Uranium uptake and depuration in the aquatic invertebrate Chironomus tentans Jorgelina R. Muscatello * , Karsten Liber Toxicology Centre, 44 Campus Dr, University of Saskatchewan, Saskatoon, SK, S7N 5B3 Canada Aqueous uranium uptake and depuration in Chironomus tentans are rapid processes that appear to be associated with passive and active process of depuration. article info Article history: Received 17 June 2009 Received in revised form 19 November 2009 Accepted 25 November 2009 Keywords: Uranium Uranium uptake Uranium depuration Chironomus tentans abstract Evaluation of aqueous uranium (U) uptake and depuration in larvae of the midge Chironomus tentans were investigated in two separated experiments. First, a static-renewal experiment was performed with 10-d old C. tentans larvae exposed to 300 mg U/L. The animals steadily accumulated U (K u ¼ 20.3) approaching steady-state conditions (BAF ¼ 56) in approximately 9–11 d. However, accumulated U was readily depurated (K d ¼ 0.36) with U tissue concentration decreasing rapidly within 3 d of the larvae being placed in clean water (t 1/2 ¼ 1.9 d). Also, the growth of C. tentans larvae appeared to decrease after 6–11 d of U exposure, probably due to the reallocation of resources into U detoxification mechanisms. However, growth significantly increased once C. tentans were transferred to clean water. A separate short-term experiment was performed to evaluate the possible mechanism of U uptake in this inver- tebrate. Results suggested a passive mechanism of U uptake coupled with an active mechanism of U depuration but no details related to the type of mechanisms or pathway was investigated. Ó 2009 Elsevier Ltd. All rights reserved. 1. Introduction Uranium (U) concentrations in aquatic environments can increase as a consequence of anthropogenic activities such as mining. The background median aqueous U concentration upstream of U mines in northern Saskatchewan is in the range of 0.05–0.35 mg/L and the median sediment concentration is in the range of 3.7–29.5 mg/kg dry weight (dw) (Environment Canada and Health Canada, 2001). However, elevated U concentrations have been reported to occur in surface water (100–500 mg/L) and sedi- ments (1000 mg/kg dw) downstream of U mining and milling operations located in this area (Environment Canada and Health Canada, 2001; Melville, 1995; Hynes et al., 1987). The higher U concentrations found in water and sediment at downstream loca- tions indicate that these may be sites for potential impacts of U on aquatic systems. Very few studies have assessed the effects of U on freshwater macroinvertebrates (Poston et al. 1984; Khangarot, 1991; Bywater et al.,1991; Hynes et al., 1993a,b Khun et al., 2002; Dias et al., 2008; Muscatello and Liber, 2009). Therefore, there is a particular need for more data to further understand U mecha- nisms of toxicity to such organisms. Mechanisms of essential metal assimilation by aquatic organ- isms are not always sufficiently selective. Metals can therefore be accumulated by organisms whether or not those metals are essential for proper metabolic functions. As a result, non-essential metals may enter cells by transport mechanisms used by essential metals (Beeby, 1991; Hare, 1992). A metal entering an insect body must first cross the membrane which separates the animal from its environment and which constitutes an important barrier to the entry of metals (Hare, 1992). Both active and passive transport mechanisms have been proposed to explain the uptake of metal from solution into aquatic invertebrates. The active transport of metals across membranes requires the expenditure of energy and can be protein carrier-mediated (e.g., copper, zinc), via ion pump (e.g., cadmium, calcium), and/or by endocytosis (e.g., iron, lead) (Hare, 1992). Conversely, passive transport does not require energy and can occur by facilitated diffusion (down a concentration gradient), through protein channels and/or via protein carriers (e.g., cadmium), or by passive diffusion where neutral metal species dissolve in the membrane’s lipid bilayer and cross it rapidly (e.g., mercury; Hare, 1992) Once a metal has entered the body of an aquatic invertebrate it can remain metabolically available until the physiology of the invertebrate interacts to excrete it (e.g., in feces or through the exuvia), or to detoxify it (e.g., via metallothioneins and/or insoluble metaliferous granules) (Rainbow, 1996, 2002; Hare, 1992). There- fore, metal accumulation and potential toxicity generally occurs * Corresponding author. Present address: Golder Associates Ltd. 500-4260 Still Creek, Burnaby, BC, V5C 6C6 Canada. Tel.: þ1 604 296 4331. E-mail address: jorgelina_muscatello@golder.com (J.R. Muscatello). Contents lists available at ScienceDirect Environmental Pollution journal homepage: www.elsevier.com/locate/envpol 0269-7491/$ – see front matter Ó 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.envpol.2009.11.032 Environmental Pollution 158 (2010) 1696–1701