Effects of petroleum-based and biopolymer-based nanoplastics on aquatic organisms: A case study with mechanically degraded pristine polymers.

Mismanaged plastic litter submitted to environmental conditions may breakdown into smaller fragments, eventually reaching nano-scale particles (nanoplastics, NPLs). In this study, pristine beads of four different types of polymers, three oil-based (polypropylene, PP; polystyrene, PS; and low-density polyethylene, LDPE) and one bio-based (polylactic acid, PLA) were mechanically broken down to obtain more environmentally realistic NPLs and its toxicity to two freshwater secondary consumers was assessed. Thus, effects on the cnidarian Hydra viridissima (mortality, morphology, regeneration ability, and feeding behavior) and the fish Danio rerio (mortality, morphological alterations, and swimming behavior) were tested at NPLs concentrations in the 0.001 to 100 mg/L range. Mortality and several morphological alterations were observed on hydras exposed to 10 and 100 mg/L PP and 100 mg/L LDPE, whilst regeneration capacity was overall accelerated. The locomotory activity of D. rerio larvae was affected by NPLs (decreased swimming time, distance or turning frequency) at environmentally realistic concentrations (as low as 0.001 mg/L). Overall, petroleum- and bio-based NPLs elicited pernicious effects on tested model organisms, especially PP, LDPE and PLA. Data allowed the estimation of NPLs effective concentrations and showed that biopolymers may also induce relevant toxic effects.

Tracking nanoplastics in freshwater microcosms and their impacts to aquatic organisms.

In this work, we used palladium-doped polystyrene NPLs (PS-NPLs with a primary size of 286 ± 4 nm) with an irregular surface morphology which allowed for particle tracking and evaluation of their toxicity on two primary producers (cyanobacterium, Anabaena sp. PCC7120 and green algae, Chlamydomonas reinhardtii) and one primary consumer (crustacean, Daphnia magna). the concentration range for Anabaena and C. reinhardtii was from 0.01 to 1000 mg/L and for D. magna, the range was from 7.5 to 120 mg/L.EC50 s ranged from 49 mg NPLs/L for D. magna (48hEC50 s) to 248 mg NPLs/L (72hEC50 s for C. reinhardtii). PS-NPLs induced dose-dependent reactive oxygen species overproduction, membrane damage and metabolic alterations. To shed light on the environmental fate of PS-NPLs, the short-term distribution of PS-NPLs under static (using lake water and sediments) and stirring (using river water and sediments) conditions was studied at laboratory scale. The results showed that most NPLs remained in the water column over the course of 48 h. The maximum percentage of settled particles (∼ 30 %) was found under stirring conditions in comparison with the ∼ 10 % observed under static ones. Natural organic matter increased the stability of the NPLs under colloidal state while organisms favored their settlement. This study expands the current knowledge of the biological effects and fate of NPLs in freshwater environments.

Identification and toxicity towards aquatic primary producers of the smallest fractions released from hydrolytic degradation of polycaprolactone microplastics.

Bioplastics are thought as a safe substitute of non-biodegradable polymers. However, once released in the environment, biodegradation may be very slow, and they also suffer abiotic fragmentation processes, which may give rise to different fractions of polymer sizes. We present novel data on abiotic hydrolytic degradation of polycaprolactone (PCL), tracking the presence of by-products during 132 days by combining different physicochemical techniques. During the study a considerable amount of two small size plastic fractions were found (up to âˆ¼ 6 mg of PCL by-product/g of PCL beads after 132 days of degradation); and classified as submicron-plastics (sMPs) from 1 µm to 100 nm and nanoplastics (NPs, <100 nm) as well as oligomers. The potential toxicity of the smallest fractions, PCL by-products < 100 nm (PCL-NPs + PCL oligomers) and the PCL oligomers single fraction, was tested on two ecologically relevant aquatic primary producers: the heterocystous filamentous nitrogen-fixing cyanobacterium Anabaena sp. PCC 7120, and the unicellular cyanobacterium Synechococcus sp. PCC 7942. Upon exposure to both, single and combined fractions, Reactive Oxygen Species (ROS) overproduction, intracellular pH and metabolic activity alterations were observed in both organisms, whilst membrane potential and morphological damages were only observed upon PCL-NPs + PCL oligomers exposure. Notably both PCL by-products fractions inhibited nitrogen fixation in Anabaena, which may be clearly detrimental for the aquatic trophic chain. As conclusion, fragmentation of bioplastics may render a continuous production of secondary nanoplastics as well as oligomers that might be toxic to the surrounding biota; both PCL-NPs and PCL oligomers, but largely the nanoparticulate fraction, were harmful for the two aquatic primary producers. Efforts should be made to thoroughly understand the fragmentation of bioplastics and the toxicity of the smallest fractions resulting from that degradation.

