Do amphipods have the same concentration-response to contaminated sediment in situ as in vitro?

Abstract An underlying assumption of laboratory-based toxicity tests is that the sensitivity of organisms in the laboratory (in vitro) is comparable to that in the field (in situ). We tested this assumption by exposing estuarine amphipods (Chaetocorophium cf. lucasi) to a concentration series of cadmium-spiked sediments in vitro and in situ for 10 d. In situ exposures were conducted within plastic-mesh cages on an intertidal mudflat. To characterize exposure, we measured interstitial water cadmium concentrations (IWCd), acid volatile sulfide (AVS), and simultaneously extracted Cd (SEMCd) at the beginning and end of the exposures. Between day 0 and day 10, AVS decreased in both in vitro and in situ exposures, while IWCd levels declined less in vitro (median 27%) than in situ (median 76%). Despite more extreme conditions of temperature (10–36°C) and salinity (18–22%o) in situ, in vitro and in situ exposures showed comparable survival responses based on SEMCd/AVS (LC50 [95% CI]: 1.6 [1.46–1.78] and 1.8 [1.76–1.83], respectively), with the onset of marked mortality above a SEMCd/AVS value of about one and minimal survival (<5%) above a value of two. Based on IWCd concentrations, however, sensitivity was significantly greater in vitro (LC50 = 0.41 μg Cd/L [0.171–0.959], in situ LC50 = 1.6 μg Cd/L [1.15–2.16]). We concluded that, in our tests, amphipod sensitivity in vitro was equal to or greater than its sensitivity in situ.