Nature's double agent: How dissolved organic matter controls nanopollutant fate

Engineered nanomaterials (ENMs)—microscopic particles designed for use in everything from cosmetics and medicine to environmental cleanup—are becoming increasingly common. While their unique properties offer significant benefits, their inevitable release into the environment poses potential risks to ecosystems and human health. A comprehensive review published in Carbon Research summarizes the critical and complex role that dissolved organic matter (DOM), a ubiquitous natural substance, plays in determining the fate and impact of these nanomaterials.

The Promise and Peril of Nanotechnology

ENMs are prized for their high efficiency in removing pollutants like heavy metals and organic dyes from water. However, their story doesn't end there. Once released into aquatic environments, these same nanoparticles can become pollutants themselves. They can cause harm through physical damage to cells, the generation of damaging reactive oxygen species (ROS), or by leaching toxic metal ions into the water. Understanding how these materials behave in real-world environments is crucial for balancing their benefits against their risks.

Nature's Ubiquitous Ingredient

Enter dissolved organic matter (DOM). This complex mixture of molecules is formed from the decomposition of plants and animals and is found in virtually all natural waters and soils. The review highlights that the interaction between ENMs and DOM is not a matter of 'if' but 'when'. This interaction fundamentally alters the properties of the nanomaterials, leading to a cascade of effects on both their pollution-fighting abilities and their toxicity.

A Double-Edged Sword in Pollution Cleanup

The review details the dual nature of DOM's influence on environmental remediation. On one hand, DOM can hinder the process by competing with pollutants for binding sites on the nanomaterial's surface, effectively reducing its cleanup capacity. It can also act as a "filter," blocking the UV light that some nanomaterials need to catalytically break down contaminants. On the other hand, under certain conditions, DOM can synergistically promote pollutant degradation or even be used to create novel "DOM-modified nanocomposites" with enhanced performance for removing contaminants like chromium and azo dyes.

Taming the Toxicity

One of the most significant roles of DOM is its ability to mitigate the toxicity of nanomaterials. By coating the surface of an ENM, DOM can create a protective barrier, preventing the nanoparticle from directly contacting and damaging living organisms. It can also bind with toxic metal ions (like silver or copper) released from the nanomaterials, sequestering them into less harmful forms. Furthermore, DOM can act as an antioxidant, neutralizing the harmful ROS produced by ENMs and reducing oxidative stress on aquatic life.

When Good Goes Bad: Enhancing Toxicity

Conversely, DOM isn't always a hero. The review also explains how it can sometimes amplify the negative effects of ENMs. By coating nanoparticles, DOM can prevent them from clumping together and settling out of the water. This keeps them suspended and mobile for longer, increasing their chances of being ingested by organisms. In some cases, DOM can even accelerate the release of toxic metal ions or, when exposed to sunlight, produce its own reactive oxygen species, adding to the overall oxidative stress in the environment.

A Roadmap for Safer Nanotechnology

The authors conclude that the relationship between DOM and ENMs is a delicate balancing act governed by a host of environmental factors like pH, temperature, and the specific composition of the DOM itself. This review provides a critical framework for future research, emphasizing the need for studies that use environmentally realistic concentrations of ENMs and explore the full diversity of naturally occurring DOM. By untangling this complex interplay, scientists and engineers can better design safer, more effective nanotechnologies and accurately assess the environmental risks of these revolutionary materials.

Corresponding Author:
 

Zhixiang Xu, Xuejun Pan

Original Source:
 

https://doi.org/10.1007/s44246-022-00026-0

Contributions:
 

Xianyao Zheng: Investigation and Writing the original draft. Zhixiang Xu: Conceptualization, Methodology, Supervision and Review. Jun Liu: Investigation and Writing the original draft. Yu Luo: Review and Visualization. Lipeng Gu: Literature search and Data analysis. Dimeng Zhao: Investigation and Data analysis. Siyuan Hu: Review and Visualization. Xuejun Pan: Supervision, Review and Funds acquisition. The author(s) read and approved the final manuscript.