Presence of microplastics in six bivalve species (Mollusca, Bivalvia) commercially exploited at the Pacific coast of Costa Rica, Central America.

Microplastic pollution represents a serious threat to coastal marine systems. We evaluated the presence of microplastics (MPs) in 168 specimens of six commercially exploited bivalve species in the Golfo de Nicoya, Costa Rica. MPs were present in 100 % of the specimens of Leukoma asperrima and L. ecuadoriana, 74 % of Mytella strigata, 82 % of M. guyanensis, 84 % of Asthenometis asthenodon, and 82 % of Tagelus affinis. When considering all specimens, we found on average 4.8 ±â€¯8.0 pieces per individual and 2.1 ±â€¯3.3 items g-1 of wet tissue. There were significant differences between species with L. asperrima and L. ecuadoriana containing the highest number of pieces. Fibers and particles comprised 92 % and 8 %, respectively. This is the first study from the Central America's Pacific region showing the presence of MPs in bivalve species.

Competing specific interactions investigated by molecular dynamics: analysis of poly(p-dioxanone)/poly(vinylphenol) blends.

Molecular dynamics simulations (MD) were carried out to model the miscibility behavior of blends of poly(p-dioxanone) (PPDO) with poly(vinylphenol) (PVPh). The Hildebrand solubility parameters of the pure polymers and the Flory-Huggins interaction parameters of the blends at different compositions were computed. Negative interaction parameters were found across the whole range of compositions, suggesting the miscibility of the system, in agreement with the experimental results. The interaction parameter obtained from melting point depression studies was also found to be in good agreement with the value computed from the simulations. The repeat unit of PPDO contains one ether and one ester group, and both can act as hydrogen bond acceptors. The radial distribution functions (RDFs) between those groups and the hydroxyl groups of PVPh were computed to investigate the competence between the acceptor groups for the specific interactions. The RDFs indicate that interassociation occurs mainly with the ester groups, which is detrimental to the ether groups. This result was also corroborated by the analysis of the hydroxyl stretching region of the blends using Fourier transform infrared spectroscopy (FTIR). The good overall agreement found between the simulated and the experimental data reveals the importance of the molecular modeling techniques in the analysis of the miscibility behavior of polymer blends.