Metallothioneins pattern during ontogeny of coastal dolphin, Pontoporia blainvillei, from Argentina

Geographic and tissue-specific variations of the trace elements and trophic niches of three offshore cetaceans in Chinese waters

Systematical investigation on trace elements' (TEs) distribution and trophic niches of cetaceans are essential to understand marine mammal ecology and environmental toxicology. Here, the concentrations of 10 TEs and isotopic values in six tissues of stranded Stenella attenuata (SA) and Kogia breviceps (KB) from the northern South China Sea (SCS) and Peponocephala electra (PE) from the East China Sea (ECS) were investigated. The TEs levels of the studied cetaceans were characterized by geo- and tissue-specific distributions. For SA and KB, most TEs levels were in the normal ranges, with low toxicological risk. For PE, several toxic TEs accumulated above the thresholds up to 892.80 μg/g of Hg and 335.24 μg/g of Cd, indicating that land-based anthropogenic pollution may be an ongoing threat to top predators in the ECS. The liver, spleen, and kidney are the main organs that accumulate toxic TEs, and there are strong positive, such as Se-Hg, correlations in several tissues. In particular, for PE with severe Hg and Cd exposure, tissue-specific distribution and correlations were more obvious. The results of stable carbon and nitrogen isotopes showed partly overlapped trophic niches of the three cetaceans, with similar calculated trophic levels in a narrow range of 4.29-4.43.

What do small cetaceans tell us about trace elements pollution on the Argentinean coast? Franciscana dolphin as a biomonitor

Trace elements (TEs) constitute the oldest emerging pollutants globally, most occur from natural sources, but a few are derived from anthropogenic sources. Marine mammals are considered bioindicators of ecosystem contamination. The aims of this review is compile reports on essential and nonessential TEs occurrence in small cetaceans from Argentinean waters; and to review the existing information on the concentration of TEs in the Franciscana dolphin, a biomonitor species of the Argentine coastal marine ecosystem. We searched reports where levels of TEs were present in small cetaceans from and eight species were analysed: Pontoporia blainvillei, Tursiops truncatus gephyreus, Kogia breviceps, Delphinus delphis, Lagenorhynchus obscurus, Lagenodelphis hasei, Cephaloryhchus commersonii and Ziphius cavirostris. Essential TEs like Zn, Cu, Mn, Cr, Fe, Co, Ni, Mo, Se, As, Au, Ag, Sn, and nonessential TE as Pb, Cd, Hg, As was considered. The reports compiled in this article analysed kidney, liver, muscle and occasionally brain, skin, lung and spleen, covering a temporal range of 30 years, from 1982 to 2016. Of data analysis, we identify knowledge gaps, species of small cetaceans for which the concentration of trace metals is not yet known and areas on the Argentine coast where there are no reports that analyse them. The most recent information corresponds to the 2010 decade, and in those subsequent publications, the samples were taken at that time. This emphasizes the importance of reviewing this data, in order to compare old and new datasets, create contamination timelines and evaluate possible increases or decreases of contaminants in different study areas. The information recopilated will serve as valuable baselines to detect the future impact of increasing human, even natural, activities on marine ecosystems in the South Atlantic Ocean.

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.).

Metal and trace element concentrations in cetaceans worldwide: A review

This bibliographical review is a compilation of different scientific publications that reported data on metal concentrations in the muscle tissue of different species of cetaceans from seas and oceans around the world. Forty-nine scientific articles were selected, published over a fifteen-year period (2006-2021) with data on heavy metals and trace elements. The different groups of cetaceans considered in this study generally presented low concentrations of Cd and Pb. The same cannot be said of Hg. The highest concentrations of Hg were found in the groups of false killer whales. Similarly, the use of these groups of cetaceans as bioindicators of metal contamination shows that the Mediterranean Sea is one of the most metallically contaminated areas in the world. This may be due to the closed nature of the Mediterranean Sea and to the fact that it is also a highly populated and industrialized area.

