Environ Monit Assess (2010) 171:661–669 DOI 10.1007/s10661-010-1311-0 Toxicity of Hg, Cu and Zn on early developmental stages of the European clam (Ruditapes decussatus) with potential application in marine water quality assessment Salem Fathallah · Mohamed Néjib Medhioub · Amel Medhioub · Mohamed Mejdeddine Kraiem Received: 17 July 2009 / Accepted: 15 January 2010 / Published online: 30 January 2010 © Springer Science+Business Media B.V. 2010 Abstract The toxicity of mercury, zinc and cop- per on sperm viability, fertilisation and embryo- genesis of Ruditapes decussatus was examined. Cu did not affect sperm viability at all the con- centrations tested. Conversely, the Zn and Hg significantly ( P < 0.01) reduced sperm viability only at the highest concentration (respectively 512 and 256 μg/l). Cu caused a significant de- crease ( p < 0.05) of less than 6% in the fertili- sation rate at 128 μg/l and Zn of up to 13% at 64 μg/l. Hg significantly ( p < 0.01) inhibited fer- tilisation at concentrations as low as 32 μg/l. The median effective concentrations (EC50) reducing rates of embryogenesis by 50% were 21.1 μg Hg/l (0.1 μM), 46.3 μg Cu/l (0.72 μM) and 43.4 μg Zn/l. Therefore, Hg is up to seven times more toxic than Cu (on a molar basis). Ecotoxicity of mercury on larvae survival was also assessed in this work. Result showed a significant ( p < 0.05) reduction of survival after exposure to 4 and 12 μg/l of Hg. The fertilisation rate and embryogenesis were the most sensitive endpoints, although the latter is S. Fathallah (B ) · M. N. Medhioub · A. Medhioub · M. M. Kraiem Laboratoire d’Aquaculture, Institut National des Sciences et Technologies de la Mer BP59, route de Khniss 5000 Monastir, Tunisia e-mail: salem.fathallah@yahoo.fr more advisable for routine assessment of seawater quality because of its greater sensibility. Keywords Heavy metals · Ruditapes decussatus · Fertilisation · Embryogenesis · Bioassay Introduction Human activities strongly increase the back- ground levels of toxic trace metals such as mercury and copper in natural water. Traditionally, marine pollution has been assessed in terms of chemi- cal analyses of contaminants present in different environmental matrices; however, these measure- ments do not provide information about the toxic effects upon living organisms and should be com- plemented with bioassays that allow the pollution estimation with biological criteria (Long et al. 1996). The validity of the ecotoxicological studies based on biological assays and accurate interpre- tation of results require a good knowledge of the biology of the species used in the bioassay and its optimum handling in laboratory conditions. The test protocol shall be defined precisely and must be easily standardisable, in particular when deal- ing with the highly sensitive early stages of marine invertebrates (His et al. 1999). Bivalve have been used to provide biological material for embryo- larval bioassay (Brereton et al. 1973; Calabrese et al. 1973; Martin et al. 1981; His et al. 1983, 1997;