COMPARING MICROPLASTIC ACCUMULATION IN BEACH SANDS FROM LACUSTRINE AND COASTAL MARINE SYSTEMS: LAKE WINNIPESAUKEE, NH AND SANDY HOOK, NJ

In addition to the now ubiquitous occurrence of microplastics (MPs; <5mm) in the Earth’s hydrosphere, atmosphere, cryosphere, and biosphere, these materials are being deposited in beach sands around the world. While many studies have measured beach sand microplastic concentrations using a host of flotation-based extraction methods, little comparative work has been done across freshwater and marine coastal sites using one MP extraction technique.

Here we present new microplastic concentration data using one simple saturated NaCl floatation method from beach sands in the Lake Winnipesaukee, NH freshwater system (n>9) and the Sandy Hook, NJ marine coastal system (n>12). Three separate ~50g aliquots of sand from each collection locality were stirred in saturated NaCl solution (~1.21 g/cc) for floated MPs. This was completed 5 times for each aliquot with each float vacuum sieved through P8 filter paper. Isolated MPs were analyzed by type (fiber, foam, film, fragment, or pellet). We also analyzed beach sand grain size/sorting data and recovery frequency of “spiked” treatments across all of the analyzed samples.

In our comparison, sampled sands from Lake Winnipesaukee beaches yielded higher microplastic concentration on average than those from Sandy Hook (~180 MPs/kg sand vs ~120 MPs/kg). Most MPs in both collection sets were fibers. While Lake Winnipesaukee and Sandy Hook did not exhibit significant differences in average grain sorting, those collected sands from the less wave energetic shores of Lake Winnipesaukee were finer on average. Spiked microplastic recovery rates averaged ~91% for the Lake Winnipesaukee sands and ~88% for those from Sandy Hook.

Our MP concentration and type results are consistent with recent reports from other locales in both freshwater and coastal marine settings. While MP concentration in the freshwater system may have been expected to have been lower due to fresh- vs. saltwater density, we found the opposite. We note however that the coastal marine setting at Sandy Hook is both windier on average and subject to tidal variance, which may impact the results. As studies concerning MPs in shoreline deposits increase, it is important to understand how comparisons can be made across the different depositional environments of this new sedimentary material.