Key Points:
- Microplastic sampling and analysis methods vary widely, leading to inconsistent data. The use of different sampling tools (e.g., nets, buckets, filters) and variable laboratory protocols makes it difficult to compare results across studies.
- Significant improvements in instrumentation and resolution are required to routinely detect and quantify nanoplastics in environmental matrices.
- Microplastics in sludge and soil amendments can introduce co-contaminants into terrestrial ecosystems. These pollutants can be taken up by plants, disrupt microbial communities, and even accumulate in the food chain.
The reliable detection and quantification of microplastics in wastewater and sludge is a significant analytical challenge, with implications for environmental safety, regulatory policy, and public health. In this article, LCGC International spoke to Damià Barceló, professor of chemistry at the University of Almeria, Almeria, Spain, to explore the technical and methodological barriers to microplastic analysis in complex environmental matrices.
Given the widespread occurrence of microplastics in the environment, what are the main challenges involved in analyzing these particles in wastewater and sludge?
There are a few challenges that need to be solved. First, there is a great diversity of sampling methods. In the case of water, nets, buckets, bottles, pumps, and traps, among others, are utilized. For sediments, grab and manual, and in the case of biota, fishing nets, local fishermen, fishing rods, and by hand. Such a variety of sampling methods can lead to discrepancies in reporting units and in the evaluation of the pollution of a given study region or area.
Concerning the analytical protocols, we first need to consider the laboratory conditions. A specific laboratory for microplastics sample treatment and analysis is needed with a strict control of blank samples, that is, a rigorous filtration of liquids including H2O2 and ethanol using filter paper of a few micrometers. In addition, all laboratory equipment, such as beakers, glass jars, and flasks, will need to be cleaned and protected with aluminium foil before use. Lastly, oxidative and/or enzymatic digestion will need to be performed carefully to remove only the interferences and not damage the polymers. These procedures are necessary before conducting analytical determinations using spectroscopic methods such as Fourier transform infrared (FT-IR), Raman, or pyrolysis gas chromatography–mass spectrometry (py-GC–MS).
In your review article, you mention the potential underestimation of smaller nanoplastics due to current sample preparation limitations (1). What advancements are needed to accurately quantify particles smaller than 1 μm?
The determination of particles smaller than 1 µm is a problem not yet solved. In short, the equipment needed is not available in many laboratories. µFTIR or µRaman equipment is needed; however, they are limited to measuring at a resolution of a few micrometers and cannot measure at a 1 µm level. When using py-GC–MS, the only requirement is that filtration of the water sample takes place with a filter of 1 µm, which is the current protocol for determining microplastics in water samples. In this regard, py-GC–MS is the best technique for particles smaller than 1 µm. The disadvantage is that py-GC–MS cannot distinguish between fibers, fragments, and other particles; therefore, microscopy—either alone or combined with FTIR—is required for this purpose.
What specific strategies do you recommend for developing standardized, validated methods for microplastic and nanoplastic detection across different laboratories?
A step-by-step approach would be the best solution. I would suggest comparing qualitative data of pure polymers, like polyethylene (PE), polypropylene (PP), polyvinyl chloride (PVC), or polyethylene terephthalate (PET). Samples could be sent to all participating laboratories using different methods (µFTIR, µRaman, and py-GC–MS), as they seek to identify the polymers at different sizes, that is, 5 µm and 50 µm. After spiking the microplastic samples in the water matrix and comparing the various methods of sample preparation, analysis should take place. In the final phase, the use of real-world samples already characterized by an expert laboratory will need to be identified and quantified by all participants. Concentration units could be reported in particles per liter for the µFTIR and µRaman or µg/L for py-GC–MS. As a follow-up to this exercise, another experiment could be performed using other samples, such as soil and biota. I would recommend between 15 and 20 laboratories taking part.
Considering the presence of microplastics in sludge used as soil amendments, what implications does this have for soil and plant health?
