Mercury (Hg) is a widespread and potential harmful persistent contaminate of aquatic ecosystems. Except for the northern most populations of American alligators (Alligator Mississippiensis) found in North Carolina, the potential adverse health impacts of Hg on ecosystems and humans consuming alligator meat has been studied for over three decades. Now that alligators are being recreationally hunted and consumed across their range, it is especially important to monitor toxic contaminant levels to best understand possible adverse impacts of exposures on alligator populations and human health. In this study we evaluated blood Hg levels in American alligators from an urbanized site in Wilmington, NC, a nearby site at Lake Waccamaw, NC, and a site on the St Johns River in Florida. Median blood total Hg concentrations were particularly high at Lake Waccamaw (526 ng/g, range 152–946 ng/g), resulting in median muscle concentrations (0.48 ppm, range 0.13–0.88 ppm) above the US EPA/FDA fish consumption advisory level of 0.3 ppm. Median concentrations at the Wilmington site (69 ng/g, range 22–336 ng/g) were low, and Hg concentrations from the St Johns River site (143 ng/g, range 54–244 ng/g) were comparable to those reported in previous studies. Analysis of relationships between total Hg concentrations and a panel of blood chemistry biomarkers found only modest concentration dependent impact on biomarkers of renal function. The results of this study reveal that local environmental factors greatly impact Hg bioaccumulation in alligators, findings that reaffirm that local contaminant biomonitoring in alligator populations will be critical for affective management and determination of guidelines for safe consumption of harvested alligators.
Research Article
Comparative Assessment of Blood Mercury in American Alligators (Alligator mississippiensis) from Coastal North Carolina and Florida
https://doi.org/10.21203/rs.3.rs-1495035/v1
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bioaccumulation
biomonitoring
ecotoxicology
mercury
metals
reptile
Mercury (Hg), whether in elemental (Hg0), inorganic (Hg2+) or organic forms, is persistent and pervasive in the environment. Natural and anthropogenic mercury is released into the atmosphere and becomes deposited into soils and sediments where it becomes transformed primarily to organic methyl mercury (MeHg) by microbial methylation of Hg2+ (Gilmour and Henry, 1991; Graham et al., 2012). Along with the volume of atmospheric wet and dry deposition, the production and bioaccumulation of MeHg in aquatic environments and food webs is dependent on a variety of factors including pH, dissolved organic matter, and percentage of wetland area in a watershed (Gilmour and Henry, 1991; Graham et al., 2012; Guentzel, 2009; Miller et al., 2007).
In animals MeHg is a potent developmental neurotoxicant with a slow elimination half-life due to its high affinity for glutathione and reduced sulfhydryl groups (-SH) present in other cellular proteins. As a result, MeHg accumulates in various tissues to cause additional adverse effects on hepatic, renal and reproductive functions in humans and wildlife (Landrigan et al., 2020; Lemaire et al., 2021; Mergler et al., 2007). Because of its efficient trophic transfer through aquatic food webs, MeHg constitutes > 95% of the total organic mercury in biota with concentrations found in large apex predators that may be millions of times higher than in surface water (Compeau and Bartha, 1985; Lavoie et al., 2013; Wagemann et al., 1998, 1997). Such effectual bioaccumulation and biomagnification can result in MeHg accumulating to toxic levels in fish and other fish eating apex predators; the consumption of contaminated fish and wildlife is a potential risk for humans, especially exposures occurring during pre- and perinatal periods of development (Jagoe et al., 1998; Landrigan et al., 2020; Lavoie et al., 2013; Lawson et al., 2020; Nilsen et al., 2017a; Yanochko et al., 1997)
In crocodilian species the bioaccumulation of anthropogenic toxic metals including Hg has been most well studied in the American alligator (Alligator mississippiensis) of southeastern and south central United States (Burger et al., 2000; Delany et al., 1988; Elsey et al., 1999; Jagoe et al., 1998; Khan and Tansel, 2000; Lawson et al., 2020; Nilsen et al., 2019, 2017b; Rumbold et al., 2002). Along with being a large and long-lived apex and keystone species across its range, American alligators often share rural and urban environments with humans and are important non-migratory sentinels of local adverse impacts from environmental pollutants (Somaweera et al., 2020). Wild caught alligator meat is also consumed extensively by humans throughout most of its range in the southeastern United States where annual recreational hunts and nuisance alligator programs exist. During 2020 in Florida, for example, more than 208,000 pounds (94,530 kg) of alligator meat were produced through farming, and more than 17,000 additional alligators were reported as harvested on private lands and through recreational hunting and nuisance programs (FWC, 2022). The potential public health effects resulting from consumption of alligator meat contaminated with toxic metals and other pollutants is unclear. Previous analysis in South Carolina were at total of 253 alligators were harvested in 2020 found that alligator hunters were at potential risk from mixtures of perfluoroalkyl substances (PFAS) and other environmental contaminants in alligator meat (SCDNR, 2022; Tipton et al., 2017a, 2017b).
