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Are Nitric Acid (HNO3) Digestions Efficient in Isolating Microplastics from Juvenile Fish?


A standard method for the detection and isolation of microplastics is required to adequately investigate plastic ingestion by juvenile fish. Dissections of juvenile fish guts require precise handling, which can affect the processing time if sample numbers are high. To investigate the efficacy of nitric acid (HNO3) in aiding the isolation of microplastics using whole fish, we digested juvenile glassfish, Ambassis dussumieri (Cuvier, 1828), at room temperature and at 80 °C. For a complete digestion, overnight incubation in 10 mL of 55% analytical-reagent (AR) HNO3 was sufficient for a whole fish of 1 g at room temperature. When coupled with elevated temperature, the digestion time is shortened to a few minutes and larger fish of 3 g can be digested in 30 min. Four of the five types of plastic survived the process, with nylon being the exception. This is a shortfall to the method; however, until a better method replaces it, we still value the use of HNO3 for its simple, inexpensive, swift and complete digestions of whole fish. Four fish species from two feeding guilds were digested using this method to validate its use. The number of plastic particles ingested did not differ between benthic and pelagic species and microplastic fibres comprised the majority of the plastic types found.

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The authors would like to thank ANCHOR Environmental Consulting for the provision of samples and Durban Transnet authorities for allowing us access to the port for collection.


This work was supported by the Rufford Foundation, grant number 18333-1, and the National Research Foundation (NRF), PhD grant number SFH14072177807.

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Correspondence to Trishan Naidoo.

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The authors declare that they have no conflict of interest.

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• HNO3 digestions on juvenile fish are simple, inexpensive and swift.

• Overnight incubation was sufficient for whole fish of 1 g at room temperature.

• With elevated temperature, fish of 3 g digested in 30 min.

• Four of the five types of plastic survived the digestion, nylon being the exception.

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Naidoo, T., Goordiyal, K. & Glassom, D. Are Nitric Acid (HNO3) Digestions Efficient in Isolating Microplastics from Juvenile Fish?. Water Air Soil Pollut 228, 470 (2017).

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  • Ambassis dussumieri
  • Fish
  • Microplastics
  • Plastics
  • Nitric acid
  • Fish digestion