Combining analytical and in vitro techniques for comprehensive assessments of chemical exposure and effect in green sea turtles (Chelonia mydas)

Investigating chemical risk in green and loggerhead turtles foraging in Moreton Bay using species-specific cell-based bioassays

Differences in trophic level may result in differences in chemical exposure between species of sea turtles, as pollutants may bioaccumulate differentially in diet items. It is, therefore, crucial to understand species-specific differences in exposure and effect to accurately assess chemical risk to individual species. This study used blood collected from green and loggerhead turtles foraging in Moreton Bay, Queensland, Australia, to assess differences in chemical exposure and effect of two species foraging in the same area at different trophic levels. Organic contaminants were extracted from green and loggerhead turtle blood samples and assessed for cytotoxicity in species-specific cell cultures. The results indicated that chemical exposure to organic contaminants was similar between the two species, despite differences in trophic level. Overall, chemical risk was relatively low in both species, but temporal changes in toxicity observed in other similar studies illustrate the importance of ongoing toxicological assessments of sea turtle populations.

Distinct population-wide differences in contaminants and blood parameters in foraging green sea turtles

The rising diversity and concentration of contaminants have surpassed ecological thresholds, threatening marine ecosystems. The effects of pollutants on marine animals, particularly sea turtles, are receiving increased attention due to their role as indicators of human impacts. This study examined the health implications of contaminant exposure in three green turtle (Chelonia mydas) foraging sites in the southern Great Barrier Reef, Australia. Assessments were performed on 45 immature turtles from offshore (Heron, Lady Elliot Island) and inshore (Hervey Bay) foraging sites, hypothesising greater anthropogenic exposure inshore. A cytotoxicity assay tested blood toxicity, while trace element concentrations were compared with baseline reference intervals. Interestingly, this analysis revealed elevated cobalt and manganese levels in Hervey Bay turtles, and offshore turtles showed higher cytotoxicity despite appearing healthier, contrasting with low cytotoxicity and low body condition in Hervey Bay. These findings highlight the complexities of ecotoxicology and the need for comprehensive data on contaminant impacts.

Trace elements and high sulfur levels in the blood of rehabilitated eastern Mediterranean Sea green sea turtles (Chelonia mydas)

The Eastern Mediterranean Sea (EMS) exhibits high temperature and salinity, low levels of biologic production and is considered oligotrophic. Nonetheless, it is also a hotspot of biodiversity, with several important endangered flagship species, including several species of sea turtles. These turtles serve as bioindicators for the health of their ecologic systems, due to changes in diet, habitat and migration patterns that characterize different stages in their lives. This study covered 100 blood samples taken between 2008 and 2019 from 72 green sea turtles (Chelonia mydas) tested for 67 elements, some of which carry toxic potential. The turtles were treated at the Israeli Sea Turtle Rescue Center (ISTRC) after being rescued from sea, exhibiting a variety of health conditions and Injuries. The data were compared to similar studies worldwide and serve as a basis for monitoring the health status of the green sea turtles' EMS populations. The results of all animals presented noticeably high levels of sulfur - an order of magnitude higher than sea turtles from other locations around the world. This paper discusses the possible origins of this element, as well as its potential effects, while raising the question regarding the ability of these sea turtles to endure such sulfur levels.

Tracing troubles: Unveiling the hidden impact of inorganic contamination on juvenile green sea turtle

