Next Article in Journal
Exploring the Roles of Dietary Herbal Essential Oils in Aquaculture: A Review
Next Article in Special Issue
Cellular Prion Protein Expression in the Brain Tissue from Brucella ceti-Infected Striped Dolphins (Stenella coeruleoalba)
Previous Article in Journal
Citrus Pulp Replacing Corn in the Supplement Decreased Fibre Digestibility with No Impacts on Performance of Cattle Grazing Marandu Palisade Grass in the Wet-Dry Transition Period
Order Article Reprints
Font Type:
Arial Georgia Verdana
Font Size:
Aa Aa Aa
Line Spacing:
Column Width:

A Correlational Analysis of Phthalate Exposure and Thyroid Hormone Levels in Common Bottlenose Dolphins (Tursiops truncatus) from Sarasota Bay, Florida (2010–2019)

Environmental and Sustainability Studies Graduate Program, College of Charleston, Charleston, SC 29424, USA
Environmental Health Sciences Graduate Program, University of South Carolina, Columbia, SC 29208, USA
Chicago Zoological Society’s Sarasota Dolphin Research Program, c/o Mote Marine Laboratory, Sarasota, FL 34236, USA
National Oceanic and Atmospheric Administration, National Ocean Service, National Centers for Coastal Ocean Science, Charleston, SC 29412, USA
Department of Health and Human Performance, College of Charleston, Charleston, SC 29424, USA
Authors to whom correspondence should be addressed.
Animals 2022, 12(7), 824;
Received: 10 February 2022 / Revised: 17 March 2022 / Accepted: 21 March 2022 / Published: 24 March 2022
(This article belongs to the Special Issue Frontiers in Marine Mammal Health and Immunity)



Simple Summary

Phthalate exposure is prevalent in common bottlenose dolphins sampled from Sarasota Bay, Florida. With evidence of potential adverse effects as identified in human and laboratory studies, there is a concern for bottlenose dolphin health. This study investigated potential correlations between serum hormone levels and urinary phthalate metabolite concentrations to begin to understand whether health effects would be expected in dolphins. We observed a positive relationship between free thyroxine and mono(2-ethylhexyl) phthalate (MEHP) for both adult female and male dolphins, suggesting potential associations with normal thyroid production.


Phthalates are chemical esters used to enhance desirable properties of plastics, personal care, and cleaning products. Phthalates have shown ubiquitous environmental contamination due to their abundant use and propensity to leach from products to which they are added. Following exposure, phthalates are rapidly metabolized and excreted through urine. Common bottlenose dolphins (Tursiops truncatus) sampled from Sarasota Bay, Florida, have demonstrated prevalent di(2-ethylhexyl) phthalate (DEHP) exposure indicated by detectable urinary mono(2-ethylhexyl) phthalate (MEHP) concentrations. Widespread exposure is concerning due to evidence of endocrine disruption from human and laboratory studies. To better understand how phthalate exposure may impact dolphin health, correlations between relevant hormone levels and detectable urinary MEHP concentrations were examined. Hormone concentrations measured via blood serum samples included triiodothyronine (T3), total thyroxine (T4), and free thyroxine (FT4). Urinary MEHP concentrations were detected in 56% of sampled individuals (n = 50; mean = 8.13 ng/mL; s.d. = 15.99 ng/mL). Adult female and male FT4 was significantly correlated with urinary MEHP concentrations (adult female Kendall’s tau = 0.36, p = 0.04; adult male Kendall’s tau = 0.42, p = 0.02). Evidence from this study suggests DEHP exposure may be impacting thyroid hormone homeostasis. Cumulative effects of other stressors and resultant endocrine impacts are unknown. Further research is warranted to understand potential health implications associated with this relationship.

1. Introduction

Phthalates are a class of man-made chemical esters commonly used as plasticizers to increase the flexibility and durability of polyvinyl chloride (PVC) [1]. As an extremely versatile additive, phthalate use is not limited to PVC but includes a myriad of consumer goods such as personal care products, packaging, agricultural insecticides and pesticides, and medical devices [1,2,3]. Phthalates can easily leach from the products to which they are added [4,5], providing abundant exposure opportunities for humans and wildlife. Human exposure can occur via dermal absorption [6], ingestion [7], inhalation [8], or through intravenous medical device usage [9]. Following exposure, phthalate parent compounds are rapidly metabolized and excreted through urine and feces as metabolites [10,11]. As a result, phthalate exposure is signaled by detectable phthalate metabolite concentrations.
Phthalates are considered endocrine-disrupting chemicals (EDCs) and have been linked with altered hormone concentrations, including reproductive (e.g., reduced testosterone and elevated progesterone [12,13,14]), adrenal (e.g., reduced cortisol and aldosterone [15,16]), and thyroid hormones (e.g., reduced triiodothyronine and free thyroxine [16]). Laboratory rodent studies and human observational studies have demonstrated that endocrine disruption can vary and is likely dependent on a number of factors, including phthalate ester type [17], dose [18], exposure window [19], species [20], sex [21], age [22], and pregnancy status [23]. Toxin metabolism generally occurs in at least two steps: phase I hydrolysis followed by phase II conjugation [24]. Long-branched phthalates, such as di-(2-ethylhexyl) phthalate (DEHP), may undergo further hydroxylation and oxidation in order to be excreted [24]. The metabolic process involves the peroxisome proliferator-activated receptor alpha (PPAR-α), which can be activated by mono(2-ethylhexyl) phthalate (MEHP) [25]. PPARs are nuclear receptors responsible for cholesterol uptake and transport; so, proliferation may play a role in downregulated steroidogenesis [26,27,28].
Evidenced in epidemiological and laboratory studies, this endocrine disruption may result in male reproductive abnormalities (e.g., malformations of external genitalia [29,30] and altered sperm function [31,32]), early pregnancy loss [33], disrupted male sexual differentiation [29], increased breast cancer risk [34], increased oxidative stress [35], and adverse effects on growth and development [36]. The timing of exposure (e.g., pre/postnatal) seems to be an important determinant in the severity of some phthalate-mediated health impacts; previous studies have linked phthalate exposure with severe fetal neurodevelopmental impacts [22,37]. Similarly, gestational, and perinatal phthalate exposure may have long-term health implications, even after exposure has ceased [38,39]. Previous phthalate studies have focused on humans and rodents; so, health effects detected in other higher-order mammalian species are not well studied.
Recently, prevalent phthalate exposure has been detected in free-ranging common bottlenose dolphins (Tursiops truncatus) that are long-term residents of Sarasota Bay, Florida (i.e., ~75% of sampled individuals had detectable urinary concentrations of at least one phthalate metabolite [40,41,42]). Dziobak et al. (2021) did not find demographic-dependent susceptibility to exposure, and some metabolite concentrations exceeded levels reported for human reference populations [42]. Higher dolphin MEHP concentrations were notable considering humans are exposed to phthalates through the active use of phthalate-containing products, while dolphins are exposed due to environmental contamination. Specific sources and persistence of phthalate exposure are still unknown; but, given that DEHP exhibits low water solubility and preferentially partitions to suspended particles and sediments in water [1,43], dolphin exposure could rely on food-based sources (e.g., consuming microplastic-contaminated prey that may release phthalates [44]). The health impacts from this heightened exposure in dolphins are currently unknown. Epidemiological studies have been conducted to understand relationships between marine mammal health impacts and exposure to polychlorinated biphenyls (PCBs) [45], organochlorine pesticides (OCPs) [45], and polybrominated diphenyl ethers (PBDEs) [45], thus providing a framework for the exploration of hormonal correlates with phthalate exposure. Unlike these environmentally persistent chemicals that have been observed to bioaccumulate in dolphin tissue, phthalates’ metabolism is expected to occur rapidly [11]; however, the exact mechanism in dolphins is unknown.
The ongoing release of phthalates into the environment [46] presents a chronic exposure risk for this community. Given the high prevalence of MEHP exposure in dolphins, MEHP concentrations that exceed human reference populations, and the potential for phthalate-induced endocrine disruption, the objective of this study was to examine the relationship between urinary MEHP concentrations and a suite of hormones (adrenal, reproductive, and thyroid) in free-ranging bottlenose dolphins. Chronic phthalate exposure has been observed to negatively impact human health; so, similar health impacts may be expected for Sarasota Bay dolphins as well. Findings from this study can be used to better understand the extent of estuarine phthalate contamination and potential health risks to exposed wildlife.

