Macro- and microplastics as complex threats to coral reef ecosystems

Distribution characteristics and transport pathways of soil microplastics in coral reef islands with different developmental stages and human activities

Microplastics have attracted substantial attention on remote coral sand islands owing to their delicate ecosystems. However, the distribution, transport pathways, and control mechanisms of soil microplastics on these islands are yet to be elucidated. The coral reef islands of China's Xisha Archipelago in the South China Sea are at varying stages of development and experience differing levels of human activity, rendering them an ideal location to investigate the environmental characteristics of microplastics. This study conducted a comparative analysis of the distribution characteristics of microplastics in surface soils and beach sands, which were collected from coral cays and islands. We further analyzed the potential impacts of plant cover, geomorphology, soil environmental factors and human activities on accumulation and transport of microplastics. The results show that their abundance varies from 1068 to 1616 particles/kg on the different reef islands. Total organic carbon and dissolved organic carbon in the soils exert a significant influence on the accumulation of microplastics. The abundance of microplastics in the exposed areas showed an increasing trend with the degree of island development, and the human activities have a significant impact on the distribution of microplastics across the islands. Analysis of the microplastic abundance at different locations of the atoll reveals that ocean currents and monsoons are the primary drivers of microplastic accumulation on the coral reef islands. This study provides a scientific basis for the management of microplastic pollution and environmental conservation on remote islands.

Microplastics and nanoplastics co-exposure modulates chromium bioaccumulation and physiological responses in rats

The environmental fragmentation of plastics generates a mixture of plastic particles of various sizes, which frequently co-occur with other mobile and persistent environmental pollutants. Despite the prevalence of such scenarios, the interaction between micro- and nanoplastics (MNPs) and their combined effects with environmental pollutants, such as highly toxic hexavalent chromium (Cr(VI)), remain almost entirely unexplored in mammalian species. This study demonstrated that nanoplastic and microplastic particles co-aggregate and together influence Cr bioaccumulation patterns and related physiological alterations in rats. Following a four-week repeated intragastric exposure of Wistar rats to MNPs and Cr(VI), either alone or in combination, MNPs significantly enhanced Cr bioaccumulation in the liver, heart, brain, and skin. Under co-exposure conditions, Cr(VI) was the primary driver of cellular effects observed in the blood, including shifts in immune cell subpopulations (e.g., neutrophils, lymphocytes) and alterations in red blood cell indices, while serum biochemistry reflected limited physiological stress. MNPs per se decreased creatine kinase activity and increased cholesterol levels. In summary, polystyrene MNPs increase Cr(VI) distribution and bioavailability, but co-exposure does not uniformly exacerbate toxicity. Instead, their interaction may selectively alter physiological responses, emphasizing the need for a deeper understanding of their combined effects and potential health risks.

Unveiling the risk of marine litter and derelict fishing gear in remote coral reefs of the Andaman and Nicobar Islands, North Indian Ocean

An increasing amount of plastic litter and derelict fishing gear in the global oceans poses significant threats to corals and reef-associated marine biota. In this context, an underwater marine litter survey was conducted along the fringing coral reefs in the Andaman and Nicobar Islands- a remote archipelago in the Bay of Bengal, Northern Indian Ocean. The result revealed entanglement and smothering of coral colonies by plastic and derelict fishing gear. The survey recorded an average litter density of 0.42 ± 0.08 items/m2 (range: 0.23 ± 0.02 to 0.71 ± 0.09) and a mean mass of 138.61 ± 42.15 g/m2 (range: 70.17 ± 7.74 to 303.4 ± 2.55). Plastic was the most dominant litter (60.82 %) recorded in the reef environment. Derelict fishing gear made of plastic comprised 33.65 % of the total litter. Plastic Abundance Index (PAI), Hazardous Item Index (HII), and Clean Environment Index (CEI) were used to assess the ecological impact of marine litter. These indices highlighted the significant risks posed by marine litter to the coral reef environment. The finding helps to strengthen the assessment of marine litter in remote islands and underscores the urgent need for improved waste management, stricter regulations on the disposal of fishing gear, and effective removal of derelict fishing gear from the coral reef environments. Present study offers actionable insights for policymakers and stakeholders to prioritize interventions for managing marine litter to safeguard vulnerable coral reef systems.

