Osmo-ionic responses of the freshwater shrimp Macrobrachium amazonicum in response to polyethylene micro- and nanoplastic exposure

Resumo

INTRODUCTION: Driven by the discharge of urban and industrial effluents and the improper disposal of solid waste, the contamination of aquatic environments has been progressively increasing, with microplastics (MPs) and nanoplastics (NPs) emerging as significant pollutants of concern. MPs and NPs have been shown to cause morphological damage to gill tissues, potentially impairing respiratory and osmoregulatory functions. OBJECTIVE: The objective of this study was to evaluate the MPs and NPs impact on osmoregulation of freshwater shrimps. MATERIALS AND METHODS: Total hemolymph osmolality, ion concentrations, and Na⁺/K⁺-ATPase (NKA) immunoreactive area in the gills and antennal gland of Macrobrachium amazonicum was analyzed following 120-hour exposure to an environmental relevant concentration of polyethylene phosphorescent microspheres (55–63 µm) and polyethylene nanospheres (200–9900 nm), 1 mg. L-1. RESULTS AND DISCUTION: Na⁺, K⁺, and total osmolality remained unaltered after the treatments. While Cl⁻ was elevated in MP group (25,14%; p < 0.05), Ca²⁺ was reduced in the NP group (47,07%; p < 0.05). The total NKA-immunoreactive area remained unchanged in gills but had a significant reduction in antennal gland in both MP and NP groups (MP = 61,06%, NP = 59,83%; p < 0.05). MPs and NPs can compromise cellular membranes and cause cytotoxic effects, potentially disrupting ion transport and changing the molting frequency. In freshwater decapods, Ca²⁺ is involved in cuticular calcification and is stored in the hemolymph; therefore, the reduction in Ca²⁺ levels may be associated with mobilization toward cuticular calcification during molting. Furthermore, the reduction in NKA activity in the antennal gland may be attributed to the physicochemical properties of MPs and NPs, such as their small size and large surface area, which may facilitate tissue penetration and cellular damage, thereby impairing ATPase function. CONCLUSION: Overall, exposure to MPs and NPs induced osmoregulatory disturbances in M. amazonicum, potentially leading to ion imbalance, disruption of electrochemical gradients, and reduced ion uptake. After evidencing short-term exposing triggers relevant functional alterations, longer-term investigations are necessary to diagnose the impact of MPs and NPs on ionoregulation in freshwater crustaceans.