Temporal trends of trace elements bioaccumulation by a vulnerable cetacean (Pontoporia blainvillei) before and after one of the largest mining disasters worldwide

One of the largest environmental disasters worldwide occurred on November 5th^, 2015, when the Fundão dam collapsed in Mariana (Minas Gerais State, Southeast Brazil). The tailing mud flooded the Doce River basin and reached the sea in the coast of Espírito Santo State (ES), Southeast Brazil. This coastal region is the habitat of the most isolated population of franciscana dolphins (Pontoporia blainvillei), with the lowest populational census and lowest genetic diversity in Franciscana Management Area Ia (FMA Ia) - 18° 25'S and 21° 17'S. This study aimed to assess the bioaccumulation of trace-elements (As, Cd, Cu, Fe, Hg, Mn, and Zn) in muscle, liver and kidney of franciscana dolphins collected near the Doce River's mouth before (n = 32) and after (n = 19) the tailing mud reached the sea. The Generalized Additive Model (GAM) showed increasing temporal trends of Hg and Zn in muscle and liver after the dam failure, probably related to higher concentrations and bioavailability in the water column and sediments from the Doce River. Declining trends were found for As and Cu muscular and hepatic concentrations and Fe concentrations in kidney due to their lower bioavailability after the disaster, caused by association with tailings mud trapped in the riverbanks and suspended particulate material. Additionally, higher As and Hg concentrations found in the first period of sampling may be due to historical contamination by mining activities. The full extent of the impacts caused by the Fundão dam failure is still unknown. However, due to their rapid increase and remobilization process, toxic effects can be induced in the biota by these elements. Elements' bioaccumulation in this study contributes to the knowledge of franciscana dolphins from FMA Ia. Considering the conservation concern regarding this franciscana population and its scarce knowledge, the impact of this disaster can be alarming for species conservation.

Effect of size on concentrations and cadmium inducibility of metallothionein in the shore crab Carcinus maenas

Metallothionein (MT) plays an important role in protecting organisms from the adverse effects of Cd, Hg, Zn and Cu. Investigations on mammals show variations in metallothionein concentrations and inducibility with age. This has never been investigated in invertebrates, and we determined the concentrations and inducibility of metallothionein in gills and midgut gland of different size classes of shore crabs from uncontaminated areas. Metallothionein concentrations in gills and midgut gland ranged between 30 and 40 μg g^-1 dry weight with no differences among the different size classes. Concentrations of cadmium, copper and zinc in the midgut gland increased with increasing size of the crabs when the concentrations were expressed on a dry weight basis; water content in the midgut gland increased with the size and only the cadmium concentration increased with size when concentrations were expressed on wet weight basis. There was an inverse relationship between metallothionein and both copper and cadmium concentrations. Smaller crabs exposed to 1 mg Cd L^-1 accumulated higher concentrations of cadmium in midgut gland and gills than larger ones and metallothionein concentrations in the midgut gland were higher in the smaller crabs. However, the increase in metallothionein concentration per accumulated unit of cadmium showed a linear increase with the size of the crabs. The ratio [Cd]_midgut/[Cd]_gills decreased with the size of the crabs. The overall conclusion is that baseline metallothionein concentrations do not change with age in shore crabs, but that the inducibility of metallothionein upon cadmium challenge does.

