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

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.

Study of trace elements in stranded green turtles (Chelonia mydas), hawksbill turtles (Eretmochelys imbricata), and olive ridley turtles (Lepidochelys olivacea) in Gulf of Thailand and Andaman Sea

The purpose of this study was to survey and compare the amounts of elements in the serum of stranded sea turtles from the Gulf of Thailand and the Andaman Sea. The sea turtles from the Gulf of Thailand had Ca, Mg, P, S, Se, and Si concentrations significantly higher than those in sea turtles from the Andaman Sea. The Ni and Pb concentrations of sea turtles from the Gulf of Thailand was higher, but not significantly so, than in sea turtles from the Andaman Sea. Rb was detected only in sea turtles from the Gulf of Thailand. This may have been related to the industrial activities in Eastern Thailand. The concentration of Br in the sea turtles from the Andaman Sea were significantly higher than those in sea turtles from the Gulf of Thailand. The higher serum concentration of Cu in hawksbill (H) and olive ridley turtles (O) than in green turtles may be due to hemocyanin, as an important component in the blood of crustaceans. The higher Fe concentration in the serum from green turtles than for H and O may be due to chlorophyll, which is an important component of chloroplasts in eel grass. Co was not found in the serum of green turtles but was found in the serum of H and O. The monitoring of important elements in sea turtles may be used as a tool to assess the levels of pollution in marine ecosystems.

Dose metric evaluation of a cell-based bioassay for assessing the toxicity of metals to Dugong dugon: Effect of metal-media interactions on exposure concentrations

Cell-based toxicity testing has emerged as a useful tool in (eco)toxicological research, allowing the ethical assessment of the effects of contaminants such as trace metals on marine megafauna. However, metal interactions with various dissolved ligands in the microplate environment may influence the effective exposure concentrations. Hence, the cells are not exposed to the nominal concentrations within the test system. This study aimed to establish and evaluate the effectiveness of cell-based bioassays for investigating the toxicity of selected metals in dugongs through the following objectives: (1) measure the cytotoxic potential of cadmium (Cd²⁺), and chromium (Cr⁶⁺) to dugong skin cell cultures, (2) investigate the interactions between media constituents and selected trace metals in cell-based bioassays, and (3) evaluate the risk to a free-ranging population of dugong based on effect values. Chromium was the most toxic of the metals tested (EC₅₀ = 1.14 µM), followed by Cd (EC₅₀ = 6.35 µM). Assessment of ultrafiltered (< 3 kDa) exposure media showed that 1% and 92.5% of Cr and Cd were associated with larger organic components of the media. Further, the binding of Cd to media constituents was calculated to underestimate Cd toxicity in cell-based assays by an order of magnitude. This understanding of metal partitioning in cell-based bioassays provides a more accurate method for assessing toxicity in cell-based bioassays. In addition, this study illustrated that dugong cells are more sensitive to Cr and Cd than other marine wildlife species. The chemical risk assessment found the dugong population in Moreton Bay to be at high risk from Cd exposure.

Field-scale monitoring of green sea turtles (Chelonia mydas): Influence of site characteristics and capture technique on the blood metabolome

Given their threatened status, there is considerable interest in establishing monitoring techniques that can be used to evaluate the health of sea turtles in the wild. The present study represents a methodological contribution towards field-scale metabolomic assessment of sea turtles, by exploring differences in blood biochemistry associated with site characteristics and capture technique. We compared the metabolome of blood from animals at three locations (two coastal and one reefal), collected from turtles that were either resting or active, and sampled across multiple seasons at one location. Our results show clear differences in the metabolome of turtles from the three locations, some of which are likely attributable to differences in diet or forage quality and others which may reflect differences in other factors (e.g., occurrence of land-based contaminants or other biotic and/or abiotic stressors) between coastal and reefal sites. Our analysis also revealed the influence of capture technique on metabolite profiles, with numerous markers of physical exertion in animals captured while active that were absent in turtles sampled while resting. We observed a modest potential for temporal differences in the metabolome, but controlling for sampling time did not change the overall conclusions of our study. This suggests that temporal differences in the metabolome warrant consideration when designing studies to evaluate the status of sea turtles in the wild, but that site characteristics and capture technique are bigger drivers. However, sample size for this comparison was relatively small and further investigation of seasonal differences in the metabolome are warranted. Research exploring each of these factors more closely will further contribute towards achieving robust metabolomics analysis of sea turtles across large spatial and temporal scales.