2. Materials and Methods

2.1. Dolphin Community and Sample Collection

Dolphins sampled for this study were individuals considered to be members of the year-round, multi-decadal, multi-generational resident community in Sarasota Bay, FL, USA (n~160) [47]. High site fidelity has enabled long-term research efforts regarding the life history, behavior, and health of this population [48,49]. Urine and blood samples for this study (2010–2019) were collected during routine, periodic, catch-and-release health assessments [48,50] conducted under Scientific Research Permits #522-1785, #15543, and #20455 from the National Oceanic and Atmospheric Administration’s (NOAA) National Marine Fisheries Service (NMFS). All catch-and-release and sampling methodologies for the health assessments were reviewed and approved annually by Mote Marine Laboratory’s Institutional Animal Care and Use Committee (IACUC). Blood was drawn prior to other biological sampling, so all individuals sampled for urine had corresponding blood samples. Some dolphins (n = 13) were sampled more than once, but the analyses conducted herein relied upon the most recently obtained sample.
Blood and urine collection methods have been previously described [48,51,52]. Briefly, blood was drawn from the ventral fluke via butterfly catheter into serum separator tubes. Serum samples were kept at room temperature for 45 min before being centrifuged and frozen in liquid nitrogen in preparation for overnight shipment. Samples were shipped to Cornell University’s Animal Health Diagnostic Center’s (AHDC) Endocrinology Laboratory (Ithaca, NY, USA) for hormone analyses. Following blood draw, dolphins were brought aboard a specially designed veterinary examination vessel where urine was opportunistically collected. Standardized urine collection methods as previously reported [41,50] involved insertion of a catheter (Kendall Sovereign Feeding Tube and Urethral Catheter 8Fr/Ch × 22 in 27 mm × 56 cm, Covidien, Dublin, Ireland) coated with a sterile surgical lubricant (Surgilube®, Stoelting, Wood Dale, IL, USA) into the urethra by a trained veterinarian.

2.2. Sample Processing and Analysis

Analysis, quantification, and quality control methods for urinary phthalate metabolite screening have been described [40,41], and were based on protocols established by the Centers for Disease Control and Prevention (CDC). Individual urine samples were analyzed in batches, and quality assurance/quality control (QA/QC) samples (reagent blanks, field blanks, reagent spikes, matrix spikes, and SRM 3672 Organic Contaminants in Smokers’ Urine) were processed concurrently [40,41]. Sample integrations were performed using Analyst software (ver 1.5, SCIEX, Framingham, MA, USA). MEHP, the first metabolite of di(2-ethylhexyl) phthalate (DEHP; ATSDR, 2019), was the most frequently reported metabolite by Dziobak et al. (2021) and used for analyses herein. Serum sent to AHDC was analyzed for triiodothyronine (T3), total thyroxine (T4), and free thyroxine (FT4) concentrations. Hormone analyses using Siemens Immulite Total T3 Chemiluminescent Assay (Gwynedd, United Kingdom; LOD = 19 ng/dL), Siemens Immulite Total T4 Chemiluminescent Assay (Gwynedd, United Kingdom; LOD = 0.30 ug/dL), and Antech Free T4 by Dialysis Radioimmunoassay (Irvine, CA, USA; LOD = 0.15 ng/dL) kits were performed by one laboratory at Cornell University as inter-laboratory variations can be significant [51].

2.3. Statistical Methods

Descriptive statistics were used to summarize phthalate metabolite concentrations and measured hormone levels overall and by sex and age class. Dolphins were classified as juveniles or adults based on sexual maturity status as determined by several factors including age, pregnancy diagnosis, calving history, and sex hormone concentrations [41]. Thyroid hormone values lower than the limit of detection (LOD) were set to zero [53], and phthalate metabolite data as reported in Dziobak et al. (2021) were used for descriptive, bivariate, and correlational analyses. Censored analyses were performed for any analyte where at least 20% of the values were below LOD to compare demographically and generate Kendall’s tau (NADA2 R package, R Foundation for Statistical Computing, Vienna, Austria) [54]. A Shapiro–Wilk test was used to evaluate the Gaussian distribution of each analyte. For analytes that were distributed normally, an independent t-test was used to compare concentrations demographically. Censored analytes were compared demographically with a permutation test of differences [55]. Samples from pregnant dolphins were excluded from analysis [56,57] (n = 1).
Demographic stratification strategies were determined by generalized linear modeling (GLM), which identified significant relationships with sex, age class, and the interaction of sex and age class. Relationships between MEHP and thyroid hormones were analyzed using the Akritas–Theil–Sen (ATS) line for censored data to compute Kendall’s tau correlation coefficient and p-value. Following previously reported values [40,41,42], sample normalization (via creatinine or specific gravity) was not conducted prior to quantification. All statistical analyses were conducted using Statistica (Version 13, Dell Inc., Round Rock, TX, USA) and R (Version 3.2, R Foundation for Statistical Computing, Vienna, Austria) software packages. Statistical significance was evaluated using α = 0.05.

3. Results

Excluding repeated sampling events and pregnancies, 50 matched serum and urine samples were collected from unique Sarasota Bay dolphins during 2010–2019 (female n = 29; male n = 21; adult n = 33; juvenile n = 17). A total of 56% of individuals demonstrated detectable urinary MEHP concentrations. Adult females (n = 29) had the highest MEHP detection frequency (66.67%), and adult males (n = 21) had the lowest (43.75%; Table S3). T4 and FT4 were detected in 100% of individuals (Table 1).
MEHP and thyroid hormone concentrations are summarized by sex and age class in Table 2 and Table 3, respectively. A permutation test of differences found no variation in MEHP concentrations between sexes (p = 0.16) or age classes (p = 0.25). Results from the GLM identified a significant association between age class and T4 (p < 0.0001), as well as a significant association between both sex and age class parameters and FT4 (p < 0.05; Table 4). The interaction of sex and age class was not significantly associated with any thyroid hormone.
In adult females and males, FT4 exhibited a significant positive correlation with MEHP (Figure 1 and Figure 2). The remaining hormones, T3 and T4, were not significantly associated with MEHP, regardless of the stratification method (Table S1).

4. Discussion

4.1. Overall Findings

To our knowledge, this is the first study investigating phthalate-associated endocrine disruption in free-ranging dolphins. We examined relationships between thyroid hormones and urinary MEHP concentrations in Sarasota Bay dolphins sampled during 2010–2019. FT4 values reported in this study were similar to values previously reported for dolphins sampled from Sarasota Bay [56,58]. FT4 values from this study were also similar to ranges reported for dolphins sampled near Charleston, South Carolina [59]; however, values from different locations may not be comparable. Thyroid hormone concentrations can vary based on the specific conditions present at each location (e.g., water temperature, prey availability, and nutritional quality of prey [58,59]). FT4 was found to be significantly related to MEHP for both adult females and males, suggesting a potential role in thyroid homeostasis. In humans, MEHP is generally inversely associated with FT4 levels [16,23]; however, some studies of female children have found a positive relationship [21,60]. In fact, Weng et al. (2017) reported similar results to this study, where MEHP was positively associated with FT4 in girls, but was not associated with T3 or T4. Disrupted thyroid function appears to be more prevalent in women compared to men [61], potentially related to the sex-specific regulation of thyroid hormones in the brain [62]. Still, significant associations between MEHP and FT4 have been demonstrated in adult male humans [16]. Health effect differences reported in human studies could be due to phthalate metabolism differences. Compared to adults, children have reduced toxin-metabolizing enzymes and diminished renal excretion capacity [63,64], which could affect their ability to metabolize phthalates. In fact, children have shown higher excretion levels of oxidized DEHP metabolites (e.g., mono(2-ethyl-5-oxo-hexyl) phthalate (MEOHP) and mono(2-ethyl-5-hydroxyhexyl) phthalate (MEHHP)) than adults, implying age-related differences in phthalate elimination routes [65,66].
Phthalate metabolism is likely different between humans and dolphins as well; Kluwe (1982) observed variations in DEHP metabolism among terrestrial mammals, and differences in the ability to metabolize other common marine contaminants (e.g., PCBs) have been observed in marine–terrestrial mammal comparative studies [67]. Thus, it is reasonable to expect marine mammal differences in phthalate metabolism. Additionally, measured thyroid weight-to-body weight ratios are reportedly higher in dolphins than terrestrial mammals [68], further suggesting the potential for metabolic differences. It is important to consider metabolic capabilities with regards to expected health outcomes because different chemical forms exhibit different bioactivities. Metabolism is generally known to detoxify and facilitate excretion of xenobiotics; however, DEHP metabolism has been shown to increase toxicity as MEHP is the more bioactive form [69,70]. As a result, it might be expected that differing metabolic capabilities would result in different associated health impacts as well. Further research is needed to understand whether the determined association between MEHP and FT4 is impacting dolphin health.

4.2. Mechanisms of Disruption

The mechanisms of DEHP-induced thyroid disruption are not well understood. The thyroid-stimulating hormone (TSH) mediates thyroid hormone release by stimulating the thyroid gland [71]. Previous studies have linked DEHP exposure with thyroid gland hyperactivity in that exposure was associated with increases in T3 and T4 [72] as well as physical changes to the gland consistent with hyperactivity (e.g., shrunken colloid, hypertrophy of the Golgi apparatus, and dilation of the rough endoplasmic reticulum [73]). While not completely understood, there is evidence from zebrafish models suggesting that DEHP may upregulate mRNA expression of the TSH gene, resulting in increased T4 levels [74]. Since TSH can initiate T4 synthesis, perhaps the observed increase was a direct result of abnormal gene expression [74] The relationship we found between MEHP and FT4 in this study may also be due to interferences with transthyretin (TTR). TTR is a transport protein mainly responsible for binding and transporting T4 [75]. DEHP exposure may inhibit TTR internalization and expression [76] or competitively bind to TTR [77,78], resulting in higher levels of FT4. TSH is sensitive to minor changes in thyroid hormones; so, future research should examine relationships between MEHP and TSH.

