Elucidating temporal trends in trace element exposure of green turtles (Chelonia mydas) using the toxicokinetic differences of blood and scute samples

Global mercury concentrations in biota: their use as a basis for a global biomonitoring framework

An important provision of the Minamata Convention on Mercury is to monitor and evaluate the effectiveness of the adopted measures and its implementation. Here, we describe for the first time currently available biotic mercury (Hg) data on a global scale to improve the understanding of global efforts to reduce the impact of Hg pollution on people and the environment. Data from the peer-reviewed literature were compiled in the Global Biotic Mercury Synthesis (GBMS) database (>550,000 data points). These data provide a foundation for establishing a biomonitoring framework needed to track Hg concentrations in biota globally. We describe Hg exposure in the taxa identified by the Minamata Convention: fish, sea turtles, birds, and marine mammals. Based on the GBMS database, Hg concentrations are presented at relevant geographic scales for continents and oceanic basins. We identify some effective regional templates for monitoring methylmercury (MeHg) availability in the environment, but overall illustrate that there is a general lack of regional biomonitoring initiatives around the world, especially in Africa, Australia, Indo-Pacific, Middle East, and South Atlantic and Pacific Oceans. Temporal trend data for Hg in biota are generally limited. Ecologically sensitive sites (where biota have above average MeHg tissue concentrations) have been identified throughout the world. Efforts to model and quantify ecosystem sensitivity locally, regionally, and globally could help establish effective and efficient biomonitoring programs. We present a framework for a global Hg biomonitoring network that includes a three-step continental and oceanic approach to integrate existing biomonitoring efforts and prioritize filling regional data gaps linked with key Hg sources. We describe a standardized approach that builds on an evidence-based evaluation to assess the Minamata Convention's progress to reduce the impact of global Hg pollution on people and the environment.

Biological and ecological traits rather than geography control mercury (Hg) in scutes of marine turtles from the Southwest Atlantic

The use of sentinel species in monitoring programs for toxic metals such as mercury (Hg) is essential to understand these pollutants' impact on the environment. For this purpose, it is essential to use organisms that have a lifespan compatible with the residence time of Hg in the oceans, and preferably with a wide geographical distribution, such as sea turtles. Here, we assess the regional variability of Hg concentrations using carapace scutes of four sea turtle species along the foraging and spawning area in the northeast coastline of Brazil. Mercury concentrations in samples showed no relationship with the environmental Hg levels (obtained from literature). Rather, Hg concentrations varied according to species-specific biological, and ecological traits. Characteristics such as the ontogenetic shift in the diet of Chelonia mydas, capital breeding in females, depth of foraging in oceanic waters, and selectivity of food items, such as in Eretmochelys imbricata, significantly influenced Hg concentrations.

Green Turtle (Chelonia mydas) Blood and Scute Trace Element Concentrations in the Northern Great Barrier Reef

Marine turtles face numerous anthropogenic threats, including that of chemical contaminant exposure. The ecotoxicological impact of toxic metals is a global issue facing Chelonia mydas in coastal sites. Local investigation of C. mydas short-term blood metal profiles is an emerging field, while little research has been conducted on scute metal loads as potential indicators of long-term exposure. The aim of the present study was to investigate and describe C. mydas blood and scute metal profiles in coastal and offshore populations of the Great Barrier Reef. This was achieved by analyzing blood and scute material sampled from local C. mydas populations in five field sites, for a suite of ecologically relevant metals. By applying principal component analysis and comparing coastal sample data with those of reference intervals derived from the control site, insight was gleaned on local metal profiles of each population. Blood metal concentrations in turtles from coastal sites were typically elevated when compared with levels recorded in the offshore control population (Howick Island Group). Scute metal profiles were similar in Cockle Bay, Upstart Bay, and Edgecumbe Bay, all of which were distinct from that of Toolakea. Some elements were reported at similar concentrations in blood and scutes, but most were higher in scute samples, indicative of temporal accumulation. Coastal C. mydas populations may be at risk of toxic effects from metals such as Co, which was consistently found to be at concentrations magnitudes above region-specific reference intervals. Environ Toxicol Chem 2023;42:2375-2388. © 2023 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Understanding contaminant exposure risks in nesting Loggerhead sea turtle populations

