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Accumulation of microplastics in North Atlantic sharks: causes, potential effects, and bioremediation strategies
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Abstract(s)
O plástico é um material versátil amplamente utilizado em muitos setores económicos e tem sido produzido em massa desde a década de 1950. No entanto, o plástico é composto por polímeros de difícil degradação que, devido à gestão inadequada atual e outros fatores, resulta na acumulação de grandes quantidades desses polímeros em diferentes ecossistemas da Terra, incluindo nos oceanos. Como o plástico é ubíquo em vários sistemas oceânicos, eventualmente interage com organismos marinhos, levando a eventos de emaranhamento ou ingestão. Muitos estudos têm demonstrado a acumulação de macro- e microplásticos em organismos marinhos. Entre eles, os predadores de topo de vida longa são muito propensos a acumular grandes quantidades de resíduos plásticos devido aos processos de bioacumulação e biomagnificação. Por essa razão, os tubarões carnívoros podem ser considerados bons sentinelas de contaminação por microplásticos, devido à sua alta posição trófica e à diversidade de habitats que podem ocupar (ou seja, desde bentónicos a pelágicos e de ambientes costeiros a oceânicos).
O principal objetivo da presente tese foi avaliar a acumulação de microplásticos e outras partículas antropogênicas na espécie de tubarão bentónico Scyliorhinus canicula e compará-la aos dados gerados para o tubarão pelágico Prionace glauca da mesma área geográfica, com ambos os estudos seguindo a mesma metodologia. Tal teve como propósito avaliar diferenças na ingestão de partículas antropogénicas entre os dois tubarões, com a hipótese de que o lixo antropogénico não se acumula uniformemente em diferentes zonas marinhas e, portanto, os organismos marinhos podem tender a acumular partículas antropogénicas mais presentes nos seus respetivos ecossistemas. Além disso, também se pretendia avaliar se os resultados do presente estudo estariam alinhados com a literatura existente sobre a acumulação de partículas antropogénicas em outros tubarões e ecossistemas marinhos (ou seja, água do mar e leito oceânico). Por último, este trabalho também visou estudar como parâmetros digestivos, como enzimas e condições de pH ácido, poderiam afetar as partículas antropogénicas retidas no trato gastrointestinal dos tubarões, a fim de entender que mudanças as partículas antropogénicas podem sofrer durante a sua passagem pelo trato digestivo do tubarão. Além disso, o estudo dos efeitos enzimáticos sobre os plásticos também visou avaliar o potencial biotecnológico dessas enzimas digestivas para a degradação de plásticos. Os resultados mostraram uma incidência de 100% de partículas antropogénicas em ambos os tubarões, com Scyliorhinus canicula acumulando menos partículas por indivíduo (7.84 ± 3.49) do que Prionace glauca (36.31 ± 23.7). Em relação à forma dos itens ingeridos, os tubarões pata-roxa acumularam até 4 vezes menos fragmentos do que os tubarões-azuis. No entanto, para ambos os tubarões, as fibras foram a forma de partículas mais acumulada. Em relação ao tipo de polímero, S. canicula ingeriu principalmente partículas de origem natural (por exemplo, celulose, algodão e outros) e a maioria dos itens ingeridos tinha uma densidade maior do que a da água do mar (flutuação negativa), enquanto P. glauca ingeriu principalmente itens de origem sintética (por exemplo, polietileno, polipropileno e outros), e uma grande proporção das partículas acumuladas tinha uma densidade menor que a da água do mar (flutuação positiva). Por último, em relação aos testes digestivos in vitro, ao simular algumas das condições do trato gastrointestinal dos tubarões, a enzima pepsina foi capaz de causar perda de peso em filamentos de poliamida (4.64%), em filmes de polietileno de baixa densidade (2.32%) e causou alterações estruturais em fibras de algodão.
Este estudo destaca a importância de monitorizar a ingestão de partículas antropogénicas em predadores de topo para demonstrar ainda mais a vulnerabilidade desses organismos marinhos à acumulação de lixo marinho, o que pode resultar em potenciais impactos para a saúde dos mesmos, ao mesmo tempo em que oferece informações sobre os diferentes níveis de poluição antropogênica em diferentes áreas marinhas (bentônicas versus pelágicas). Além disso, este estudo também destaca a importância de compreender como as partículas ingeridas se podem comportar dentro do trato digestivo dos organismos para futuramente explorar os seus possíveis efeitos.
