PAHs and siloxanes in urban and suburban areas of the Anacostia River, Washington DC.

Abstract:

Challenges facing urban rivers include water stormwater runoff and changing water chemistry, not only from nutrient loading, but PAHs from car exhaust and other industrial chemicals. Here we examine organic contaminants from 5 sites in the watershed of the Anacostia River in Washington DC collected in 2018 and 2019. The sites include suburban tributaries of the Anacostia, plus two sites in the tidal main stem near the Kenilworth Aquatic Gardens and Bladensburg MD. The PAHs fluoranthene, pyrene and naphthalene, as well as the siloxane decamethylcyclopentasiloxane (D5) were found at all sites. Little is known about potential harms from siloxanes, however the European Chemical Agency considers concentrations above 0.1% in water to be potentially dangerous. For PAHs, no differences in concentrations were observed among the sites. Preliminary results suggest the mean ± standard deviation concentrations for fluoranthene (2.52 x 10^-4 ± 4.74 x 10^-5 M/g), naphthalene (3.308 x 10^-4 ± 6.415 x 10^-9 M/g), and pyrene (2.012 x 10^-4 ± 3.656 x 10^-5 M/g) were higher in sediments than expected. The average D5 concentration was 8.22 x 10^-4 ± 4.27 x 10^-4 M/g . Siloxanes are commonly used in cosmetics and it is possible that they are delivered to the tidal Anacostia by combined sewage outflow (CSO). They may be delivered to suburban sites by leaking sewers Washington DC is aggressively reducing CSO and continued monitoring will show whether organic contaminants are reduced as CSO is abated.