Queensland loggerhead turtle nest numbers at Mon Repos (MR) indicate population recovery that doesn't occur at Wreck Island (WI). Previous research illustrated that MR and WI turtles forage in different locations, potentially indicating risks differences. Blood, scute, and egg were collected from turtles nesting at MR and WI, with known foraging sites (from concurrent studies). Trace element and organic contaminants were assessed via acid digestion and in vitro cytotoxicity bioassays, respectively. WI turtles had significantly higher scute uranium and blood molybdenum compared to MR turtles, and arsenic was higher in WI turtles foraging north and MR turtles foraging south. Egg and blood titanium, manganese, cadmium, barium, lead, and molybdenum, and scute and egg selenium and mercury significantly correlated. Blood (75 %) extracts produced significant toxicity in vitro in turtle fibroblast cells. In conclusion, reducing chemical exposure at higher risk foraging sites would likely benefit sea turtles and their offspring.

A Pilot Study of Mercury Distribution in the Carapace of Four Species of Sea Turtles from Northeastern Brazil

Scutes present very complex morphologies with different growth rates at different areas of the carapace that can change the accumulation process of essential and non-essential metals. To infer the effects of morphology and growth on Hg concentrations in scutes, we mapped them in the carapace of one individual of four species of sea turtles sampled along the Brazilian coast. The results showed that Hg concentrations were higher in the vertebral scutes of Chelonia mydas and Eretmochelys imbricata suggesting variation in growth rates of different carapace areas since the vertebral area is the first to develop prior to costal areas. Caretta caretta and Lepidochelys olivacea did not show differences between carapace areas. The preliminary data from this pilot study indicate that vertebral scutes may be suitable for monitoring Hg in C. mydas and E. imbricata, since they reflect longer exposure period. A species-to-species comparison of Hg concentrations is not possible due to the small number of sampled individuals, nevertheless, E. imbricata showed remarkably lower Hg concentrations compared to the other three species. Further studies are required for all four species, with a larger number of individuals, preferentially of varying life stages, due to the unknown effects of different diets, Hg exposure, and migration histories.

An integrative approach to define chemical exposure threshold limits for endangered sea turtles

Environmental contaminants pose serious health threats to marine megafauna species, yet methods defining exposure threshold limits are lacking. Here, a three-pillar chemical risk assessment framework is presented based on (1) species- and chemical-specific lifetime bioaccumulation modelling, (2) non-destructive in vitro and in vivo toxicity threshold assessment, and (3) chemical risk quantification. We used the effects of cadmium (Cd) in green sea turtles (Chelonia mydas) as a proof of concept to evaluate the quantitative mechanistic modelling approach. A physiologically-based kinetic (PBK) model simulated Cd tissue concentrations (liver, kidney, muscle, fat, brain, scute, and 'rest of the body') in C.mydas. The validated PBK model then translated species-specific in vitro results to in vivo effects. The results showed that the resilience of C.mydas towards Cd kidney toxicity is age-dependent and differs with changing physiology and feeding ecology. Using the model in reverse mode, a steady-state exposure threshold of 0.1 µg/g dry weight Cd in forage was derived and compared to real-world exposure scenarios. Three out of the four globally distinct C.mydas populations assessed are exposed to Cd levels above this threshold limit. This approach can be adapted to other marine species and chemicals to prioritize measures for managing potentially harmful chemical exposures.

