Microplastic (MP) contamination has become a pervasive global problem, affecting terrestrial and aquatic environments, and its potential health hazards are of widespread concern. MP-contaminated foods have a major impact on vulnerable consumers who rely on fish as a source of protein and as a staple food, as well as on fish themselves. Thus, human exposure to MP is becoming a significant threat to global public health. The evidence of the seriousness of MP in aquaculture feeds calls for control measures to reduce MP in these feeds for sustainable aquaculture production.
Introduction
In 2022, global fisheries and aquaculture production soared to an all-time high of 223.2 million tonnes, with aquaculture alone producing 94.4 million tonnes of aquatic animals, surpassing capture fisheries for the first time. In 2022, the capture fisheries sector produced 92.3 million tonnes, with 62.3 percent of marine fishery stocks being fished within biologically sustainable levels. From 1961 to 2021, the consumption of aquatic animal foods increased by 483%, with an average annual growth rate of 3.0%, nearly double the global population growth rate. Despite a noticeable decline in global capture fisheries production [1], aquaculture has admirably filled the gap in aquatic animal protein needs, with projections indicating a production surge to 202 MT by 2030. Approximately 4.5 billion people worldwide rely on protein from fisheries and aquaculture, underlining the crucial role of aquaculture as one of the fastest-growing sectors internationally. India, in particular, has witnessed exponential growth in aquaculture, attributed to rapid population expansion and soaring demand. The aquaculture sector employs millions and helps support food and nutritional security in India. Indian fish production escalated from 0.75 million metric tonnes (MMT) in 1950-51 to the current level of 14.2 MMT. Concurrently, the aquarium trade emerges as a significant multi-billion-dollar industry, holding considerable economic and social importance.
The prosperity and sustainability of aquaculture operations are intricately tied to the quality and composition of the feed provided to cultured organisms. In aquaculture, the primary aim is to generate high-protein compounds, while in the ornamental fish industry, there is an added emphasis on maintaining vibrant body colour. Aquaculture and aquarium feed typically consist of powders, cakes, or pellets abundant in animal or plant protein content. Fish and shrimp meals serve as rich protein sources, offering balanced amino acids and numerous growth-promoting factors, making them integral to aquaculture practices. Given that animal aquaculture production heavily relies on feed, it is notable that fish feed’s primary ingredients, fishmeal, and fish oil, derive over 70% of each from the fish catch, highlighting the significant contribution of capture fisheries to fish feed sources. However, feed often challenges marine and freshwater finfish culture, with many farms resorting to low-value and discarded fish as feed. Pelagic fishes, bycatch, and fish processing wastes primarily constitute fishmeal. A series of unintentional causes during industrial transformation, such as fishmeal processing, packaging, and ensuing trade activities, may also enhance MP contamination. Hence, it is essential to monitor the processing and packaging procedures of the aquaculture feed; its quality and ingredients is crucial, especially considering they are destined for human consumption.
Nonetheless, recent research highlights the alarming escalation of marine plastic pollution and microplastic contamination in fish. Fish meal typically constitutes 50% to 70% of the total material in fish feed. In India, commercially valuable fishes like sea bass, pompano, and cobia rely on aquaculture feeds for nutrition, often opting for floating and sinking feeds due to promising results, thereby gaining popularity among various stakeholders. Globally, fish remains a primary source of aquaculture feed, with the robust fishmeal and fish oil (FMFO) industry in India relying on trash fish, notably the bycatch from trawlers, as a key raw material. The fish meal is consumed as a raw material in the aquaculture and animal feed manufacturing sectors. Microplastics (MPs), an emerging peril, have garnered global attention due to their widespread presence and enduring nature in the environment. Formed from the breakdown of larger plastic items or the release of microbeads from personal care products, MPs have emerged as a significant environmental concern, impacting aquatic organisms and potentially infiltrating the food chain. Major sources of marine debris include rivers, storms, agricultural runoff, industrial and sewage effluents, shipping, and the fisheries sector. Mismanagement of plastic waste exacerbates the discharge of plastic into marine environments, posing a growing scientific concern. Due to their diminutive size (<5 mm), aquatic organisms easily ingest MPs, either intentionally or inadvertently. Various marine species have been found to ingest MPs, from zooplankton to sea birds. Consequently, the fish or fishery resources used in fishmeal production can introduce plastic contamination, transferring marine plastics to farmed animals and ultimately to humans consuming farmed aquatic products.
Marine fish farming in sea pens or aquaculture systems face the risk of MP ingestion both from fishmeal and the environment, primarily through water sources, plastic degradation in fishing gear, sewage discharge, agricultural runoff, and rainfall. Similarly, in freshwater aquaculture systems, studies indicate that MP abundance in fishmeal and feed can introduce MPs into water bodies. These MPs accumulate in edible tissues and may affect the physiological and behavioral aspects of cultured fishes and shellfish. High concentrations of MPs have been observed in cultured species like Salmon salar and Procambarus clarki, resulting in histopathological changes in the intestine, increased globular cell numbers, and swelling. Furthermore, the study also provides scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM/EDX) to characterize the surface texture of the MPs from the fishmeal to highlight the critical function of its morphology and to determine the type of minerals and accumulated metals adsorbed onto its surface using EDX.
