Abstract:Microplastic pollution has become a pressing global environmental issue in recent years. Extensive research has documented the ingestion of microplastics by various aquatic organisms, and this phenomenon poses a significant threat to organisms residing in aquaculture water environments as well. In the context of aquaculture activities, the use of aquafeeds has emerged as a potential pathway for the external input of microplastics into aquaculture systems. Therefore, accurately determining the content of microplastics in aquafeeds is of crucial importance for scientifically assessing the potential risks that microplastics may pose to the safety of aquaculture environments and the quality of aquaculture products. At present, existing studies have provided some insights into the status of microplastic pollution in certain types of aquafeeds and fishmeal. However, there are still obvious gaps in domestic research related to this field. Particularly, research data on aquafeed materials other than fishmeal—such as plant-based raw materials and novel alternative raw materials for fishmeal—remain extremely scarce. To address these research limitations, the present study focused on aquafeeds and their raw materials that are commonly used in China’s aquaculture industry. Specifically, the aquafeeds selected in this study were designed for 5 typical aquaculture species, including fish and crustaceans. A total of 10 aquafeed samples and 9 feed material samples were collected and subjected to detailed analysis. In this research, a combination of analytical methods was employed to investigate microplastics in the samples. These methods included chemical digestion, which was used to remove organic matter from the samples and isolate microplastics; microscopic counting, which enabled the quantification of microplastics to determine their abundance; and Fourier transform infrared (FTIR) spectroscopy, which was applied for the qualitative identification of the polymer types of the detected microplastics. Through a systematic study on the characteristics of microplastic pollution in the 5 types of aquafeeds (targeting major aquaculture species in China) and the 9 types of feed materials, the study confirmed that all the collected aquafeed samples and feed material samples were contaminated with microplastics. The average abundance of microplastics in the aquafeed samples was (0.77±0.21)items·g?1, while the average abundance of microplastics in the feed material samples was (1.09±0.24) items·g?1. When compared with global research data on microplastic pollution in aquafeeds and their materials, the concentration of microplastics in the samples from this study was found to be at a moderately low level worldwide. In terms of the morphological characteristics of microplastics in the samples, fibers were identified as the most dominant shape in both aquafeeds and feed materials. Specifically, fibers accounted for 69.57% of the total microplastics in aquafeeds and 59.32% in feed materials. However, a notable difference was observed in specific types of feed materials: film-shaped microplastics were found to be the most abundant type in American chicken meat meal, Australia beef of bone meal, and China fish meal. Regarding the particle size distribution of microplastics, the peak particle size range was determined to be between 500 and 1500μm. Additionally, the particle size ranges of microplastics in aquafeed samples and feed material samples were found to be relatively similar, indicating a potential connection between the microplastics in materials and those in the final aquafeeds. From feed materials to finished aquafeeds, the polymer composition shifts from being dominated by Rayon to being dominated by polypropylene (PP) and polyethylene terephthalate (PET); this shift suggests that the aquafeed production process itself may be a significant contributor to PP particles. An in-depth analysis of the sources of microplastic pollution in aquafeeds revealed that contamination of feed materials is one of the key factors contributing to microplastic pollution in aquafeeds. Additionally, the aquafeed processing process exhibits certain removal mechanisms for microplastics, but it also carries risks of introducing new microplastics. In light of these findings, greater attention should be directed toward addressing microplastic pollution in aquafeeds. On one hand, it is recommended to strengthen the supervision and control measures throughout the entire process of aquafeed and feed material production, including processing, packaging, and transportation, to minimize the introduction of microplastics. For example, avoiding the use of plastic materials in the packaging and storage of aquafeeds and feed materials can help reduce the risk of microplastic contamination, thereby ensuring the safety of aquafeeds and promoting the development of sustainable aquaculture practices. On the other hand, based on the specific conditions of the production environments where feed materials are sourced (such as water quality, soil conditions, and existing pollution levels), appropriate physical, chemical, or biological degradation methods can be selected to reduce the amount of microplastics in the environment. This, in turn, can help decrease the level of microplastic contamination in feed materials. This study found that among aquafeeds and feed materials, microplastic contamination was the most significant in Crab feed and Bran, while the much-concerned fish feed and fish meal showed relatively less contamination by comparison. Contamination of feed materials is an important cause of microplastic pollution in aquafeeds, and the final impact of aquafeed processing on microplastic content is the result of a dynamic balance formed by the interplay between refined removal and high-risk introduction of microplastics. The results obtained from this research provide a solid scientific basis for clarifying the actual status of microplastic pollution in aquafeeds in China, serve as a fundamental reference for assessing the sources of microplastic pollution in aquaculture systems, and offer valuable insights for ultimately improving the quality and safety of aquaculture products.
