Natural Organic Matter Reduces Aquatic Toxicity of Nanoparticles

Although the effect of natural organic matter (NOM) on nanoparticles (NPs) in the food chain has not been investigated, studies have shown that NOM influences the toxicity and behavior of NPs in aquatic environments.

Study: Effect of organic matter on the trophic transfer of silver nanoparticles in an aquatic food chain† Image Credit: Tim7914/Shutterstock.com

In a recently published article in the Dangerous Substances Magazineresearchers 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 showed that NOM reduced Ag NPs toxicity T. thermophila and E coli through mechanisms of influence such as reduction of Ag NPs accumulation or Ag . formation^† 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 2-fold increase in Ag NPs trophic transfer factor (TTF), with NOM increasing the capacity of T. thermophila to expel the Ag during exocytosis. The present study provided insight into the influence of NOM on disrupting the ecological disturbances caused by Ag NPs entering the food chain.

Applications of NPs and their effect on the food chain

POIs have widespread use in various fields. Thus, it is critical to monitor the environmental and human health risks arising from the excessive presence of these NPs. The extensive use of Ag NPs and consequent large production resulted in their accumulation in water bodies and caused pollution in aquatic systems. In addition, Ag NPs found on the surface of water bodies can be taken up by various microorganisms and aquatic organisms, resulting in toxic effects.

The 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 primary pathway for NP uptake by predators. In addition, bio-amplification of NPs through the trophic transfer through food chains can affect organisms with a high trophic level.

Several factors influence the trophic transfer of the NP, and the impact of NOM is of primary importance due to its ubiquitous presence in the aquatic environment. In addition, NOM is adsorbed on the surface of NPs to form a coating, which significantly influences 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 current study, the researchers established a food chain model with E coli bacteria and the T. thermophila protozoa belonging to two different trophic levels and examined 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 at a concentration of 0.1 and 1 milligram, respectively. per liter of artificial fresh water.

NOM forms 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 previously mentioned complex organic compounds present in NOM. The presence of BSA and SA did not affect the hydrodynamic diameter of the Ag NP. However, HA promoted the agglomeration of the NPs, resulting in a higher hydrodynamic diameter.

Consequently, polyvinylpyrrolidone (PVP) was used as a surface coating agent on Ag NPs because it can control the morphology of Ag NPs and prevent their agglomeration. Investigating the bioaccumulation of Ag NPs and their toxic effects on E coli were performed in the presence of HA, BSA and SA. 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 of E coli until T. thermophila†

Conclusion

In summary, the researchers experimentally demonstrated that the Ag NPs accumulated in bacteria were subsequently transferred to the organisms with a higher trophic level, resulting in biomagnification of Ag NPs in T. thermophila from E coli† Protozoa with high phagocytic capacity enhance the trophic transfer of Ag NPs, leading to their loss of motility. In addition, the infected cells can be ingested by natural predators and cause accelerated biomagnification of Ag NPs across the food web.

NOM also altered Ag . accumulation^† ions in E coli bacterial species, 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. Dangerous Substances Magazine. https://www.sciencedirect.com/science/article/pii/S0304389422013140?via%3Dihub

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