Aquatic Toxicology 87 (2008) 146–156 Increased effects of internal alpha irradiation in Daphnia magna after chronic exposure over three successive generations F. Alonzo a,∗ , R. Gilbin b , F.A. Zeman b , J. Garnier-Laplace a,b a Laboratory of Environmental Modelling, DEI/SECRE/LME, Institute of Radioprotection and Nuclear Safety (IRSN), Cadarache, Building 159, BP3, 13115 St-Paul-lez-Durance Cedex, France b Laboratory of Radioecology and Ecotoxicology, DEI/SECRE/LRE, Institute of Radioprotection and Nuclear Safety (IRSN), Cadarache, Building 186, BP3, 13115 St-Paul-lez-Durance Cedex, France Received 8 November 2007; received in revised form 18 January 2008; accepted 21 January 2008 Abstract A 70-day experiment was performed with Daphnia magna exposed to waterborne Am-241 on a range of concentrations (from 0.4 to 40 Bq ml -1 ) in order to test chronic effects of internal alpha irradiation on respiration, somatic growth and reproduction over three successive generations. Changes in Am-241 concentrations were followed in the water and in daphnid tissues, eggs and cuticles. Corresponding average dose rates of 0.3, 1.5 and 15 mGy h -1 were estimated. This study confirmed that oxygen consumption increased significantly in the first generation (F0) after 6 days of exposure to a dose rate ≥1.5 mGy h -1 . Consequences were limited to a reduction in body length (5%) and dry mass of females (16%) and eggs (8%) after 23 days of exposure, while mortality and fecundity remained unaffected. New cohorts were started with neonates of broods 1 and 5, to examine potential consequences of the reduced mass of offspring for subsequent exposed generations. Results strongly contrasted with those observed in F0. At the highest dose rate, an early mortality of 38–90% affected juveniles while survivors showed delayed reproduction and reduced fecundity in F1 and F2. At 0.3 and 1.5 mGy h -1 , mortality ranged from 31 to 38% of daphnids depending on dose rate, but was observed only in generation F1 started with neonates of the brood 1. Reproduction was affected through a reduction in the proportion of breeding females, occurring in the first offspring generation at 1.5 mGy h -1 (to 62% of total daphnids) and in the second generation at 0.3 mGy h -1 (to 69% of total daphnids). Oxygen consumption remained significantly higher at dose rates ≥0.3 mGy h -1 than in the control in almost every generation. Body size and mass continued decreasing in relation to dose rate, with a significant reduction in mass ranging from 15% at 0.3 mGy h -1 to 27% at 15 mGy h -1 in the second offspring generation. © 2008 Elsevier B.V. All rights reserved. Keywords: Daphnia; 241 Am; Internal alpha irradiation; Multi-generation; Survival; Respiration; Growth; Reproduction 1. Introduction Over the last decade, the International Commission on Radiological Protection has recommended that a specific radio- protection system is developed for the environment in addition to radioprotection standards already established for humans. This required that animals and plants are taken into account, not only as alimentary items for man, but as components of natural biota where biodiversity is protected (ICRP, 1991, 2007). In this aim, one major objective of the ERICA project (European Commu- nity) was to evaluate the risk of radionuclides to ecosystems, under environmentally relevant conditions of exposure and at ∗ Corresponding author. Fax: +33 4 42 19 91 43. E-mail address: frederic.alonzo@irsn.fr (F. Alonzo). various levels of biological and ecological organisation (ERICA, 2006, 2007). Until very recently, available data on effects of ionising radiation concerned mainly acute external gamma radi- ation, while studies on chronic effects of gamma radiation were scarce. A gap of knowledge was highlighted for many wildlife groups and for alpha and beta emissions (FASSET, 2003; R´ eal et al., 2004). To respond to this situation, several recent works investigated chronic effects of radionuclides at dose rates below 1 mGy h -1 in species which play important ecological roles in ecosystems, such as aquatic invertebrates. In the freshwater microcrustacean Daphnia magna, larval resistance to starvation was significantly reduced after chronic external gamma irradi- ation of females for 9-day at 31 mGy h -1 , and for 21 days at 0.41 mGy h -1 (Gilbin et al., 2008). Chronic exposure to beta- emitting tritium was shown to induce mortality and abnormal development in larvae and genetic damages in adults of marine 0166-445X/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.aquatox.2008.01.015