Trace metals in striped dolphins (Stenella coeruleoalba) stranded along the Murcia coastline, Mediterranean Sea, during the period 2009–2015.
Introduction
Increasing human populations and related anthropogenic activities have resulted in the release of contaminants into the environment with temporal trends indicating increases in certain elements, both regionally and globally (Braune, 2007, Dietz et al., 2000, Riget et al., 2004). Although metals generally occur at low concentrations in the oceans, marine organisms bioaccumulate trace elements with a significant increase of metal burdens through the food chain, especially toxic heavy metals such as Hg or Cd (Gerpe et al., 2006, Meador et al., 1999).
Heavy metals are well known environmental pollutants that accumulate in the bodies of odontocetes and potentially constitute a toxicological risk for the species (Caurant et al., 1996, Haraguchi et al., 2000, Endo et al., 2002, Stavros et al., 2008, Stavros et al., 2011). Seawater enrichment with heavy metals from natural occurrence or from anthropogenic impact may lead to an increase of metal burdens entering marine food chains (Fernandes et al., 2007). Additionally, they are usually species that live for many years so they can be exposed throughout their lifetimes to high concentrations of metals, from conception to exposure in the uterus, during breastfeeding, and during juvenile and adulthood through the marine trophic chain, especially the super predatory species (Kurzel and Cetrulo, 1985).
The main potential effects described for these pollutants are endocrine cycle disruption, failure of the reproductive process, immune system suppression and metabolic disorders that could generate cancer and genetic defects (Borrell et al., 2014). Although the analysis of pollutants in marine mammals, including cetaceans, has a high relevance, there is still a great uncertainty about the specific effects of contaminants in marine mammals, in what measure these effects can occur in these species in their natural environment, and what impact these effects are having on the population dynamics. In response to these concerns, numerous studies have been conducted over the last decades on trace metals in marine mammals (Riget and Dietz, 2000, Bennett et al., 2001, Caurant et al., 2006, Capelli et al., 2008, Law et al., 2012, Robin et al., 2012; Rojo-Nieto and Fernández-Maldonado, 2017.
The Mediterranean Sea, because of geographic and geomorphological characteristics, receives an important amount of pollutants from industrialized countries in Western Europe, in addition to natural inputs of some trace metals such as Hg (Bacci, 1989). Metal contamination has been especially important in the Western Mediterranean due to the proximity of significant metalliferous deposits at the Baetical area exploited from very early ages. In Southeastern Spain, the origin of contamination has been dated at 3900 cal years BP (García-Alix et al., 2013). Besides, one of the most heavily metal-polluted areas of the western Mediterranean Sea is situated on the Murcia coastline (Cartagena marine area) where high concentrations of Pb, Hg and Cd, among other metals, have been reported in sediment and/or biota (Robinson et al., 2016), even sublethal contaminant related effects in mussels and red mullet (Martínez-Gomez et al., 2012). Besides, the limited water movement and replacement enhance the accumulation of these pollutants, contributing to chronic exposure of cetaceans that inhabit it (Tintore et al., 1988).
The striped dolphin is worldwide classified as “Least concern” by IUCN (Hammond et al., 2008). However, Mediterranean Sea populations have been pointed out as “Vulnerable” (Aguilar and Gaspari, 2012) and conform 60% of strandings in this sea.
In this sense, research using stranded marine animals can yield substantial information on the health and ecology of these fascinating but often little understood species, while also helping to highlight some of the conservation issues they may face (Perrin et al., 2002). The long term accumulation of stranding data facilitates the investigation of spatial-temporal trends and patterns in stranding numbers and mortality. Post-mortem examinations additionally provide unique insight into wider metrics such as age, sex, body condition, cause of death, pollutant levels, reproductive patterns, diet, disease burden and pathology of the stranded population (Chan et al., 2017). Besides, the reappearance of dolphin morbillivirus affecting the Mediterranean cetacean population (Raga et al., 2008, Soto et al., 2011a, Soto et al., 2011b, Rubio-Guerri et al., 2013) reinforces the importance of continuous monitoring of cetacean strandings to understand the influence of environmental contaminants. This information can provide essential baseline data to help detect any future outbreaks of disease, unusual mortality events, anthropogenic stressors, and other health issues. It also enables assessment of pressures and threats, possible population dynamics, and responses to environmental stressors as well as specific conservation measures.
