Temporal variations in microplastic- associated oxidative stress and fillet quality of whiting (Merlangius merlangus) and potential human intake: A multi-year field study.

While global microplastic (MPs) pollution threatens aquatic ecosystems and food safety, the widespread presence of MP sin marine fish and the associated health risks have raised significant concerns. This study aims to detect/characterize the presence of MP in whiting (Merlangius merlangus) fish caught in different regions of the Black Sea over two years on a seasonal basis, to determine the toxicity potential in fish (biochemical, histopathological, and immunohistochemical), fillet quality (protein oxidation), and the effects on potential MPs intake levels in humans during 2 years. MPs were detected across all sampling regions, seasons, and examined tissues, although their occurrence and abundance varied according to year, season, and region, with relatively higher MP burdens observed in samples from the Western and Eastern Black Sea. Year-to-year analysis of polymer composition showed that polyethylene (PE) was the dominant polymer, increasing from 38.7% in the first year to 48.6% in the second year. Polyvinyl chloride (PVC) was the second most frequent polymer, increasing from 22.6% to 27.0% between the first and second years, respectively. Higher tissue MPs burdens coincided with changes in antioxidant enzyme activities and elevated levels of MDA, MPO, IL-6, TNF-α, 8-OHdG, and Caspase-3 in some sampling groups, although the magnitude of these responses varied among tissues, seasons, and sampling regions. However, because this was an observational field study, these co-occurring patterns should not be interpreted as evidence of a direct causal effect of MPs.Biochemical and molecular biomarker analyses conducted in multiple target tissues (gills, liver, muscle, and the digestive system) revealed significant tissue-specific and seasonal changes. Stronger physiological stress responses were observed in some seasons and sampling regions with relatively higher tissue MPs burdens.Significant upward trends were observed in the markers evaluated. In particular, winter samples from the first year revealed severe tissue-level inflammation, with TNF-α reaching 267 ng/L in muscles and 491.8 ng/L in the digestive system, accompanied by marked lipid peroxidation (MDA up to 10.3 μmol/mL in muscles); which demonstrates that environmental stress factors triggered coordinated toxicological pathways in these target systems. Histomap mapping and immunohistochemistry data revealed findings consistent with biochemical analysis results. During the meat quality assessment phase, changes in SS and SH bonds in protein oxidation data, increases in carbonyl content and lactic acid levels, and decreases in muscle glycogen levels and pH were observed (p < 0.05). When the potential MPs intake level for people consuming whiting (Merlangius merlangus) fish is evaluated on a daily basis, the effects of season, and year are taken into account. Based on the food safety evaluation, average domestic consumers (Scenario A) were estimated to have an annual MPs exposure between 0.0000 and 0.0958 items/year, whereas intake for high-level consumers in the 90th percentile (Scenario C) peaked at 0.3327 items/year. Even though formal regulatory limits or toxicological thresholds for MPs have not yet been established, these calculated ingestion rates offer an essential foundation for assessing seafood safety. Our findings indicate that while growth characteristics in whiting fish show strong biological consistency, MP presence varies significantly depending on the year and season, with MP load being higher in some regions. Furthermore, the higher MPs accumulation observed in larger individuals suggests a possible influence of body size and cumulative environmental exposure on MP burden.