Microplastic distribution and composition in mudflat sediments and varnish clams (Nuttallia obscurata) at two estuaries of British Columbia, Canada: An assessment of potential anthropogenic sources

Widespread microplastic contamination affects the marine-coastal ecosystems in British Columbia, Canada. To understand the characteristics and spatial distribution of of microplastics (MPs), we compared the MPs in sediments (n = 159) and Varnish clams (Nuttallia obscurata; n = 160) collected from two estuarine ecosystems (Cowichan and K'ómoks) experiencing different anthropogenic impacts; primarily resource extraction (i.e., logging) at Cowichan and urban development at K'omoks. Our objective wasto determine the MP abundance levels in sediments and clams and infer possible sources of MPs at the two estuaries. Microplastic polymer type was confirmed through FTIR spectrometry. The average abundance of MPs in sediments were 14.37 ± 11.57 particles/kg in the Cowichan Estuary and 30.96 ± 14.58 particles/kg in the K'ómoks Estuary. Varnish clam samples contained average abundance of 3.62 ± 2.58 particles/g and 2.24 ± 1.96 particles/g in Cowichan and K'ómoks estuaries, respectively. The Cowichan Estuary's marine terminal and K'ómoks Marina were found to be hotspots for MPs, likely due to a combination of industrial and local sources. Fibers were the most common type of MPs found in both sediment (53.34 %) and clam samples (53.5 %) from Cowichan, as well as in clam samples in% K'ómoks, indicating a potential link to textile sources contributing to the widespread presence of MPs in the marine environment. There was no clear signal based on the primary use of the estuary. Polyethylene was the predominant polymer type of MPs found in sediment and clam samples at Cowichan, whereas Polyester was most common at K'ómoks. Our study revealed the ubiquitous nature of these emerging pollutants in the sensitive estuarine environments of BC, with implications for plastic waste management and the reduction of plastic pollution at the regional level.

Exposure to polypropylene microplastics induces the upregulation of protein digestion-associated genes and microbiome reorganization in the octocoral Junceella squamata

Microplastics, a new type of pollutants found in coral reefs, have attracted increasing attention. However, most of the current research focuses on the scleractinian corals and few reports on Octocorallia. To reveal the impact of microplastic exposure on Octocorallia, we analyzed the transcriptional response of the coral hosts Junceella squamata along with changes to the diversity and community structure of its symbiotic bacteria following exposure to polystyrene microplastics. These results suggest that the microplastics have adverse impacts on nutrient metabolism and absorption in J. squamata. The symbiotic bacteria of J. squamata exhibited a clear response after exposure to microplastics, which may also reflect an adaptation mechanism of corals, and help to maintain the physiological function of coral symbiotic function under the exposure of microplastics. This study has revealed the impact of microplastic exposure on J. squamata, providing new insights for coral protection against the background of increased microplastics pollution.

Assessment of marine litter interactions with urban coral reefs in Okinawa, Japan

This study assessed different reef zones (lagoon, reef crest, reef slope) in three urban locations around Okinawa Island (Mizugama, Ginowan, Sunabe) and two marine protected areas around nearby Aka Island (Hizushi, Sakubaru) for marine litter pollution and litter interactions with reef organisms. A total reef area of 2250 m2 was surveyed by scuba diving, and 46 marine litter items were recorded. Litter density ranged from 0.01 to 0.05 items/m2, and plastics (76.09 %) and metals (15.22 %) were the most common litter types. The substrates for litter items were live corals (52.17 %), followed by dead corals and algae (26.09 %), sand (13.04 %), and rocks (8.70 %). Litter items on live corals were entangled exclusively with branching Acropora spp. (95.83 %) and Pocillopora spp. (4.17 %). This study highlights the need to protect coral reef ecosystems from the impacts of urbanisation in order to conserve and sustain their ecological and economic benefits.

