The possible routes of microplastics uptake in sea cucumber Holothuria cinerascens (Brandt, 1835)

Investigating the routes of microplastic uptake in sea cucumber is crucial in this plastics pollution age considering their non-selective feeding process, nutritional, biomedical and ecological importance. The guts, respiratory trees and coelomic fluids of Holothuria cinerascens were sampled and examined for microplastic after exposure to fluorescent microplastic fragments and microfibres. The madreporite pore size was also determined. 90% of the animals sampled ingested microplastic fragments via their feeding tentacles. Microplastic ingested ranged from 0 to 24 fragments intestine-1 (8.7 ± 2.11). All (100%) the animals sampled had microfibre in their coelomic fluid ranging from 32 to 227 microfibres coelom-1 (79.58 ± 10.53). Microfibres were found attached to all undigested respiratory trees examined. Microfibres were also found in 57.8% of digested respiratory trees with a range of 0-12 microfibres respiratory tree-1 (1.74 ± 0.66). Notably, there was no fluorescent microplastic fragments/microfibres found in the gut, coelomic fluid, and respiratory trees of animals in the control group. The madreporite pore size ranged from 0.59 to 2.90 μm (1.22 ± 0.03 μm). Microfibres found in the coelomic fluid were transferred from the respiratory trees because the size of microfibre used for this experiment was assumed larger for it to have passed through the gut into the coelom. Although the madreporite pore size is smaller than microfibre used in this study, madreporite can act as another channel to transport nanoplastics from the coelom into the animal tissue. This study showed that sea cucumber uptake microplastics from the environment using the feeding tentacles and the respiratory trees. Chemicals desorption from microplastics into H. cinerascens when ingested may pose a risk to the animals and their consumers. Further study is required to determine if microfibres transfer from the respiratory trees to the coelomic fluid is dependent on microfibre concentration and water temperature.