Plastic is a versatile material used extensively in many economic sectors and has been mass-produced size 1950s. Nevertheless, plastic is composed of hardly degradable polymers which, due to the current inadequate management and other factors, results in the accumulation of large quantities of such polymers in different Earth ecosystems, including oceans. As plastic is ubiquitous across various oceanic systems, it eventually interacts with marine organisms, leading to entanglement or ingestion events. Many studies have demonstrated the accumulation of macro- and microplastics in marine organisms. Among these, long-lived top predators are very prone to accumulate large quantities of plastic debris due to bioaccumulation and biomagnification processes. For that reason, carnivorous sharks can be considered good sentinels of microplastic contamination given their high trophic position and the diversity of habitats they can occupy (i.e., from benthic to pelagic and from coastal to oceanic environments). The main objective of the present thesis was to evaluate the accumulation of microplastics and other anthropogenic particles in the benthic shark species Scyliorhinus canicula and comparing it to the data generated for the pelagic shark Prionace glauca from the same geographical area, with both studies following the same methodology. This was done with the purpose of assessing differences in the ingestion of anthropogenic particles between both sharks, hypothesizing that anthropogenic litter does not accumulate uniformly across different marine zones and therefore, marine organisms may tend to accumulate anthropogenic particles more present in their respective ecosystems. Additionally, it was also intended to assess if the findings of the present study would align with existing literature on anthropogenic particle accumulation in other sharks and marine ecosystems (i.e. seawater and seabed). Lastly, this work also aimed to study how digestive parameters, such as enzymes and acidic pH values, could affect the anthropogenic particles retained in shark’s gastrointestinal track, to understand which changes can anthropogenic particles undergo during their passage through the shark's digestive tract. Furthermore, the study of enzymatic effects on plastics also aimed to assess the biotechnological potential of these digestive enzymes for plastic degradation. The results showed a 100% incidence of anthropogenic particles in both sharks, with Scyliorhinus canicula accumulating less particles per individual (7.84 ± 3.49) than Prionace glauca (36.31 ± 23.7). Regarding the shape of the items ingested, the small-spotted catsharks accumulated up to 4 times less fragments than the blue sharks. However, for both sharks, fibres were the most accumulated shape of particles. In relation to the type of polymer, S. canicula ingested mainly particles of natural origin (e.g. cellulose, cotton and others) and most of the items ingested had higher density than seawater (negative buoyancy), while P. glauca ingested mostly items of synthetic origin (e.g. polyethylene, polypropylene and others), and a large proportion of the particles accumulated had a lower density than seawater (positive buoyancy). Lastly, concerning the digestive in-vitro tests, when simulating some of the gastrointestinal track conditions of sharks, pepsin enzyme was able to produce weight loss in polyamide filaments (4.64%), in low-density polyethylene films (2.32%) and caused structural alterations in cotton fibres. This study highlights the importance of monitoring the ingestion of anthropogenic particles in marine top predators to further demonstrate the vulnerability of these organisms to accumulate marine litter, which may result in potential health impacts, while also offering insights into the varying anthropogenic pollution levels in different marine zones (benthic versus pelagic). Additionally, this study also emphasizes the importance of understanding how ingested particles may behave within the digestive tract of organisms to further explore their possible effects.
Plastic is a versatile material used extensively in many economic sectors and has been mass-produced size 1950s. Nevertheless, plastic is composed of hardly degradable polymers which, due to the current inadequate management and other factors, results in the accumulation of large quantities of such polymers in different Earth ecosystems, including oceans. As plastic is ubiquitous across various oceanic systems, it eventually interacts with marine organisms, leading to entanglement or ingestion events. Many studies have demonstrated the accumulation of macro- and microplastics in marine organisms. Among these, long-lived top predators are very prone to accumulate large quantities of plastic debris due to bioaccumulation and biomagnification processes. For that reason, carnivorous sharks can be considered good sentinels of microplastic contamination given their high trophic position and the diversity of habitats they can occupy (i.e., from benthic to pelagic and from coastal to oceanic environments). The main objective of the present thesis was to evaluate the accumulation of microplastics and other anthropogenic particles in the benthic shark species Scyliorhinus canicula and comparing it to the data generated for the pelagic shark Prionace glauca from the same geographical area, with both studies following the same methodology. This was done with the purpose of assessing differences in the ingestion of anthropogenic particles between both sharks, hypothesizing that anthropogenic litter does not accumulate uniformly across different marine zones and therefore, marine organisms may tend to accumulate anthropogenic particles more present in their respective ecosystems. Additionally, it was also intended to assess if the findings of the present study would align with existing literature on anthropogenic particle accumulation in other sharks and marine ecosystems (i.e. seawater and seabed). Lastly, this work also aimed to study how digestive parameters, such as enzymes and acidic pH values, could affect the anthropogenic particles retained in shark’s gastrointestinal track, to understand which changes can anthropogenic particles undergo during their passage through the shark's digestive tract. Furthermore, the study of enzymatic effects on plastics also aimed to assess the biotechnological potential of these digestive enzymes for plastic degradation. The results showed a 100% incidence of anthropogenic particles in both sharks, with Scyliorhinus canicula accumulating less particles per individual (7.84 ± 3.49) than Prionace glauca (36.31 ± 23.7). Regarding the shape of the items ingested, the small-spotted catsharks accumulated up to 4 times less fragments than the blue sharks. However, for both sharks, fibres were the most accumulated shape of particles. In relation to the type of polymer, S. canicula ingested mainly particles of natural origin (e.g. cellulose, cotton and others) and most of the items ingested had higher density than seawater (negative buoyancy), while P. glauca ingested mostly items of synthetic origin (e.g. polyethylene, polypropylene and others), and a large proportion of the particles accumulated had a lower density than seawater (positive buoyancy). Lastly, concerning the digestive in-vitro tests, when simulating some of the gastrointestinal track conditions of sharks, pepsin enzyme was able to produce weight loss in polyamide filaments (4.64%), in low-density polyethylene films (2.32%) and caused structural alterations in cotton fibres. This study highlights the importance of monitoring the ingestion of anthropogenic particles in marine top predators to further demonstrate the vulnerability of these organisms to accumulate marine litter, which may result in potential health impacts, while also offering insights into the varying anthropogenic pollution levels in different marine zones (benthic versus pelagic). Additionally, this study also emphasizes the importance of understanding how ingested particles may behave within the digestive tract of organisms to further explore their possible effects.
Description
Keywords
Marine pollution Anthropogenic particles Top predators Marine ecosystems Poluição marinha Partículas antropogénicas Predadores de topo Ecossistemas marinhos Digestão Degradação enzimática Digestion Enzymatic degradation