OXIDATIVE STRESS AND HISTOPATHOLOGICAL CHANGES IN COMMON GOLDFISH WHEN EXPOSED TO MICROPLASTICS

Plastics are inextricable to the everyday lives of most people around the world, leading to substantial plastic waste.  When plastics are inappropriately disposed of, they end up in natural waterways  that eventually degrade into smaller pieces, known as microplastics (MPs) that range from 1 to 1,000 μm in size.  Initially, it was believed these pose little to no danger to fish. However, increasing research is showing MPs can adversely affect energetic status, digestive enzyme activity, reproduction, oxidative status as well as the internal organs.  The aim of this study was to examine the effects of increasing MP exposure, in the form polyvinyl chloride (PVC) at 0, 0.1 or 0.5 mg/L on the oxidative status and histological changes in goldfish, Carassius auratus, after 4 days.

The M Ps were confirmed to contain no heavy metals, polyaromatic hydrocarbons, polychlorinated biphenyls, or phthalates. Approx. 10% were <40 mm, 50%<140 mm, and 90%< 310 mm.  MPs were directly added to the water. Each treatment was triplicated with 5 fish in each and the study duration was 4 days. Aeration was provided, which was sufficient to keep the MPs in suspension throughout the study. After 4 days, the blood was drawn to measure the hemoglobin and hematocrit while the gills and liver/intestine were removed fixed for later histological examination.  Meanwhile, the gills, liver and brain were sampled for oxidative parameters.

Based on histological examination of the intestine, MPs were clearly present in the goldfish exposed to 0.1 or 0.5 mg/L.  Despite their presence, damage was not observed nor to the gills.  In contrast, the liver showed some classic instances of inflammation (lipofuscin-like material and white blood cell infiltrations) and vacuolization (Fig. 1).  This was supported with preliminar y analysis indicating the liver exhibited oxidative stress. However, hematocrit, hemoglobin or viscerosomatic indices were unaffected.

Clearly , MPs are not harmless to fish, based on the adverse histopathological changes under environmentally relevant concentrations.  Due to the ubiquity of MPs in aquatic systems, further research should examine any adaptive strategies fish might have to cope with such challenges.