Temporal and geographical variations of mercury and selenium in eggs of Larus michahellis and Larus audouinii from central Mediterranean islands

ABSTRACT

In this study, we determined mercury and selenium levels in abandoned unhatched eggs of the yellow-legged gull (Larus michahellis) and Audouin’s gull (Larus audouinii) collected during 2004–2005 from the Tuscan archipelago and Sardinia (Italy). The different feeding habits of the two species probably determine the different uptakes of trace elements, as the study shows highly significant differences for selenium and mercury levels as well as shell thickness and Hg:Se molar ratio values. Audouin’s gulls nesting on the coasts of the Tuscan archipelago showed significantly higher selenium levels than did gulls from colonies from the islands around Sardinia. Comparisons with a similar investigation previously conducted in the same area suggested that mercury and selenium concentrations, although in line with reports in the literature, were significantly lower than levels encountered in gulls in the early 1980s. Mercury (mg/kg d.w.) dropped from 8.631 to 5.030 in Audouin’s gulls and from 2.509 to 0.828 in yellow-legged gulls. The regional decline in mercury levels following reduced use of the metal in industry and the probable food depletion effects linked to the overfishing of fish prey of these two gull species are discussed as hypotheses that could explain the decrease in mercury levels found in eggs.

KEYWORDS:

• Mercury and selenium
• gulls
• eggs
• Mediterranean Sea
• temporal variations
• overfishing

Disclosure statement

No potential conflict of interest was reported by the author(s).

Notes on contributors

Nicola Bianchi was born in Siena in 1973 and graduated in Natural Sciences at the University of Siena. He completed his Ph.D. with a research on Eleonora's falcon ecotoxicology by using non disruptive sampling methods and then continued the research activity at the Environmental Sciences Department, collaborating with the Prof. Claudio Leonzio research group working on biomonitoring projects and research studies on the ecotoxicology and ecophysiology of trace elements, particularly on birds and marine organisms. As Temporary Researcher in the 2010–2011 period, he has been involved in the study on the problem of lead pollution from hunting activity in Italian wetlands and then in a study on the biomonitoring of areas around incinerators. As collaborator of the Department of Medicine, Surgery and Neuroscience with the research group of the Prof. ssa Paola Rottoli, he conducted studies on respiratory physiology on bronchoalveolar lavage on patients with sarcoidosis. He is author or co-author of over 40 scientific and technical publications.

Nicola Baccetti was born in Florence in 1961 and completed all his studies in Siena, graduating in Biological Sciences in 1983. After graduation, he won a scholarship at the University of Florence. He collaborated in the renovation of museums and was one of the coordinators of the Atlas Project of breeding birds in Tuscany, participating at the same time in the National Atlas Project. In 1986, he won a competition for Technical-Professional Collaborator at the National Institute of Game Biology. In this institution (today ISPRA), he worked as Researcher since 1990 and as Senior Researcher since 1996. Since 1992, he is scientific manager and coordinator of the activities and personnel of the museum section of the Institute. His main activities were those related to the activity of bird marking with rings detectable at a distance, to the management and conservation of wetlands, to migration strategy of aquatic and marine birds, and to ornithological issues for Marine Strategy. He is member of the Italian Ornithological Commission of CISO and is Chairman of the international association Medmaravis, for conservation of Mediterranean seabirds. He is author or co-author of over 100 scientific and technical publications.

Claudio Leonzio is Full Professor of Ecology in the Department of Physics, Earth and Environmental Sciences of the University of Siena. Since 1976, he has been actively working on heavy metals and organochlorine compounds distribution in the marine environment of the Mediterranean area and in particular on the dynamic accumulation of mercury in the trophic chain in relation to the anomalies of Mediterranean area. Later, these studies have been focused on birds with long-term monitoring studies of population of marine species, evaluating both residues and biomarkers, particularly mixed function oxidases system. A particular aspect of mercury contamination was investigated through the inter-relationship between mercury and selenium as phenomenon of antagonism and detoxification. This research was conducted on birds and more recently on marine mammals as well as in experimental animals. He is teaching Ecology, Environmental Impact assessment and Conservation of Nature. He is author of more than 100 papers in international scientific journals as well as many articles in Italian language and communications to scientific congresses. Claudio Leonzio is member of several Scientific Institutions: Society of Environmental Toxicology and Chemistry (SETAC), European Cetacean Society (ECS), Italian Society of Ecology (SITE), and Italian Society of Marine Biology (SIBM).

Pietro Giovacchini graduated in Natural Sciences at the University of Siena and completed the Master in Biomonitoring and Management of Coastal Areas at the same University. Since 1985, he worked in field activities as ornithologist. He is Member of the Tuscan Ornithological Center and of the Italian Center for Ornithological Studies. Collaborator of the Institute for Environmental Protection and Research (former INFS section), in 1996, he was appointed expert ornithologist for the Museum of Natural History of the Maremm and subsequently collaborated with the Department of Environmental Sciences of the University of Siena. He has drafted two Ornithological Atlases in 2004 and promoted the establishment of a working group, the first in Europe, to study the “Occhione” (Burhinus oedicnemus) wintering. Currently is employed by the Tuscany Region, sector Protection of Nature and the Sea in Grosseto.

Stefania Ancora was born in 1968 in Brindisi and graduated in Biological Sciences in 1993 at the University of Siena. She won a research grant at the CNR (Nationa Research Council) in Lesina (Fg) in 1994. From 1995 to 1998, she completed her Ph.D. in Environmental Biology, carrying out research on the “Role of blood as an exchange pool in the internal compartmentalisation processes of methylmercury in marine organisms belonging to the highest trophic levels” and participated in 1997–98 at the Socrates / Erasmus Program at the University of Plymouth (UK). From 2000 to 2004, as Researcher fellow at the University of Pisa, worked on the interactions of heavy metals with biological structures in marine organisms and on the biomonitoring techniques for heavy metal contamination in industrialized areas. From June 2004 to September 2008, she was temporary technical staff of the Department of Environmental Sciences of the University of Siena working on the study of the problem of lead pollution from hunting activity in Italian wetlands. From October 2008, she is permanent technical staff at the Department of Environmental Sciences of the University of Siena carrying out both laboratory activities as the determination of trace elements by atomic spectrometry, and research activity also as scientific manager of research project. She is author of over 40 publications in national and international scientific journals and has participated in numerous national and international congresses.