Tracking anthropogenic microparticles in wildlife of an alpine insular environment

Despite the isolation of remote natural regions, it has been discovered that they are experiencing the accumulation of anthropogenic microparticles (i.e., microplastics or natural or semisynthetic cellulosic particles). Teide National Park (Canary Islands, Spain) is a high-mountain protected area known for its rich biodiversity. This study aims to assess the occurrence of coloured anthropogenic particles in the faecal matter of wild mammals, specifically rabbits and mouflons, residing in the park. With this purpose, faeces were collected from 68 systematically distributed sampling points. A stereomicroscopy-guided grinding process allowed a chemical-free and quick visual inspection of 616 individual excreta, revealing that 96% were particle-free. However, 37 anthropogenic particles were found, which correspond to 0.79 ± 0.20 items per gram of dry faecal matter. The archetypical particle was a cellulosic blue microfibre of 2721 ± 407 µm, though poly(ethylene-vinyl acetate) and polypropylene were also identified via micro Fourier-transform infrared spectroscopic analysis. Atmospheric deposition and touristic pressure may be the sources of the anthropogenic particles, as they were randomly found in 36% of the sampling points. These findings represent the first evidence of anthropogenic particle ingestion by wild rabbits and mouflons, signifying the introduction of microplastics into terrestrial food chains in a remote high-mountain environment.

Beneath the water column: Uncovering microplastic pollution in the sublittoral coastal sediments of the Canary Islands, Spain

Marine ecosystems pollution by microplastics (MPs) is a global problem of special concern. The present study examines the prevalence and distribution of MPs and cellulosic particles in sublittoral coastal sediments of the Canary Islands archipelago (Spain). At twenty-six different locations alongside seven islands, three samples were taken parallel to the shoreline between 1 and 10 m depth (n = 78). Sediment samples were primarily digested with a H2O2 solution followed by four flotations in a saturated NaCl solution. The mean concentration obtained was 3.9 ± 1.6 items/g of dry weight. A similar distribution pattern was observed across all islands concerning particles morphology, color, size and composition: mainly colorless/translucent and blue fibers (60.0%). Additionally, fragments were also found, and to a much lesser extent microbeads, films and tangled messes. MicroFourier Transform Infrared spectroscopy analysis of 12.5% of the fibers, showed that they were mainly cellulosic (54.5%) -either natural or semisynthetic- followed by polyester (22.7%) and acrylic (4.5%). The potential correlation between particle distribution in nearshore sediments and wave intensity was also explored. This work provides the first comprehensive report on the current MPs content of the seabed of the region.

Three-dimensional evaluation of beaches of oceanic islands as reservoirs of plastic particles in the open ocean

The quantification of plastic debris on beaches has been extensively used as an indicator of plastic pollution in the marine environment. However, most efforts have focused on surface layers, with few investigations looking deeper into the substrate, thus underestimating total standing stocks. Such information is crucial to improve our understanding of where plastic accumulates in the oceans. In this study, we investigated the three-dimensional distribution of plastic (>1 mm) in three sandy beaches located in oceanic islands of the North Atlantic (Azores and the Canary Islands) that are known to accumulate significant quantities of small plastic debris at the surface layer. On each beach, we collected a total of 16 sediment cores down to 1 m depth, from the high tide line up to the backshore following a stratified random sampling design spread across four different levels across the beach. Samples were taken every 10 cm down to 1 m into the sand. Our results revealed the presence of plastic items in the deepest layers with subsurface layers accounting for 84 % of the total plastic abundance and with a similar pattern in terms of size, shape, colour and composition. Furthermore, we found increasing plastic concentrations towards the upper levels of the beach, indicating longer term accumulation in the backshore. Collectively, this study suggests that the plastic items reaching sandy beaches of the Macaronesia are being incorporated into its deepest layers, acting as reservoirs of plastic in the open ocean.

How harmful are exotic plantations for soils and its microbiome? A case study in an arid island

