Enrichment of biogenic lipids, hydrocarbons and PCBs in stream-surface foams

Water and foam samples from five streams in eastern Tennessee were analyzed for lipid content, lipid-class composition, and polychlorinated biphenyls (PCBs). Total lipid contents and lipid-class compositions varied substantially among streams and between the water and foam fractions within streams. However, lipid contents in foams were always greater than in the water from the same site (up to 100-fold). Major lipid classes in the water and foam samples were phospholipids, free fatty acids, and hydrocarbons; these lipid classes indicate the stream status with respect to viable microbial biomass, organic decay, and petroleum pollution, respectively. Concentrations of PCBs in stream-water and foam samples were also measured, and a laboratory experiment using stream water, reconstituted natural foam, and Aroclor 1254 was conducted to assess partition ratios of PCBs for water and foam. The results of the field and laboratory studies showed that the foam concentrated PCBs (relative to the parent waters) by factors of up to 10. The concentration of biogenic lipids and lipophilic pollutants in natural foams may influence the downstream transport of pollutants and affect their bioavailability to stream organisms.