This study highlights the complex interactions between tributyltin (TBT), a legacy pollutant with enduring presence in marine ecosystems, and nanoplastics (NPs). TBT and NPs have seen much interest within the scientific literature and mainstream media, due to the emotive response triggered by anthropogenic pollution in our oceans. However, the synergistic interaction between the two species is currently unexplored. This study aims to address this literature gap, with a focus on the implications for marine life and environmental risk assessment.

The potential of various sized NPs (Nanopolystyrene, PS-NP, 40 to 765 nm) to act as vectors for TBT in marine environments was quantified. PS-NP particles were fully characterised for size, shape, topography, composition, purity, and surface area. Through adsorption experiments conducted in several water matrices (Milli-Q water, artificial and natural seawaters, and brackish water), it was discovered that PS-NPs had a significant capacity to adsorb TBT (between 7.6 and 49.5% w/w). The extent of adsorption was influenced by particle size/surface area, and the presence of competitive ions. This suggests that NPs may facilitate increased mobility of TBT in marine systems, thereby enhancing its availability to aquatic organisms, especially to those inhabiting surface and tidal zones such as Mytilus Edulis. Distribution coefficients (Kd between 193 ± 9 L g^-1 and 2853 ± 291 L g^-1) indicate that nanoplastics could rival natural sediments in terms of TBT adsorption potential, however, the lower density of NPs compared to benthic sediments raises concerns about their role in the remobilisation of TBT into the water column.

Laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) and laser-induced breakdown spectroscopy (LIBS) were deployed to view the distribution of TBT within Mytilus Edulis tissue. Quantification was possible through the preparation of homemade matrix-matched standards, and by employing a novel correction method using hydrogen and oxygen LIBS signals as an internal standard, comparable calibration linearity, and improved signal to noise ratio were achieved over MS internal standards. This methodology allows for a detailed examination of TBT bioaccumulation in mussels, with spatial resolution of approximately 75 µm, and helps to address one of the main hinderances of LA-ICP-MS with the use of matrix-matched standards and internal standard correction. To demonstrate the application of the newly developed LA/LIBS-ICP-MS method, the bioaccumulation of TBT by Mytilus Edulis with and without the presence of PS-NPs was assessed. The findings reveal that a shielding effect is taking place, whereby the accumulation of TBT is significantly reduced when bound to PS-NPs compared to aqueous TBT. This was reflected in the spatial distribution maps from LA/LIBS-ICP-MS and by whole-body ICP-MS. Aqueous TBT accumulation was observed within the mussel’s gills, hepatopancreas and inhalant/exhalant siphons, reaching concentrations greater than 500 ng g^-1 shot^-1. The half-life (108 ± 15 h) and bioconcentration factor (BCF, 1490 ± 117 mL g^-1) for aqueous TBT were calculated from the kinetic exposure model and were consistent with previous aqueous TBT exposures in the literature.

Collectively, the findings of this study serve as an initial step toward a more comprehensive environmental risk assessment of NPs, and their role in influencing the impact of legacy pollutants, like TBT, on marine ecosystems. The research provides critical insights into capacity of TBT adsorption by NPs, the detection of TBT within marine organisms, and the implications of NPs on the bioaccumulation of TBT.