The plantation of exotic species has been a common practice in (semi-) arid areas worldwide aiming to restore highly degraded habitats. The effects of these plantations on plant cover or soil erosion have been widely studied, while little attention has been paid to the consequences on soil quality and belowground biological communities. This study evaluates the long-term (>60 years) effects of the exotic species Acacia cyclops and Pinus halepensis revegetation on soil properties, including microbiome, in an arid island. Soils under exotic plantation were compared to both degraded soils with a very low cover of native species and soils with well-preserved native plant communities. Seven scenarios were selected in a small area (~25 ha) with similar soil type but differing in the plant cover. Topsoils (0-15 cm) were analyzed for physical, chemical and biochemical properties, and amplicon sequencing of bacterial and fungal communities. Microbial diversity was similar among soils with exotic plants and native vegetation (Shannon's index = 5.26 and 5.34, respectively), while the most eroded soils exhibited significantly lower diversity levels (Shannon's index = 4.72). Bacterial and fungal communities' composition in degraded soils greatly differed from those in vegetated soils (Canberra index = 0.85 and 0.92, respectively) likely due to high soil sodicity, fine textures and compaction. Microbial communities' composition also differed in soils covered with exotic and native species, to a greater extent for fungi than for bacteria (Canberra index = 0.94 and 0.89, respectively), due to higher levels of nutrients, microbial biomass and activity in soils with native species. Results suggest that reforestation succeeded in avoiding further soil degradation but still leading to relevant changes in soil microbial community that may have negative effects on ecosystem stability. Information gained in this research could be useful for environmental agencies and decision makers about the controversial replacement of exotic plants in insular territories.

High Diversity of Bradyrhizobial Species Fix Nitrogen with Woody Legume Spartocytisus supranubius in a High Mountain Ecosystem

The symbiosis between rhizobia and legumes is of pivotal importance in nitrogen-poor ecosystems. Furthermore, as it is a specific process (most legumes only establish a symbiosis with certain rhizobia), it is of great interest to know which rhizobia are able to nodulate key legumes in a specific habitat. This study describes the diversity of the rhizobia that are able to nodulate the shrub legume Spartocytisus supranubius in the harsh environmental conditions of the high mountain ecosystem of Teide National Park (Tenerife). The diversity of microsymbionts nodulating S. supranubius was estimated from a phylogenetic analysis of root nodule bacteria isolated from soils at three selected locations in the park. The results showed that a high diversity of species of Bradyrhizobium and two symbiovars can nodulate this legume. Phylogenies of ribosomal and housekeeping genes showed these strains distributed into three main clusters and a few isolates on separate branches. These clusters consist of strains representing three new phylogenetic lineages of the genus Bradyrhizobium. Two of these lineages belong to the B. japonicum superclade, which we refer to as B. canariense-like and B. hipponense-like, as the type strains of these species are the closest species to our isolates. The third main group was clustered within the B. elkanii superclade and is referred to as B. algeriense-like as B. algeriense is its closest species. This is the first time that bradyrhizobia of the B. elkanii superclade have been reported for the canarian genista. Furthermore, our results suggest that these three main groups might belong to potential new species of the genus Bradyrhizobium. Analysis of the soil physicochemical properties of the three study sites showed some significant differences in several parameters, which, however, did not have a major influence on the distribution of bradyrhizobial genotypes at the different locations. The B. algeriense-like group had a more restrictive distribution pattern, while the other two lineages were detected in all of the soils. This suggests that the microsymbionts are well adapted to the harsh environmental conditions of Teide National Park.

Nanoplastics in the soil environment: Analytical methods, occurrence, fate and ecological implications

Soils play a very important role in ecosystems sustainability, either natural or agricultural ones, serving as an essential support for living organisms of different kinds. However, in the current context of extremely high plastic pollution, soils are highly threatened. Plastics can change the chemical and physical properties of the soils and may also affect the biota. Of particular importance is the fact that plastics can be fragmented into microplastics and, to a final extent into nanoplastics. Due to their extremely low size and high surface area, nanoplastics may even have a higher impact in soil ecosystems. Their transport through the edaphic environment is regulated by the physicochemical properties of the soil and plastic particles themselves, anthropic activities and biota interactions. Their degradation in soils is associated with a series of mechanical, photo-, thermo-, and bio-mediated transformations eventually conducive to their mineralisation. Their tiny size is precisely the main setback when it comes to sampling soils and subsequent processes for their identification and quantification, albeit pyrolysis coupled with gas chromatography-mass spectrometry and other spectroscopic techniques have proven to be useful for their analysis. Another issue as a consequence of their minuscule size lies in their uptake by plants roots and their ingestion by soil dwelling fauna, producing morphological deformations, damage to organs and physiological malfunctions, as well as the risks associated to their entrance in the food chain, although current conclusions are not always consistent and show the same pattern of effects. Thus, given the omnipresence and seriousness of the plastic menace, this review article pretends to provide a general overview of the most recent data available regarding nanoplastics determination, occurrence, fate and effects in soils, with special emphasis on their ecological implications.

