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This research aims to compare the toxicological effects of treated and untreated cotton and polyester microfibers on Mediterranean mussels.

May 8, 2026Open Access

Toxicological effects of chemically treated and untreated cotton and polyester microfibers on mediterranean mussels

Key Points

This research aims to compare the toxicological effects of treated and untreated cotton and polyester microfibers on Mediterranean mussels.
Mussels were exposed to 0, 100, 1,000, and 10,000 fibers L⁻¹ for five weeks in a static-tank setup.
Measured oxidative stress and immune defense biomarkers, as well as organism-level metrics like clearance rate and respiration rate.
Quantified microfiber ingestion and retention in gills, gastrointestinal tract, and other tissues.
Cotton fibers increased superoxide dismutase levels by 3–5-fold in gill tissue, indicating significant oxidative stress.
Polyester exposure resulted in moderate biomarker responses and efficient fiber depuration, suggesting partial recovery after removal.
Chemical treatments had minor effects compared to the differences between fiber types, challenging assumptions of natural fibers being safe.

Abstract

Microfibers are the dominant microplastic morphology found in marine environments, yet direct comparative studies between synthetic and natural fibers under environmentally relevant conditions remain limited. This thesis evaluates the chronic sub-lethal effects of cotton (natural) and polyester (polyethylene terephthalate, PET) microfibers, including treated and untreated chemical variants (with and without dyeing and softeners), on adults of the Mediterranean mussel (Mytilus galloprovincialis). Mussels were exposed for five weeks to 0, 100, 1,000, and 10,000 fibers L⁻¹ in a fully factorial static-tank renewal setup, followed by a one-week depuration phase. Measured variables included oxidative stress biomarkers (catalase (CAT)), superoxide dismutase (SOD), immune defense enzymes (acid phosphatase (ACP)), alkaline phosphatase (ALP), neurotoxicity enzymes (acetylcholinesterase (AChE)), and organism-level metrics (clearance rate, respiration rate, body condition index (BCI)). Microfiber ingestion, translocation, and retention were quantified in the gills, gastrointestinal tract (GIT), and remaining tissues. Both fiber types induced identifiable biological responses, but magnitude and persistence differed. Cotton exposure elicited stronger and more consistent positive dose responses in oxidative stress and immune biomarkers, particularly in gill tissue, with 3–5-fold elevations in SOD relative to controls. Cotton fibers also showed increased retention and incomplete depuration from remaining tissues, which was accompanied by sustained effects to AChE activity, suggesting long-term cholinergic disruptions. In contrast, polyester exposure produced more moderate and variable biomarker responses, with more efficient fiber depuration and partial physiological recovery after depuration. Chemical treatments on the textile fibers had minor and inconsistent effects relative to fiber type. Overall, results show that natural fibers cannot be assumed to be inert. Fiber morphology and retention dynamics appear to be the major drivers of biological responses. By integrating multi-tissue biochemical markers with organism-level metrics under environmentally relevant microfiber concentrations, this thesis provides a mechanistic ecotoxicological framework for assessing textile microfibers in costal ecosystems and challenges assumptions regarding the relative safety of natural versus synthetic materials.

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