Simultaneous measurement of uptake and elimination of cadmium by caddisfly (Trichoptera: Hydropsychidae) larvae using stable isotope tracers

The use of stable isotopes coupled with inductively coupled plasma-mass spectrometry provides a unique opportunity to investigate pathways of metals in aquatic invertebrates. In this study, the simultaneous uptake and elimination of cadmium (Cd) in stream-dwelling caddisfly (Trichoptera: Hydropsychidae) larvae was measured in laboratory experiments with stable isotopes of Cd. In one experiment, animals were exposed to low levels (0.5 mug/L) of Cd-114 in filtered river water and uptake was measured for 9 d, followed by 9 d during which the larvae were exposed to either Cd-114, Cd-113, or filtered river water. In a second experiment, the initial exposure concentration of Cd-114 varied from 0.1 to 1.6 mug/L for 5 d, followed by 5 d during which the larvae were exposed to the same respective levels of Cd-113. The purpose of the two experiments was to test whether or not elimination of Cd-114 from Hydropsyche larvae was the same in the presence or absence of Cd in the water and also whether or not elimination rates were dependent on exposure concentration. The results indicated that elimination of Cd by Hydropsyche larvae (elimination rate constant similar to0.21-0.24/d) in the presence of Cd in the water was the same as the depuration when no metal was present. Furthermore, the elimination rate was independent of exposure concentrations, ranging between 0.1 and 1.6 mug/L. Thus, the stable isotope tracer technique enabled the simultaneous measurement of uptake and elimination of Cd in hydropsychid larvae and may have the potential to facilitate the labeling of various compartments (e.g., water, sediment, and food) in the aquatic environment.