Occurrence and accumulation of heavy metals in algal turf particulates and sediments on coral reefs

Algal turfs form a critical interface on coral reefs that interacts with several key ecosystem processes. While we know these turfs have a remarkable propensity to accumulate sediments, which can have a range of ecosystem impacts, their role as sinks for heavy metals remains largely unexamined. Here we quantified the concentration of 15 metals in algal turf sediments from Lizard Island and Orpheus Island on the Great Barrier Reef, and specifically explored how the loads of arsenic, cobalt, iron and lead were related to turf length. Metal composition differed markedly between the two islands, with the composition at Orpheus Island suggesting closer links to terrestrial sediment sources. Furthermore, metal loads increased significantly with turf length, suggesting that longer turfs can accumulate these pollutants on reefs. Given that algal turfs are a crucial component of herbivorous/detritivorous trophic pathways, this could represent a key juncture at which these metals enter food chains.

An assessment of heavy metals in green sea turtle (Chelonia mydas) hatchlings from Saudi Arabia's largest rookery, Ras Baridi

Background

Anthropogenic sources can lead to the accumulation of heavy metals in marine organisms through ingestion, absorption, or inhalation. For sea turtle embryos, heavy metals can be absorbed into the egg from the incubation environment or be maternally transferred to the offspring causing neurological, reproductive, and developmental problems. Here, we report heavy metal concentrations in green turtle hatchlings from the largest rookery on the Red Sea, Ras Baridi.

Methods

Deceased hatchlings were collected from two beaches near a cement factory at Ras Baridi, from which heavy metal concentrations (chromium (Cr), manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni), copper (Cu), zinc (Zn), arsenic (As), selenium (Se), cadmium (Cd), and lead (Pb)) were measured from the liver, muscle, and residual yolk of the hatchlings.

Results

Although based on a small sample of hatchlings, the data presented here provides the first measurements of heavy metals from sea turtles in the Red Sea and highlights the link between human activity and its impact on the ecology of sea turtles. In general, the heavy metal concentrations of heavy metals were not significantly different between the beach next to the cement factory and the beach downwind from the factory. However, the concentrations of heavy metals were significantly different between sampled tissues (liver, muscle, and residual yolk).

Discussion

This study provides insight into current heavy metal levels in green turtle hatchlings, which can be used as bio-indicators for environmental contaminants as coastal development increases in the Red Sea. Moreover, we found a lack of standardized methodology to evaluate heavy metals in hatchling sea turtles. Future efforts should work toward creating comparable techniques for long-term heavy metal monitoring, as this is a useful determinant of anthropogenic pollution.

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.

Determinants of Legacy Persistent Organic Pollutant Levels in the European Pond Turtle (Emys orbicularis) in the Camargue Wetland, France

Many banned persistent organic pollutants (POPs) remain for decades in the aquatic environment and can have harmful effects on long-lived predators because of their high bioaccumulation and biomagnification potentials. We investigated the occurrence and levels of 18 polychlorinated biphenyls (PCBs) and 16 organochlorine pesticides in European pond turtles (n = 174) from April to July 2018 in the Camargue wetland, France. Although the Camargue was highly contaminated in previous decades, plasma occurrence and levels of POPs were very low: we were able to quantify only 3 of the 34 compounds we analyzed in >10% of the turtles. The burdens from POPs did not differ between males and females and were uncorrelated with sampling date and body mass. We observed differences in POP burdens between turtles from the 2 sampling sites. One possible explanation is that the sampling sites were in different agricultural hydraulic systems: plasma occurrence and levels were higher for PCB-52 and hexachlorobenzene in turtles captured in drainage channels and for PCB-153 at the site that receives irrigation. Finally, the occurrence and levels of PCB-153 in turtles increased with age, likely because of bioaccumulation and much higher exposure 20 to 30 yr ago than now. Environ Toxicol Chem 2021;40:2261-2268. © 2021 SETAC.

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.

Internal and Maternal Distribution of Persistent Organic Pollutants in Sea Turtle Tissues: A Meta-Analysis

We aimed to identify patterns in the internal distribution of persistent organic pollutants (POPs) and assess contributing factors using sea turtles and their offspring as a case study of a long-lived wildlife species. We systematically synthesized 40 years of data and developed a lipid database to test whether lipid-normalized POP concentrations are equal among tissues as expected under steady state for lipophilic compounds. Results supported equal partitioning among tissues with high blood flow or perfusion including the heart, kidney, muscle, and lung. Observed differences in the brain, fat, and blood plasma, however, suggest the physiological influence of the blood-brain barrier, limited perfusion, and protein content, respectively. Polybrominated diphenyl ethers partitioned comparably to legacy POPs. Polycyclic aromatic hydrocarbons, meanwhile, partitioned more into the lung, colon, and muscle compared to the liver under chronic and acute field exposure. Partitioning ratios of individual POPs among tissues were significantly related to the lipophilicity of compounds (as estimated by K_ow) in half of the observed cases, and significant differences between juveniles and adults underscore physiological differences across life stages. The comprehensive tissue partitioning patterns presented here provide a quantitative basis to support comparative assessments of POP pollution derived from biomonitoring among multiple tissues.