Multiple toxicity endpoints induced by carbon nanofibers in Amazon turtle juveniles: Outspreading warns about toxicological risks to reptiles

The toxicity of carbon-based nanomaterials (CNs) has been observed in different organisms; however, little is known about the impact of water polluted with carbon nanofibers (CNFs) on reptiles. Thus, the aim of the current study was to assess the chronic effects (7.5 months) of 1 and 10 mg/L of CNF on Podocnemis expansa (Amazon turtle) juveniles (4 months old) based on different biomarkers. Increased total organic carbon (TOC) concentrations observed in the liver and brain (which suggests CNF uptake) were closely correlated to changes in REDOX systems of turtles exposed to CNFs, mainly to higher nitrite, hydrogen peroxide and lipid peroxidation levels. Increased levels of antioxidants such as total glutathione, catalase and superoxide dismutase in the exposed animals were also observed. The uptake of CNFs and the observed biochemical changes were associated with higher frequency of erythrocyte nuclear abnormalities (assessed through micronucleus assays), as well as with both damage in erythrocyte DNA (assessed through comet assays) and higher apoptosis and necrosis rates in erythrocytes of exposed turtles. Cerebral and hepatic acetylcholinesterase (AChE) increased in turtles exposed to CNFs, and this finding suggested the neurotoxic effect of these nanomaterials. Data in the current study reinforced the toxic potential of CNFs and evidenced the biochemical, mutagenic, genotoxic, cytotoxic, and neurotoxic effects of CNFs on P. expansa.

PLASMA BIOCHEMISTRY PROFILES OF JUVENILE GREEN TURTLES (CHELONIA MYDAS) FROM THE BAHAMAS WITH A POTENTIAL INFLUENCE OF DIET

Plasma biochemistry profiles aid health assessment of marine turtles, but knowledge of the influence of regional biological factors (e.g., habitat, diet) on marine turtle blood plasma values is limited. To investigate the influence of diet on plasma biochemistry values in juvenile green turtles (Chelonia mydas), we used carbon and nitrogen stable isotopes to provide a quantitative estimate of forage items in green turtles feeding at two distinct areas (Bonefish Hole and South Flats) in Bimini, Bahamas. Plasma samples were obtained from 13 turtles in Bonefish Hole (a mangrove tidal estuary) and 15 turtles in South Flats (an open water seagrass bed) in 2018. All turtles appeared outwardly healthy. Sessile filter feeders contributed the largest proportion of diet in Bonefish Hole, and seagrass contributed the highest proportion of diet in South Flats. Turtles at Bonefish Hole presented significantly lower cholesterol, total protein, phosphorus, triglycerides, and aspartate transaminase compared to South Flats. Across all turtles, those feeding primarily on red algae presented the highest uric acid and alkaline phosphatase, and turtles with a seagrass-dominated diet had the highest cholesterol. Understanding dietary influence on plasma biochemistry may help explain variances seen in local health and nutritional evaluations, and the trends reported can aid the interpretation of plasma analyte values in marine turtles.

Editorial - Virtual special issue (VSI) green turtles as silent sentinels of pollution in the Great Barrier Reef - Rivers to Reef to Turtles project

This special issue of STOTEN is dedicated to presenting the results of the WWF-Australia "Rivers to Reef to Turtles" project, which focused on investigating pollutants in the environment, food and bodies of green turtles (Chelonia mydas) on the Great Barrier Reef (GBR). The project brought together organic and inorganic trace chemical analysis, bioanalytical tools and individual health monitoring to investigate potential causes of an unusual mortality event in 2012. Together, the ten studies in this special issue highlight the shortcomings of current chemical monitoring and impact assessment programmes, which are focused on a limited number of prioritised chemicals and fail to account for the incredible diversity of toxicants released by human activities. It is essential that future management efforts consider the impact of these contaminants on the GBR, already under threat from global warming and sediment and nutrient runoff. Understanding the impact that chemical contaminants have on turtles not only informs green turtle conservation but can also, as they are sensitive and long-lived bioindicators of environmental health, guide efforts to protect, conserve and restore marine ecosystems such as the GBR.