4.3. Implications of Thyroid Dysfunction

Thyroid hormones, through regulation of growth, thermogenesis, and metabolism, affect virtually every organ system [79]. As a result, deviations from normal levels can significantly impact overall health. Hyperthyroidism, characterized by increased thyroid levels, has been associated with dementia [80], all-cause mortality [81], and frailty in adult men (i.e., multiple organ system deterioration that leads to diminished capacity to cope with stressors, and increased risk of death and disability [80]) as well as bone deterioration in postmenopausal women [82]. Non-sex-specific associations with hyperthyroidism include increased low-density lipoprotein cholesterol [83] and thyroid cancer [84,85]. It is not understood how the relationship between adult FT4 and MEHP will affect dolphin health, but outcomes observed in hyperthyroidic humans raise concerns. While adult thyroid disruption can lead to serious consequences, related health impacts may be more severe for developing fetuses. Fetuses do not produce their own thyroxine and, instead, rely on maternal inputs to maintain normal thyroid function [86,87]. In humans, maternal hyperthyroidism can result in reduced fetal growth, low birth weight, and even fetal death [88]. Currently, the broader health impacts of hyperthyroidism are unknown for bottlenose dolphins; but, in harbor seals, hyperthyroidism has resulted in significant impacts to energy metabolism during diving, such as increased post-dive lactate concentrations and decline in heart rate [89]. For bottlenose dolphins, additional research on impacts from thyroid imbalance is warranted.

4.4. Triiodothyronine (T3)

We did not find significant correlations between MEHP and T3. Given the relationship with FT4, the lack of correlation between MEHP and T3 was surprising. Previous contaminant studies have demonstrated concurrent associations with T3 and FT4 [16,58]. While the thyroid gland releases some T3, the majority is produced through T4 deiodination [71,90]. As a result, it would be expected that an association between MEHP and FT4 would also be observed with T3; however, this was not the case with dolphins. This could be a result of sample size limitations as not every dolphin had detectable T3 levels. A post hoc power analysis was conducted and found power for the correlations was less than the 80% threshold previously determined [91] (Table S2). A larger sample size is warranted to establish whether the findings from this study are true. It is also possible that feedback mechanisms regulating hormone production prevented MEHP-related fluctuations in T3. Thyroid hormone signaling is substantially modulated by deiodinases that enzymatically activate or deactivate thyroid hormones [92,93]. In cases of increased T4, deiodinases can inactivate T3 as well as prevent further activation of T4, thus providing some measure of protection against hyperthyroidism [94].
While sample size and biological or physiological differences between bottlenose dolphins and humans may partially explain deviations from laboratory and human epidemiological findings, extrinsic factors, such as exposure to contaminant mixtures, should also be considered. For example, Sarasota Bay dolphins are exposed to a mixture of toxins and toxicants related to thyroid function (PCB mixtures [45,49]); but, we are uncertain how endocrine homeostasis is impacted by chemical mixtures. Further study is warranted to investigate synergistic or antagonistic impacts of DEHP exposure and concurrent exposure to other environmental contaminants.

4.5. Strengths and Limitations

This was the first investigation to correlate urinary phthalate metabolite concentrations with circulating hormone levels in dolphins, providing insight into potential health effects posed by phthalate exposure. Long-term monitoring programs and periodic health assessments conducted in Sarasota Bay facilitated biological sample collection over a 10-year sampling period, which helped to maximize sample sizes for correlation assessments by key demographic factors. This stratification is necessary for analyses of sex- and age-dependent hormones. We used matched samples so that urinary phthalate metabolite and hormone concentrations were obtained from the same dolphin. Additionally, we employed statistical methods that included values below LOD to examine hormonal relationships with dolphins that had little to no indication of phthalate exposure. Seasonality can significantly alter circulating thyroid hormone concentrations, where decreased concentrations of thyroid hormones have been linked with increased water temperatures [59]. The majority of samples from this study were collected in May, with some sampling occurring in June and July. Water temperature from May to July typically ranges from 79° F to 86° F [95]; so, significant, seasonal fluctuations in thyroid hormones would not be expected.
This study relied on opportunistic sampling of wild dolphin urine and blood, limiting our ability to select individuals based on desired demographics. As a result, we had an uneven distribution of individuals between age classes, which may have limited our ability to detect correlations when age class was used as a stratification method, particularly for juvenile dolphins. While phthalates are not expected to be stored in tissue [11], recent studies have provided some evidence for phthalate metabolite detection in marine mammal blubber (e.g., MEHP detected in harbor porpoises, Phocoena phocoena [96], and fin whales, Balaenoptera physalus [97]). As such, dolphin body condition may play a role in phthalate bioavailability for metabolism; however, further research is needed to understand this potential relationship. Additionally, our analyses only focused on linkages between hormones and phthalate exposure; however, Sarasota Bay dolphins are also exposed to other toxins and toxicants with endocrine-disrupting effects (e.g., PCBs [45,49,98], hexachlorobenzene (HCB) [98], mercury [99], OCPs [45], and PBDEs [45]). Potential cumulative and interactive effects between phthalates and other contaminants are not yet understood for bottlenose dolphins; however, multiple stressors can interact additively, synergistically, or antagonistically, and potentially result in significantly different effects [100]. Relationships between circulating hormone levels and chemical contaminant detection in dolphins have been reported for PCBs [53,58], DDTs [53], chlordane [53], mirex [53], dieldrin [53], HCB [53], and brominated diphenyl ethers (BDEs) [53]. As many of these chemicals have also been detected in Sarasota Bay dolphins, phthalate exposure may be one of many influences on endocrine function. For example, significant interactive effects have been reported between PCBs and DEHP, resulting in reproductive impairment in humans, dogs, and rats [101,102]. As such, interactive effects between PCBs and DEHP may be observed in dolphins as well. Future studies should seek to identify the pollutant mixtures in Sarasota Bay and examine relationships between determined contaminants and circulating hormone levels to further elucidate potential mechanisms of hormone impairment. The relationship between FT4 and MEHP reported in this study may be true; however, other factors, such as diet, have also been shown to alter FT4 concentrations. Although not statistically significant, a decrease in bottlenose dolphin FT4 has been observed during fasting, followed by an increase in FT4 up to 11 h after re-feeding as compared to baseline levels [103]. As a result, there is the potential for the observed relationship to be associated with factors other than phthalate exposure.

5. Conclusions

Potential health risks posed by phthalate exposure are complex and rely on numerous factors to determine specific endpoints. Exposure to a chemical can influence disease processes through multiple mechanisms of action; so, it is important to investigate multiple avenues of potential health effects. Bottlenose dolphins from Sarasota Bay, Florida, were evaluated for relationships between detectable phthalate metabolite concentrations and circulating hormone levels. In adult female dolphins, FT4 was found to have a significant relationship with MEHP. Health effects resulting from this association are currently unknown; so, further monitoring of thyroid hormone levels is warranted. Hyperthyroidism indicated by elevated FT4 levels has been associated with weight loss in humans and dogs [104,105]; so, monitoring dolphin body condition may provide preliminary insight into potential thyroid disruption. Human biomonitoring studies have shown decreased MEHP detection in recent years; however, sources of dolphin exposure to DEHP are likely different as dolphins have demonstrated significantly higher MEHP concentrations compared to human reference populations. Currently, the only restriction on phthalate use is a rule written by the Consumer Product Safety Commission (CPSC) enacted in April 2018. This rule permanently prohibits any children’s toy or childcare article from containing more than 0.1% of a series of phthalates, including DEHP, dibutyl phthalate (DBP), benzyl butyl phthalate (BBP), diisononyl phthalate (DINP), diisobutyl phthalate (DIBP), di-n-pentyl phthalate (DPENP), di-n-hexyl phthalate (DHEXP), and dicyclohexyl phthalate (DCHP) [106]. Some states have implemented restrictions providing further protections than the federal regulations. California, for example, has become the first state to ban DBP and DEHP from cosmetic and personal care product formulations [107]. This bill will not be completely enacted until 2025, so it is unclear how effective these measures may be in mitigating phthalate exposure. Consideration of further mitigation measures may be required to promote wildlife health.

Supplementary Materials

The following supporting information can be downloaded at Table S1: Kendall’s tau correlation coefficient and p-values between mono(2-ethylhexyl) phthalate and hormones in common bottlenose dolphins (Tursiops truncatus) sampled from Sarasota Bay, Florida (2010–2019). Statistical significance observed at α = 0.05 (n = 50); Kendall’s tau (p). Table S2: Power analysis for correlations between mono(2-ethylhexyl) phthalate (MEHP) and hormones in urine sampled from common bottlenose dolphins (Tursiops truncatus) sampled from Sarasota Bay, Florida, during 2010–2019. Table S3: Analyte detection frequency by demographic group for common bottlenose dolphins (Tursiops truncatus) sampled from Sarasota Bay, Florida, during 2010–2019.

