Uptake of ¹⁰⁹Cd and ²⁰³Hg from particulates, dissolved medium, and food by Mysidopsis almyra : a marine hypopelagic mysid

Abstract

Surface biouptake of particulate ¹⁰⁹Cd and ²⁰³Hg by the mysid Mysidopsis almyra was investigated. Uptake from a medium with particulates prepared from a natural marine sediment slurry spiked with ¹⁰⁹Cd and ²⁰³Hg in the presence of 0.1 millimolar Na₂S was compared to that from a particle-free medium containing the same isotopes. Exposure was accomplished using a flow-through system. Repeated radioanalyses were performed on the mysids keeping them continuously submerged to avoid the surface disruption that would have resulted from transit through the air-water interface. Following uptake the mysids were subjected a series of increasingly vigorous surface treatments to evaluate tracer loss. The treatments included a brief rinse with either dilute acid or stable seawater, or a 9 day depuration in stable seawater. Particulate phase uptake was more variable but otherwise comparable to dissolved phase uptake. The brief surface treatments and the prolonged depuration resulted in similar losses, suggesting that a threshold in surface disturbance due to handling had been exceeded in both the seawater wash and acid dip treatments. Compartment analysis of the depuration data indicated a single compartment pattern of tracer loss in all exposure modes except that of particulate ¹⁰⁹Cd, which exhibited a 2 compartment loss pattern. Suspended sediment particles in the absence of mysids retained ²⁰³Hg but desorbed ¹⁰⁹Cd relatively quickly. Tracer losses by the mysids during depuration were similar to those predicted from the tracer loss pattern of free particles, suggesting that the ¹⁰⁹Cd lost from the particle-exposed mysids during depuration was desorbed from externally attached particles. Depuration losses were consistent with those expected from particulates with 0% to 50% of the surface occluded by attachment to the mysids. Uptake of particulates amounted to 0.1% to 0.3% of mysid body weight (wet basis) per 24 hours in the 2 experiments. The findings indicate an external compartment for particulate contaminants on mysids and probably crustacea in general. This poorly documented mode for toxicant and trace metal entry into the aquatic biota could be important ecologically.