A preliminary assessment of polycyclic aromatic hydrocarbon distributions in the lower Mississippi River and Gulf of Mexico

Water samples were collected in the lower Mississippi River and the Gulf of Mexico in April 1999; sites in the river were sampled again in November 1999. Samples were separated into particulate (CP) and dissolved (CW) phases using 0.7 μm glass fiber filters. Each phase was analyzed for polycyclic aromatic hydrocarbons (PAHs). Total PAH abundance in river samples was higher in November of 1999 (CP: 1300–7000 ng gdw−1; CW: 77–430 ng l−1) than in April 1999 (CP: 1100–1700 ng gdw−1; CW: 12–25 ng l−1), despite higher total suspended sediment concentrations in April. Concentration profiles of PAHs in the lower Mississippi River indicate that compositional differences in PAH particle-water distributions were a function of seasonal discharge across the year. For example, higher PAH distribution coefficients in November correspond to a greater degree of combustion-driven processes indicated by black carbon abundance analyzed in the same samples in a complementary study. Concentrations of three specific PAHs isolated in the Mississippi River and the Gulf of Mexico (anthracene, benzo[a]anthracene, and benzo[g,h,i]perylene) were fit into a mass balance model in an attempt to constrain sources of PAHs into the gulf. This portion of the study was based on a limited number of samples. However, these preliminary mass balance calculations indicated that in 1999 on an annual scale, fluvial and atmospheric contributions of PAHs to the Gulf of Mexico were relatively negligible (100 kg) and that coastal erosion (103 kg) may have been the most significant source of PAHs into the gulf.