Author Contributions

Conceptualization, L.B.H.; methodology, L.B.H.; validation, M.K.D. and E.C.P.; formal analysis, M.K.D. and L.B.H.; investigation, M.K.D., R.S.W. and L.B.H.; resources, R.S.W., E.C.P. and E.F.W.; data curation, R.S.W., L.B.H. and E.F.W.; writing—original draft preparation, M.K.D. and L.B.H.; writing—review and editing, R.S.W., E.C.P. and E.F.W.; visualization, M.K.D. and L.B.H.; supervision, L.B.H.; project administration, R.S.W. and L.B.H.; funding acquisition, M.K.D., R.S.W. and L.B.H. All authors have read and agreed to the published version of the manuscript.


Funding for this work was provided by an anonymous donor and internal grants from the College of Charleston’s Master of Environmental and Sustainability Studies Student Association, School of Humanities and Social Sciences, Graduate School Office, School of Education, Health, and Human Performance, and the Department of Health and Human Performance.

Institutional Review Board Statement

Urine and blood samples for this study (2010–2019) were collected during routine, periodic, catch-and-release health assessments conducted under Scientific Research Permits #522-1785, #15543, and #20455 from the National Oceanic and Atmospheric Administration’s (NOAA) National Marine Fisheries Service (NMFS). All catch-and-release and sampling methodologies for the health assessments were reviewed and approved annually by Mote Marine Laboratory’s Institutional Animal Care and Use Committee (IACUC).

Data Availability Statement

Restrictions apply to the availability of these data. Dolphin hormone data were obtained from The Sarasota Dolphin Research Program (SDRP) and are available from the authors with the permission of SDRP. The phthalate data used for this study can be accessed through the 4TU.Research Data international data repository for science, engineering, and design Accessed 17 April 2021.


We thank Ashley Boggs-Russell, Peter Key, Tessa Pfeifer, and journal peer-reviewers for their assistance in enhancing the manuscript. Dolphin samples were obtained through health assessments supported primarily by Dolphin Quest, Inc. We are grateful to the staff, collaborators, and volunteers of the Sarasota Dolphin Research Program for ensuring the safe capture, sampling, and release of the dolphins.

Conflicts of Interest

The authors declare no conflict of interest.


The scientific results and conclusions, as well as any views or opinions expressed herein, are those of the author(s) and do not necessarily reflect those of NOAA or the Department of Commerce.