Concentrations of trace elements in tissues of loggerhead turtles (Caretta caretta) from the Tyrrhenian and the Ionian coastlines (Calabria, Italy)

Toxic trace elements from both, natural and anthropogenic origin, pose a threat to aquatic environments and marine wildlife due to their long-range transport, bioaccumulative nature, and biomagnification through the food chain. Being long-lived and migratory animals, sea turtles can be exposed to elevated levels of toxic elements, and are therefore considered sentinel species for chemical pollution. In this study, concentrations of trace elements (arsenic, cadmium, lead, mercury) were determined in tissues of 46 loggerhead sea turtles (Caretta caretta) stranded along Tyrrhenian and Ionian coasts of Calabria, in Southern Italy, between 2014 and 2020. Curved carapace length (CCL), curved carapace width (CCW), body mass (BM), and sex were determined and the correlations of these parameters with toxic elements concentrations were investigated. During necropsy, kidney, liver, and muscle tissues were collected and the concentration and distribution of metals determined. Muscle tissues showed the lowest toxic element burdens, except for As that showed the highest mean concentrations in this tissue. The kidney was the main accumulation organ for Cd, while similar levels of Hg and Pb were measured in kidney, liver, and muscle tissues. The risk assessment performed for Cd, Hg, and Pb in sea turtles' liver highlighted possible negative effects on sea turtles' health and the need for marine turtle toxicology researches. This is the first study reporting levels and distribution of toxic elements in tissues of Caretta caretta turtles from the Tyrrhenian and Ionian coasts of Calabria.

Distribution and toxicity of persistent organic pollutants and methoxylated polybrominated diphenylethers in different tissues of the green turtle Chelonia mydas

Investigating environmental pollution is important to understand its impact on endangered species such as green turtles (Chelonia mydas). In this study, we investigated the accumulation and potential toxicity of selected persistent organic pollutants (POPs) and naturally occurring MeO-PBDEs in liver, fat, kidney and muscle of turtles (n = 30) of different gender, size, year of death, location and health status. Overall, POP concentrations were low and accumulation was highest in liver and lowest in fat which is likely due to the poor health of several animals, causing a remobilization of lipids and associated compounds. PCBs and p,p'-DDE dominated the POP profiles, and relatively high MeO-PBDE concentrations (2'-MeO-BDE 68 up to 192 ng/g lw, 6-MeO-BDE 47 up to 79 ng/g lw) were detected in all tissues. Only few influences of factors such as age, gender and location were found. While concentrations were low compared to other marine wildlife, biological toxicity equivalences obtained by screening the tissue extracts using the micro-EROD assay ranged from 2.8 to 356 pg/g and the highest values were observed in muscle, followed by kidney and liver. This emphazises that pollutant mixtures found in the turtles have the potential to cause dioxin-like effects in these animals and that dioxin-like compounds should not be overlooked in future studies.

Inorganic elements in live vs dead nesting olive ridley marine turtles in the Mexican Pacific: Introducing a new statistical methodology in ecotoxicology

This study reports the largest inorganic elements database in the blood of live marine turtles (Lepidochelys olivacea), with 241 live as well as 38 dead nesting turtles sampled and analyzed for 26 inorganic elements, including essential (Al, As, B, Ca, Co, Cr, Cu, Fe, K, Mg, Mn, Mo, Na, Ni, P, Se, S, V, and Zn) and non-essential elements (Cd, Li, Pb, Sr, Ti, Tl, and Hg). We compared inorganic element concentrations in live and dead olive ridleys from the arribada beach "La Escobilla" located on the Pacific coast of southeastern Mexico. The most outstanding result of our study is the higher Cd concentration in dead (mean 4.27 μg g^-1 ww: min 0.01-max 81.5) compared with live animals (mean 0.14 μg g^-1 ww: min 0.02-max 0.52). This population has been previously reported to have the highest Cd concentration worldwide in kidney and liver samples from marine turtles (with 150.88 ± 110.99 and 82.88 ± 36.65 μg g^-1 ww, respectively). Other important findings of this study include the low Hg concentration along with the decrease in Pb over the years in this population. The study also uses a new statistical method - the iconography of correlations - in which all available information is used without removing individuals or variables with missing information for the whole analysis, which is a common problem in ecotoxicology. A major advantage of this method compared to other multivariate methods is that the missing information can be easily handled, because the correlations (2 variables) and partial correlations (3 variables) are estimated only with the available data using a one-at-a-time strategy.

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.