Recycled wastewater as a potential source of microplastics in irrigated soils from an arid-insular territory (Fuerteventura, Spain)

In this work, the occurrence of microplastics (MPs) in irrigation recycled wastewaters (RWWs) and a desalinated brackish water (DBW) from the arid territory of Fuerteventura (Canary Islands, Spain) was studied. Besides, the presence of MPs in two types of soils (sandy-loam and clay-loamy; with no mulch film or fertilization with sewage sludge applied) irrigated with both water qualities was addressed. Results showed the prevalence presence of cellulosic and polyester microfibers (between 84.4 and 100%) of blue and transparent colors (up to 55.6 and 33.3%, respectively), with an average length of 786.9 ± 812.1 μm in the water samples. DBW had the lowest MP concentration (2.0 ± 2.0 items·L^-1) while RWW showed concentrations up to 40.0 ± 19.0 items·L^-1. Similarities were also observed between the MPs types and sizes found in both soils top layer (0-5 cm), with an average concentration three times greater in soil irrigated with RWW than in soil under DBW irrigation (159 ± 338 vs. 46 ± 92 items·kg^-1, respectively). In addition, no MPs were extracted from non-irrigated/non-cultivated soils, suggesting agricultural activities as the unique source of MPs in soils of this arid area. Results show that RWWs constitute a potential source of MPs in irrigated soils that should be considered among other pros and cons linked to the use of this water quality in agricultural arid lands.

Microplastic pollution in sublittoral coastal sediments of a North Atlantic island: The case of La Palma (Canary Islands, Spain)

In this work, the microplastic content of sediments collected in July 2020 between 5 and 7 m depth was studied in four locations of La Palma island (Canary Islands, Spain). At each sampling location, three samples were taken parallel to the shoreline. The microplastic content in each sampling corer was studied every 2.5 cm depth after digestion with a H₂O₂ solution followed by flotation in a saturated NaCl solution. Visualization of the final filtrates under a stereomicroscope revealed that all the sediment samples evaluated contained mostly microfibers (98.3%) which were mainly white/colorless (86.0%) and blue (9.8%), with an average length of 2423 ± 2235 (SD) mm and an average concentration of 2682 ± 827 items per kg of dry weight, being the total number of items found 1,019. Fourier Transform Infrared microscopy analysis of 13.9% (n = 139) of the microfibers also showed that they were mainly cellulosic (81.3%). No significant differences were found between the depths of the sediment. However, significant differences were found between the number of fibers from the sampling sites at the east and west of the island. Such variability could be driven by the winds and ocean mesoscale dynamics in the area. This study confirms the wide distribution of microfibers in sediments from an oceanic island like La Palma, providing their first report in marine sediments of the Canary Islands.

Assessment of microplastic content in Diadema africanum sea urchin from Tenerife (Canary Islands, Spain)

Sea urchins are highly abundant in the marine ecosystem where they graze limiting algal biomass and also serving as food for other predators. In this work, the presence of microplastics in the digestive tracts and gonads of 33 Diadema africanum sea urchins collected at two sampling points in Tenerife (Canary Islands, Spain) was studied. After separation and digestion of the digestive tracts and the gonads, the visualization of the filtrates under the stereomicroscope revealed the presence of 320 items which were microfibers (97.5%), fragments (1.9%) and films (0.6%), mainly blue (43.3 and 47.0% in the two sampling points, Tajao and El Porís, respectively) and translucent white (32.5 and 39.5%, respectively). Statistical analysis revealed that there were no significative differences in the contents of gonads and digestive tracts between both sampling locations. Regarding microfibers lengths, significative differences were only observed between the two sampling points, not between tissues. μRaman analysis showed that they were mainly cellulosic (46.0%), polypropylene (24.3%) and polyethylene terephthalate (24.3%). This study confirms for the first time the presence of microplastics in sea urchins from the Macaronesian region and also from Spain.

Arenas Blancas (El Hierro island), a new hotspot of plastic debris in the Canary Islands (Spain)

The present work has studied the incidence and type of micro (1-5 mm), meso (5-25 mm) and macroplastics (>25 mm) that have reached Arenas Blancas beach, located in the north coast of El Hierro island, in the Canary Islands (Spain), from October 2019 to May 2020 (13 sampling dates with 3 sampling points each). Taking into consideration the three studied plastic debris fractions (macro, meso and microplastics), a total of 9206 items were found, which had a total weight of 1169.7 g and a concentration of 891.3 ± 91.5 items/m² (118.3 ± 17.8 g/m² and 2.3 ± 0.4 g/L). Regarding their colour, most of them were transparent/white/clear, especially in the microplastic fraction in which they accounted for a 68% of the total. Attenuated Total Reflectance Fourier Transform Infrared spectroscopy of meso and microplastic fractions indicated that most of the particles were either polypropylene and polyethylene followed by polystyrene in a much lower amount. In general, the total amount of plastic debris that arrives to the beach by the persistent oceanic current pattern linked to the easternmost branch of the North Atlantic Subtropical Gyre is comparable to those of the most contaminated beaches of the Canary Islands archipelago, suggesting that a new hotspot of plastic debris arrival has been found.