drance for comparison of microplastics in fishmeal. A more suitable extraction technique for microplastics in fishmeal is encouraged. The researchers found that the potassium hy- droxide digestion method is commonly used for microplastic extraction from fish and fishmeal. However, recovering mi- croplastics sized < 150 µm seems impossible for fishmeal with this method. This is a major drawback of the KOH meth- od (potassium hydroxide preparation), since smaller particles may be prevalent as some studies have shown; in one such study, all microplastics in S. pilchardus were 39–857 µm. In this study, the researchers successfully used the NaCl flota- tion method to extract microplastics from fishmeal. This method can extract smaller microplastics (from 55 µm) than the potassium hydroxide digestions; this was important since 35% of potential microplastics in the fishmeal samples were < 150 µm, highlighting the importance of recovering smaller microplastics and the suitability of the NaCl method. In this study, the overall recovery rate from dosing trials with white- fish fishmeal was about 71.3%, and about 49.3% for sardine/ anchovy fishmeal, proving that NaCl is a good extraction method. Even polymers of greater density than the NaCl solu- tion (e.g., polyester, rayon) were extracted with this tech- nique. In addition, there were low standard deviations within the same type of fishmeal, suggesting high repeatability of recovery rates.
Measuring microplastics in fishmeal Polymer identification is important, especially if you want to reduce overestimates of potential microplastic counts. For this reason, it is imperative to conduct spectroscopy or other poly- mer identification methods. In this study, approximately 90% of potential microplastics were assessed with Raman spectros- copy. A total of 11 particles were confirmed to be biomaterials, such as tricalcium phosphate, while 19 potential microplastics were confirmed to be plastic. Most of the microplastics found were polyethylene − a material used to make storage bags for fishmeal. Based on the correction for recovery rates of 71.3% and spectroscopy assessment rate of 89.1%, the mean con- centration of non-fibrous microplastics per kg of fishmeal was calculated to be about 71.9 items. However, other studies re- ported even up to 4000 – 6000 microplastics per kg. of fish- meal. As the microplastics could be introduced at any point in fishmeal processing, the concentrations in fishmeal are gener- ally higher than in the raw materials.
Microplastics in fish In marine fish, the potential microplastic exposure is likely to arise from ingestion of particles in the water column or on the seafloor that resemble prey, or by ingesting prey that pre- viously ingested microplastics themselves. It was shown in this study that, based on the review of species destined to be included whole in fishmeal, approximately 36 microplastics per kilogram of fishmeal can be expected from the raw mate-
rial. For the types of fish assessed for microplastics, the order of mean microplastic concentrations per individual fish were as follows: Sprattus sprattus > Trachurus trachurus > Engraulis spp. > Micromesistius poutassou > Ammodytes personatus > Euthynnus affinis.
Controlling microplastics contamination The scientists found that even under strict control measures, atmospheric contamination may be unavoidable. Several studies show that most researchers conduct their work in laminar flow cabinets, but they lack implementation of airborne controls. For this reason, using airborne contami- nation monitoring such as dampened filter papers during the extraction process should be considered even in clean environments. It was concluded that while microplastic extraction from whitefish fishmeal using a simple NaCl density separation method is suitable for microplastics > 55 µm, the NaCl meth- od might not be suitable for all types of fishmeal, and the de- velopment of further methods is recommended to enable their applicability to different fishmeal types and to enable extraction of particles as small as 1 µm. On the other hand, understanding the relationship of microplastics between cap- ture fish and fishmeal is important, as is their implications for direct and indirect consumers of fishmeal, given the impor- tance of fishmeal for food security. In addition, to improve comparability, future studies should provide size-related information of the extracted microplastics.
▶ ALL ABOUT FEED | Volume 29, No. 2, 2021
Some of the mi- croplastics pres- ent in the envi- ronment come from decompo- sition of larger pieces of plastic waste.
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PHOTO: ANP
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