Human activities and climate change have negatively affected the world's oceans, leading to a decline of 30 to 60 % in coastal ecosystems' biodiversity and habitats. The projected increase in the human population to 9.7 billion by 2050 raises concerns about the sustainability of marine ecosystem conservation and exploitation. Marine turtles, as sentinel species, accumulate contaminants, including trace elements, due to their extensive migration and long-life span. However, there is a lack of data on the degree of contamination and their effects on marine turtles' health. This study focuses on assessing in-situ inorganic contamination in juvenile green sea turtles from La Réunion Island and its short-term impact on individual health, using conventional biomarkers and proteomics. The goals include examining contamination patterns in different tissues and identifying potential new biomarkers for long-term monitoring and conservation efforts. The study identified differential metal contamination between blood and scute samples, which could help illuminate temporal exposure to trace elements in turtle individuals. We also found that some conventional biomarkers were related to trace element exposure, while the proteome responded differently to various contaminant mixtures. Immune processes, cellular organization, and metabolism were impacted, indicating that contaminant mixtures in the wild would have an effect on turtle's health. Fifteen biomarker candidates associated with strong molecular responses of sea turtle to trace element contamination are proposed for future long-term monitoring. The findings emphasize the importance of using proteomic approaches to detect subtle physiological responses to contaminants in the wild and support the need for non-targeted analysis of trace elements in the biomonitoring of sea turtle health.

Advancing Maternal Transfer of Organic Pollutants across Reptiles for Conservation and Risk Assessment Purposes

Embryonic exposure through maternally transferred pollutants can affect embryo vitality, survival, and health. Reptiles face global declines and are sensitive to embryonic pollutant exposure. Yet, they are often neglected in pollution risk assessment and conservation. We analyzed maternal transfer of organic pollutants in reptiles through a systematic extraction, homogenization, and integration of published data on organic pollutants measured in mother-egg pairs into a comprehensive database (DOI:10.5281/zenodo.10900226), complemented with molecular physical-chemical properties of the pollutants. Over four decades, 17 publications provided 19,955 data points shifting from legacy to emerging contaminants although research on newer contaminants lags regulatory and societal demands. Challenges including taxonomic bias, heterogeneity in sampled tissues, and 73% of censored data complicate comparative analyses. However, significant opportunities were identified including the use of the turtle Malachlemys terrapin and snake Enhydris chinensis as flagship species where a large amount of data is available across tissues (allowing investigation into physiological relations) and compounds (allowing insights into maternal transfer across the chemical universe). Data on other freshwater and marine turtles provide the possibility of exploring taxonomic patterns in this subgroup. The analysis, integrated database, and discussion present opportunities for research in an era where science needs to achieve more with limited wildlife data.

Species-specific bioassays reveal spatial variation in chemical contamination of green sea turtles

The rapid increase of anthropogenic activity at shipping ports and surrounding coastal areas has been correlated with higher chemical contamination entering the surrounding marine environment. Chemical contaminants in marine environments can lead to significant health problems for green turtles (Chelonia mydas), especially when these contaminants accumulate in their foraging grounds. This study examined the exposure and toxicological effects of chemical contaminants on green turtle cells using a species-specific cell viability assay. Using the QuEChERs extraction, organic contaminants were extracted from 60 blood samples collected from green turtles in three foraging locations: Port Curtis, and two reefs (Heron Reef and Hoskyn-Fairfax Reefs) within the Capricorn Bunker Group of the outer Great Barrier Reef. Blood extracts were tested for cytotoxicity against primary green turtle fibroblast cells using an in vitro resazurin bioassay to assess cell viability. Extracts from Gladstone and Heron Reef indicated significant chemical contamination, at levels high enough to cause adverse health effects of green turtles. Very low toxicity values at the Hoskyn-Fairfax Reefs location indicate its potential to be established as a reference site for the southern Great Barrier Reef.

Adaption and application of cell-based bioassays to whole-water samples

The increasing presence of contaminants of emerging concern in wastewater and their potential environmental risks require improved monitoring and analysis methods. Direct toxicity assessment (DTA) using bioassays can complement chemical analysis of wastewater discharge, but traditional in vivo tests have ethical considerations and are expensive, low-throughput, and limited to apical endpoints (mortality, reproduction, development, and growth). In vitro bioassays offer an alternative approach that is cheaper, faster, and more ethical, and can provide higher sensitivity for some environmentally relevant endpoints. This study explores the potential benefits of using whole water samples of wastewater and environmental surface water instead of traditional solid phase extraction (SPE) methods for in vitro bioassays testing. Whole water samples produced a stronger response in most bioassays, likely due to the loss or alteration of contaminants during SPE sample extraction. In addition, there was no notable difference in results for most bioassays after freezing whole water samples, which allows for increased flexibility in testing timelines and cost savings. These findings highlight the potential advantages of using whole water samples in DTA and provide a framework for future research in this area.

