ABSTRACT
Sea spray aerosol (SSA) is one of the largest global sources of atmospheric aerosol, but little is known about SSA generated in coastal regions with salinity gradients near estuaries and river outflows. SSA particles are chemically complex with substantial particle-to-particle variability due to changes in water temperature, salinity, and biological activity. In previous studies, the ability to resolve the aerosol composition to the level of individual particles has proven necessary for the accurate parameterization of the direct and indirect aerosol effects; therefore, measurements of individual SSA particles are needed for the characterization of this large source of atmospheric aerosol. An integrated analytical measurement approach is required to probe the chemical composition of individual SSA particles. By combining complementary vibrational microspectroscopic (Raman and optical photothermal infrared, O-PTIR) measurements with elemental information from computer-controlled scanning electron microscopy with energy-dispersive X-ray analysis (CCSEM-EDX), we gained unique insights into the individual particle chemical composition and morphology. Herein, we analyzed particles from four experiments on laboratory-based SSA production using coastal seawater collected in January 2018 from the Gulf of Maine. Individual salt particles were enriched in organics compared to that in natural seawater, both with and without added microalgal filtrate, with greater enrichment observed for smaller particle sizes, as evidenced by higher carbon/sodium ratios. Functional group analysis was carried out using the Raman and infrared spectra collected from individual SSA particles. Additionally, the Raman spectra were compared with a library of Raman spectra consisting of marine-derived organic compounds. Saccharides, followed by fatty acids, were the dominant components of the organic coatings surrounding the salt cores of these particles. This combined Raman, infrared, and X-ray spectroscopic approach will enable further understanding of the factors determining the individual particle composition, which is important for understanding the impacts of SSA produced within estuaries and river outflows, as well as areas of snow and ice melt.
ABSTRACT
Triclosan (TCS), an emerging contaminant linked to antimicrobial resistance, has been the focus of many surface water studies to date. However, these initial studies have predominantly used sampling locations downstream of large volume (i.e., >0.5 million gallons per day) wastewater treatment plants (WWTPs). This approach overlooks potential inputs from their low volume counterparts as well as non-point sources, such as sewage network leaks, biosolid application to agricultural fields and leach fields associated with septic systems. Here we examine the range of concentrations, overall loading, and potential controls on TCS delivery to the East Branch of the Brandywine Creek (EBBC), a rural to suburban watershed located in southeastern Pennsylvania. TCS measurements were collected from 13 locations in the EBBC during baseflow conditions and immediately following a storm event. A regulatory database review identified WWTP density an order of magnitude greater than the national average, thereby confirming their pervasiveness in rural to urban systems. Detectable concentrations of TCS in the EBBC ranged from 0.2 to 0.6 ng/L during baseflow conditions and 0.5 to over 1000 ng/L following a storm event. The lack of a statistical relationship between TCS concentrations and yields with the number of upstream WWTPs and/or volume of treated effluent during both sampling periods confirm the importance of individual WWTP practices and the volume of the receiving water body, while a positive statistically-significant relationship between TCS concentrations and upstream developed open space following the storm event was likely influenced by runoff of spray-applied treated wastewater and/or sewage network leaks. Furthermore, the presence of detectable concentrations of TCS in sub-watersheds with no WWTP systems implies field applied biosolids or treated wastewater, as well as septic tank related leach fields are all viable sources of TCS. These findings suggest we must greatly expand our consideration of sources for emerging contaminants in waterways.