Development and use of a tissue-destruction method to extract microplastics in blue crabs (callinectes sapidus)

Abstract

Plastic materials are nearly ubiquitous throughout the marine environment and are often ingested by marine organisms. Assessing this contamination requires extraction and identification of consumed microplastics, which can be challenging due to their small size and the complexity of the tissues in which they accumulate. Existing methods often favor tissue destruction techniques that use corrosive chemicals to break down organismal tissue to assess microplastic contamination. However, extensive validation of these methods is required because the chemical interactions between the digestants and plastic polymers are not fully understood. For this study, the chemical compatibility between four digestants (hydrochloric acid (HCl), nitric acid (HNO3), sulfuric acid (H2SO4), and hydrogen peroxide (H2O2)) and three polymers (low-density polyethylene (LDPE), polystyrene (PS), and nylon) was assessed. All three acids (HCl, HNO3, H2SO4) readily attacked nylon upon contact. Because of this, a microplastic recovery method involving low-temperature tissue destruction with 30% H2O2 as a digestant was developed. This method was then validated on blue crabs by spiking known quantities of green nylon fibers, clear nylon fibers, white polyvinyl chloride (PVC) fragments, blue polyethylene (PE) fragments, and black PS fragments into collected stomach tissue before processing them using the developed method. High recovery rates were achieved for PS, PE, and green nylon fibers (>95%) while clear nylon fibers (84%) and white PVC fragments (63%) yielded sub-optimal recoveries. Once validated, the developed method was then used to assess microplastic contamination in 39 blue crabs collected near Corpus Christi Bay, TX. From these blue crabs, 0.44 synthetic fragments/fibers per crab were recovered, with 25.6% of collected blue crabs observed to contain synthetic fragments and fibers within their stomach. The developed method provides a less destructive alternative for assessing microplastic contamination in marine organisms when compared to published acid-based methods. Additionally, this study provides initial evidence of microplastic contamination in blue crabs, with approximately 25% of sampled blue crabs found to have microplastics or synthetic fibers within their stomachs.