Hyper-accumulation of perfluorooctane sulfonate (PFOS) and metals in buoyant foam in a high conservation-value river (Belubula River, NSW, Australia)

This study investigated river foam that accumulated on river edges and amongst in-stream debris in the Belubula River, an endangered ecological community and known habitat for platypus, draining a mostly agricultural catchment to the west of the Great Dividing Range in NSW. Samples of both water and accumulated foam from the river were tested for 15 metals and five per- and poly fluoroalkyl substances (PFAS) of which only perfluorooctane sulfonate (PFOS) was detected. The concentration of PFOS in foam (median 375,000 ng/L) was 18,750 times greater than in water (20 ng/L). Metals in river foam were more abundant than in river water. The median copper in river water was 3 µg/L and nearly 1000 times greater in river foam (median 2900 µg/L). Several metal toxicants (including mercury, cadmium, selenium and lead) were only detected in river foam where they were orders of magnitude higher than ecosystem protection levels. We speculate that aeration of river flow through rapids and waterfalls contributed air bubbles that produced surface foam in a similar process to foam fractionation. Although foam containing PFOS has previously been documented within a freshwater lake, the hyperaccumulation of metals within PFOS-enriched foam on the surface of a river appears to be a novel phenomenon and warrants further investigation to determine the bioavailability of the hyperaccumulated chemicals. In addition to the potential ecological impacts from such highly contaminated foam, it also poses potential human-health and agricultural pollution risks.