Limited transfer of uranium to higher trophic levels by Gammarus pulex L. in contaminated environments J€ org Schaller, * Carsten Brackhage and E. Gert Dudel Received 31st March 2009, Accepted 18th June 2009 First published as an Advance Article on the web 6th July 2009 DOI: 10.1039/b906420f In contrast to the classification of most invertebrate shredders being sensitive to uranium, a G. pulex L. population with reproduction was found in a stream at a former uranium mining site with uranium concentrations of 150 mgl 1 in water and up to 2000 mg kg 1 DW 1 (dry weight) in litter born organic sediments. The survival of G. pulex, collected from a site without uranium contamination, was tested in a laboratory microcosm experiment using synthetic uranium-contaminated water and uranium-contaminated but nutrient rich food, simulating physicochemical conditions of water from former uranium mining sites. The results reveal that there are no significant differences in survival rate between individuals exposed and those not exposed to uranium. The uptake of uranium by G. pulex in environments with concentrations in food of 1152 mg kg 1 in DM (dry mass, organically bound) and in water of 63.9 mgL 1 is very low (4.48(1.93–8.46) mg kg 1 in DM). The accumulation of uranium in these invertebrates was verified to be via two pathways: body surface and food. A relevant amount of uranium adsorbs to the body surface where it can readily be desorbed. Introduction The effect of heavy metal pollution on food webs and hence ecosystem processes in running water is a global problem. The uptake of essential metals (e.g. Zn) by crustaceans (e.g. Daphnia magna Strauss) can take place via two different pathways, either directly via surfaces and/or delayed via ingestion and uptake in the alimentary channel. 1 For example it was shown that even in water dissolved Zn has negative effects on Daphnia magna Strauss. Most invertebrate species are sensitive to metal contamination. 2,3 Hyalella azteca and G. pulex are also classified as very sensitive to inorganic pollutants. 4–6 The survival of shredders in a uranium polluted environment (in water and inorganic sediments, but not in food) was mainly tested for Hyalella (e.g. Ref. 7), while little is known for the European shredder Gammarus sp. and the influence of polluted food. Uranium in aquatic environments is of special interest because of its radiotoxicity and its chemotoxicity. 8 In contrast to this, G. pulex was found in a stream with mean water concentrations of uranium of 150mgL 1 under alkaline, aerobic conditions, 9 and up to 2000mg kg 1 of uranium in dry leaf litter 10 at a former uranium mining site in Neuensalz- Mechelgr€ un, Eastern Germany. These leaf litter are the main food source for shredders. 11 The shredders are an important food base for fish. 12 Therefore it may result in an enrichment of uranium in higher trophic levels of the aquatic food web (biomagnification). Consequently, we investigated the effect of uranium rich alder leaves (Alnus glutinosa) in early phases of decomposition on G. pulex in a laboratory experiment. In the course of the investigations, we quantified the amount of uranium accumu- lating in the invertebrates and determined whether the uptake of uranium is mainly via surface (including gills and digestion system) absorption or even via ingestion. Finally, we examined the amount of stable uranium bound in G. pulex by desorption experiments. Experimental Test organisms Individuals of G. pulex used in the study were collected from Prießnitz, a stream near Dresden (Germany) with low uranium background, and kept in the laboratory for ten days before the beginning of the experiment. During this pre-experiment period, G. pulex was kept in 40 L of water at 12–15  C under faint lighting (100 lx) for 14 hours per day. They were fed with degrading leaves of alder (Alnus glutinosa). The alder leaves had an uranium content below detection limit prior to feeding G. pulex. Fixation/desorption of uranium by/from G. pulex Uranium concentrations of 55 mg L 1 (prepared from UO 2 (NO 3 ) 2 ) were used for a 24 hour fixation experiment. In this experiment 5 L of the contaminated solution were inoculated with 40 specimens of G. pulex. The ‘‘synthetic’’ uranium water used in the experiments were adjusted to pH 7.5 through addition of NaHCO 3 to simulate natural conditions (chemical speciation of uranium were: 72.51% of UO 2 (CO 3 ) 2 2 , 24.2% of UO 2 (CO 3 ) 3 4 , 3.24% of UO 2 CO 3 , 0.05% of UO 2 OH + ) calculated with a geochemical modelling software (PhreeqC 2.13.1). To stabilize the redox-potential (at Eh 400mV) an aeration pump (0.5 L min 1 ) and two air diffuser were used. Five individuals were sampled for evaluation of the uranium content at intervals of 10, 30, 90, and 1440 minutes. The desorption experiment was Dresden University of Technology, Institute of General Ecology and Environmental Protection, Tharandt, D-01062 Dresden, Germany. E-mail: schaller@forst.tu-dresden.de; Fax: +49 351 463 31399; Tel: +49 351 463 31375 This journal is ª The Royal Society of Chemistry 2009 J. Environ. Monit., 2009, 11, 1629–1633 | 1629 PAPER www.rsc.org/jem | Journal of Environmental Monitoring