Sludge and soil amendments are a sink for microplastics. A point that must be considered is that higher density polymers such as polyester and polyvinyl acetate, with densities higher than 1.6–1.7 g/cm3, exhibit a higher tendency to remain in the solid material, whereas low density polymers, such as PE or PP with densities < 1 g/cm3, will remain in the water phase. The fact that some microplastics remain in soil has implications for plant health because microplastics—together with the chemical sorbed in the polymer surface, such as antibiotics, per- and polyfluoroalkyl substances (PFAS), pesticides, and metals—can be transported through the plant roots and into the plant. This will also be the case when wastewater treatment and reuse are applied in agriculture, particularly under increasing water scarcity and climate change pressures.
Do you see artificial intelligence (AI) as having a role in making microplastic detection more efficient and environmentally friendly?
Let’s hope that AI will help to make the detection of microplastics easier, but what we still need now is improved instrumentation capabilities to be able to measure micro- and nanoplastics of smaller sizes, that is, from 5–10 nm to 1–5 µm, on a routine basis. There is not much information on the microplastics present at such smaller sizes.
What are the most promising strategies for microplastic removal from wastewater treatment plants before release into the environment?
There is a comprehensive list of commonly proposed technologies for removing microplastics from surface waters and wastewaters, such as membrane filtration, adsorption with advanced materials, magnetic separation, coagulation, electrocoagulation (EC), plasma treatment, hydrothermal carbonization, and advanced oxidation processes (AOPs) such as Fenton’s reaction, photocatalysis with TiO₂, and ozonation (O₃). In addition, eco-friendly and nature-based solutions have been explored, including microbial degradation and constructed wetlands (2). Many of these methods were used in pilot laboratory experiments, but applications to real-world pollution problems are still scarce (3).
What challenges exist in assessing the combined effects of microplastics and co-contaminants (like heavy metals and pharmaceuticals) in terrestrial ecosystems?
The effects of co-contaminants like heavy metals or pharmaceuticals on the microplastic surface offer new challenges. They can change the bacterial composition of the agroecosystems, affect soil properties, and impact the types of crops that can be grown in specific areas. Some metals can increase the soil and plant toxicity. Others can change the soil bacterial composition. There are already a few examples of increased toxicity in crops, that is, cadmium from sludge present in soil amendments, and/or antibiotics that can be present in cow milk following exposure of cattle in a terrestrial contaminated environment (4).
References
(1) Mallek, M.; Barcelo, D. Sustainable Analytical Approaches for Microplastics in Wastewater, Sludge, and Landfills: Challenges, Fate, and Green Chemistry Perspectives. Adv. Sample Prep. 2025, 14, 100178. DOI: 10.1016/j.sampre.2025.100178
(2) Cheng, L.; Lian, J.; Wang, X.; et al. Evaluating a Soil Amendment for Cadmium Mitigation and Enhanced Nutritional Quality in Faba Bean Genotypes: Implications for Food Safety. Plants 2025, 14, 141. DOI: 10.3390/plants14010141
(3) Kumar, V.; Sharma, N.; Duhan, L.; et al. Microbial Engineering Strategies for Synthetic Microplastics Clean Up: A Review on Recent Approaches. Environ. Toxicol. Pharmacol. 2023, 98, 104045. DOI: 10.1016/j.etap.2022.104045
(4) Sarti, C.; Cincinelli, A.; Bresciani, R.; et al. Microplastic Removal and Risk Assessment Framework in a Constructed Wetland for the Treatment of Combined Sewer Overflows. Sci. Total Environ. 2024, 952, 175864. DOI: 10.1016/j.scitotenv.2024.175864
Damià Barceló is an honorary adjunct professor in the Chemistry and Physics Department at the University of Almeria, Almeria, Spain. His expertise lies in the analysis, fate, risk, and removal of emerging contaminants, nanomaterials, and microplastics from water, as well as sewage epidemiology of drugs and proteins using advanced mass spectrometric techniques. He has supervised > 67 PhD students since 1992. From 1993 to the present day, he has been editor or co-editor of 40 books on environmental chemistry.