  1. ATSDR. Toxicological Profile for Di(2-Ethylhexyl)Phthalate (DEHP); Draft for Public Comment; ATSDR: Atlanta, GA, USA, 2019.
  2. ATSDR. Toxicological Profile for Diethyl Phthalate; ATSDR: Atlanta, GA, USA, 1995. [CrossRef]
  3. ATSDR. Toxicological Profile for Di-n-Butyl Phthalate; ATSDR: Atlanta, GA, USA, 2001.
  4. Aurela, B.; Kulmala, H.; Soderhjelm, L. Phthalates in Paper and Board Packaging and Their Migration into Tenax and Sugar. Food Addit. Contam. 1999, 16, 571–577. [Google Scholar] [CrossRef] [PubMed]
  5. FDA. Safety Assessment of Di (2-Ethylhexyl) Phthalate (DEHP) Released from PVC Medical Devices; FDA: White Oak, MA, USA, 2001.
  6. Sugino, M.; Hatanaka, T.; Todo, H.; Mashimo, Y.; Suzuki, T.; Kobayashi, M.; Hosoya, O.; Jinno, H.; Juni, K.; Sugibayashi, K. Safety Evaluation of Dermal Exposure to Phthalates: Metabolism-Dependent Percutaneous Absorption. Toxicol. Appl. Pharmacol. 2017, 328, 10–17. [Google Scholar] [CrossRef] [PubMed][Green Version]
  7. Serrano, S.E.; Braun, J.; Trasande, L.; Dills, R.; Sathyanarayana, S. Phthalates and Diet: A Review of the Food Monitoring and Epidemiology Data. In Environmental Health: A Global Access Science Source; BioMed Central Ltd.: London, UK, 2014; p. 43. [Google Scholar] [CrossRef][Green Version]
  8. Fromme, H.; Lahrz, T.; Kraft, M.; Fembacher, L.; Dietrich, S.; Sievering, S.; Burghardt, R.; Schuster, R.; Bolte, G.; Völkel, W. Phthalates in German Daycare Centers: Occurrence in Air and Dust and the Excretion of Their Metabolites by Children (LUPE 3). Environ. Int. 2013, 61, 64–72. [Google Scholar] [CrossRef]
  9. Green, R.; Hauser, R.; Calafat, A.M.; Weuve, J.; Schettler, T.; Ringer, S.; Huttner, K.; Hu, H. Use of Di(2-Ethylhexyl) Phthalate-Containing Medical Products and Urinary Levels of Mono(2-Ethylhexyl) Phthalate in Neonatal Intensive Care Unit Infants. Environ. Health Perspect. 2005, 113, 1222–1225. [Google Scholar] [CrossRef] [PubMed][Green Version]
  10. Genuis, S.J.; Beesoon, S.; Lobo, R.A.; Birkholz, D. Human Elimination of Phthalate Compounds: Blood, Urine, and Sweat (BUS) Study. Sci. World J. 2012, 2012, 615068. [Google Scholar] [CrossRef] [PubMed][Green Version]
  11. Staples, C.A.; Peterson, D.R.; Parkerton, T.F.; Adams, W.J. The Environmental Fate of Phthalate Esters: A Literature Review. Chemosphere 1997, 35, 667–749. [Google Scholar] [CrossRef]
  12. Brehm, E.; Rattan, S.; Gao, L.; Flaws, J.A. Prenatal Exposure to Di(2-Ethylhexyl) Phthalate Causes Long-Term Transgenerational Effects on Female Reproduction in Mice. Endocrinology 2018, 159, 795–809. [Google Scholar] [CrossRef] [PubMed]
  13. Meeker, J.D.; Ferguson, K.K. Urinary Phthalate Metabolites Are Associated with Decreased Serum Testosterone in Men, Women, and Children from NHANES 2011–2012. J. Clin. Endocrinol. Metab. 2014, 99, 4346–4352. [Google Scholar] [CrossRef] [PubMed][Green Version]
  14. Sathyanarayana, S.; Barrett, E.; Butts, S.; Wang, C.; Swan, S.H. Phthalate Exposure and Reproductive Hormone Concentrations in Pregnancy. Reproduction 2014, 147, 401–409. [Google Scholar] [CrossRef]
  15. Martinez-Arguelles, D.B.; Campioli, E.; Lienhart, C.; Fan, J.; Culty, M.; Zirkin, B.R.; Papadopoulos, V. In Utero Exposure to the Endocrine Disruptor Di-(2-Ethylhexyl) Phthalate Induces Long-Term Changes in Gene Expression in the Adult Male Adrenal Gland. Endocrinology 2014, 155, 1667–1678. [Google Scholar] [CrossRef] [PubMed][Green Version]
  16. Meeker, J.D.; Calafat, A.M.; Hauser, R. Di(2-Ethylhexyl) Phthalate Metabolites May Alter Thyroid Hormone Levels in Men. Environ. Health Perspect. 2007, 115, 1029–1034. [Google Scholar] [CrossRef]
  17. Meeker, J.D.; Calafat, A.M.; Hauser, R. Urinary Metabolites of Di(2-Ethylhexyl) Phthalate Are Associated with Decreased Steroid Hormone Leveis in Adult Men. J. Androl. 2009, 30, 287–297. [Google Scholar] [CrossRef] [PubMed]
  18. Wang, X.; Wang, L.; Zhang, J.; Yin, W.; Hou, J.; Zhang, Y.; Hu, C.; Wang, G.; Zhang, R.; Tao, Y.; et al. Dose-Response Relationships between Urinary Phthalate Metabolites and Serum Thyroid Hormones among Waste Plastic Recycling Workers in China. Environ. Res. 2018, 165, 63–70. [Google Scholar] [CrossRef] [PubMed]
  19. Johns, L.E.; Ferguson, K.K.; McElrath, T.F.; Mukherjee, B.; Meeker, J.D. Associations between Repeated Measures of Maternal Urinary Phthalate Metabolites and Thyroid Hormone Parameters during Pregnancy. Environ. Health Perspect. 2016, 124, 1808–1815. [Google Scholar] [CrossRef][Green Version]
  20. Johnson, K.J.; McDowell, E.N.; Viereck, M.P.; Xia, J.Q. Species-Specific Dibutyl Phthalate Fetal Testis Endocrine Disruption Correlates with Inhibition of SREBP2-Dependent Gene Expression Pathways. Toxicol. Sci. 2011, 120, 460–474. [Google Scholar] [CrossRef] [PubMed]
  21. Morgenstern, R.; Whyatt, R.M.; Insel, B.J.; Calafat, A.M.; Liu, X.; Rauh, V.A.; Herbstman, J.; Bradwin, G.; Factor-Litvak, P. Phthalates and Thyroid Function in Preschool Age Children: Sex Specific Associations. Environ. Int. 2017, 106, 11–18. [Google Scholar] [CrossRef] [PubMed]
  22. Kim, Y.; Ha, E.H.; Kim, E.J.; Park, H.; Ha, M.; Kim, J.H.; Hong, Y.C.; Chang, N.; Kim, B.N. Prenatal Exposure to Phthalates and Infant Development at 6 Months: Prospective Mothers and Children’s Environmental Health (MOCEH) Study. Environ. Health Perspect. 2011, 119, 1495–1500. [Google Scholar] [CrossRef] [PubMed][Green Version]
  23. Kim, M.J.; Moon, S.; Oh, B.C.; Jung, D.; Choi, K.; Park, Y.J. Association between Diethylhexyl Phthalate Exposure and Thyroid Function: A Meta-Analysis. Thyroid 2019, 29, 183–192. [Google Scholar] [CrossRef] [PubMed]
  24. Frederiksen, H.; Skakkebæk, N.E.; Andersson, A.M. Metabolism of Phthalates in Humans. Mol. Nutr. Food Res. 2007, 51, 899–911. [Google Scholar] [CrossRef] [PubMed]
  25. Lapinskas, P.J.; Brown, S.; Leesnitzer, L.M.; Blanchard, S.; Swanson, C.; Cattley, R.C.; Corton, J.C. Role of PPARα in Mediating the Effects of Phthalates and Metabolites in the Liver. Toxicology 2005, 207, 149–163. [Google Scholar] [CrossRef] [PubMed]
  26. Borch, J.; Metzdorff, S.B.; Vinggaard, A.M.; Brokken, L.; Dalgaard, M. Mechanisms Underlying the Anti-Androgenic Effects of Diethylhexyl Phthalate in Fetal Rat Testis. Toxicology 2006, 223, 144–155. [Google Scholar] [CrossRef] [PubMed]
  27. Casals-Casas, C.; Desvergne, B. Endocrine Disruptors: From Endocrine to Metabolic Disruption. Annu. Rev. Physiol. 2011, 73, 135–162. [Google Scholar] [CrossRef] [PubMed][Green Version]
  28. Ito, Y.; Kamijima, M.; Nakajima, T. Di(2-Ethylhexyl) Phthalate-Induced Toxicity and Peroxisome Proliferator-Activated Receptor Alpha: A Review. Environ. Health Prev. Med. 2019, 24, 47. [Google Scholar] [CrossRef] [PubMed][Green Version]
  29. Parks, L.G.P.; Ostby, J.S.; Lambright, C.R.; Abbott, B.D.; Klinefelter, G.R.; Barlow, N.J.; Gray Jr, L.E. The Plasticizer Diethylhexyl Phthalate Induces Malformations by Decreasing Fetal Testosterone Synthesis during Sexual Differentiation in the Male Rat. Toxicol. Sci. 2000, 58, 339–349. [Google Scholar] [CrossRef] [PubMed]
  30. Swan, S.H.; Sathyanarayana, S.; Barrett, E.S.; Janssen, S.; Liu, F.; Nguyen, R.H.N.N.; Redmon, J.B.; TIDES Study Team. First Trimester Phthalate Exposure and Anogenital Distance in Newborns. Hum. Reprod. 2015, 30, 963–972. [Google Scholar] [CrossRef] [PubMed]
  31. Duty, S.M.; Silva, M.J.; Barr, D.B.; Brock, J.W.; Ryan, L.; Chen, Z.; Herrick, R.F.; Christiani, D.C.; Hauser, R.; Silva, M.; et al. Phthalate Exposure and Human Semen Parameters. Epidemiology 2003, 14, 269–277. [Google Scholar] [CrossRef] [PubMed]
  32. Hauser, R.; Meeker, J.D.; Singh, N.P.; Silva, M.J.; Ryan, L.; Duty, S.; Calafat, A.M. DNA Damage in Human Sperm Is Related to Urinary Levels of Phthalate Monoester and Oxidative Metabolites. Hum. Reprod. 2007, 22, 688–695. [Google Scholar] [CrossRef] [PubMed][Green Version]
  33. Toft, G.; Jönsson, B.A.G.; Lindh, C.H.; Jensen, T.K.; Hjollund, N.H.; Vested, A.; Bonde, J.P. Association between Pregnancy Loss and Urinary Phthalate Levels around the Time of Conception. Environ. Health Perspect. 2012, 120, 458–463. [Google Scholar] [CrossRef] [PubMed][Green Version]
