Two cetacean species reveal different long-term trends for toxic trace elements in European Atlantic French waters

Low ecological risks for heavy metals and total petroleum hydrocarbons on typical coastal petrochemical sewage discharge waters: Monitoring and evaluation under One Health framework

Petrochemical industrial zone wastewater is a complex source of pollutants. This study used a One Health framework to investigate the impact of typical petrochemical industrial zone wastewater discharge on adjacent bay. An analysis was conducted on the content and distribution characteristics of heavy metals (HMs) and total petroleum hydrocarbons (TPHs) in the seawater, sediment, and organisms. The assessment of the marine environment utilized the single-factor standard index method alongside the Hakanson ecological risk index method to investigate potential ecological risks. The findings indicated that the average levels of Cd and As in the water were primarily influenced by the sewage discharge, whereas the concentrations of Pb, Zn, and Hg in the sediments were predominantly impacted by the coastal area. The research sea area is considered to be at low risk, and the sewage discharge from the petrochemical industrial zone and its coastline does not endanger the ecosystem. The ranking of metal element pollution in seawater is as follows: Zn > Cu > As > Pb > Cd > Hg; While in sediments, the order is Zn > Pb > Cu > As > Hg > Cd. Furthermore, both crustaceans and mollusks demonstrate elevated concentrations of HMs, thereby serving mollusks as effective bioindicators for the monitoring of HMs pollutants in seawater and crustaceans as effective bioindicators for the monitoring of HMs pollutants in sediment.

Long-term trends (2002-2016) reveal an increase of mercury levels along with the decline of several metal elements in striped dolphins (Stenella coeruleoalba) stranded in the North-West Mediterranean

The determination of 18 metals and metalloids was realized in 4 tissues of 62 Stenella coeruleoalba specimens stranded along the French Mediterranean coastline from 2010 to 2016. While most concentrations were comparable to mean worldwide levels, Hg levels were alarming (1190 μg g-1 dw, in average). The results were discussed together with previous measurements in the same area, from 2002 to 2009. The elements Ni and Pb (-81 % and -88 % in liver in 2010-16 compared to 2002-09), and Cd (-40 % in kidney in 2010-16 compared to 2002-09) as well as V (-79 % in liver in 2013-16 compared to 2010-12), showed promising decreasing trends, and the decrease of Zn and Cu levels below baseline values could indicate a global decreasing burden of metal contaminants. In contrary, Hg dramatically increased in dolphins since 2007 (+135 % in liver in 2010-16 compared to 2002-09), regardless of total length. On the other hand, Se levels increased only slightly since 2012, potentially not offering anymore an efficient protection against Hg, with mean Se-to-Hg molar ratios below unity in most tissues (0.26, 0.56, 1.81, and 0.57 in liver, kidney, lung and muscle, respectively).

Trace element concentrations in dolphins of south-east Australia; mercury a cause for concern in the region

Concentrations of nine trace elements (As, Cd, Cr, Cu, Hg, Mn, Ni, Se, Zn) in hepatic, renal and epidermal tissues were investigated in three dolphin species (Burrunan dolphin, Tursiops australis; common bottlenose dolphin, T. truncatus; short-beaked common dolphin, Delphinus delphis) within southeast Australia. Elevated hepatic Hg was found in critically endangered Burrunan dolphins (62.5-4990 mg/kg dw) and common bottlenose dolphins (102-1770 mg/kg dw), amongst the highest for the taxa globally, exceeding the short-beaked common dolphins (3.24-370 mg/kg dw), likely due to dietary differences. Hepatic Hg:Se molar ratios exceeded 1 in 60 % of dolphins, suggesting Hg toxicity. Essential trace elements showed little variation across species, but epidermal Se was notably low in Burrunan dolphins. Due to ongoing freshwater skin disease/health concerns, and the importance Se plays in epidermal health, it is recommended that epidermal Se and skin health are further investigated within the Burrunan dolphin.

Mediterranean Marine Mammals: Possible Future Trends and Threats Due to Mercury Contamination and Interaction with Other Environmental Stressors