Coastal bays and coral cays: Multi-element study of Chelonia mydas forage in the Great Barrier Reef (2015-2017)

There is increasing interest in understanding potential impacts of complex pollutant profiles to long-lived species such as the green sea turtle (Chelonia mydas), a threatened megaherbivore resident in north Australia. Dietary ingestion may be a key exposure route for metals in these animals and marine plants can accumulate metals at higher concentrations than the surrounding environment. We investigated concentrations of 19 metals and metalloids in C. mydas forage samples collected from a group of offshore coral cays and two coastal bays over a period of 2-3 years. Although no samples exceeded sediment quality guidelines, coastal forage Co, Fe, and V concentrations were up to 2-fold higher, and offshore forage Sr concentrations were ~3-fold higher, than global seagrass means. Principal Component Analysis differentiated coastal bay from coral cay forage according to patterns consistent with underlying terrigenous-type or marine carbonate-type sediment geochemistry, such that coastal bay forage was higher in Fe, Co, Mn, Cu, and Mo (and others) but forage from coral cays was higher in Sr and U. Forage from the two coastal bays was differentiated according to temporal variation in metal profiles, which may be associated with a more episodic sediment disturbance regime in one of the bays. For all study locations, some forage metal concentrations were higher than previously reported in the global literature. Our results suggest that forage metal profiles may be influenced by the presence of some metals in insoluble forms or bound to ultra-fine sediment particles adhered to forage surfaces. Metal concentrations in Great Barrier Reef forage may be present at levels higher than expected from the global seagrass literature and appear strongly influenced by underlying sediment geochemistry.

Seagrass habitat in Tarawa Lagoon, Kiribati: Service benefits and links to national priority issues

This paper presents a review around seagrass habitat in Tarawa Lagoon, Kiribati and explores the links between seagrass occurrence and the national priority issues of climate change, urban development, human health, nearshore fisheries, threatened species, ocean policy, research capacity and awareness. The contribution of healthy seagrass habitats to many aspects of these national issues is often overlooked and there is need to establish the knowledge gaps and priority actions that can enable mitigation of issues that impact on valuable seagrass resources and their management. Research data on seagrass habitats in Kiribati, and the wider Pacific Island region, is limited and this hinders informed decisions at local, national and regional levels. We present a comprehensive review on seagrass within a national context to aid prioritisation and uptake of information for resource owners, and wider stakeholders, in Kiribati while acknowledging local expertise. The paper highlights data and knowledge gaps that if addressed, will provide information useful to Kiribati nationals, communities and government stakeholders. Recommendations for actions that fill these gaps and build understanding of seagrass resources in Kiribati are provided.

Distribution of metals in tissues of captive and wild Morelet's crocodiles and the potential of metallothioneins in blood fractions as a biomarker of metal exposure

The distribution of Hg, Cd, Cu, and Zn in keratinized tissues, blood fractions, and excretory organs, and MTs in blood fractions and excretory organs was determined in captive, semicaptive, and wild Morelet's crocodiles and they were compared to select the most useful non-destructive tissues for the monitoring of metal exposure and to assess the potential of MTs as a biomarker. Our results indicate blood plasma, claws, and caudal scutes altogether are suitable tissues for xenobiotic metals exposure, with concentrations in blood plasma being an indicator of recent exposure, whereas concentrations in claws and caudal scutes are indicators of chronic exposure. Results in keratinized tissues suggest they are an important detoxification strategy in crocodiles, and claws presented the highest concentrations of metals in both captive (Hg = 0.44 ± 0.23 μg g^-1, Cd = 11.10 ± 5.89 μg g^-1, Cu = 45.98 ± 23.18 μg g^-1, Zn = 124.75 ± 75.84 μg g^-1) and wild populations (Hg = 1.31 ± 0.32 μg g^-1, Cd = 26.47 ± 21.15 μg g^-1, Cu = 191.75 ± 165.91 μg g^-1, Zn = 265.81 ± 90.62 μg g^-1). Thus, they are an appropriate tool for assessing metal exposure in populations where scutes clipping as a marking technique is not allowed, and their collection is less complicated than with other tissues. MTs are a suitable biomarker in blood plasma, whereas in erythrocytes detoxification processes might depend on hemoglobin, rather than MTs. Future studies should consider the implementation of these tools for the monitoring of wild populations.

