Scavenging and retention of bismuth by marine plankton and biogenic particles

Abstract

We did radiotracer experiments using 207Bi to quantify the bioavailability, accumulation, and retention of bismuth in marine plankton and biogenic detritus. The accumulation of 207Bi by two species of phytoplankton (Dunaliella tertiolecta and Emiliana huxleyi) was very rapid, approaching steady state after ~1 d. Emiliana cells without coccoliths reached a volume concentration factor (VCF) roughly twice that attained by cells with coccoliths. VCFs were 5 × 105 for Dunaliella and (4–9) × 106 for Emiliana after exposure for approximately 5 d. The radioactivity associated with Dunaliella was released with a biological half‐time of 3–5 d. Copepods (Anomalocera patersoni and Acartia species) grazing radiolabeled Dunaliella assimilated ~4% of the ingested 207Bi. Unassimilated radioactivity, voided in fecal pellets, was lost from pellets relatively slowly (half‐times of 26 d for Anomalocera and 58 d for Acartia). These release rates were similar to copepod fecal pellets that had scavenged 207Bi directly from water. Scavenging of bismuth from water by fecal pellets was considerable and extremely rapid, and uptake rates were similar to those of various size fractions of marine snow collected in a sediment trap. Release of scavenged 207Bi from the fresh fecal pellets was relatively slow, and very little release of radionuclide from the different size fractions of marine snow was observed. The biogeochemical behavior of bismuth in the marine environment closely resembles that of other particle‐reactive uranium‐thorium (U–Th) series and transuranic elements.