Microplastics in remote coral reef environments of the Xisha Islands in the South China Sea: Source, accumulation and potential risk

Microplastics (MPs) are of great concern to coral health, particularly enhanced biotoxicity of small microplastics (< 100 µm) (SMPs). However, their fate and harm to remote coral reef ecosystems remain poorly elucidated. This work systematically investigated the distributions and features of MPs and SMPs in sediments from 13 islands/reefs of the Xisha Islands, the South China Sea for comprehensively deciphering their accumulation, sources and risk to coral reef ecosystems. The results show that both MPs (average, 682 items/kg) and SMPs (average, 375 items/kg) exhibit heterogeneous distributions, with accumulation within atolls and dispersion across fringing islands, which controlled by human activities and hydrodynamic conditions. Cluster analysis for the first time reveals a pronounced difference in their compositions between the southern and northern Xisha Islands and resultant distinct sources, i.e., MPs in the north part were leaked mainly from local domestic sewage and fishing waste, while in the south part were probably derived from industrial effluents from adjacent countries. Our ecological risk assessment suggests that the ecosystem within the Yongle Atoll is exposed to a high-risk of MPs pollution. The novel results and proposed framework facilitate to effectively manage and control MPs and accordingly preserve a fragile biosphere in remote coral reefs.

Biomarkers of oxidative stress, inflammation, and genotoxicity to assess exposure to micro- and nanoplastics. A literature review

The increased awareness about possible health effects arising from micro- and nanoplastics (MNPs) pollution is driving a huge amount of studies. Many international efforts are in place to better understand and characterize the hazard of MNPs present in the environment. The literature search was performed according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) methodology in two different databases (PubMed and Embase). The selection of articles was carried out blind, screening titles and abstracts according to inclusion and exclusion criteria. In general, these studies rely on the methodology already in use for assessing hazard from nanomaterials and particles of concern. However, only a limited number of studies have so far directly measured human exposure to MNPs and examined the relationship between such exposure and its impact on human health. This review aims to provide an overview of the current state of research on biomarkers of oxidative stress, inflammation, and genotoxicity that have been explored in relation to MNPs exposure, using human, cellular, animal, and plant models. Both in-vitro and in-vivo models suggest an increased level of oxidative stress and inflammation as the main mechanism of action (MOA) leading to adverse effects such as chronic inflammation, immunotoxicity and genotoxicity. With the identification of such biological endpoints, representing critical key initiating events (KIEs) towards adaptive or adverse outcomes, it is possible to identify a panel of surrogate biomarkers to be applied and validated especially in occupational settings, where higher levels of exposure may occur.

Unveiling the hidden threat of microplastics to coral reefs in remote South Atlantic islands

The widespread presence of marine microplastics (< 5 mm) is a significant concern, as it may harm marine biodiversity and ocean ecosystems. Corals' capacity to ingest microplastics has emerged as a significant threat to reef ecosystems, owing to the detrimental physiological and ecological effects it can trigger. The extent of the impact of microplastics on Brazilian corals remains unclear and this study aimed to investigate its distribution and characteristics in four coral species: Favia gravida, Mussismilia hispida, Montastrea cavernosa, and Siderastrea stellata, found in the Trindade and Martim Vaz Islands - the most isolated archipelago of Brazil, located about 1200 km (680 miles) east of the coast. This study aims to reveal the extent of microplastic distribution in the coral reef environment, assess the amount of microplastics in different coral species, and compare each species' capacity to adhere and accumulate microplastics. A high concentration of ingested and adhered microplastics was detected in all coral species evaluated in the present study. No significant differences were observed in the sampling points which indicates that although the sampling points are located at different distances from the coast, the microplastic pollution is equally distributed in the region. Polyethylene (PE), polyvinyl chloride (PVC), polypropylene (PP), poly(methyl methacrylate) (PMMA), Rayon, and Nylon particles were detected, with a predominance of PE (45.5 %). No significant differences in microplastic concentration were detected among the various species and locations studied. Our research presents findings that demonstrate the extensive occurrence of microplastic contamination in coral colonies located on remote islands.