The review, led by Mustafa Mudhafar and colleagues at the Centre for Research on Environment and Renewable Energy at the University of Kerbala in Iraq, argues that current risk assessment frameworks remain fragmented and often fail to capture the dynamic, context-dependent behaviour of nanoscale materials. Nanoparticles, defined roughly as particles between 1 and 100 nanometres across, behave very differently from the same substances in bulk form. Their enormous surface area to volume ratio, altered reactivity and ability to cross biological barriers give them unique functions, but also unique hazards. The authors stress that understanding these hazards requires a life cycle perspective rather than a snapshot of toxicity in a laboratory dish.

The researchers classify environmental nanoparticles into three broad categories. Engineered nanoparticles are deliberately manufactured for specific applications, such as silver nanoparticles in antibacterial coatings, titanium dioxide in sunscreens and paints, zinc oxide in cosmetics, and zero valent iron in groundwater remediation. Incidental nanoparticles arise as unintended by-products of human activity, including welding fumes, vehicle exhaust, industrial emissions and the weathering of manufactured materials. Naturally occurring nanoparticles, finally, have always existed in the environment, produced by volcanic ash, forest fires, ocean spray, dust storms and biological processes. While natural nanoparticles have shaped Earth systems for billions of years, the review notes that the explosion of engineered nanomaterials since the 1990s has introduced substances with no natural analogue into ecosystems at rapidly growing rates.

Release into the environment occurs through multiple pathways. Wastewater treatment plants, which are not specifically designed to capture nanoscale particles, release a portion of the nanoparticles they receive into rivers and sludge. Sludge applied to agricultural land then carries nanoparticles into soils. Atmospheric emissions deposit particles onto land and water surfaces far from their source. Direct discharge from products, such as sunscreen washing off swimmers into lakes, adds further loads. A frequently cited field study at the Old Danube recreational lake in Austria documented measurable release of titanium dioxide nanoparticles from sunscreens into surface waters over an entire swimming season, demonstrating that consumer products are a genuine environmental source rather than a theoretical concern.

Once released, nanoparticles undergo a series of transformations that determine their fate. The review identifies aggregation, dissolution, surface alteration and interactions with both living and non living components as the principal processes. Aggregation, in which particles clump together, is governed by ionic strength, pH and the presence of natural organic matter. In fresh water with low salt content, particles may remain dispersed and travel long distances, while in seawater or hard water they tend to clump and settle into sediments. Natural organic matter can coat particles and stabilise them, actually increasing their mobility and persistence. Dissolution is equally important, particularly for metal based nanoparticles. Silver nanoparticles slowly release silver ions, zinc oxide releases zinc ions, and copper oxide releases copper ions. This means the toxicity observed in an organism may come partly from the dissolved metal rather than the particle itself, complicating any attempt to attribute harm to the nanoscale form.

Surface alteration includes sulfidation, oxidation, adsorption of molecules and the formation of what researchers call an eco corona, a layer of biomolecules acquired from the surrounding environment. Just as a protein corona forms when nanoparticles enter the bloodstream, an eco corona forms when they enter soil or water, fundamentally changing how organisms perceive and take up the particles. The review highlights recent work from the MISTRA environmental nanosafety project in Europe arguing that regulatory testing must incorporate eco corona formation and biotransformation, because a nanoparticle tested in its pristine form may behave entirely differently after environmental ageing. Aged silver nanoparticles, for example, show different toxicity to freshwater algae than freshly coated ones, and the ageing process itself can either increase or decrease hazard depending on conditions.

Transport through the environment follows three main compartments. In the atmosphere, nanoparticles can travel considerable distances, and the review notes growing concern about airborne micro and nanoplastics, which share toxicological paradigms with engineered nanoparticles in terms of cellular uptake and inflammatory responses. In aquatic systems, nanoparticles interact with sediments, biofilms and suspended particles, with aggregation and settling determining whether they remain in the water column or accumulate on the bottom. In soils, the picture is most complex, as pH, clay content, organic matter and microbial activity all influence whether particles stay mobile, bind to soil components or dissolve. The review cites work showing that titanium dioxide nanoparticles affect soil enzymes and microbial communities, and that copper oxide nanoparticles in biosolid amended soils alter the structure and function of soil microbial populations, with potential consequences for nutrient cycling and plant health.