Despite decreasing anthropogenic mercury (Hg) emissions in Europe and the banning and restriction of many persistent organic pollutants (POPs) under the Stockholm Convention, Mediterranean marine mammals still have one of the highest body burdens of persistent pollutants in the world. Moreover, the Mediterranean basin is one of the most sensitive to climate change, with likely changes in the biogeochemical cycle and bioavailability of Hg, primary productivity, and the length and composition of pelagic food webs. The availability of food resources for marine mammals is also affected by widespread overfishing and the increasing number of alien species colonizing the basin. After reporting the most recent findings on the biogeochemical cycle of Hg in the Mediterranean Sea and the physico-chemical and bio-ecological factors determining its exceptional bioaccumulation in odontocetes, this review discusses possible future changes in the bioavailability of the metal. Recent ocean-atmosphere-land models predict that in mid-latitude seas, water warming (which in the Mediterranean is 20% faster than the global average) is likely to decrease the solubility of Hg and favor the escape of the metal to the atmosphere. However, the basin has been affected for thousands of years by natural and anthropogenic inputs of metals and climate change with sea level rise (3.6 ± 0.3 mm year-1 in the last two decades), and the frequency of extreme weather events will likely remobilize a large amount of legacy Hg from soils, riverine, and coastal sediments. Moreover, possible changes in pelagic food webs and food availability could determine dietary shifts and lower growth rates in Mediterranean cetaceans, increasing their Hg body burden. Although, in adulthood, many marine mammals have evolved the ability to detoxify monomethylmercury (MMHg) and store the metal in the liver and other organs as insoluble HgSe crystals, in Mediterranean populations more exposed to the metal, this process can deplete the biological pool of Se, increasing their susceptibility to infectious diseases and autoimmune disorders. Mediterranean mammals are also among the most exposed in the world to legacy POPs, micro- and nanoplastics, and contaminants of emerging interest. Concomitant exposure to these synthetic chemicals may pose a much more serious threat than the Se depletion. Unfortunately, as shown by the literature data summarized in this review, the most exposed populations are those living in the NW basin, the main feeding and reproductive area for most Mediterranean cetaceans, declared a sanctuary for their protection since 2002. Thus, while emphasizing the adoption of all available approaches to mitigate anthropogenic pressure with fishing and maritime traffic, it is recommended to direct future research efforts towards the assessment of possible biological effects, at the individual and population levels, of chronic and simultaneous exposure to Hg, legacy POPs, contaminants of emerging interest, and microplastics.

Adhesive Bowel Obstruction (ABO) in a Stranded Narrow-Ridged Finless Porpoise (Neophocaena asiaeorientalis sunameri)

In this case report, we present a rare occurrence of a narrow-ridged finless porpoise (Neophocaena asiaeorientalis sunameri), discovered on the coast of Jeju Island, Republic of Korea, that was afflicted with adhesive bowel obstruction (ABO), a life-threatening condition that has scarcely been reported in cetaceans. Diagnosis of ABO was confirmed via radiological and clinical assessments. Post-mortem computed tomography and necropsy revealed ABO between two loops of the jejunum at the L8 level. The mesenteric tissue covering the intestinal lesion was severely thickened with increased tension. Both bowel loops were fixed to the mesentery and acutely angulated, leading to asymmetrical thickening of the cross-sectional bowel walls. The intestinal lumen was stenosed because of pressure from the firm mesenteric band, and no fecal matter was observed in the lumen of the posterior bowel or rectum. Calcified nodules were detected, and histological analysis suggested parasitic or suspected post-parasitic infections. The primary cause of the intestinal lesions is presumed to be a reaction related to parasitic infection. However, further investigations would establish a definitive link between parasitic infections and ABO in this species. This case highlights the importance of studying rare medical conditions in wildlife, providing valuable insights into marine mammal health.

Development of an integrated indicator to assess chemical contamination in different marine species: The case of mercury on the French Atlantic continental shelf

Good Environmental Status (GES) for Descriptor 8 (D8) of the Marine Strategy Framework Directive (MSFD) is considered to be achieved when concentrations of contaminants are at levels not giving rise to pollution effects. This study proposes a framework to assess GES in marine waters adjacent to France, including four groups of species (bivalves, fish, birds and mammals) living on the continental shelf and covering different dimensions of the marine environment. This framework is applied to mercury (Hg) in the three marine regions along the French Atlantic coast and includes two assessment types: i) an absolute assessment by comparing contamination levels with environmental thresholds, and ii) a relative assessment by comparing contamination levels over time, performed for bivalves and mammals that had long time-series available. Mercury concentrations were higher than environmental thresholds for bivalves and fish in all the three studied regions. Plus, they significantly increased since the 2000s for most bivalve stations and for the common dolphin Delphinus delphis. Our results therefore indicate that Hg concentrations have increased in marine waters and have reached levels possibly giving rise to pollution effects in biota from the three marine regions. The present study also highlighted the complementarity of monitoring Hg concentrations in each group of species and each type of assessment, making it possible to propose a conceptual framework for assessing the environmental pressure of bioaccumulated and biomagnified contaminants over the continental shelf.

Assessment of Knowledge on Metal Trace Element Concentrations and Metallothionein Biomarkers in Cetaceans

Cetaceans are recognized as bioindicators of pollution in oceans. These marine mammals are final trophic chain consumers and easily accumulate pollutants. For example, metals are abundant in oceans and commonly found in the cetacean tissues. Metallothioneins (MTs) are small non-enzyme proteins involved in metal cell regulation and are essential in many cellular processes (cell proliferation, redox balance, etc.). Thus, the MT levels and the concentrations of metals in cetacean tissue are positively correlated. Four types of metallothioneins (MT1, 2, 3, and 4) are found in mammals, which may have a distinct expression in tissues. Surprisingly, only a few genes or mRNA-encoding metallothioneins are characterized in cetaceans; molecular studies are focused on MT quantification, using biochemical methods. Thus, we characterized, in transcriptomic and genomic data, more than 200 complete sequences of metallothioneins (mt1, 2, 3, and 4) in cetacean species to study their structural variability and to propose to the scientific research community Mt genes dataset to develop in future molecular approaches which will study the four types of metallothioneins in diversified organs (brain, gonad, intestine, kidney, stomach, etc.).