With the exception of the northern most populations of American alligators found in North Carolina, Hg concentrations and potential adverse health impacts of MeHg exposure has been periodically assessed in American alligators (Burger et al., 2000; Delany et al., 1988; Horai et al., 2014; Jagoe et al., 1998; Khan and Tansel, 2000; Lawson et al., 2020; Nilsen et al., 2020, 2019, 2017a, 2017b; Rumbold et al., 2002; Yanochko et al., 1997). As is the case elsewhere, Hg is a pervasive pollutant in North Carolina that has resulted in a state-wide fish consumptions advisories for largemouth bass established upon the presence of high levels of Hg, and for bluegill, bowfin, and channel catfish from the Cape Fear River for elevated levels of Hg and other toxic metals (NC DPH, 2022). Based on the known elevation of Hg in these prey species of coastal North Carolina alligators, we sought to evaluate blood Hg concentrations in alligators from an urbanized site along the Cape Fear River, and from more rural sites surrounding Lake Waccamaw, NC which is located in the adjoining Lumber River watershed. To better contextualize our findings from the NC alligator populations, we also sampled alligators from the St John’s River in Florida. Further, to evaluate potential adverse health impacts related to exposures we also assessed the relationships between total Hg (tHg) concentrations in blood with a panel of blood chemistry biomarkers.
Animal procedures
All animal procedures were performed with approval by the North Carolina State University Institutional Animal Care and Use Committee (protocol #18-085-O) and under approved permits issued by NC Wildlife Resource Commission (21-ES00535) and by the Florida Fish and Wildlife Conservation Commission (SPGS-20-49). Alligators were sampled using active capture methods that employed snatch hooks from Greenfield Lake (34.2107388211135, 77.93707241283391) Wilmington, NC near the Cape Fear River, around Lake Waccamaw, NC in the adjacent Lumber River basin (34.28726947673369, -78.50965117663293), and from the St. John’s River in Brevard and Orange Counties Florida (between 28.371883105432342, -80.87122410169327 and 28.451699007759952, -80.89630680361354). Sampling in NC occurred between February 29 to October 29, 2021, and in FL from February 6 to February 8, 2021.
Alligators were visually examined for general health, and external injuries were noted and photographed. Sex was determined by cloacal examination with total length, snout to vent length, tail girth, head/snout, and rear foot measurements recorded. Following sample/data collection, passive integrated transponder (PIT) tags were implanted intramuscularly into the right base of the tail of alligators in NC. In Florida, PIT tags were inserted into the right jowl and sampled alligators were also identified by a numbered toe web tag. All alligators were released at the site of capture. A typical time from first contact to release of animal was dependent on animal size with the average time to release being < 15 minutes.
Blood sampling procedures
Immediately following capture a 10–15 mL a whole venous blood sample was collected from the post-occipital spinal sinus using a sterile 20 g or 18 g needle and a 30 mL syringe (Myburgh et al., 2014). Whole blood samples were transferred to blue caped EDTA whole blood for metals analysis, and green capped lithium heparin containing tubes (Vacutainer, BD). Samples were mixed by gentle inversion and immediately stored on ice. After field collections, EDTA tubes were frozen until thawed for Hg analysis. Serum and packed blood cells in the lithium heparin tubes were separated by centrifugation (1800 x g for 10 min at 4°C). Serum fractions were immediately aliquoted into cryovials. Samples collected in NC were transported on wet ice and FL samples were transported on dry ice. All samples were archived at -80°C until analysis.
