Fate and transport of emerging contaminants across a dynamic urban landscape.

Two major classes of emerging contaminants (flame retardants/plasticizers and current-use pesticides (CUPs)) were measured across Houston, TX. Atmospheric particulate matter (PM) samples were taken at high spatial resolution in conjunction with NASA’s DISCOVER-AQ Houston campaign, a month-long, sampling intensive campaign in September 2013. Samples were taken at four ground-based sampling sites (300 filter-based PM samples) at least daily, improving temporal resolution, in both PM₂.₅ (PM less than 2.5 μm in aerodynamic diameter) and TSP (total suspended particulate) sample size fractions. Select samples collected during this campaign were analyzed for organophosphate esters (OPEs; emerging flame retardants/plasticizers) and CUPs (including mosquito adulticides). To analyze samples for these and other compounds of interest, a method first had to be developed for the simultaneous extraction of over 130 organic tracers (e.g., current- and historic-use pesticides, PCBs, OPEs, PBDEs, PAHs, alkanes, hopanes, and steranes). The extraction is carried out using pressurized liquid extraction, an automated technique, with extracts capable of being analyzed on multiple instruments to expand analysis capabilities. OPEs and CUPs (including mosquito adulticides) were examined for spatial and temporal heterogeneity, with large variability observed among urban, suburban, and industrial sampling sites, as well as day-to-day and diurnal differences. OPEs were also compared to bulk carbon measurements to improve understanding of atmospheric transport across the four sites. For mosquito adulticides, the oxidation of malathion was of particular interest. This oxidation not only appears to proceed faster than previous estimates from agricultural-based studies (hours compared to days), oxidation appears to occur during the night, due to reaction with either ozone or nitrate radicals. Determinations of atmospheric PM concentrations of emerging contaminants, specifically flame retardants and CUPs, lies at the interface of environmental and human health, as both classes of compounds have known benefits to humans, but also known toxicities. Additionally, spatial and temporal heterogeneity of these emerging contaminants in an urban area suggest that long-term sampling schemes (24 h samples taken on a 1-in-6 or 1-in-12 day sampling schedule) may not be representative of the day-to-day atmospheric PM concentrations present in these dynamic urban landscapes.