Uptake and detoxification of trace metals in estuarine crabs: insights into the role of metallothioneins

The detoxification process of trace metals in the estuarine burrowing crab Neohelice granulata, after previously being exposed to anthropogenic pressures in the field, is described for the first time. The objectives of this study were (a) to assess the metal content (Cd, Cu, Pb, Zn, Mn, Ni, Cr, Fe) in the sediments and the uptake of these elements in the hepatopancreas of N. granulata; (b) to quantify trace metal concentrations in the hepatopancreas before and after the detoxification experiment; and (c) to relate this information to metallothionein (MT) induction or reversibility. The detoxification assay was performed for 25 days with artificial seawater under controlled conditions in a culture chamber. The results showed higher uptake and bioaccumulation of Zn and Cu from the sediments, and the hepatopancreas exhibited increased levels of Zn and lower concentrations of the rest of the metals and MTs after the assay, mainly Fe and Mn that were significantly lower. We conclude that trace metals could be translocated to and accumulated in the hepatopancreas, the main metabolic organ, and then eliminated under controlled conditions with corresponding reversibility of MTs. Graphical abstract.

From Mexico to the Beagle Channel: A review of metal and metalloid pollution studies on wildlife species in Latin America

Emissions of metals and metalloids (Hg; Cd; Cr; Cu; Pb; Ni; Zn; Fe; Mn; As; Se) generated by natural (e.g., geothermal activity) or anthropic causes (eg., industry or mining) represent a worldwide contamination problem, especially in developing countries. Exposure to high concentrations of these elements is harmful to living beings, including humans. Information on this type of contamination is scarce and fragmented, limiting research which could benefit from these data. To know the state of the research, we reviewed the studies of environmental pollution by metals and metalloids carried out on animal species in Latin America. The use of animals as biomonitors of contamination by metals and metalloids is a continuously expanding practice that allows for early detection of problems. With this work, we were able to identify the most studied areas in Latin America (Amazon, Gulf of California, coastal area between Rio de Janeiro and Florianopolis and River Plate Estuary). Moreover, we provide information on the most studied metals (Hg, Cd, Cu, Pb, Zn) and wild species, which evidence the use of endangered species. The data reviewed should help researchers to direct their efforts towards sparsely researched areas and facilitate bibliographic consultation of scientific information on exposure to metals and metalloids in Latin America.

Metals as chemical tracers to discriminate ecological populations of threatened Franciscana dolphins (Pontoporia blainvillei) from Argentina

Franciscana dolphins are the most impacted small cetacean in the Southwestern Atlantic Ocean, classified as Vulnerable A3d by IUCN. Essential (Fe, Mo, Mn, Cr, Ni, Co) and non-essential (Ag, Pb, Sn) trace elements (TEs) were measured in liver, kidney, and brain samples of by-catch Franciscana dolphins that were living in estuarine (n = 21) and marine (n = 21) habitats (1) to assess whether TEs posed a threat and (2) to evaluate the suitability of TEs for discriminating ecological populations of this species in Argentinean waters. Essential TEs showed little variation in tissues from both groups in agreement with levels reported for other cetaceans and suggesting that these concentrations correspond to normal physiological levels. Non-essential TEs were higher in estuarine juveniles and adults dolphins than in marine specimens. These results suggest anthropogenic sources associated with estuarine area and that Franciscana dolphins are good sentinels of the impact of the environment. The difference in the concentrations of TEs beetwen ecological populations appeared to be related to distinct exposures in both geographical areas, and it is suggested that Ag and Sn concentrations in adults are good chemical tracers of anthropogenic input of TEs. These results provide additional information for improved management and regulatory policy.

The role of metallothioneins, selenium and transfer to offspring in mercury detoxification in Franciscana dolphins (Pontoporia blainvillei)

The concentrations of mercury (Hg), selenium (Se) and metallothioneins (MT) were evaluated in fetuses, calves, juveniles and adults of the endangered coastal Franciscana dolphin (Pontoporia blainvillei) from Argentina. Mercury concentrations varied among analyzed tissues (liver, kidney, muscle and brain), with liver showing the higher concentrations in all specimens. An age-dependent accumulation was found in liver, kidney and brain. No significant relationship between Hg and MT concentrations was found for all tissues analyzed. Hepatic Hg molar concentrations were positively correlated with those of Se, indicating a great affinity between these two elements. Furthermore, dark granules of HgSe were observed in Kupffer cells in the liver by electron microscopy, suggesting the role of this macrophage in the detoxification of Hg. A transfer of Hg through placenta was proved. The presence of Hg in brain in all age classes did not show concentrations associated with neurotoxicity.

