Microplastics in fish and fishmeal: an emerging environmental challenge?

Abstract

Microplastics are contaminants of emerging concern; they are ingested by marine biota. About a quarter of global marine fish landings is used to produce fishmeal for animal and aquaculture feed. To provide a knowledge foundation for this matrix we reviewed the existing literature for studies of microplastics in fishmeal-relevant species. 55% of studies were deemed unsuitable due to focus on large microplastics (> 1 mm), lack of, or limited contamination control and polymer testing techniques. Overall, fishmeal-relevant species exhibit 0.72 microplastics/individual, with studies generally only assessing digestive organs. We validated a density separation method for effectiveness of microplastic extraction from this medium and assessed two commercial products for microplastics. Recovery rates of a range of dosed microplastics from whitefish fishmeal samples were 71.3 ± 1.2%. Commercial samples contained 123.9 ± 16.5 microplastics per kg of fishmeal-mainly polyethylene-including 52.0 ± 14.0 microfibres-mainly rayon. Concentrations in processed fishmeal seem higher than in captured fish, suggesting potential augmentation during the production process. Based on conservative estimates, over 300 million microplastic particles (mostly < 1 mm) could be released annually to the oceans through marine aquaculture alone. Fishmeal is both a source of microplastics to the environment, and directly exposes organisms for human consumption to these particles.

Figure 1

Mean abundance of microplastics per individual in studies assessing microplastics in fishmeal-relevant fish species. Only concentrations of ‘whole fish’ species used in fishmeal production are shown; 12 reviewed studies examined those species—four of those analysed two of such species each. n/r mean abundance was not reported. Error bars are 1× standard deviation of mean abundance per species of each study.

Figure 2

Kernel density estimation of potential microplastic size distribution based on 40 out of 58 particles extracted with NaCl density separation from whitefish fishmeal (n = 6). 87.2% were microparticles ≤ 1000 µm and 12.8% microparticles 1000–5000 µm. Note: the single > 5000 µm particle (6436 µm) is excluded from microplastic calculations.

Figure 3

Identification of six particles found in fishmeal samples. (a,b) Microfilms identified as acrylonitrile butadiene styrene—match score of 88.0 and 93.3% respectively, (c,d) polyethylene microfilms—match score of 86.3 and 86.1% respectively, (e) acrylonitrile/butadiene/styrene resin or styrene/acrylonitrile copolymer fragment with blue dye—match score 90.2%, (f) fragment of biomaterial (top suggestion: calcium phosphate—match score 93.6%).

Figure 4

Fishmeal as a pathway for microplastics to the marine environment from capture fisheries via fishmeal production to mariculture feed. Food particles (open circle), microplastics (red filled circle). Microplastic fragmentation possible during fishmeal production steps (heating and grinding) or through contamination, leading to increased microplastic concentrations fed back into the environment.