Total Mercury Analysis
Mercury analysis was performed beginning 11/22/2021 and completed 01/04/2022. Total mercury (tHg) in whole blood samples was quantified using a MA-3000 mercury analyzer (Nippon Instruments, Osaka, Japan) by thermal decomposition amalgamation, and atomic absorption spectrophotometry following guidance outlined in US EPA methods 7473 (https://www.epa.gov/esam/epa-method-7473-sw-846-mercury-solids-and-solutions-thermal-decomposition-amalgamation-and). Each control and experimental whole blood sample was thawed, vortexed, and approximately 10 µl aliquots were weighed at room temperature in a ceramic sample boat that was previously heated for a minimum of 30 minutes in a muffle furnace at 800 Co. Total Hg concentrations in each sample was determined in duplicate using a linear equation derived from a calibration curve that ranged from 0.1 ng to 1000 ng (r2 = .9999) Hg. The aqueous HgCl2 standards were made by serial dilution of a certified HgCl2 standard in 2% HCl (1000 ± 5 µg/ml; lot # 1923928, AGS Scientific, Bryan, Tx). Matrix-matched quality control samples were prepared by combining aliquots from a randomly selected subset of analyzed blood samples. The concentration of total Hg in the pooled blood was determined and used as reference material (M = 204.94 ± 5.14 ppb, CV% = 2.51, n = 23), with pooled blood samples included every 10 sample measurements. Additional quality control samples included method blanks, and aqueous standards of known Hg concentration (0.1, 10.0, or 100 ng) that were included throughout the analysis. Aliquots of the pooled alligator blood were spiked with 1 ng/µl of the HgCl2 standard and was used to calculate recoveries. The mean percent recovery of Hg in 10 µl of the pooled blood was 96.92% ± 2.89% (n = 3) and the limit of detection defined as [LOD = meanblanks + 3(SDblanks)] was 0.01 ng (n = 20).
Analysis of blood chemistry biomarkers
Blood chemistry values for 11 parameters (listed in supplemental table S1) were obtained for a subset of samples with sufficient volume and quality of serum for analysis (CFR: n = 11, LW: n = 30; SJR, n = 24) using a VetScan VS2 Whole Blood chemistry analyzer with Avian/Reptilian Profile Plus rotors (# 500–7131; Abaxis, Union City, CA). Samples not meeting individual assay QC assessments were excluded from the analysis. All procedures followed manufacturer’s protocols using 100 µl of serum. Bile acids are included on the blood chemistry panel, but values were not reported because none were above the limit of assay detection (< 35 µmol/L). A similar finding was observed in other alligator populations (Hamilton et al., 2016). For the other analytes values below the linear range of detection were interpolated (values = LOD/√2), and reported values above the maximum of the linear range were substituted with the maximum value for the specific assay.
Data and Statistical Analysis
Each animal/blood sample was assigned a randomized numeric code at the time of collection. Samples were decoded for site and morphometric measures/sex only after measurement/analysis and biological marker analysis were completed. Descriptive data analysis was performed in Excel (Microsoft) with statistical comparisons and data visualization done using Prism (version 9.3, GraphPad La Jolla, CA). For tHg concentration data, the central tendencies of tHg concentrations (mean or median) and ranges were determined for each site. A D'Agostino & Pearson test was used to assess normality of data; [tHg] data was log10 transformed, for morphometric and serum biomarker data was analyzed using non-parametric statistics. Linear regression and Spearman’s rank correlation coefficient were used to calculate relationships between tHg concentrations, SVL, and serum biomarkers. Multivariant analysis was first used to evaluate differences between, sites, log10 [tHg] and serum biomarkers were significant. ANOVA and Tukey’s multiple comparison was used to evaluate differences in SVL between sites, and a Kruskal-Willis test and Dunn’s multiple comparison’s test was used to evaluate differences individual blood biochemistry endpoints between sites. Estimated tHg concentrations in muscle (mg kg− 1) were calculated using the formula 
and body mass index (BMI) was estimated using the formula 
(Lawson et al., 2020; Nilsen et al., 2017b, 2017a). A minimal level of statistical significance for differences in values among or between groups was considered p ≤ .05.