Hepatic and renal metallothionein concentrations in Commerson's dolphins (Cephalorhynchus commersonii) from Tierra del Fuego, South Atlantic Ocean

The Commerson's dolphin is the most common endemic odontocete of subantarctic waters of Tierra del Fuego, Argentina incidentally caught in fishing nets. The species is classified as "Data Deficient" by the IUCN. Metallothioneins (MTs) are considered as suitable biomarkers for health and environmental monitoring. The aims of the study were to assess MT concentrations in the liver and kidney of bycaught specimens. Moreover, correlations with Zn, Se, Cd, Ag and Hg, and the molar ratios of MT:metals were estimated to evaluate if there is an indication of their respective protective role against metal toxicity in tissues. Hepatic and renal MT concentrations were similar, ranging from 11.6 to 29.1nmol·g(-1) WW, and Kidney/Liver ratios ranging from 0.73 to 1.93 corresponded to normal ranges. Results suggest that MTs are related to physiological ranges for the species. This information constitutes the first MT report on Commerson's dolphins and possibly considered as baseline for species' conservation.

Beak deviations in the skull of Franciscana dolphins Pontoporia blainvillei from Argentina

The Franciscana dolphin Pontoporia blainvillei is characterized by a long rostrum, a feature that is shared with the families formerly classified as river dolphins (Pontoporiidae, Platanistidae, Iniidae, Lipotidae). Although there are occasional reports on the existence of beak deformations, very little published information exists describing this process. The object of the present study was to describe and quantify the beak anomalies of Franciscana dolphins from the coastal waters of Argentina. Of 239 skulls analyzed 12% showed beak deviations (BD), affecting the premaxillary-maxillary and dentary bones to different extents. The occurrence of BD in the dentary bone represented 58%, whereas premaxillary-maxillary BDs were observed in 14% of the studied specimens, while the complete rostrum (dentary, premaxillary and maxillary) was affected in 28% of the skulls. Dorsoventral axis BD was more frequent than lateral BD (48 and 38%, respectively), and double BD was only observed in the dentary bone. Most of the BD observed in this study could be classified as mild/moderate, and we assume that it did not affect the feeding activities of individuals; however, 2 specimens (<1%) showed a severe and complex curvature that probably did affect them. The cause of these anomalies (natural or anthropogenic origins) is unknown but may be related to important parasite loads, heavy metal and organic contaminants and plastic ingestion that could affect the coastal dolphin in different ways. A more detailed and thorough study of these cranial anomalies is necessary.

Mercury species, selenium, metallothioneins and glutathione in two dolphins from the southeastern Brazilian coast: Mercury detoxification and physiological differences in diving capacity

In the present study, the concentration of trace elements, total mercury (Hg) and selenium (Se) and mercury forms (MeHg, Hginorg and HgSe) in the vulnerable coastal dolphins Pontoporia blainvillei and Sotalia guianensis were appraised and compared, using metallothioneins (MT) and glutathione (GSH) as biomarkers for trace element exposure. The trace element concentrations varied between muscle and liver tissues, with liver of all dolphin specimens showing higher Hg and Se concentrations than those found in muscle. Hg, MeHg and Hginorg molar concentrations showed a clear increase with Se molar concentrations in the liver of both dolphins, and Se concentrations were higher than those of Hg on a molar basis. Se plays a relevant role in the detoxification of MeHg in the hepatic tissue of both dolphins, forming Hg-Se amorphous crystals in liver. In contrast, MT were involved in the detoxification process of Hginorg in liver. GSH levels in P. blainvillei and S. guianensis muscle tissue suggest that these dolphins have different diving capacities. Muscle Hg concentrations were associated to this tripeptide, which protects dolphin cells against Hg stress.