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.

Green Sea Turtles (Chelonia mydas) Accumulate Heavy Metals Near a Former Skeet Shooting Range in Kailua, O'ahu, Hawai'i

The present study determined if green sea turtles (Chelonia mydas) in Kailua Bay, Oahu, in the Hawaiian Islands have elevated blood and scute lead (Pb), arsenic (As), and antimony (Sb) concentrations resulting from lead deposition at a historic skeet shooting range. Blood and scute samples were collected and analyzed for Pb, As, and Sb via inductively coupled plasma-mass spectrometry. Prey, water, and sediment samples were also analyzed. Turtle samples in Kailua Bay (45) have blood Pb concentrations (328 ± 195 ng/g) greater than a reference population (Howick Group of Islands, 29.2 ± 17.1 ng/g). Compared with other green turtle populations, only turtles in Oman, Brazil, and San Diego, CA have blood Pb concentrations greater than turtles in Kailua Bay. The estimated daily exposure of Pb from algae sources in Kailua Bay (0.12 mg/kg/day) was significantly lower than the no observed adverse effect level (100 mg/kg) of red-eared slider turtles. However, the chronic effects of Pb on sea turtles is poorly understood and continued monitoring of this population will increase our understanding of the Pb and As loads of sea turtles in Kailua Bay. Environ Toxicol Chem 2023;42:1109-1123. © 2023 SETAC. This article has been contributed to by U.S. Government employees and their work is in the public domain in the USA.

Non-targeted proteomics reveals altered immune response in geographically distinct populations of green sea turtles (Chelonia mydas)

All seven species of sea turtle are facing increasing pressures from human activities that are impacting their health. Changes in circulating blood proteins of an individual, or all members of a population, can provide an early indicator of adverse health outcomes. Non-targeted measurement of all detectable proteins in a blood sample can indicate physiological changes. In the context of wildlife toxicology, this technique can provide a powerful tool for discovering biomarkers of chemical exposure and effect. This study presents a non-targeted examination of the protein abundance in sea turtle plasma obtained from three geographically distinct foraging populations of green turtles (Chelonia mydas) on the Queensland coast. Relative changes in protein expression between sites were compared, and potential markers of contaminant exposure were investigated. Blood plasma protein profiles were distinct between populations, with 85 out of the 116 identified proteins differentially expressed (p < 0.001). The most strongly dysregulated proteins were predominantly acute phase proteins, suggestive of differing immune status between the populations. The highest upregulation of known markers of immunotoxicity, such as pentraxin fusion and complement factor h, was observed in the Moreton Bay turtles. Forty-five different organohalogens were also measured in green turtle plasma samples as exposure to some organohalogens (e.g., polychlorinated biphenyls) has previously been identified as a cause for immune dysregulation in marine animals. The few detected organohalogens were at very low (pg/mL) concentrations in turtles from all sites, and are unlikely to be the cause of the proteome differences observed. However, the changes in protein expression may be indicative of exposure to other chemicals or environmental stressors. The results of this study provide important information about differences in protein expression between different populations of turtles, and guide future toxicological and health studies on east-Australian green sea turtles.

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.