Study sites
During spring and summer of 2021, we collected blood samples from a total of 68 immature and sexually mature alligators at two sites in NC, and from a site in FL where Hg levels had previously been assessed (Fig. 1A). The CFR site was chosen because of the relatively high density of alligators located in an urban location. This site has direct access to the CFR which has well defined upstream industrial sources of pollution from nearby coal-fly ash storage ponds and fluorochemical use and production (Aly et al., 2021; McCord and Strynar, 2019). Lake Waccamaw, the largest of the Bay Lakes found on the North Carolina coastal plain, is located 50 kilometers northwest of the CFR site in the adjacent Lumbar River basin. This location has a similarly high density of American alligators that inhabit the canals and extensive wetlands surrounding the lake. We further selected this site for comparison because wet and dry mercury deposition at Lake Waccamaw has been tracked weekly by the National Atmospheric Deposition Program since 1996 allowing us to compare mean weekly deposition at Lake Waccamaw with deposition at two sites in Florida with similar durations of long-term deposition tracking (Fig. 1A, 1B;(NADP, 2022). Between 1996 and 2020 mean weekly Hg deposition (µg/m2) at Lake Waccamaw (NC05; M = 10.89, SD = 2.42) was significantly lower (F(2, 69) = 58.35, p < .0001, η2 = .628) than deposition at sites in the Everglades (FL11; M = 19.62, SD = 3.52; p < .0001) or Chassahowitzka National Wildlife Refuge (FL05; M = 15.91, SD = 2.87; p < .0001).
Population characteristics
There was a marked male bias in the sex of animals sampled from all 3 sites with males accounting for 84.8% of the entire study population (Table 1). A male sex bias in alligator populations is frequently reported in scientific sampling studies and in annual alligator harvests suggesting that some populations of American alligators maybe male biased (FWC, 2022; Lance et al., 2000). We believe the notable sex bias could also have resulted from numerous factors related to the opportunistic sampling approach that we used, differences in behavior between sexes, and our repeated annual sampling at the North Carolina sites. Because the study is underpowered for determination of sex related differences, males and females were combined and analyzed in aggregate.
Table 1. Sample size, sex, snout to vent length, and BMI for each population
|
Location |
N= |
Sex (F/M) |
Snout-Vent Length (cm) Mean (± SD) Min-Max |
BMI Mean (± SD) Min-Max |
|
Cape Fear River, NC |
13 |
0/13 |
94.7 ± 37.2 50.4 - 190.8 |
0.230 ± 0.013 0.215 - 0.254 |
|
Lake Waccamaw, NC |
31 |
7/24 |
95.4 ± 27.5 57.6 - 148.9 |
0.226 ± 0.014 0.202 - 0.263 |
|
St. Johns River, FL |
24 |
4/20 |
119.1 ± 31.9a 50.9 - 163.1 |
0.226 ± 0.015 0.178 - 0.260 |
a. ANOVA found mean SVL of alligators from the St Johns River was significantly greater than the Lake Waccamaw alligators p = .018. BMI, body mass index; F, female; M, male
The population of alligators at the SJR was composed almost entirely of mature alligators where we observed a higher density of large alligators with few immature alligators found in accessible portions of the river. Unlike the NC sites, this site is largely devoid of overhanging tree and shrub growth along its banks that serves as protective habitat for immature alligators. We were able to observe and more readily sample a variety of size classes of alligators that ranged from juveniles to mature adult alligators at both NC sites. Those observations were supported by our analysis of variance that found a main effect of sampling site on snout-vent length [(SVL), F(2, 65) = 4.59, p = .014, η2 = .124]. Post-test analysis using Tukey’s multiple comparisons test indicated that the mean SVL for alligators sampled from the SJR was significantly greater than those from both NC sites (Table 1). Using a Kruskal-Wallis test no significant differences in calculated BMI were found across the sampling sites suggesting sampled alligators were similar in body condition (Table 1; p = .551).
