Changes in haematology, metabolic rate, and cellular structure of spleen and head kidney of brown trout, Salmo trutta, after exposure to polystyrene microplastic particles

Salmo trutta (weight 31 ± 8 g, total length: 14 ± 2 cm) were fed a feed containing a mixture of 1, 5, and 10 µm spherical polystyrene particles (5 × 10 particles/g feed) for 30 days. Thirty days after completion of polystyrene administration, polystyrene concentrations in blood, spleen and head kidney were 9.2 - 51.6 µg/g tissue and 1.2 × 10 to 8.7 × 10 particles/g tissue with the highest concentrations in the spleen and the lowest in the kidney. Particles of 1 µm represented the largest proportion (80 %) in tissue, while 5 µm particles were much less frequent (20 %), and 10 µm particles were not detected at all. Effect of polystyrene on hematological parameters, on routine metabolic rate as well as on the cellular composition of the spleen and head kidney were investigated. Over the course of the experiment, mortality was < 5 % and was similar between the control group and polystyrene exposed fish. Due to polystyrene exposure the concentration of erythrocytes and of hemoglobin were significantly reduced, those of erythroblasts was increased. Also erythrocyte size was increased. These changes were an indication for macrocytic anemia. Polystyrene exposed S. trutta had also significant higher metabolic rate. Taken together the combination of an elevated metabolic rate and macrocytic anaemia can pose a substantial risk to fish fitness. Also the concentrations of granulocytes and of immunoglobulin were significantly reduced in polystyrene exposed fish, an indication for a compromised immune system. In serum of polystyrene-exposed fish, activities of aspartate aminotransferase and alanine aminotransferase, as well as protein concentration were significantly elevated, indicating hepatic inflammation or injury. In the spleen of polystyrene-exposed fish, erythrocytes were reduced, which likely reflects microplastic-induced anaemia. Monoblasts, monocytes, and macrophages were increased suggesting that polystyrene stimulates phagocytotic processes. In the head kidney of polystyrene-exposed fish only minor effects were observed. A 35-fold lower polystyrene concentration (0.5 × 10 particles/g feed) induced similar effects in blood cell count and haemoglobin concentrations, while at 350-fold lower concentrations concentration (0.05 × 10 particles/g feed) no effects were detectable.