The presence of plastic particles in oceans has been recognized as a major environmental concern. The decrease in particle size increases their ability to directly interact with biota, with particles in the nanometer size range (nanoplastics—NPs) displaying a higher ability to penetrate biological membranes, which increases with the decrease in particle size. This study aimed to evaluate the role of life stages in the effects of poly(methyl)methacrylate (PMMA) NPs on the polychaete Hediste diversicolor, a key species in the marine food web and nutrient cycle. Thus, behavioral (burrowing activity in clean and spiked sediment) and biochemical endpoints (neurotransmission, energy reserves, antioxidant defenses, and oxidative damage) were assessed in juvenile and adult organisms after 10 days of exposure to spiked sediment (between 0.5 and 128 mg PMMA NPs/Kg sediment). Overall, the results show that H. diversicolor is sensitive to the presence of PMMA NPs. In juveniles, exposed organisms took longer to burrow in sediment, with significant differences from the controls being observed at all tested concentrations when the test was performed with clean sediment, whereas in PMMA NP-spiked sediment, effects were only found at the concentrations 8, 32, and 128 mg PMMA NPs/Kg sediment. Adults displayed lower sensitivity, with differences to controls being found, for both sediment types, at 8, 32, and 128 mg PMMA NPs/Kg sediment. In terms of Acetylcholinesterase, used as a marker of effects on neurotransmission, juveniles and adults displayed opposite trends, with exposed juveniles displaying increased activity (suggesting apoptosis), whereas in adults, overall decreased activity was found. Energy-related parameters revealed a generally similar pattern (increase in exposed organisms) and higher sensitivity in juveniles (significant effects even at the lower concentrations). NPs also demonstrated the ability to increase antioxidant defenses (higher in juveniles), with oxidative damage only being found in terms of protein carbonylation (all tested NPs conditions) in juveniles. Overall, the data reveal the potential of PMMA NPs to affect behavior and induce toxic effects in H. diversicolor, with greater effects in juveniles.

Coastal ecosystems are increasingly threatened by climate change, especially the rising frequency of marine heatwaves (MHWs), which often co-occur with emerging nanomaterials such as graphene oxide (GO), whose ecological risks are still being evaluated. While the effects of GO have been studied in isolation, little is known about its interaction with thermal stress events. This research studied the combined effects of temperature (18 °C and 23 °C, simulating control and MHW conditions) and GO nanosheets exposure (0.01 mg/L) on two key estuarine bivalves: the clam Scrobicularia plana and the mussel Mytilus galloprovincialis. After 7 days of exposure (duration of many MHWs), energy metabolism, antioxidant defenses, oxidative damage, and neurotransmission were assessed. The results revealed that clams exhibited lower ETS and SOD activity when exposed to MHWs and lower SOD and AChE activities at MHW + GO, compared to the control treatment. Mussels relied primarily on SOD activity across treatments but showed increased susceptibility to GO nanosheets, with higher LPO levels and a significant reduction in AChE activity when exposed to GO at both temperatures. Overall, our findings suggest that S. plana shows a stronger response to the environmental alterations tested than M. galloprovincialis. Combined exposure to GO + MHW triggers species-specific biochemical responses in estuarine bivalves, highlighting how physiological traits shape the assessment of ecological risks posed by nanomaterial pollution under climate change.

Nanoplastics (NPs) pose a significant environmental threat due to their small sizes, widespread distribution, and bioavailability, enabling interactions with marine organisms from pelagic to benthic species. In this study, the effects of 10 days of exposure to waterborne poly(methyl)methacrylate (PMMA) NPs were evaluated in the crab Carcinus maenas by assessing behavioral and biochemical endpoints (in gills, hepatopancreas, muscle, and hemolymph). Behavioral assessments using an open field test revealed that exposure to PMMA NPs resulted in an increase in distance walked (from 73.662 ± 17.137 cm in control to 248.560 ± 25.462 cm in the highest PMMA NPs concentration) and in random movement patterns. Muscle acetylcholinesterase (AChE) activity decreased from 10.83 ± 0.73 to 6.75 ± 0.45 nmol/min/mg of protein with PMMA NPs concentration increase, which, combined with behavioral responses, suggests neurological incapacities. In the gills and hepatopancreas, defense and detoxification mechanisms were activated, with a significant increase in superoxide dismutase (SOD) activity (at 20 µg/L in gills and 80 µg/L in hepatopancreas) and glutathione S-transferases (GSTs) activity (all PMMA NPs concentrations in gills and 20 and 320 µg/L in hepatopancreas). Despite these activations, oxidative damage was observed, with a significant increase in protein carbonylation (PC) levels (20, 80, and 320 µg/L in gills and 5, 20, and 80 µg/L in hepatopancreas) and lipid peroxidation (LPO) (80 and 320 µg/L in gills and 80 µg/L in hepatopancreas). Effects on hemolymph followed a pattern similar to those reported for gills and hepatopancreas. An increase in SOD hemolymph activity was observed in organisms exposed to 5 and 80 µg/L, and GSTs activity increased in crabs exposed to 80 µg/L. Oxidative damage in hemolymph was only detected through LPO at 5 and 320 µg/L. Overall, this study showed that PMMA NPs induce biochemical alterations and damage in different tissues of C. maenas and affect its behavior with potential impacts at a population level.