  34. Crobeddu, B.; Ferraris, E.; Kolasa, E.; Plante, I. Di(2-Ethylhexyl) Phthalate (DEHP) Increases Proliferation of Epithelial Breast Cancer Cells through Progesterone Receptor Dysregulation. Environ. Res. 2019, 173, 165–173. [Google Scholar] [CrossRef] [PubMed]
  35. Zhou, L.; Beattie, M.C.; Lin, C.-Y.; Liu, J.; Traore, K.; Papadapolous, V.; Zirkin, B.R.; Chen, H. Oxidative Stress and Phthalate-Induced down-Regulation Ofsteroidogenesis in MA-10 Leydig Cells. Reprod. Toxicol. 2013, 42, 95–101. [Google Scholar] [CrossRef] [PubMed][Green Version]
  36. Brucker-Davis, F. Effects of Environmental Synthetic Chemicals on Thyroid Function. Thyroid 1998, 8, 827–856. [Google Scholar] [CrossRef] [PubMed]
  37. Ghassabian, A.; Trasande, L. Disruption in Thyroid Signaling Pathway: A Mechanism for the Effect of Endocrine-Disrupting Chemicals on Child Neurodevelopment. Front. Endocrinol. 2018, 9, 204. [Google Scholar] [CrossRef] [PubMed]
  38. Chiang, C.; Flaws, J.A. Subchronic Exposure to Di(2-Ethylhexyl) Phthalate and Diisononyl Phthalate during Adulthood Has Immediate and Long-Term Reproductive Consequences in Female Mice. Toxicol. Sci. 2019, 168, 620–631. [Google Scholar] [CrossRef] [PubMed]
  39. Neier, K.; Cheatham, D.; Bedrosian, L.D.; Gregg, B.E.; Song, P.X.K.; Dolinoy, D.C. Longitudinal Metabolic Impacts of Perinatal Exposure to Phthalates and Phthalate Mixtures in Mice. Endocrinology 2019, 160, 1613–1630. [Google Scholar] [CrossRef] [PubMed]
  40. Hart, L.B.; Beckingham, B.; Wells, R.S.; Flagg, M.A.; Wischusen, K.; Moors, A.; Kucklick, J.; Pisarski, E.; Wirth, E. Urinary Phthalate Metabolites in Common Bottlenose Dolphins (Tursiops truncatus) from Sarasota Bay, FL, USA. GeoHealth 2018, 2, 313–326. [Google Scholar] [CrossRef] [PubMed]
  41. Dziobak, M.K.; Wells, R.S.; Pisarski, E.C.; Wirth, E.F.; Hart, L.B. Demographic Assessment of Mono(2-ethylhexyl) Phthalate (MEHP) and Monoethyl Phthalate (MEP) Concentrations in Common Bottlenose Dolphins (Tursiops truncatus) from Sarasota Bay, FL, USA. GeoHealth 2021, 5, e2020GH000348. [Google Scholar] [CrossRef] [PubMed]
  42. Hart, L.B.; Dziobak, M.K.; Pisarski, E.C.; Wirth, E.F.; Wells, R.S. Sentinels of Synthetics—A Comparison of Phthalate Exposure between Common Bottlenose Dolphins (Tursiops truncatus) and Human Reference Populations. PLoS ONE 2020, 15, e024050. [Google Scholar] [CrossRef] [PubMed]
  43. EPA. Toxic Chemical Release Inventory Reporting Forms and Instructions: Revised 2005 Version; Section 313 of the Emergency Planning and Community Right-to-Know Act (Title III of the Superfund Amendments and Reauthorization Act of 1986); EPA: Washington, DC, USA, 2006.
  44. Deng, T.; Du, Y.; Wang, Y.; Teng, X.; Hua, X.; Yuan, X.; Yao, Y.; Guo, N.; Li, Y. The Associations of Urinary Phthalate Metabolites with the Intermediate and Pregnancy Outcomes of Women Receiving IVF/ICSI Treatments: A Prospective Single-Center Study. Ecotoxicol. Environ. Saf. 2019, 188, 109884. [Google Scholar] [CrossRef] [PubMed]
  45. Yordy, J.E.; Wells, R.S.; Balmer, B.C.; Schwacke, L.H.; Rowles, T.K.; Kucklick, J.R. Life History as a Source of Variation for Persistent Organic Pollutant (POP) Patterns in a Community of Common Bottlenose Dolphins (Tursiops truncatus) Resident to Sarasota Bay, FL. Sci. Total Environ. 2010, 408, 2163–2172. [Google Scholar] [CrossRef]
  46. Gao, D.W.; Wen, Z.D. Phthalate Esters in the Environment: A Critical Review of Their Occurrence, Biodegradation, and Removal during Wastewater Treatment Processes. Sci. Total Environ. 2016, 541, 986–1001. [Google Scholar] [CrossRef] [PubMed]
  47. Wells, R.S. Social structure and life history of Bottlenose dolphins near Sarasota Bay, Florida: Insights from four decades and five generations. In Primates and Cetaceans; Yamagiwa, J., Karczmarski, L., Eds.; Springer: Tokyo, Japan, 2014; pp. 149–172. [Google Scholar] [CrossRef]
  48. Wells, R.S. Learning from Nature: Bottlenose Dolphin Care and Husbandry. Zoo Biol. 2009, 28, 635–651. [Google Scholar] [CrossRef]
  49. Wells, R.S.; Tornero, V.; Borrell, A.; Aguilar, A.; Rowles, T.K.; Rhinehart, H.L.; Hofmann, S.; Jarman, W.M.; Hohn, A.A.; Sweeney, J.C. Integrating Life-History and Reproductive Success Data to Examine Potential Relationships with Organochlorine Compounds for Bottlenose Dolphins (Tursiops truncatus) in Sarasota Bay, Florida. Sci. Total Environ. 2005, 349, 106–119. [Google Scholar] [CrossRef] [PubMed]
  50. Wells, R.S.; Rhinehart, H.L.; Hansen, L.J.; Sweeney, J.C.; Townsend, F.I.; Stone, R.; Casper, D.R.; Scott, M.D.; Hohn, A.A.; Rowles, T.K. Bottlenose Dolphins as Marine Ecosystem Sentinels: Developing a Health Monitoring System. EcoHealth 2004, 1, 246–254. [Google Scholar] [CrossRef]
  51. Hall, A.J.; Wells, R.S.; Sweeney, J.C.; Townsend, F.I.; Balmer, B.C.; Hohn, A.A.; Rhinehart, H.L. Annual, Seasonal and Individual Variation in Hematology and Clinical Blood Chemistry Profiles in Bottlenose Dolphins (Tursiops truncatus) from Sarasota Bay, Florida. Comp. Biochem. Physiol. Part A Mol. Integr. Physiol. 2007, 148, 266–277. [Google Scholar] [CrossRef] [PubMed]
  52. Schwacke, L.H.; Hall, A.J.; Townsend, F.I.; Wells, R.S.; Hansen, L.J.; Hohn, A.A.; Bossart, G.D.; Fair, P.A.; Rowles, T.K. Hematologic and Serum Biochemical Reference Intervals for Free-Ranging Common Bottlenose Dolphins (Tursiops truncatus) and Variation in the Distributions of Clinicopathologic Values Related to Geographic Sampling Site. Am. J. Vet. Res. 2009, 70, 973–985. [Google Scholar] [CrossRef] [PubMed]
  53. Galligan, T.M.; Balmer, B.C.; Schwacke, L.H.; Bolton, J.L.; Quigley, B.M.; Rosel, P.E.; Ylitalo, G.M.; Boggs, A.S.P. Examining the Relationships between Blubber Steroid Hormones and Persistent Organic Pollutants in Common Bottlenose Dolphins. Environ. Pollut. 2019, 249, 982–991. [Google Scholar] [CrossRef] [PubMed]
  54. Helsel, D.R. Nondetects and Data Analysis: Statistics for Censored Environmental Data; Helsel, D.R., Ed.; John Wiley & Sons: Hoboken, NJ, USA, 2005. [Google Scholar]
  55. Helsel, D.R. Much Ado about next to Nothing: Incorporating Nondetects in Science. Ann. Occup. Hyg. 2009, 54, 257–262. [Google Scholar] [CrossRef]
  56. St. Aubin, D.J.; Ridgway, S.H.; Wells, R.S.; Rhinehart, H. Dolphin Thyroid and Adrenal Hormones: Circulating Levels in Wild and Semidomesticated Tursiops truncatus, and Influence of Sex, Age, and Season. Mar. Mammal Sci. 1996, 12, 1–13. [Google Scholar] [CrossRef]
  57. West, K.L.; Ramer, J.; Brown, J.L.; Sweeney, J.; Hanahoe, E.M.; Reidarson, T.; Proudfoot, J.; Bergfelt, D.R. Thyroid Hormone Concentrations in Relation to Age, Sex, Pregnancy, and Perinatal Loss in Bottlenose Dolphins (Tursiops truncatus). Gen. Comp. Endocrinol. 2014, 197, 73–81. [Google Scholar] [CrossRef]
  58. Schwacke, L.H.; Zolman, E.S.; Balmer, B.C.; De Guise, S.; George, R.C.; Hoguet, J.; Hohn, A.A.; Kucklick, J.R.; Lamb, S.; Levin, M.; et al. Anaemia, Hypothyroidism and Immune Suppression Associated with Polychlorinated Biphenyl Exposure in Bottlenose Dolphins (Tursiops truncatus). Proc. R. Soc. B Boil. Sci. 2012, 279, 48–57. [Google Scholar] [CrossRef] [PubMed][Green Version]
  59. Fair, P.A.; Montie, E.; Balthis, L.; Reif, J.S.; Bossart, G.D. Influences of Biological Variables and Geographic Location on Circulating Concentrations of Thyroid Hormones in Wild Bottlenose Dolphins (Tursiops truncatus). Gen. Comp. Endocrinol. 2011, 174, 184–194. [Google Scholar] [CrossRef] [PubMed]
  60. Weng, T.I.; Chen, M.H.; Lien, G.W.; Chen, P.S.; Lin, J.C.C.; Fang, C.C.; Chen, P.C. Effects of Gender on the Association of Urinary Phthalate Metabolites with Thyroid Hormones in Children: A Prospective Cohort Study in Taiwan. Int. J. Environ. Res. Public Health 2017, 14, 123. [Google Scholar] [CrossRef][Green Version]
  61. Hollowell, J.G.; Staehling, N.W.; Flanders, W.D.; Hannon, W.H.; Gunter, E.W.; Spencer, C.A.; Braverman, L.E. Serum TSH, T4, and Thyroid Antibodies in the United States Population (1988 to 1994): National Health and Nutrition Examination Survey (NHANES III). J. Clin. Endocrinol. Metab. 2002, 87, 489–499. [Google Scholar] [CrossRef] [PubMed]
