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Characteristics of Microplastics and Feed Raw Material Contamination in Common Aquatic Feeds
Summary
Scientists testing fish and shrimp feed in China found that every single sample—including raw ingredients like fishmeal and bone meal—contained tiny plastic particles called microplastics, mostly in the form of fibers. This matters because the food we feed farmed fish and shrimp could be a hidden pathway for plastic to work its way up the food chain and onto our dinner plates, though this study found contamination levels were moderate compared to other countries. The good news: much of the contamination seems to happen during processing and packaging, meaning better manufacturing practices (like avoiding plastic packaging) could help reduce the problem.
Microplastic pollution has become a pressing global environmental issue in recent years. Extensive research has documented the ingestion of microplastics by various aquatic organisms, including those raised in aquaculture systems. The use of aquafeeds has emerged as a potential pathway for increased input of microplastics into aquaculture systems. Therefore, accurately determining the content of microplastics in aquafeeds is of crucial importance for accurately assessing the potential risks that microplastics may pose to the safety of aquaculture environments and the quality of aquaculture products. Previous studies have provided some insights into the status of microplastic pollution in certain types of aquafeeds and fishmeal; however, there are still gaps in this research area, particularly with respect to aquaculture in China. Data on aquafeed ingredients other than fishmeal—such as plant-based raw materials and novel alternative raw materials for fishmeal—remain scarce. To address these limitations, we designed the present study with a focus on aquafeeds (including the raw material) commonly used in the aquaculture industry in China. The aquafeeds selected in this study are formulated for five typical aquaculture species, including fish and crustaceans. A total of 10 aquafeed samples and nine feed ingredient samples were collected and subjected to detailed analysis, including microplastic detection and analysis. 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 spectroscopy, which was applied for the qualitative identification of the polymer types of the detected microplastics. The results of our analysis confirmed that all the collected aquafeed samples and feed ingredient samples were contaminated with microplastics. The average abundance of microplastics in the aquafeed samples was (0.77±0.21) ind./g, and the average abundance of microplastics in the feed ingredient samples was (1.09±0.24) ind./g. When compared with global research data on microplastic pollution in aquafeeds and their ingredients, microplastic concentrations in the samples from this study were found to be moderately low compared to global data. In terms of the morphological characteristics of microplastics in the samples, fibers were identified as the most dominant shape in both aquafeeds and feed ingredients. Specifically, fibers accounted for 69.57% of the total microplastics in aquafeeds and 59.32% in feed ingredients. However, a notable difference was observed in specific types of feed ingredients: Film-shaped microplastics were the most abundant type in U.S.-sourced chicken meal, Australian-sourced beef bone meal, and domestically produced fishmeal. Regarding the particle size distribution, the peak particle size range was between 500 and 1,500 μm. Additionally, the particle size ranges in aquafeed samples and feed ingredient samples were relatively similar, indicating a potential connection between microplastics in ingredients andthose in the final aquafeeds. Polymer, polypropylene, and polyethylene terephthalate have relatively high contents in the aquafeed samples. In contrast, man-made fiber filaments were the most abundant polymer type in the feed ingredient samples. This difference in polymer composition is most likely attributed to the widespread application of these polymers in industrial production processes, which may lead to their incorporation into feed ingredients and subsequent presence in aquafeeds. An in-depth analysis of microplastic pollution sources in aquafeeds revealed that contamination of feed ingredients is a key contributor. Beyond ingredient contamination, aquafeeds can also be contaminated with microplastics during the processing stages (such as mixing, granulation, and drying) and packaging process (such as contact with plastic packaging materials). Accordingly, greater attention should be directed toward addressing microplastic pollution in aquafeeds. Supervision and control measures can be strengthened throughout the entire process of aquafeed and feed ingredient production, including processing, packaging, and transportation, to minimize the release of microplastics into the environment. For example, avoiding the use of plastics in packaging and storage of aquafeeds and feed ingredients can help reduce the risk of microplastic contamination, thereby ensuring aquafeed safety and promoting the development of sustainable aquaculture practices. In addition, based on the specific conditions of the production environments where feed ingredients 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 microplastic contamination in feed ingredients. Overall, our findings confirm that microplastics are prevalent in aquafeeds used in Chinese aquaculture as well as the raw materials of these aquafeeds. Contamination of feed ingredients is an important cause of microplastic pollution in aquafeeds; thus, measures to improve aquafeed processing may potentially reduce contamination. The results of this study provide a solid scientific basis for clarifying the current status of microplastic pollution in aquafeeds in China, including identifying the main microplastic pollution sources in aquaculture systems, with the ultimate goal of improving the quality and safety of aquaculture products.