Microplastics in sediments of artificially recharged lagoons: Case study in a Biosphere Reserve.

We studied the occurrence of microplastics in sediments of artificially and non-artificially recharged lagoons from the network of endorheic wetlands called "La Mancha Húmeda", declared Biosphere Reserve by UNESCO. The particles sampled in this study covered the 25 µm-5 mm range. Films were the dominant microplastic typology in non-artificially recharged lagoons, while fibres and fragments were more abundant in those receiving wastewater. The concentration of microplastics in sediments reached up to 24.4 ± 5.2 microplastics/g, while plastic litter counts yielded <1 particle/g in non-wastewater receiving lagoons. Eleven types of plastic were identified using Micro-Fourier Transform Infrared Spectroscopy (micro-FTIR), the most abundant being the polyolefins polyethylene and polypropylene, and polyester and acrylic fibres. The statistical analysis of FTIR spectra confirmed the similarity between samples taken from recharged lagoons and wastewater treatment plant effluents. Overall, our results showed that endorheic lagoons are very sensitive to the accumulation of persistent pollutants, which include microplastics. The recharge of lagoons with wastewater effluents to maintain water levels, even if correctly treated according to current standards, is not a sustainable practice. Due to the closed character of endorheic basins, the continuous input of wastewater led to the accumulation of microplastics in sediments of wastewater receiving lagoons up to 40 times over non-recharged lagoons.

Occurrence and identification of microplastics along a beach in the Biosphere Reserve of Lanzarote.

This work studied the accumulation of plastic debris in a remote beach located in La Graciosa island (Chinijo archipelago, Canary Islands). Microplastics were sampled in the 1-5 mm mesh opening range. An average plastic density of 36.3 g/m2 was obtained with a large variability along the 90 m of the beach (from 8.5 g/m2 to 103.4 g/m2). Microplastic particles preferentially accumulated in the part of the beach protected by rocks. A total number of 9149 plastic particles were collected, recorded and measured, 87% of which corresponded to fragments. Clear colours and microscopic evidence of weathering corresponded to aged plastics wind-driven by the surface Canary Current. The chemical composition of plastics particles corresponded to PE (63%), PP (32%) and PS (3%). Higher PE/PP ratios were recorded in the more protected parts of the beach, suggesting preferential accumulation of more aged fragments.

Co, Zn and Ag-MOFs evaluation as biocidal materials towards photosynthetic organisms.

In the present study, the biocidal activity of three different metal organic frameworks (MOFs) based on Co (Co-SIM1), Zn (Zn-SIM1) and Ag (Ag-TAZ) has been evaluated towards one green alga and two cyanobacteria. These organisms are present in fresh- and seawater and take part in the early stages of the biofouling process. The biocidal activity of these materials was evaluated by measuring chlorophyll a concentration and by inhibition zone testing. After 24h of exposure the three different MOFs caused >50% of chlorophyll a concentration inhibition towards both cyanobacteria, however, although the green alga presented a great sensitivity for Ag-TAZ (reaching 90% of chlorophyll a concentration inhibition), it was much more resistant to the rest of MOFs. Bioavailability of these metals was studied using ICP-MS, the chemical speciation program Visual MINTEQ, and a heavy metal bioreporter bioanalytical tool. We have elucidated that the biocidal activity presented by these MOFs was due to the dissolved metals released from them and more exactly, it depended on the bioavailability presented by these metal ions, which was closely related with the free ion concentration. This article highlights the potential use of different MOFs as biocidal material towards photosynthetic organisms and reveals important differences in the sensitivity between these organisms that should be taken into account in order to increase the biocidal spectrum of these materials.