  62. Baksi, S.; Pradhan, A. Thyroid Hormone: Sex-Dependent Role in Nervous System Regulation and Disease. Biol. Sex Differ. 2021, 12, 25. [Google Scholar] [CrossRef]
  63. Fernandez, E.; Perez, R.; Hernandez, A.; Tejada, P.; Arteta, M.; Ramos, J.T. Factors and Mechanisms for Pharmacokinetic Differences between Pediatric Population and Adults. Pharmaceutics 2011, 3, 53–72. [Google Scholar] [CrossRef][Green Version]
  64. Scheuplein, R.; Charnley, G.; Dourson, M. Differential Sensitivity of Children and Adults to Chemical Toxicity. I. Biological Basis. Regul. Toxicol. Pharmacol. 2002, 35, 429–447. [Google Scholar] [CrossRef] [PubMed][Green Version]
  65. Kasper-Sonnenberg, M.; Koch, H.M.; Wittsiepe, J.; Wilhelm, M. Levels of Phthalate Metabolites in Urine among Mother-Child-Pairs—Results from the Duisburg Birth Cohort Study, Germany. Int. J. Hyg. Environ. Health 2012, 215, 373–382. [Google Scholar] [CrossRef] [PubMed]
  66. Schütze, A.; Pälmke, C.; Angerer, J.; Weiss, T.; Brüning, T.; Koch, H.M. Quantification of Biomarkers of Environmental Exposure to Di(Isononyl)Cyclohexane-1,2-Dicarboxylate (DINCH) in Urine via HPLC-MS/MS. J. Chromatogr. B Anal. Technol. Biomed. Life Sci. 2012, 895–896, 123–130. [Google Scholar] [CrossRef]
  67. Tanabe, S.; Kannan, N.; Subramanian, A.; Watanabe, S.; Tatsukawa, R. Highly Toxic Coplanar PCBs: Occurrence, Source, Persistency and Toxic Implications to Wildlife and Humans. Environ. Pollut. 1987, 47, 147–163. [Google Scholar] [CrossRef]
  68. Harrison, R.J. Endocrine organs: Hypophysis, thyroid and adrenal. In The Biology of Marine Mammal; Academic Press: New York, NY, USA, 1969; pp. 349–390. [Google Scholar]
  69. Gray, T.J.B.; Gangolli, S.D. Aspects of the Testicular Toxicity of Phthalate Esters. Environ. Health Perspect. 1986, 65, 229–235. [Google Scholar] [CrossRef] [PubMed][Green Version]
  70. Meeker, J.D.; Calafat, A.M.; Hauser, R. Urinary Phthalate Metabolites and Their Biotransformation Products: Predictors and Temporal Variability among Men and Women. J. Expo. Sci. Environ. Epidemiol. 2012, 22, 376–385. [Google Scholar] [CrossRef]
  71. Pirahanchi, Y.; Jialal, I. Physiology, Thyroid Stimulating Hormone (TSH); StatPearls Publishing: Treasure Island, FL, USA, 2021. [Google Scholar]
  72. Gayathri, N.S.; Dhanya, C.R.; Indu, A.R.; Kurup, P.A. Changes in Some Hormones by Low Doses of Di (2-Ethyl Hexyl) Phthalate (DEHP), a Commonly Used Plasticizer in PVC Blood Storage Bags & Medical Tubing. Indian J. Med. Res. 2004, 119, 139–144. [Google Scholar] [PubMed]
  73. Price, S.C.; Chescoe, D.; Grasso, P.; Wright, M.; Hinton, R.H. Alterations in the Thyroids of Rats Treated for Long Periods with Di-(2-Ethylhexyl) Phthalate or with Hypolipidaemic Agents. Toxicol. Lett. 1988, 40, 37–46. [Google Scholar] [CrossRef]
  74. Jia, P.-P.; Ma, Y.-B.; Lu, C.-J.; Mirza, Z.; Zhang, W.; Jia, Y.-F.; Li, W.-G.; Pei, D.-S. The Effects of Disturbance on Hypothalamus-Pituitary-Thyroid (HPT) Axis in Zebrafish Larvae after Exposure to DEHP. PLoS ONE 2016, 11, e0155762. [Google Scholar] [CrossRef]
  75. Oppenheimer, J.H. Role of Plasma Proteins in the Binding, Distribution and Metabolism of the Thyroid Hormones. N. Engl. J. Med. 1968, 278, 1153–1162. [Google Scholar] [CrossRef] [PubMed]
  76. Du, Z.P.; Feng, S.; Li, Y.L.; Li, R.; Lv, J.; Ren, W.Q.; Feng, Q.W.; Liu, P.; Wang, Q.N. Di-(2-Ethylhexyl) Phthalate Inhibits Expression and Internalization of Transthyretin in Human Placental Trophoblastic Cells. Toxicol. Appl. Pharmacol. 2020, 394, 114960. [Google Scholar] [CrossRef] [PubMed]
  77. Ishihara, A.; Nishiyama, N.; Sugiyama, S.I.; Yamauchi, K. The Effect of Endocrine Disrupting Chemicals on Thyroid Hormone Binding to Japanese Quail Transthyretin and Thyroid Hormone Receptor. Gen. Comp. Endocrinol. 2003, 134, 36–43. [Google Scholar] [CrossRef]
  78. Shimada, N.; Yamauchi, K. Characteristics of 3,5,3′-Triiodothyronine (T3)-Uptake System of Tadpole Red Blood Cells: Effect of Endocrine-Disrupting Chemicals on Cellular T3 Response. J. Endocrinol. 2004, 183, 627–637. [Google Scholar] [CrossRef] [PubMed][Green Version]
  79. Shahid, M.A.; Sharma, S. Physiology, Thyroid Hormone; StatPearls Publishing: Treasure Island, FL, USA, 2021. [Google Scholar]
  80. Yeap, B.B.; Alfonso, H.; Chubb, S.A.P.; Walsh, J.P.; Hankey, G.J.; Almeida, O.P.; Flicker, L. Higher Free Thyroxine Levels Are Associated with Frailty in Older Men: The Health In Men Study. Clin. Endocrinol. 2011, 76, 741–748. [Google Scholar] [CrossRef] [PubMed]
  81. Yeap, B.B.; Alfonso, H.; Hankey, G.J.; Flicker, L.; Golledge, J.; Norman, P.E.; Chubb, S.A.P. Higher Free Thyroxine Levels Are Associated with All-Cause Mortality in Euthyroid Older Men: The Health in Men Study. Eur. J. Endocrinol. 2013, 169, 401–408. [Google Scholar] [CrossRef] [PubMed][Green Version]
  82. Hwangbo, Y.; Kim, J.H.; Kim, S.W.; Park, Y.J.; Park, D.J.; Kim, S.Y.; Shin, C.S.; Cho, N.H. High-Normal Free Thyroxine Levels Are Associated with Low Trabecular Bone Scores in Euthyroid Postmenopausal Women. Osteoporos. Int. 2016, 27, 457–462. [Google Scholar] [CrossRef]
  83. Abrams, J.J.; Grundy, S.M. Cholesterol Metabolism in Hypothyroidism and Hyperthyroidism in Man. J. Lipid Res. 1981, 22, 323–338. [Google Scholar] [CrossRef]
  84. Habra, M.A.; Hijazi, R.; Verstovsek, G.; Marcelli, M. Medullary Thyroid Carcinoma Associated with Hyperthyroidism: A Case Report and Review of the Literature. Thyroid. Thyroid 2004, 14, 391–396. [Google Scholar] [CrossRef] [PubMed]
  85. Pazaitou-Panayiotou, K.; Perros, P.; Boudina, M.; Siardos, G.; Drimonitis, A.; Patakiouta, F.; Vainas, I. Mortality from Thyroid Cancer in Patients with Hyperthyroidism: The Theagenion Cancer Hospital Experience. Eur. J. Endocrinol. 2008, 159, 799–803. [Google Scholar] [CrossRef] [PubMed][Green Version]
  86. Fisher, D.A. Fetal Thyroid Function: Diagnosis and Management of Fetal Thyroid Disorders. Clin. Obstet. Gynecol. 1997, 40, 16–31. [Google Scholar] [CrossRef] [PubMed]
  87. Shields, B.M.; Knight, B.A.; Hill, A.; Hattersley, A.T.; Vaidya, B. Fetal Thyroid Hormone Level at Birth Is Associated with Fetal Growth. Clin. Endocrinol. Metab. 2011, 96, E934–E938. [Google Scholar] [CrossRef] [PubMed][Green Version]
  88. Anselmo, J.; Cao, D.; Karrison, T.; Weiss, R.E.; Refetoff, S. Fetal Loss Associated with Excess Thyroid Hormone Exposure. J. Am. Med. Assoc. 2004, 292, 691–695. [Google Scholar] [CrossRef][Green Version]
  89. Weingartner, G.M.; Thornton, S.J.; Andrews, R.D.; Enstipp, M.R.; Barts, A.D.; Hochachka, P.W. The Effects of Experimentally Induced Hyperthyroidism on the Diving Physiology of Harbor Seals (Phoca vitulina). Front. Physiol. 2012, 3, 380. [Google Scholar] [CrossRef][Green Version]
  90. Fisher, D.A. Physiological Variations in Thyroid Hormones: Physiological and Pathophysiological Considerations. Clin. Chem. 1996, 42, 135–139. [Google Scholar] [CrossRef] [PubMed][Green Version]
  91. Cohen, J. Statistical Power Analysis. J. Am. Psychol. Soc. 1992, 1, 98–101. [Google Scholar] [CrossRef]
  92. Bianco, A.C.; Salvatore, D.; Gereben, B.; Berry, M.J.; Larsen, P.R. Biochemistry, Cellular and Molecular Biology, and Physiological Roles of the Iodothyronine Selenodeiodinases. Endocrine Reviews. Endocr. Rev. 2002, 23, 38–89. [Google Scholar] [CrossRef]
  93. Visser, T.J.; Kaptein, E.; Terpstra, O.T.; Krenning, E.P. Deiodination of Thyroid Hormone by Human Liver. Clin. Endocrinol. Metab. 1988, 67, 17–24. [Google Scholar] [CrossRef] [PubMed]
  94. Bianco, A.C.; Kim, B.W. Deiodinases: Implications of the Local Control of Thyroid Hormone Action. J. Clin. Investig. 2006, 116, 2571–2579. [Google Scholar] [CrossRef][Green Version]
  95. Sarasota Water Temp. Available online: (accessed on 10 January 2022).
  96. Rian, M.B.; Vike-Jonas, K.; Gonzalez, S.V.; Ciesielski, T.M.; Venkatraman, V.; Lindstrøm, U.; Jenssen, B.M.; Asimakopoulos, A.G. Phthalate Metabolites in Harbor Porpoises (Phocoena phocoena) from Norwegian Coastal Waters. Environ. Int. 2020, 137, 105525. [Google Scholar] [CrossRef]
