Bioaccessibility of Trace Metals and Rare Earth Elements (REE) in Microplastic

The ubiquity of microplastics on beaches worldwide is well-known and represents a global concern, as the durability of these materials is associated with potential risks to aquatic organisms and human health. When ingested by marine organisms, contaminants adsorbed onto microplastics can become bioavailable. However, there is a lack of data on the potential exposure of animals and humans to these contaminants through ingestion. Therefore, it is essential to understand how these contaminants behave in the digestive system. To address this, samples of virgin microplastic pellets—both ungrounded (UG) and grounded (G)—were separated into fractions >1 mm and <1 mm. These samples, made from four different types of plastics (linear low-density polyethylene, low-density polyethylene, polyethylene vinyl acetate, and high-density polyethylene), were contaminatedwith trace metals, including rare earth elements. Here, we evaluated whether the duration of exposure to contamination impacted the adsorption of metals. After this stage, all the samples underwent a simulation of the complete gastrointestinal tract using solutions containing salivary, gastric, duodenal, and biliary fluids, following the method of Versantvoort et al. (2005), which accounts for the individual's fed state. In this process, we added 3 mL of salivary fluid to the solids (V, G, and UG) for 5 minutes, 6 mL of gastric fluid for 2 hours, 6 mL of duodenal fluid, 3 mL of bile fluid, and 1 mL of HCO₃. All solutions were incubated at 37°C and 55 rpm. The extracts were then filtered; the supernatant was collected, and the residue underwent the optimized acid decomposition procedure. The method was validated using a mass balance approach, ensuring that the total content was equal to the sum of the supernatant and residue. Subsequently, all samples were analyzed, and the elements were determined using inductively coupled plasma mass spectrometry (ICP-MS). The main health risk posed by microplastics is not only related to the material itself but also to its additives and their potential to adsorb and release other contaminants. In this way, plastics can play a critical role in the long-distance transport of toxic chemicals. Our results show that the harmful effects of potentially contaminated solid environmental substrates may be linked to bioaccessible and orally bioavailable contaminant fractions.