Concentration Depth Profiles of Microplastic Particles in River Flow and Implications for Surface Sampling.

River flow is a major conveyance of microplastic (1-5000 µm) pollution from land to marine systems. However, the current approaches to monitoring and modeling fluvial transport of microplastic pollution have primarily relied on sampling the surface of flow and assumptions about microplastic concentration depth profiles to estimate the depth-averaged concentration. The Rouse profile was adapted to show that fluvial transport of microplastic pollution includes all traditional domains of transport (bed load, settling suspended load, and wash load), as well as additional domains specific to low-density materials with rising velocities in water (rising suspended load and surface load). The modified Rouse profile was applied to describe the positively buoyant particle concentration depth profiles and compared to field observations to showcase the utility of this approach. A procedure was developed for assessing the uncertainty and bias from using a surface sample to estimate the depth-averaged concentration while assuming either surface load or wash load concentration depth profiles. Both assumptions may introduce a large amount of uncertainty due to the range of suspended microplastic concentration depth profiles. Monitoring microplastic pollution and estimating the depth-averaged concentration of microplastics in fluvial systems would further benefit from broader adoption of depth-integrated sampling, characterization of particle concentration depth profiles, and estimation of uncertainties in depth-averaged concentration based on the sampling approach.

Prolonged Duration of Viral Shedding of SARS-CoV-2: A Case Report.

INTRODUCTION: The literature on the clinical course of severe acute respiratory syndrome coronavirus 2 (SARS-COV-2) suggests patients continue shedding viral particles typically for an average of 20 days until the body builds immunity against the infection. However, a few cases have shown prolonged duration in viral shedding and highlight the significant increased mortality in these patients. It has also been suggested that multiple strains of SARS-COV-2 exist, keying the possibility to reinfection. CASE REPORT: We present a case of a 57-year-old male who presented twice over 37 days with symptoms related to SARS-COV-2, and only on his second visit was found to be in hypoxemic respiratory failure and cardiogenic shock. He also reportedly had a period of convalescence in between presentations. DISCUSSION: This case highlights the still unclear disease course of SARS-COV-2 and the need for diligence in providing strong follow-up instructions and evaluation for sequelae of the infection.