Total Hg analysis
Our analysis of whole blood tHg found a mean concentration of 148.3 ng/g (SD = 48.9) for alligators sampled along the SJR in Florida (Table 2). Excluding the 3 immature alligators (SVL < 90 cm) did not significantly change the mean [tHg] (M = 151.0 ng/g, SD = 47.5), therefore we included these animals in our comparisons with the other sites. The tHg concentrations we observed at the SJR site were similar to concentrations previously reported for adult (M = 177.7 ng/g, SD = 84.9) and subadult alligators (M = 152.9 ng/g, SD = 84.9) from the SJR (Nilsen et al., 2016).
| Location | N = | Total Blood Hg (ng/g) Mean (± SD) Min-Max) | Calculated Muscle Hg (mg/kg) Mean (± SD) Min-Max) |
|---|---|---|---|
| Cape Fear River, NC | 13 | 79.2 ± 79.6a 21.6–335.5 | 0.56 ± 0.75 0.002–0.30 |
| Lake Waccamaw, NC | 31 | 511.1 ± 246.1b 152.2–945.9 | 0.47 ± 0.23 0.13–0.88 |
| St. Johns River, FL | 24 | 148.3 ± 48.9 54.4–244.3 | 0.12 ± 0.05 0.03–0.21 |
| a. ANOVA found mean blood [tHg] was significantly lower in alligators from the Cape Fear River compared to those from Lake Waccamaw (p < .0001) and St Johns River (p = .0005). b. blood [tHg] was significantly higher in alligators from Lake Waccamaw compared to those from both the Cape Fear River and St Johns River (p < .0001). F, female; M, male | |||
Whereas Hg deposition is significantly lower at LW, the mean blood tHg concentration for all alligators sampled at LW was significantly greater than the concentration of the SJR population (Table 2). Concentrations of tHg for adults from LW (M = 640.4 ng/g, SD = 250.8) were significantly greater (t(29 = 3.18, p = .004, d = 1.18) than mean tHg concentrations in subadult/juveniles (M = 389.9, SD = 167.4) sampled from the same site. When we compared tHg concentrations in blood of mature or immature alligators at LW with alligator from the other two sites, a significant main effect of tHg was found (F(2, 49) = 46.08, p < .0001, η2 = .653) and blood [tHg] of each size class from LW was significantly greater than the SJR population (Fig. 1C; p = .0001). For alligators from the CFR we found the average blood [tHg] of this population was significantly lower than alligators from LW and the SJR (Fig. 1C; Table 2). The average concentrations detected in the adults (M = 97.32 ng/g, SD = 94.45) and immature (M = 50.17 ng/g, SD = 28.23) alligators from the CFR was comparably low and not significantly different (p = .603) from one another. The lower concentrations of MeHg observed in the CFR alligators that inhabit this highly urbanized ecosystem in Wilmington NC were likely the result of altered hydrology, morphology, and water chemistry of the sampling site that has resulted in limited conversion of Hg into bioavailable MeHg.
Previous analysis by Lawson and coworkers (2020) identified nonlinear relationships between blood tHg concentrations and size/age of alligator in populations from Florida and South Carolina, however the predicted decreases in blood t[Hg] for largest animals in our populations do not explain the large increases in tHg found at LW. The Lake Waccamaw ecosystem itself is remarkable;as a Bay Lake it has an unusually high pH due to calcareous marine formations that buffer the acidic and high tannin blackwater entering the lake from surrounding wetlands (Stager and Cahoon, L. B., 1987). However, we anticipate that the large surrounding acidic wetlands, composed of large cypress and gum swamps from which the alligators were sampled, is a main driver of the elevated concentrations of MeHg observed in alligators from this location.