  97. Fossi, M.C.; Coppola, D.; Baini, M.; Giannetti, M.; Guerranti, C.; Marsili, L.; Panti, C.; de Sabata, E.; Clò, S. Large Filter Feeding Marine Organisms as Indicators of Microplastic in the Pelagic Environment: The Case Studies of the Mediterranean Basking Shark (Cetorhinus maximus) and Fin Whale (Balaenoptera physalus). Mar. Environ. Res. 2014, 100, 17–24. [Google Scholar] [CrossRef] [PubMed]
  98. Kucklick, J.; Schwacke, L.; Wells, R.; Hohn, A.; Guichard, A.; Yordy, J.; Hansen, L.; Zolman, E.; Wilson, R.; Litz, J.; et al. Bottlenose Dolphins as Indicators of Persistent Organic Pollutants in the Western North Atlantic Ocean and Northern Gulf of Mexico. Environ. Sci. Technol. 2011, 45, 4270–4277. [Google Scholar] [CrossRef] [PubMed]
  99. Woshner, V.; Knott, K.; Wells, R.; Willetto, C.; Swor, R.; O’Hara, T. Mercury and Selenium in Blood and Epidermis of Bottlenose Dolphins (Tursiops truncatus) from Sarasota Bay, FL: Interaction and Relevance to Life History and Hematologic Parameters. EcoHealth 2008, 5, 360–370. [Google Scholar] [CrossRef] [PubMed]
  100. Monosson, E. Chemical Mixtures: Considering the Evolution of Toxicology and Chemical Assessment. Environ. Health Perspect. 2005, 113, 383–390. [Google Scholar] [CrossRef] [PubMed][Green Version]
  101. Fiandanese, N.; Borromeo, V.; Berrini, A.; Fischer, B.; Schaedlich, K.; Schmidt, J.S.; Secchi, C.; Pocar, P. Maternal Exposure to a Mixture of Di(2-Ethylhexyl) Phthalate (DEHP) and Polychlorinated Biphenyls (PCBs) Causes Reproductive Dysfunction in Adult Male Mouse Offspring. Reprod. Toxicol. 2016, 65, 123–132. [Google Scholar] [CrossRef]
  102. Sumner, R.N.; Tomlinson, M.; Craigon, J.; England, G.C.W.; Lea, R.G. Independent and Combined Effects of Diethylhexyl Phthalate and Polychlorinated Biphenyl 153 on Sperm Quality in the Human and Dog. Sci. Rep. 2019, 9, 3409. [Google Scholar] [CrossRef]
  103. Ortiz, R.M.; Long, B.; Casper, D.; Ortiz, L.L.; Williams, T.M. Biochemical and Hormonal Changes during Acute Fasting and Re-Feeding in Bottlenose Dolphins (Tursiops truncatus). Mar. Mammal Sci. 2010, 26, 409–419. [Google Scholar] [CrossRef]
  104. Köhler, B.; Stengel, C.; Neiger, R. Dietary Hyperthyroidism in Dogs. J. Small Anim. Pract. 2012, 53, 182–184. [Google Scholar] [CrossRef] [PubMed]
  105. Trivalle, C.; Doucet, J.; Chassagne, P.; Landrin, I.; Kadri, N.; Menard, J.-F.; Bercoff, E. Differences in the Signs and Symptoms of Hyperthyroidism in Older and Younger Patients. J. Am. Geriatr. Soc. 1996, 44, 50–55. [Google Scholar] [CrossRef] [PubMed]
  106. Consumer Product Safety Commission (CPSC). Prohibition of Children’s Toys and Child Care Articles Containing Specified Phthalates; 16 CFR Part 1307; Consumer Product Safety Commission (CPSC): Bethesda, MA, USA, 2018.
  107. AB-2762. Assembly Bill No. 2762. 2020. Available online: (accessed on 9 February 2022).
Figure 1. Akritas–Theil–Sen (ATS) line for the relationship between adult female free thyroxine (FT4) and natural log transformed mono(2-ethylhexyl) phthalate (MEHP). Kendall’s tau = 0.36, p = 0.04. Dashed red lines represent intervals for censored values below the limit of detection.
Figure 1. Akritas–Theil–Sen (ATS) line for the relationship between adult female free thyroxine (FT4) and natural log transformed mono(2-ethylhexyl) phthalate (MEHP). Kendall’s tau = 0.36, p = 0.04. Dashed red lines represent intervals for censored values below the limit of detection.
Animals 12 00824 g001
Figure 2. Akritas–Theil–Sen (ATS) line for the relationship between adult male free thyroxine (FT4) and natural log transformed mono(2-ethylhexyl) phthalate (MEHP). Kendall’s tau = 0.42, p = 0.02. Dashed red lines represent intervals for censored values below the limit of detection.
Figure 2. Akritas–Theil–Sen (ATS) line for the relationship between adult male free thyroxine (FT4) and natural log transformed mono(2-ethylhexyl) phthalate (MEHP). Kendall’s tau = 0.42, p = 0.02. Dashed red lines represent intervals for censored values below the limit of detection.
Animals 12 00824 g002
Table 1. Descriptive statistics of mono(2-ethylhexyl) phthalate (MEHP) and thyroid hormone concentrations for individual dolphins (n = 50 unless otherwise specified) sampled from Sarasota Bay, Florida (2010–2019). Frequency of detection is given as %.
Table 1. Descriptive statistics of mono(2-ethylhexyl) phthalate (MEHP) and thyroid hormone concentrations for individual dolphins (n = 50 unless otherwise specified) sampled from Sarasota Bay, Florida (2010–2019). Frequency of detection is given as %.
Mono(2-ethylhexyl) phthalate (MEHP; ng/mL)0.170.4976.6056.00
Triiodothyronine (T3; ng/dL)<LOD86.55175.0060.00
Total thyroxine (T4; μg/dL)7.9415.0022.02100.00
Free thyroxine (FT4; ng/dL) (n = 49)1.001.863.51100.00
Table 2. Comparison of mono(2-ethylhexyl) phthalate (MEHP) and thyroid hormone concentrations by sex for individual dolphins (n = 50 unless otherwise specified) sampled from Sarasota Bay, Florida (2010–2019). Frequency of detection given as %.
Table 2. Comparison of mono(2-ethylhexyl) phthalate (MEHP) and thyroid hormone concentrations by sex for individual dolphins (n = 50 unless otherwise specified) sampled from Sarasota Bay, Florida (2010–2019). Frequency of detection given as %.
Female (n = 29)Male (n = 21)
Mono(2-ethylhexyl) phthalate (MEHP; ng/mL)0.172.1076.6056.000.170.5549.2065.52
Triiodothyronine (T3; ng/dL)<LOD97.40158.0060.00<LOD70.30175.0065.52
Total thyroxine (T4; μg/dL)10.5515.8022.02100.007.9414.2021.10100.00
Free thyroxine (FT4; ng/dL)
(n = 49)
Table 3. Comparison of MEHP and thyroid hormone concentrations by age class for individual dolphins (n = 50 unless otherwise specified) sampled from Sarasota Bay, Florida (2010–2019). Frequency of detection given as %.
Table 3. Comparison of MEHP and thyroid hormone concentrations by age class for individual dolphins (n = 50 unless otherwise specified) sampled from Sarasota Bay, Florida (2010–2019). Frequency of detection given as %.
Adult (n = 33)Juvenile (n = 17)
Mono(2-ethylhexyl) phthalate (MEHP; ng/mL)0.170.4276.6052.940.171.2828.4062.50
Triiodothyronine (T3; ng/dL)<LOD80.55158.0058.82<LOD102.50175.0062.50
Total thyroxine (T4; μg/dL)7.9413.9720.90100.0012.0018.8522.02100.00
Free thyroxine (FT4; ng/dL)
(n = 49)
Table 4. Generalized linear model (GLM) results testing the association between hormone concentrations and demographic factors. Values in bold are significant at p < 0.05.
Table 4. Generalized linear model (GLM) results testing the association between hormone concentrations and demographic factors. Values in bold are significant at p < 0.05.
HormoneSexAge Class(Sex) x (Age Class)
Wald StatisticpWald StatisticpWald Statisticp
Triiodothyronine (T3)0.110.741.410.230.830.36
Total thyroxine (T4)0.780.3823.11<0.00012.240.13
Free thyroxine (FT4)5.960.0114.560.00010.910.34
Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Share and Cite

MDPI and ACS Style

Dziobak, M.K.; Wells, R.S.; Pisarski, E.C.; Wirth, E.F.; Hart, L.B. A Correlational Analysis of Phthalate Exposure and Thyroid Hormone Levels in Common Bottlenose Dolphins (Tursiops truncatus) from Sarasota Bay, Florida (2010–2019). Animals 2022, 12, 824.

AMA Style

Dziobak MK, Wells RS, Pisarski EC, Wirth EF, Hart LB. A Correlational Analysis of Phthalate Exposure and Thyroid Hormone Levels in Common Bottlenose Dolphins (Tursiops truncatus) from Sarasota Bay, Florida (2010–2019). Animals. 2022; 12(7):824.

Chicago/Turabian Style

Dziobak, Miranda K., Randall S. Wells, Emily C. Pisarski, Ed F. Wirth, and Leslie B. Hart. 2022. "A Correlational Analysis of Phthalate Exposure and Thyroid Hormone Levels in Common Bottlenose Dolphins (Tursiops truncatus) from Sarasota Bay, Florida (2010–2019)" Animals 12, no. 7: 824.

Note that from the first issue of 2016, this journal uses article numbers instead of page numbers. See further details here.

Article Metrics

Back to TopTop