Singapore – A recent alarming study has revealed the widespread presence of microplastics in a diverse range of marine animals inhabiting Singapore's coastal waters. Researchers from the National University of Singapore (NUS) Tropical Marine Science Institute (TMSI) discovered these tiny plastic particles not only within the digestive systems of marine organisms but also in their respiratory organs and bodily fluids, raising serious concerns about the health of the local marine ecosystem.
The study indicates that microplastics are entering marine animals through the ingestion of contaminated food sources, as well as through respiration and movement within the water column. Furthermore, the research highlights the pervasive distribution of microplastics across various habitats in Singapore's coastal environment, including vital mangrove forests, delicate coral reefs, and seagrass meadows, suggesting a potential for transfer from one organism to another within the food web.
Dr. Neo Mei Lin, Senior Research Fellow at TMSI and co-lead of the study, emphasized that while previous research had primarily focused on the presence of macro- and microplastics in Singapore's environment, this study delved deeper into the occurrence, distribution, abundance, and composition of microplastics within local marine biota. Notably, a recent study indicated that a staggering 97% of macro- and microplastics found along Singapore's shores originated from marine-based sources, underscoring the urgency of addressing this pollution.
This latest investigation by the TMSI team is part of a larger project aimed at comprehensively analyzing the impact and risks of marine plastics in the coastal environment. According to the National Oceanic and Atmospheric Administration (NOAA) in the United States, microplastics remain a relatively understudied area, with precise information on their effects still emerging. However, laboratory studies have suggested that microplastics and the chemicals they contain can hinder the developmental stages of animals, impair reproductive capabilities, and even weaken their resistance to diseases.
For this study, the TMSI researchers selected four key marine species: the orange fiddler crab (Gelasimus vocans), the porcelain fiddler crab (Austruca annulipes), the sandfish (Holothuria scabra), and the spaghetti worm (Synaptula recta). Dr. Neo explained that these species serve as useful indicators of microplastic contamination in marine sediments due to their “habitual ingestion and processing of significant amounts of sediment.” Additionally, these species play crucial roles within the ecosystem and are commonly found across multiple study sites, facilitating comparisons and inferences about the impact of microplastics. Dr. Jenny Fong, a co-author of the study, noted the widespread presence of these species throughout Southeast Asia.
Between November 2021 and May 2022, the research team meticulously collected a total of 153 live specimens from mangrove forests, seagrass meadows, and coral reefs across seven locations in Singapore: Pasir Ris Park, St. John's Island, Kusu Island, Small Sisters' Island, Pulau Semakau, Changi Beach, and Pulau Hantu Besar. The selection of these sites was based on safety, accessibility, and the abundance of the target species, excluding other areas deemed difficult or hazardous to access due to the presence of crocodiles and snakes.
The collected marine animals were carefully dissected, and microplastic samples were extracted from various organs. In fiddler crabs, the gills, hepatopancreas (a digestive organ with functions similar to the liver and pancreas in humans), and intestines were analyzed. For sandfish, the respiratory trees (their breathing apparatus), intestines, and coelomic fluid (the fluid in their body cavity, crucial for nutrient and gas transport) were examined. As spaghetti worms lack respiratory trees, only their intestines were analyzed.
The analysis revealed a total of 1,266 microplastic samples within these organs. The research team categorized these into four primary forms: fibres, fragments, films, and spheres, and analyzed their proportions. Fibres were the most prevalent type of microplastic found, with the majority of particles being less than 1mm in size. Furthermore, the researchers identified common polymers associated with everyday items such as plastic bottles, packaging materials, synthetic textiles, and car parts.
Dr. Neo explained that the form of the microplastic can hint at its potential origin and provide insights into which types of microplastics pose the greatest threat to animals. The predominance of fibres suggests a need for further investigation into specific sources of this type of contamination.
Dr. Ashwini Suresh Kumar, a TMSI researcher involved in the study, emphasized the importance of identifying the most common types of plastics to understand which ones marine animals are most likely to ingest. This information, she added, is valuable for policymakers, potentially informing regulations on additives commonly used in the manufacturing of these polymers to mitigate bioaccumulation and environmental impact.
The researchers suggest that in fiddler crabs and sandfish, the accumulation of microplastics in their respiratory organs likely occurred through respiration and direct contact with contaminated seawater. Dr. Neo highlighted that the smallest microplastic particles found in the respiratory trees of sandfish were approximately 60 micrometres in size.
The highest number of microplastics in both types of fiddler crabs was found in the hepatopancreas, indicating that ingestion via contaminated food sources is a primary route of exposure. Notably, female fiddler crabs, which possess one larger claw compared to the two similarly sized claws of males and tend to exhibit faster and more frequent feeding behavior, showed higher levels of microplastic contamination in their organs. The researchers hypothesize that these feeding patterns contribute to the increased contamination in females.
In the case of spaghetti worms, which feed on the feces of marine sponges, the researchers suggest that the worms may be ingesting microplastics that have accumulated on the surface of sponges as they filter seawater for food. This finding is significant as it suggests a pathway for microplastics to move up the marine food chain to higher trophic levels.
Addressing the potential implications of these findings for the safety of locally sourced seafood, Dr. Neo stated that further research is necessary. She noted that the guts of contaminated animals are “typically removed and cleaned before sale,” adding that “any definitive statement about human ingestion of microplastics should be made cautiously.”
Dr. Neo concluded, “While there are no long-term impact surveys and sampling plans in place at the moment, this study has opened up new research questions, such as developing novel approaches to study microplastic distribution within organisms.”
In a parallel effort, the Singapore government announced a National Action Plan in June 2022 to reduce the flow of plastic waste from both land-based and sea-based sources into the marine environment. The findings of this study underscore the critical importance of such initiatives and highlight the ongoing need for sustained attention and effort to address the pervasive issue of microplastic pollution.
Microplastics, defined as plastic particles smaller than 5mm, originate either as intentionally manufactured microbeads found in cosmetics and detergents or through the breakdown of larger plastic debris by sunlight, waves, and microorganisms. Once in the marine environment, their small size makes them easily mistaken for food by a wide range of marine organisms.
The potential dangers of microplastics are primarily discussed in two aspects: physical and chemical impacts. Physically, microplastic particles can block or damage the digestive tracts of marine animals, hindering normal feeding and digestion. As highlighted in this study, accumulation in respiratory organs can also lead to respiratory distress. Chemically, harmful additives used in plastic manufacturing (such as plasticizers, stabilizers, and flame retardants) or toxic chemicals adsorbed from the marine environment can be ingested by organisms along with microplastics. These chemicals are known to potentially cause endocrine disruption, reproductive impairment, and weakened immune systems.
Recognizing the severity of microplastic pollution globally, numerous countries and international organizations are undertaking regulatory and research efforts. Some nations have banned the use of microbeads in cosmetics, while others are implementing policies to improve plastic waste management systems. Furthermore, extensive research is underway to understand the sources, transport pathways, and impacts of microplastics on ecosystems and human health.
Singapore's National Action Plan, launched in 2022, sets targets for reducing plastic waste and promotes various strategies, including the introduction of an Extended Producer Responsibility (EPR) scheme, the expansion of recycling infrastructure, and public awareness campaigns. The findings of this recent study further emphasize the urgency of these efforts and underscore the need for continued vigilance and proactive measures to mitigate the growing threat of microplastic pollution in Singapore's valuable coastal ecosystems.
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