Atlantic Bottlenose Dolphins (Tursiops truncatus) as A Sentinel for Exposure to Mercury in Humans: Closing the Loop

Abstract

Mercury (Hg) is a ubiquitous global contaminant with important public health implications. Mercury is released from a variety of anthropogenic, industrial processes, enters the earth's atmosphere and is re-deposited onto the earth’s surface in rainfall. Much of this Hg enters the oceans which cover the majority of the earth’s surface. In the marine environment, inorganic Hg is converted to the most toxic form of the element, methylmercury, and biomagnified through the trophic levels of the food web. The bottlenose dolphin (Tursiops truncatus) is the apex predator in many estuarine and coastal ecosystems. Due to their long life span and trophic position, bottlenose dolphins bioaccumulate high concentrations of contaminants including Hg, thus making them an important sentinel species for ecosystem and public health. Bottlenose dolphins in Florida bioaccumulate high concentrations of Hg in their blood, skin and internal organs. The concentrations of Hg in blood and skin of bottlenose dolphins of the Indian River Lagoon, FL (IRL) are among the highest reported world-wide. In previous studies, we demonstrated associations between concentrations of total Hg in the blood and skin of IRL dolphins and markers of endocrine, renal, hepatic, hematologic and immune system dysfunction. The predominant manifestation of exposure to mercury in humans is neurotoxicity. During the 1950s and 1960s, residents of Minamata bay, Japan were exposed to high concentrations of methyl mercury as the result of ingestion of fish and shellfish that had become contaminated in this infamous environmental disaster. Affected adults had severe motor and sensory abnormalities often leading to death. Methyl mercury crosses the placenta during pregnancy. Children exposed in utero were born with multiple congenital anomalies and also suffered from neurologic disorders. Significantly, local cats that consumed Hg contaminated fish developed severe signs of neurotoxicity which led to their subsequent description as the “dancing cats of Minamata bay”. Unfortunately, the cause of these strange manifestations in cats was not recognized in time to prevent hundreds of additional cases from occurring. More recent studies have shown that exposure to mercury as a result of seafood consumption during pregnancy may result in multiple cognitive and neurodevelopmental effects in children. The levels of mercury found in bottlenose dolphins and the health effects we identified alerted us to the possibility of an important public health hazard. The IRL occupies 40 percent of the east coast of Florida and is bordered by counties with approximately 2.5 million human inhabitants. Therefore, we hypothesized that local inhabitants in communities bordering the IRL could be at risk of exposure to Hg from the consumption of fish and shellfish. We measured hair Hg in 135 local residents and found a mean concentration of 1.53 µg/g which was higher than that from previous studies of sport fishermen and coastal residents in other states. Over 50% of participants had a hair Hg concen...

Causes of mortality of harbor porpoises Phocoena phocoena along the Atlantic and Pacific coasts of Canada

“…However, there is published evidence of an association between exposure to heavy metals and organic pollutants and increased susceptibility to infectious disease in harbour porpoises and other marine mammals (Bennett et al 2001, Jepson et al 2005, Reif et al 2015, Lair et al 2016). …”

Effects of Formalin Fixation on Trace Element Concentrations in Bottlenose Dolphin (Tursiops truncatus) Tissues

“…Marine mammals, including odontocetes, are long‐lived, high trophic level organisms, and as such, can accumulate high concentrations of trace elements (e.g., cadmium [Cd] and mercury [Hg]) in their tissues (Das et al 2003; Monteiro et al 2020). In addition, marine mammals are often long‐term residents of coastal environments and consume fish that are similar to those eaten by human populations, making them ideal sentinel species for ecosystem and public health (Bossart 2011; Reif et al 2015). Because of these characteristics, trace element concentrations in marine mammal tissues have been increasingly utilized to understand their population structure and ecology, to identify population‐level threats due to contaminant exposure, to assess temporal changes in environmental trace element concentrations, and to identify public health hazards (Parsons 2004; García‐Alvarez et al 2015; Reif et al 2015; Romero et al 2017).…”

Blood mercury concentrations in common bottlenose dolphins from the Indian River Lagoon, Florida: Patterns of social distribution

“…Most notably, the concentrations of total mercury (THg) in blood and skin of IRL dolphins are among the highest reported worldwide in delphinids (Reif et al . ). Further, THg concentrations in blood and skin are significantly correlated with the concentrations in liver of free‐ranging Florida dolphins (Stavros et al .…”

“…Inorganic contaminants and trace elements have also been measured in blood and skin of IRL dolphins (Stavros et al 2007(Stavros et al , 2008. Most notably, the concentrations of total mercury (THg) in blood and skin of IRL dolphins are among the highest reported worldwide in delphinids (Reif et al 2015). Further, THg concentrations in blood and skin are significantly correlated with the concentrations in liver of free-ranging Florida dolphins .…”

“…Concentrations of THg in liver, muscle, and kidney of deceased, stranded dolphins have been used as indicators of environmental contamination worldwide (Reif et al 2015). In the IRL, incorporation of photo-identification data to assign individuals to specific geographic segments demonstrated a north to south gradient in the concentrations of THg in blood (Schaefer et al 2015a).…”