The aim of the present study is to evaluate metal concentrations (Hg, Cd, Se, Pb and As) in stranded striped dolphin internal tissues (liver, kidney, brain, lung and muscle) from Murcia’s coast during the period 2009–2015, studying the influence of several variables (age, sex and stranding year) in these metal concentrations and discuss the possible effect on animal health of the obtained concentrations. This is the first study of these characteristics in the Murcia Region coastline.
Section snippets
Species of study
The Striped dolphin is widely extended in the Atlantic, Pacific and Indian oceans, and closed seas such as the Mediterranean. The Mediterranean population has been largely studied (Borrell et al., 2014, Borrell et al., 2015, Capelli et al., 2008, Cardellicchio et al., 2000, Cardellicchio et al., 2002a, Cardellicchio et al., 2002b, Monaci et al., 1998). They have a long life span, reaching a maximum of 30 years. Although they usually prefer deep oceanic waters, they can be seen in coastal areas
Tissue distribution of trace elements
The heavy metal concentrations in internal tissues of 72 striped dolphins (Stenella coeruleoalba) from Murcia Region strandings between 2009 and 2015 are shown in Table 1. The detection of these metals is a strong sign of the assimilation process that has occurred since the first contact with pollutants, until beaching on the Murcia coast.
In concordance with other studies (Andre et al., 1991, Capelli et al., 2000, Cardellicchio et al., 2002a, Cardellicchio et al., 2002b) detection rates were
Conclusions
Trace metal concentrations of Hg, Cd, Pb, As and Se detected in 72 striped dolphins from the Murcia Region are within the range of other studies carried out in the Mediterranean Sea in most cases. However, detected concentrations of Hg in liver of some adult specimens were within the range which provoke organ damage in cetaceans. Besides, in most adult and sub-adult specimens, the ratio Hg:Se in liver were close to 1, which would indicate an overload of the Hg-Se detoxify function and
Acknowledgements
The authors are greatly indebted to the Seneca Foundation for financing the MASCA 2014 project (19481/PI/14), to the staff of “El Valle” Wildlife Recovery Center for the careful sampling work and, to the LAYSA Laboratory for the accurate analysis of the samples. Thanks to Eddie Benson to revise the English grammar.
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2023, Marine Pollution BulletinTrace elements in blood of Baltic gray seal pups (Halichoerus grypus) from the Gulf of Riga and their relationship with biochemical and clinical parameters
2022, Marine Pollution BulletinCitation Excerpt :Se has been suggested as a protective mechanism against Hg toxicity trough their linkage to form inert compounds. Then, a Se:Hg molar lower than 1 virtually indicates that there is not enough Se to counteract Hg toxicity (Martínez-López et al., 2019), which may impact animal health because of both the development of Hg-mediated toxicity and the absence of Se to perform other essential functions (Bjørklund, 2015). In our study, the majority of individuals showed a Se:Hg ratio largely above 1 (mean 51.3; Table 3), so Hg does not appear to be compromising the essential functions of Se.
Two cetacean species reveal different long-term trends for toxic trace elements in European Atlantic French waters
2022, ChemosphereCitation Excerpt :Concerning cetacean species, a previous study conducted on harbour porpoise from Japan waters showed constant concentrations since 1985 to 2010 (Yasuda et al., 2012). In the Mediterranean Sea, however, decreasing concentrations were observed in liver samples of striped dolphins (Stenella coeruleolaba) stranded between 1990 and 2015, suggesting that measures to reduce Hg emissions in Western European countries have been effective to reduce Mediterranean pollution to Hg (Borrell et al., 2014; Martínez- López et al., 2019a). Later, an overview conducted on more than 101 technical reports and peer-reviewed articles published between 1972 and 2016 considering 284 total Hg measurements in the liver (e.g. main storage tissue) of 43 cetacean species, revealed that no apparent change was detected in reported concentrations between 1975 and 2010 (Kershaw and Hall, 2019).