The ecotoxicological section of the review examines effects across trophic levels. At the base of food webs, algae and cyanobacteria are particularly vulnerable because nanoparticles can attach to cell walls, generate reactive oxygen species, and interfere with photosynthesis. Studies cited include toxicity of copper oxide, zinc oxide and titanium dioxide to the microalga Pseudokirchneriella subcapitata, and impacts of zinc oxide, copper oxide and titanium dioxide on natural phytoplankton communities. In aquatic invertebrates, Daphnia magna serves as a model organism, with research showing that silver nanoparticles at environmentally relevant concentrations cause persistent metabolic disruption, and that titanium dioxide can facilitate the accumulation and toxicity of co contaminants such as arsenate. In fish, studies on Nile tilapia, goldfish, zebrafish and African catfish reveal liver and kidney damage, behavioural changes, oxidative stress and altered stress indicators following exposure to silica, zinc and silver nanoparticles. The review also notes bioaccumulation concerns, with zinc nanoparticles accumulating in goldfish tissues and nanoparticles migrating from food coatings into the food supply.

Soil organisms and microbial communities receive particular attention because soils are the ultimate sink for many nanoparticles. Earthworms, springtails and other invertebrates can ingest nanoparticles from soil, while microbes, the engines of nutrient cycling, show shifts in community composition and function following exposure. The review cites evidence that zinc oxide nanoparticles affect the stability of the soil bacterial community and that graphene based nanomaterials interact with microbial communities in ways relevant both to ecotoxicology and to bioprocess engineering. Because microbes underpin decomposition, nitrogen cycling and plant nutrition, even subtle community shifts could have cascading ecosystem consequences that standard single species toxicity tests fail to detect.

Perhaps the most important contribution of the review is its critique of current methodology and its roadmap for improvement. The authors identify significant knowledge gaps, including the lack of standardised approaches for characterising nanoparticles in complex environmental matrices, the difficulty of measuring environmentally relevant concentrations, and the challenge of extrapolating from laboratory studies using pristine particles to real world scenarios involving aged, transformed and corona coated materials. They call for risk assessment frameworks that explicitly account for the dynamic and context dependent nature of nanoparticle behaviour, for life cycle assessment models such as USEtox and SimpleBox 4 nano to be refined with size dependent characterisation factors, and for the development of safer by design nanomaterials whose environmental fate is considered from the earliest stages of product development. The review ultimately aims to enhance environmental risk assessment methodologies and facilitate the development of more sustainable nanomaterials, arguing that only by adopting a genuine life cycle perspective can society continue to benefit from nanotechnology while protecting the ecosystems on which all life depends.

Subject of Research: Tracing the environmental lifecycle of nanoparticles: pathways, persistence, and ecotoxicological impacts

Article Title: Tracing the environmental lifecycle of nanoparticles: pathways, persistence, and ecotoxicological impacts

Article References: Mudhafar, M., Al-hamdany, M. A., Kareem, Z. H., Al-saedi, M., Abdulredha, M., & Seger, M. A. (2026). Tracing the environmental lifecycle of nanoparticles: pathways, persistence, and ecotoxicological impacts. Environmental Monitoring and Assessment, 198(11), Article 1206. https://doi.org/10.1007/s10661-026-16059-6

Image Credits: AI Generated

DOI: 10.1007/s10661-026-16059-6

Keywords: nanoparticles, environmental fate, ecotoxicology, nanotoxicology, Environmental Monitoring and Assessment, risk assessment, nanomaterials, life cycle assessment, Tracing, environmental, lifecycle, pathways