Author's personal copy Concentrations of mercury in tissues of striped dolphins suggest decline of pollution in Mediterranean open waters A. Borrell ⇑ , A. Aguilar, V. Tornero, M. Drago Department of Animal Biology and Institute of Biodiversity (IRBIO), University of Barcelona, Av. Diagonal 643, Barcelona, Spain highlights  The Mediterranean is a semi-enclosed sea subject to high mercury pollution.  Monitoring temporal trends of mercury concentration is compulsory.  Dolphins integrate long-term, large-scale pollution variations in oceanic waters.  A decline in Mediterranean Hg levels is shown to occur from 1990 to 2009. article info Article history: Received 4 June 2013 Received in revised form 20 December 2013 Accepted 29 December 2013 Available online 23 January 2014 Keywords: Mercury Striped dolphins Mediterranean Sea Time trends abstract The Mediterranean is a semi-enclosed sea subject to high mercury (Hg) pollution from both natural and anthropogenic sources. With the objective of discerning temporal changes in marine Hg pollution in the oceanic waters of the northwestern Mediterranean Sea, we analysed liver and kidney from striped dol- phins (Stenella coeruleoalba) collected during 2007–2009 and compared them with previous results from a similar sample from 1990–1993. The effect of body length and sex on tissue Hg concentrations was investigated to ensure an unbiased comparison between the periods. The Hg concentrations did not show significant sex-related differences in any tissue or period but were correlated positively with body length. Using body length as a covariate, Hg concentrations in liver and kidney were higher in 1990–1993 than in 2007–2009. This result suggests that measures to reduce emissions in Western European countries have been effective in reducing mercury pollution in Mediterranean open waters. Ó 2014 Elsevier Ltd. All rights reserved. 1. Introduction Among the trace metals, mercury (Hg) is one of the pollutants of most concern because of its high toxicity, persistence and accumu- lative behaviour in the environment and biota. Hg pollution in the Mediterranean is particularly relevant because it is a semi- enclosed sea with high natural and anthropogenic inputs of this metal. Natural sources include weathering of the large cinnabar ore deposits found along the bottom (Bacci, 1989), as well as the intense geothermal and volcanic activity of this region (Ferrara et al., 2000). Anthropogenic emissions include current and past intensive mining, fossil fuel combustion, cement production and some specific industries such as chlor-alkali plants. Hg is released into the Mediterranean mostly as a result of atmospheric deposition and river inflow and, to a lesser extent, of point sources (Rajar et al., 2007). However, particulate Hg, which represents approximately 95% of the total Hg carried by rivers, is mainly deposited on the continental shelf relatively near the river mouths, so only a small percentage of the river input reaches open sea waters (Rajar et al., 2007). The identification of Hg pollution hot spots and potential hu- man health hazards is usually carried out through the monitoring of concentrations in biota. In the case of marine ecosystems, the most common procedure is to analyse bioindicators such as mussels or other shellfish (Carrasco et al., 2008; Benedicto et al., 2011; Guitart et al., 2012), fish (Polak-Juszczak, 2012), or even plants such as seagrass (Lafabrie et al., 2007a,b; Copat et al., 2012). These organisms have the advantage of being abundant and extensively distributed, so they can be readily available to monitoring programs. Hence, these organisms have been em- ployed to assess temporal trends and detect hot spot contamina- tion in nearshore waters, where environmental degradation is likely to be the greatest (Cossa, 1989; Ancora et al., 2004; Fernandes et al., 2008). However, because their distribution is limited to the continental shelf, their coverage is restricted to inshore coastal waters (Zhou et al., 2008). 0045-6535/$ - see front matter Ó 2014 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.chemosphere.2013.12.076 ⇑ Corresponding author. Address: Department of Animal Biology, University of Barcelona, Av. Diagonal 643, 08028 Barcelona, Spain. Tel.: +34 93 4021453; fax: +34 93 4034426. E-mail address: xonborrell@ub.edu (A. Borrell). Chemosphere 107 (2014) 319–323 Contents lists available at ScienceDirect Chemosphere journal homepage: www.elsevier.com/locate/chemosphere