Mercury in cetaceans: Exposure, bioaccumulation and toxicity

Abstract

The fate and transportation of mercury in the marine environment are driven by combinations of anthropogenic atmospheric and aquatic sources, as well as natural geological inputs.Mercury bioaccumulates and biomagnifies up the food chain and can result in the accumulation of toxic concentrations in organisms even when the concentrations in the marine environment remain below the threshold level for direct toxicity. As a result, mercury exposure has been recognised as a health concern for both humans and top marine predators, including cetaceans.There appears to be no overall trend in the global measured concentrations reported in cetaceans between 1975 -2010, although differences between areas show that the highest concentrations in recent decades have been measured in the tissues of Mediterranean odontocetes. There is increasing concern for the impacts of mercury in the Arctic marine ecosystem with changes in water temperatures, ocean currents and prey availability all predicted to impact the exposure of Arctic species to mercury. The accumulation of mercury in various tissues has been linked to kidney and liver damage as well as other neurotoxic, genotoxic and immunotoxic effects. These effects have been documented through studies on stranded and by-caught individuals as well as in vitro cell culture experiments. Demethylation of methylmercury and protection by selenium have been suggested as possible mercury detoxification mechanisms in cetaceans that can help to explain the very high concentrations measured in tissues of some species with no apparent acute toxicity. Thus, the ratio of selenium to mercury is of importance when aiming to determine the potential toxicity of the contaminant load at an individual level. The long-term population level effects of mercury exposure are unknown, and continued monitoring of odontocete populations in particular is advised in order to predict the uptake and impact of mercury on marine food chains in the future.

Mercury in Ringed Seals (Pusa hispida) from the Canadian Arctic in Relation to Time and Climate Parameters

“…This program works closely with the Arctic Monitoring Assessment Programme, which contributes to international initiatives to reduce the global threats from contaminants and climate change, such as the Minamata Convention on Mercury (United Nations Environment Programme 2020). Effects of Hg in marine mammals, including Arctic species, have been previously summarized (Dietz et al 2013, 2019; Scheuhammer et al 2015; Desforges et al 2016; Kershaw and Hall 2019) and include neurological changes (Krey et al 2015; Ostertag and Chan 2018) as well as liver and kidney lesions (see Kershaw and Hall 2019 for review).…”

Persistent Organic Pollutants and Mercury in Genetically Identified Inner Estuary Bottlenose Dolphin (Tursiops truncatus) Residents of the Guayaquil Gulf, Ecuador: Ecotoxicological Science in Support of Pollutant Management and Cetacean Conservation

“…Methylmercury can cause toxicity even at low concentrations (Dietz et al, 2013). Immunotoxicity, neurotoxicity, nephrotoxicity, and genotoxic effects of mercury in cetacean species, have been documented (Desforges et al, 2016;Kershaw and Hall, 2019). Specifically, mercury exposure in marine mammals (e.g., cetaceans) has been reported to affect the systemic suppression of immune function (i.e., suppression of lymphocyte proliferation and phagocytosis activity) (Desforges et al, 2016).…”

Mercury and cadmium in striped dolphins (Stenella coeruleoalba) stranded along the Southern Tyrrhenian and Western Ionian coasts

“…Even so, a high degree of mercury pollution persists, as confirmed by the high concentrations found in the organs and muscle tissue of these animals. Therefore, despite reduction in the emission of mercury, cetaceans globally continue to bioaccumulate this element (Kershaw & Hall, 2019).…”

“…In these marine mammals, the marked accumulation of contaminants can act on the immune system, reducing the immune defenses and, therefore, increasing sensitivity to various types of infections (Aguilar & Borrell, 1994;Fossi et al, 2004). Specifically, the accumulation of mercury in various tissues has been linked to renal and hepatic damage and to neurotoxic, genotoxic and immunotoxic effects (Frederick et al, 2018;Kershaw & Hall, 2019), pathological conditions that can lead to the stranding and death of these mammals.…”

“…There are many studies on the determination of heavy metals in the organs and tissues of delphinids, especially Stenella coeruleoalba, beached alive or dead, in various oceans and seas (Law, 1992;Baptista et al, 2016;Shoham-Frider et al, 2016;Rojo-Nieto et al, 2017;Martínez -Lopez et al, 2019). Some papers report the concentrations of cadmium and mercury in delphinids from the northern Tyrrhenian Sea, stranded along the coasts of Liguria and Tuscany, from the Ionian Sea and Adriatic Sea, stranded along the coasts of the Puglia region, and in Sicily, particularly in the Strait of Sicily (Leonzio et al, 1992;Monaci et al, 1998;Bellante et al, 2012;Cardellicchio et al, 2000;Cardellicchio et al, 2002).…”