Although the effect of natural organic matter (NOM) on nanoparticles (NP) in the food chain has not been explored, studies have found that NOM present in aquatic environments affects the toxicity and behavior of NPs.
Study: Effect of organic matter on trophic transfer of silver nanoparticles in an aquatic food chain. Image credit: Tim7914 / Shutterstock.com
In a recent article in the Journal of Hazardous Materials, researchers chose bacterial species Escherichia coli (E. coli) and protozoa Tetrahymena thermophila (T. thermophila) 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 to T. thermophila and E. coli by mechanisms of influence such as the reduction of Ag NPs accumulation or the formation of the Ag + ion complex, which were specific to the type of organism and NAME. Biomagnification of Ag NPs in T. thermophila was by trophic transfer.
Three typical NOMs showed an approximately twice-increased increase in trophic transfer factor (TTF) of Ag NP, where the NOM reduced the ability of T. thermophila to expel Ag during exocytosis. The present study gave an insight into the influence of NOM in disrupting the ecological disturbances caused by Ag NPs entering the food chain.
Applications of NPs and their effect on the food chain
NPs have widespread use in several fields. Therefore, it is essential to control the risks it poses to ecological and human health due to the excessive presence of these NPs. The extensive use of Ag NP and its consequent large production led to its accumulation in water bodies causing pollution in aquatic systems. In addition, Ag NPs found on the surface of water bodies could be ingested by various microorganisms and aquatic organisms, causing toxic effects.
Consumption of Ag NPs in contaminated food or water causes their bioaccumulation in living systems. In addition, previous reports mentioned that trophic transfer is the major route for the uptake of NPs by predators. In addition, bioamplification of NPs by trophic transfer through food chains can affect high-trophic organisms.
Several factors affect the trophic transfer of NP, and the impact of NOM is of major concern due to its ubiquitous existence in the aquatic environment. In addition, 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 trophic transfer of the aquatic food chain of Ag NPs
In the present study, the researchers established a food chain model with E. coli bacteria and T. thermophila protozoa belonging to two different trophic levels and investigated the impact of NOM on trophic transfer of Ag NPs. Transmission electron microscope (TEM) images showed that Ag NPs had an average particle diameter of 23.61 ± 0.20 nanometers, and the hydrodynamic diameters were 50.98 and 59.95 nanometers at a concentration of 0.1 and 1 milligram per liter of artificial fresh water, respectively.
NOM constitutes a wide range of complex organic compounds such as polysaccharides, proteins, humic acid (HA) and lipids. Therefore, bovine serum albumin (BSA), sodium alginate (SA) and HA were used as representative elements of the aforementioned complex organic compounds present in NOM. The presence of BSA and SA did not influence the hydrodynamic diameter of Ag NP. However, HA promoted NP agglomeration, resulting in a higher hydrodynamic diameter.
Consequently, polyvinylpyrrolidone (PVP) was used as a surface coating agent in Ag NPs, as it can control the morphology of Ag NPs and prevent their agglomeration. Research was conducted on the bioaccumulation of Ag NPs and their toxic effects on E. coli in the presence of HA, BSA and SA. Later, the mechanism of the impact of NOM on biological fate and trophic transfer of Ag NPs to the freshwater food chain, which was based on trophic transfer of E. coli, was studied. coli a T. thermophila.
Conclusion
In summary, the researchers demonstrated experimentally that NP Ag accumulated in bacteria were subsequently transferred to higher trophic-level organisms, resulting in bioamplification of Ag NP in E. thermophila E. coli. coli. Protozoa with high phagocytic capacity enhance trophic transfer of Ag NPs, causing their loss of motility. In addition, contaminated cells could be ingested by natural predators and cause accelerated bioamplification of Ag NPs in the food web.
NOM also altered the accumulation of Ag + ions in bacterial species of E. coli. coli, preventing its elimination by T. thermophila during exocytosis. Thus, the presence of NOM in aquatic environments influences the trophic transfer of Ag NPs and it is crucial to draw attention to the biological impact of NOM on the destination and transfer of NP within the food chain.
Reference
Liang, D., Fan, W., Wu, Y., Li, X., Dong, Z., Wang, Y. (2022) Effect of organic matter on trophic transfer of silver nanoparticles in an aquatic food chain . Dangerous materials magazine. https://www.sciencedirect.com/science/article/pii/S0304389422013140?via%3Dihub
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