Trace element concentrations in forage seagrass species of Chelonia mydas along the Great Barrier Reef

Toxic metal exposure is a threat to green sea turtles (Chelonia mydas) inhabiting and foraging in coastal seagrass meadows and are of particular concern in local bays of the Great Barrier Reef (GBR), as numerous sources of metal contaminants are located within the region. Seagrass species tend to bioaccumulate metals at concentrations greater than that detected in the surrounding environment. Little is known regarding ecotoxicological impacts of environmental metal loads on seagrass or Chelonia mydas (C. mydas), and thus this study aimed to investigate and describe seagrass metal loads in three central GBR coastal sites and one offshore site located in the northern GBR. Primary seagrass forage of C. mydas was identified, and samples collected from foraging sites before and after the 2018/2019 wet season, and multivariate differences in metal profiles investigated between sites and sampling events. Most metals investigated were higher at one or more coastal sites, relative to data obtained from the offshore site, and cadmium (Cd), cobalt (Co), iron (Fe) and manganese (Mn) were found to be higher at all coastal sites. Principle Component Analysis (PCA) found that metal profiles in the coastal sites were similar, but all were distinctly different from that of the offshore data. Coastal foraging sites are influenced by land-based contaminants that can enter the coastal zone via river discharge during periods of heavy rainfall, and impact sites closest to sources. Bioavailability of metal elements are determined by complex interactions and processes that are largely unknown, but association between elevated metal loads and turtle disease warrants further investigation to better understand the impact of environmental contaminants on ecologically important seagrass and associated macrograzers.

Temporal changes in chemical contamination of green turtles (Chelonia mydas) foraging in a heavily industrialised seaport

Port Curtis, a major shipping port, has undergone significant expansion in the last decade, with plans for further development into the future. These activities may result in an increase of contaminant concentrations, threatening local wildlife including sea turtles. This study used a species-specific in vitro bioassay to examine spatial and temporal differences in exposure to, and effects of, organic contaminants in green sea turtles foraging in Port Curtis. Blood was collected from 134 green sea turtles (Chelonia mydas) from five locations in the port over four years. Organic contaminants were extracted from blood, and the cytotoxicity of the extracts to primary green sea turtle cells was assessed. Results indicated spatially similar chemical contamination throughout Port Curtis, at levels significant to sea turtle health, and with signs that chemical contamination may be increasing over time. These results can provide valuable information on the health of green turtles as further development occurs.

Systematic review of reptile reproductive toxicology to inform future research directions on endangered or threatened species, such as sea turtles

Threatened or endangered reptiles, such as sea turtles, are generally understudied within the field of wildlife toxicology, with even fewer studies on how contaminants affect threatened species reproduction. This paper aimed to better inform threatened species conservation by systematically and quantitatively reviewing available research on the reproductive toxicology of all reptiles, threatened and non-threatened. This review found 178 studies that matched our search criteria. These papers were categorized into location conducted, taxa studied, species studied, effects found, and chemicals investigated. The most studied taxa were turtles (n = 87 studies, 49%), alligators/crocodiles (n = 54, 30%), and lizards (n = 37, 21%). Maternal transfer, sex steroid alterations, sex reversal, altered sexual development, developmental abnormalities, and egg contamination were the most common effects found across all reptile taxa, providing guidance for avenues of research into threatened species. Maternal transfer of contaminants was found across all taxa, and taking into account the foraging behavior of sea turtles, could help elucidate differences in maternal transfer seen at nesting beaches. Sex steroid alterations were a common effect found with contaminant exposure, indicating the potential to use sex steroids as biomarkers along with traditional biomarkers such as vitellogenin. Sex reversal through chemical exposure was commonly found among species that exhibit temperature dependent sex determination, indicating the potential for both environmental pollution and climate change to disrupt population dynamics of many reptile species, including sea turtles. Few studies used in vitro, DNA, or molecular methodologies, indicating the need for more research using high-throughput, non-invasive, and cost-effective tools for threatened species research. The prevalence of developmental abnormalities and altered sexual development and function indicates the need to further study how anthropogenic pollutants affect reproductive output in threatened reptiles.