Hazardous polymers can introduce xenobiotic toxins to internal organs, potentially leading to liver malfunction and reduced overall fitness. Polyvinyl chloride MPs can cause acidification in aquaculture environments by releasing chlorine. Harmful additives in MPs, such as bisphenol A and phthalates, are potential endocrine disruptors and can cause neurotoxicity and oxidative stress. Additionally, these additives may impair the immune system of fish by interfering with biochemical pathways. The bioaccumulation of these toxicants may lower the quality of aquaculture products and raise concerns for human health. A recent study [50] demonstrated that MPs can negatively impact the health and immunity of farmed fish, mainly by affecting the expression levels of cytochrome P450 1A1 and glutathione S-transferase in the liver. In this context, it is crucial to recognize that fish serve as a significant pathway for transferring the toxic elements found in plastic polymers to humans.
MPs indeed have the potential to pose various human health concerns, which can vary depending on the type of polymer from which they are derived. MPs Risk assessment (RA) presents a unique challenge because even though the polymers used to manufacture MPs are regulated and affirmed, their risk profile can differ significantly from that of their parent polymers. The hazards associated with MPs are not directly translatable from the bulk polymers, as they can exhibit different potential hazards and exposure routes. A hazard ranking model created for 55 thermoplastic and thermoset polymers using the EU regulation (EC) No 1272/2008, which is aligned with the classification, labelling and packaging (CLP) regulation, which categorizes polymers based on their hazardous properties to both the environment and human health. Hence, varied polymers might have disparate hazard classes when micro and nanoplastics degrade further.
Consuming MP contaminated feed poses significant risks to human and animal health, as MPs traverse the food chain, eventually reaching our tables and potentially harming our well-being. In the aquaculture industry, MPs can adversely affect animal health, leading to economic losses for farmers. Addressing MP contamination in feed is essential for safeguarding aquatic ecosystems and ensuring the long-term viability of these industries. Given the pervasive nature of MPs in the environment and their presence in many raw materials used in aquaculture feed, this study hypothesizes that commercial fish feed, widely utilized in aquaculture, may harbour MP contamination. This research is particularly relevant as MPs and associated chemicals can permeate the food chain and re-enter the environment through cyclical pathways. Consequently, regular feeding of MP-contaminated feed to cultured fish poses a substantial risk to global public health. This study investigates the quality and quantity of MPs, their polymers, and the Polymer Hazard Index (PHI) in ten commercial fish feeds sourced from six different countries.
Collection of fishmeal samples
The study examined ten commercial fish feeds, including both aquaculture and aquarium feed, procured from diverse outlets across India. These feeds encompassed fish and shrimp feed sourced from six countries—Denmark, US, Germany, India, Taiwan, and Vietnam—spanning three continents: Asia, North America, and Europe. Samples were obtained from ten distinct companies for the study. Detailed information about the fish and aquarium feed samples utilized in this research, including their ingredients
Results
The presence of MP contamination was detected in commercial aquaculture and aquarium feeds and their images are provided in Fig.1. Samples from ten selected companies chosen for MP studies revealed the presence of MPs, comprising the polymers Polyethylene terephthalate (PET), Polypropylene (PP), Polymethyl methacrylate (PMMA), Polyamide (PA), Polyurethane (PU), and Polystyrene (PS) with fibre (85%) and fragment (15%) as types. A total of 11300 MP particles were recorded across the ten fishfeeds
Discussion
Various undesirable elements that may originate from the environment or the manufacturing process can contaminate fish feed and the materials used. These impurities are easily transferred from feed to farmed fish and then to fish consumers. One of the main contaminants is microplastics that can concentrate in the fish body through bioaccumulation. Microplastics (≤ 5 mm) are generally defined as the by-products of the decomposition of macroplastics or polymers.
Aquaculture has emerged as an important solution to meet the increasing demand for fish while alleviating the pressure on wild fish populations from capture fisheries. The aquaculture industry is a major player in global food production. However, in aquaculture sectors, feed contamination with MPs poses significant risks.
The predominant focus of many studies has been to investigate the presence of microplastics (MPs) in feed ingredients, with a focus on fishmeal. Fishmeal is an essential component incorporated into the diets of carnivorous marine species. Its MP content can range from 0 to 17.3 PL/g. The specific value within this range depends on the fishing areas from which the fishmeal is sourced, as indicated by various studies. It is noteworthy that fishmeal obtained from fish caught in contaminated fishing areas had the highest concentrations of MP, thus highlighting the impact of marine pollution on the safety of feed constituents. Furthermore, it is noteworthy that plant-based meals, which are frequently used as fishmeal substitutes in animal feed production, had similar levels of microplastics (ranging from 0.8 to 1.7 particles per gram).
Aquaculture has emerged as a significant solution to meet the escalating demand for fish while alleviating pressure on wild fish populations from capture fisheries. The aquaculture industry stands as a major player in global food production.. However, within the aquaculture and aquarium sectors, MP contamination in feeds poses significant risks to both
Conclusions
The results of this study with convincing evidence of the prevalence of microplastic contamination of aquaculture feeds highlight the urgent need to take effective measures to reduce MP contamination in the aquaculture feed sector through the use of alternative packaging materials and strategies to protect the health of fish and shrimp as well as the health of human consumers and thus contribute to the sustainability of aquaculture. In addition, the presence of heavy metals Ni, Pb and Co transferred by MPs in fish feeds poses an additional risk to consumer health. By addressing this issue, we can contribute to the sustainability of aquaculture and protect the health of our fish, aquatic ecosystems and consumers of aquaculture products.
Reference : Devi, S. S., Jayan, S., & Kumar, A. B. (2024). Microplastic assessment in aquaculture feeds: Analyzing polymer variability across commercial fishfeeds from three continents. Journal of Hazardous Materials, 135621. https://doi.org/10.1016/j.jhazmat.2024.135621
