs and their toxic effects on E. coli in the presence of HA, BSA, and SA were performed. Later, the mechanism of NOM impact on the biological fate and trophic transfer of Ag NPs was studied in the freshwater food chain, which was based on trophic transfer from E. coli to T. thermophila.
Conclusion
In summary, the researchers experimentally demonstrated that the Ag NPs accumulated in bacteria were transferred subsequently to the organisms of higher trophic level, which resulted in Ag NPs biomagnification in T. thermophila from E. coli. Protozoa with high phagocytic capacity enhance the trophic transfer of Ag NPs, leading to their motility loss. Furthermore, the contaminated cells could be ingested by natural predators and cause accelerated biomagnification of Ag NPs across the food web.
NOM also altered the accumulation of Ag+ ions in E. coli bacterial species, consequently preventing their removal by T. thermophila during exocytosis. Thus the presence of NOM in aquatic environments influences the trophic transfer of Ag NPs and it is critical to draw attention to the biological impact of NOM on the fate and transfer of NPs within the food chain.
Reference
Liang, D., Fan, W., Wu, Y., Li, X., Dong, Z., Wang, Y. (2022) Effect of Organic Matter on the Trophic Transfer of Silver Nanoparticles in an Aquatic Food Chain. Journal of Hazardous Materials. https://www.sciencedirect.com/science/article/pii/S0304389422013140?via%3Dihub
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