Monitoring the health of green turtles in northern Queensland post catastrophic events

Between 2014 and 2017, the Rivers to Reef to Turtles (RRT) project examined the health of green turtles at two coastal sites impacted by urban and agricultural human activities (Cleveland and Upstart Bays) and one proposed pristine site (Howick Group of Reefs) in northern Queensland, Australia, through blood biochemistry and haematology, plasma protein electrophoresis, and clinical assessments including body condition and barnacle counts. Furthermore, cases of mortality were subjected to comprehensive postmortem examination. In an attempt to advance diagnostics, associations between specific contaminants and health of turtles in this region were tested. No comprehensive health assessments had been conducted at these sites prior to this study. The coastal Cleveland and Upstart Bays both demonstrated effects likely to be in response to stressors suspected to be anthropogenic in origin (elevated total white cell counts and creatinine kinase levels across the populations, respectively). This was associated with a suite of trace elements, in particular cobalt. While these indicators of stress resolved by the final year of the study, a chronic stressor was suspected to be persisting with ongoing low albumin: globulin. Necropsies did not elucidate any specific diseases. Although body condition index did not closely correlate with site health, barnacle counts in juvenile turtles may prove a reliable indicator of site health. Based on previously established indicators of poor health, barnacle counts showed that 10% of the population was in poor health at Upstart Bay and nearly 20% of the population at Cleveland Bay. This is above what would be expected for a normal population. Overall, the health component of this study suggested that the pristine turtle population was healthy and the coastal turtle populations were under active stressors, possibly caused by anthropogenic effectors such as chemical pollutants, when initially examined in 2014. These stressors resolved by the conclusion of the study in 2017; but chronic stressors remained absent in the pristine site and present within each of the studied coastal populations.

Evaluating internal exposure of sea turtles as model species for identifying regional chemical threats in nearshore habitats of the Great Barrier Reef

Marine megafauna that forage in proximity to land can be exposed to a diverse mixture of chemicals that - individually or combined - have the potential to affect their health. Characterizing such complex exposure and examining associations with health still poses considerable challenges. The present study summarizes the development and application of novel approaches to identifying chemical hazards and their potential impacts on the health of coastal wildlife, using green sea turtles as model species. We used an epidemiological study approach to collect blood and keratinized scute samples from free-ranging turtles foraging in nearshore areas and an offshore control site. These were analyzed using a combination of non-targeted, effect-based and multi-chemical analytical screening approaches to assess internal exposure to a wide range of chemicals. The screening phase identified a suite of elements (essential and non-essential) as priority for further investigation. Many of these elements are not commonly analyzed in marine wildlife, illustrating that comprehensive screening is important where exposure is unknown or uncertain. In particular, cobalt was present at highly elevated concentrations, in the order of those known to elicit acute effects across other vertebrate species. Several trace elements, including cobalt, were correlated with clinical indicators of impaired turtle health. In addition, biomarkers of oxidative stress (e.g. 3-indolepropionic acid and lipid peroxidation products) identified in the blood of turtles showed significant correlations with clinical health markers (particularly alkaline phosphatase and total bilirubin), as well as with cobalt. To assist interpretation of trace element blood data in the absence of sufficient information on reptile toxicity, we established exposure reference intervals using a healthy control population. In addition, trace element exposure history was investigated by establishing temporal exposure indices using steady-state relationships between blood and scute. Overall, the data provide a strong argument for the notion that trace element exposure is having an impact on the health of coastal sea turtle populations.