Microplastics in a Post-hurricane Peat Deposit, Long Key, Florida

We investigated the occurrence and distribution of microplastics (63 - 500 µm) in a sediment core (30 cm depth) from a mangrove beach at Long Key, Florida. A thin bark layer occurred at 27.5 cm depth bounded by sand deposits (~5 cm thick), suggesting a hurricane deposit. Overlaying the hurricane deposit is a 25 cm thick peat deposit. We hypothesize that microplastics will be more abundant in the post-hurricane than the pre-hurricane sand deposit, and there will be no difference in microplastic abundance throughout the overlaying accumulated peat. Peat subsamples were targeted at six levels within the core. To obtain total dry weight and peat particle size distribution, subsamples from each level were wet sieved, dried at 50°C for 24 hours, and weighed. Subsamples were treated with 30% H 2 O 2 and dried at 60°C for 12 hours to dissolve organic matter. Using a density separation technique, we suspended collected inorganic matter in 40 ppt NaCl solution for 10 minutes to isolate microplastics. After vacuum filtration, separated microplastics and sediments were dried at 60°C for three hours and weighed. Here, we report the dry weight percentages of microplastics in the core. We found that the abundance of microplastics increased (1.6 to 12.5%) from pre- to post-hurricane deposit and remained abundant throughout the overlaying accumulated peat (~12.8%); however, there was a significant decrease of microplastic abundance in the surficial peat layer. These results support that extreme weather events, including hurricanes, deposit high amounts of microplastics into coastal environments. Of concern, microplastic contamination in accumulated peat could disrupt organism-peat interactions. Our next steps are to identify and classify microplastic particles by microplastic type.