Accumulation of microplastics in stomach tissues of Japanese common squid (Todarodes pacificus)

As a new type of marine environmental pollutant, microplastics are chemically stable and difficult to degrade, and can accumulate in the marine environment for a long time and be deposited in marine organisms, which may eventually pose a threat to human health, and therefore, are of concern to scholars from all areas. To investigate the microplastics uptake characteristics in stomach tissues of Todarodes pacificus (T. pacificus) and its relationship with individual size (mantle length and body weight), stomach tissue weight and feeding grade. In this study, a total of 30 samples of T. pacificus were collected in the East China Sea from January to March 2018 with Chinese production survey vessels. The accumulation characteristics of microplastics in their stomach tissues were investigated using statistical and correlation analysis. The study results showed that the mantle length of T. pacificus ranged from 87-208 mm, with an average mantle length of 159.6 mm; body weight ranged from 16-188 g, with an average weight of 91.6 g; stomach weight ranged from 0.1-7.3 g, with an average stomach weight of 0.71 g. The presence of microplastics was found in the stomach tissues of 16 samples of T. pacific, with a detection rate of 53.3%. In this study, 18 microplastic particles were found, and the abundance of microplastic ranged from 0 to 3 items/individual, with an average abundance of 0.6 items/individual; the size of particles ranged from 0.332 to 4.337 mm, with an average particle size of 1.252 mm, with 72% of the microplastic particles smaller than 1 mm. The colors of microplastics were mainly black (38.9%), white (33.3%), blue (22.2%) and gray (5.6%), and they consisted of cotton, polyester and rayon, accounting for 44.5%, 33.3% and 22.3% of the total, respectively. The correlation analysis showed that the content of microplastics in the stomach tissues of T. pacificus was not significantly correlated with its stomach tissues weight and feeding grade, but was significantly and positively correlated with mantle length, body weight and age. Conclusion The content of microplastics in the stomach tissues of T. pacificus increased gradually with the increase of mantle length, body weight and age. The deposition of microplastics in the stomach tissues of T. pacificus gradually increased with their individual growth, which indicated that their intake of microplastics was greater than its excretion. Whether this accumulation phenomenon continus unceasingly or the dynamic balance of intake and excretion is maintained when a certain amount is reached requires further study.