Validation of density separation for the rapid recovery of microplastics from sediment

Several density separation techniques using numerous brine solutions have been developed for the separation of microplastics from sediment. The aim of this study was to validate the use of various brine solutions in a relatively rapid, reproducible, low cost single stage method that can deliver consistently high recoveries for different microplastic polymers <1 mm appropriate for monitoring programmes. The recovery of environmentally relevant microplastics (200 – 400 µm and 800 – 1000 µm) from post-consumer products was tested against tap water and brine solutions of varying density including sodium chloride (NaCl), sodium bromide (NaBr), sodium iodide (NaI) and zinc bromide (ZnBr₂). A general trend of increasing microplastic recovery with increasing solution density was observed, with NaI and ZnBr2 having significantly (p ≤ 0.001) higher rates of microplastic recovery. Microplastic size was found to influence recovery rates and needs to be taken into consideration when choosing a brine solution. From this work it is evident that density separation recovery tests are needed to validate the use of brine solutions for microplastic recovery and that ZnBr₂ is a novel and appropriate brine solution for microplastic extraction. This study represents the most in depth validation of brine solutions for the density separation of microplastic from sediments undertaken to date.