A recent review highlights that assessing the intestinal fate and uptake of nanomaterials remains analytically challenging. It proposes a testing strategy using multiple analytical techniques. Meanwhile, both the European Food Safety Authority (EFSA) and the Organisation for Economic Co-operation and Development (OECD) are increasingly focusing on characterising the transformation of nanomaterials under realistic exposure conditions. RIVM notes that better harmonisation and validation of analytical approaches are crucial for reducing uncertainty in nanosafety assessments. 

Understanding the fate of nanomaterials in the gastrointestinal tract 

A recent review by the Italian National Institute of Health highlights the ongoing analytical challenges in understanding what happens to nanomaterials during digestion and whether they cross the intestinal barrier. The intestinal fate affects systemic exposure and, consequently, the potential health risk of food-related nanomaterials. The authors propose a strategy using multiple analytical techniques to investigate the fate of nanomaterials in the gastrointestinal environment. The strategy is relevant in view of ongoing developments at the EFSA and the OECD, both of which stress the importance of characterising dissolution, dispersion stability and transformations under biologically relevant conditions. 

The analytical challenges of studying nanomaterials in the gastrointestinal tract 

In gastrointestinal environments, particles can undergo various changes, such as dissolving, agglomerating, re-forming, or interacting with biomolecules to form coronas. These changes substantially change their behaviour compared with pristine materials characterised in a laboratory setting. The review emphasises that, despite major advances over the past 15 years, no single analytical technique can reliably characterise these processes in complex biological matrices such as digestive fluids, food matrices, intestinal cells and tissues. Instead, a combination of complementary techniques is needed to distinguish between particulate and dissolved fractions, determine particle size distributions, and identify nanoparticles within biological matrices. This would include combining techniques for mass concentration, such as mass spectrometry, and size distribution, such as electron microscopy. 

Impact of sample preparation on nanoparticle bioavailability 

The procedures for sample preparation like dispersion protocols can strongly influence the results of studies investigating nanoparticles in the gastrointestinal tract. Dispersion stability and agglomeration state can substantially influence the intestinal fate, uptake, and bioavailability of nanoparticles. This complicates the interpretation of results for risk assessment, makes it challenging to compare between studies and limits harmonisation across the field.  

Developments at international agencies 

EFSA is becoming increasingly aware of the challenges associated with detecting nanomaterials in the food chain. This awareness is reflected in their guidance, which emphasises the need to demonstrate whether particles retain their particulate nature during gastrointestinal digestion. A central concept in EFSA’s guidance is that materials that dissolve quickly during intestinal digestion may be assessed similarly to conventional soluble substances. In contrast, persistent particles require a nanospecific assessment. If there is insufficient analytical evidence to determine the fate of the particles, a precautionary approach is typically taken. This means that materials may need to be assessed as persistent nanoparticles, even if their actual biological behaviour is uncertain. Similar to EFSA, the OECD increasingly recognises that robust nanosafety assessment depends not only on intrinsic material characterisation, but also on understanding how these materials transform under realistic exposure conditions. To address this, the OECD is developing guidance to assess these transformations. 

Reflections by RIVM 

The review highlights that analytical limitations remain a key challenge for robust nanosafety assessment. Despite major advances in analytical technologies, reliable discrimination between particulate and dissolved forms remains difficult, especially in complex biological matrices. The lack of harmonisation in analytical methods slows regulatory implementation and creates uncertainty when interpreting toxicokinetic and hazard data. As a consequence, regulators often have to make conservative assumptions in the absence of sufficient analytical evidence.  

The increasing emphasis by the OECD and EFSA on assessing dissolution behaviour, dispersion stability and the intestinal fate of particles is an important step towards more scientifically robust nanosafety assessment approaches. However, further work is needed to translate advanced analytical methodologies into practical, standardised and regulatory-accepted testing strategies. In particular, the harmonisation of analytical protocols and validation of multi-method approaches will be essential to improve confidence in nanosafety assessments and support evidence-based regulation.