In 2018 limited Alligator hunting became legal in North Carolina despite the much lower density of animals compared to populations in more southern states (NCWRC, 2018). To evaluate whether consumption of alligator meat represents a potential threat to consumers we estimated muscle concentrations using previously developed conversion factors that estimate muscles concentrations of tHG in alligator muscle/meat (Lawson et al., 2020; Nilsen et al., 2017b, 2017a). The calculated average tHg concentrations for the alligators from LW (M = 0.47 mg/kg, SD = 0.23) were found to be well above the US EPA and FDA consumption advisory level for Hg in fish (Table 2 (US EPA, 2022)). Highlighting the need to understand local influences in Hg cycling and concentrations in fish and wildlife consumed by humans, even the smallest immature alligator sampled from LW (total length 111.5 cm, SVL 58.5 cm) had a blood tHg level (360 ng/g) sufficiently high to result in an estimated muscle concentration of 0.332 mg/kg (Table S2).
Blood biochemistry
Our analysis of blood chemistry values and multiple regression analysis found few changes across parameters that were correlated with tHg concentrations (Table 3). For the entire sampled study population, only uric acid and phosphorous were positively correlated with log10 transformed [tHg], Spearman’s r(57) = .375, p = .004 and r(64) = 0.363, p = .003. Using Kruskal–Wallis tests (Chi square = 12.51, p = .002, df = 2) followed with Dunn’s multiple comparison test we also found a significant increase in uric acid in the samples from LW compared to samples from the SRJ (p = .001). Those findings suggest that a small but detectable impact on renal function may be resulting from elevated Hg exposure at LW. Elevated phosphorous levels are also predictive of kidney disease in humans and an established indicator of renal dysfunction in experimental animal studies (O’Seaghdha et al., 2011; Raikou, 2021). However, the importance of the correlation between increasing Hg concentrations and serum phosphorus levels that we observed is less clear; complex interactions between agricultural phosphorus run-off, eutrophication, and the bioavailable Me-Hg in aquatic and estuarine environments cannot be ruled out as contributing to the changes in plasma serum levels that we observed (Pakhomova et al., 2018; Soerensen et al., 2016). While AST in SJR samples was significantly elevated compared to each of the NC sites, a concomitant increase in creatine kinase that was significantly correlated with SVL (Spearman’s r(68) = .333, p = .008) was also observed in this population of larger alligators SJR. We interpret those increases in AST and CK as unrelated to exposure, but rather due to factors related to sampling and muscle release of these enzymes. The significant increase in blood glucose levels found in the CFR population (p = .03) is not correlated with Hg concentrations and does not appear related to Hg exposure (Table 3).
| Dynamic Range | Plasma Bioanalyte Concentration/Activity Mean ± SD (N) | |||
|---|---|---|---|---|
| Cape Fear River | Waccamaw | St Johns | ||
| AST (U/L) | 5–2000 U/L | 128.2 ± 43.6 (9) | 165.5 ± 51.3 (30) | 213.7 ± 44.0 (24) |
| Creatine Kinase (U/L) | 5–14000 U/L | 380 ± 117 (9) | 675 ± 445 (29) | 1286 ± 1171 (24) |
| Total Protein (g/dL) | 2–14 g/dL | 4.5 ± 1.3 (9) | 4.5 ± 1.0 (30) | 4.8 ± 0.7 (24) |
| Albumin (g/dL) | 1–6.5 g/dL | 1.1 ± 0.2 (10) | 1.0 ± 0.3 (30) | 0.9 ± 0.2 (24) |
| Globulin (g/dL) | 0–13 g/dL | 3.4 ± 1. 2 (9) | 3.5 ± 0.7 (30) | 3.8 ± 0.6 (24) |
| Glucose (mg/dL) | 10–700 mg/dL | 117.9 ± 27.0 (10) | 92.0 ± 27.0 (30) | 93.4 ± 20.8 (24) |
| Calcium (mg/dL) | 4–16 mg/dL | 12.0 ± 0.9 (9) | 12.1 ± 1.7 (30) | 11.9 ± 1.2 (24) |
| Phosphorus (mg/dL) | 0.2–20 mg/dL | 6.1 ± 1.9 (10) | 6.7 ± 1.7 (30) | 6.1 ± 1.6 (24) |
| Potassium (mmol/L) | 1.5–8.5 mmol/L | 6.9 ± 1.0 (10) | 6.3 ± 1.1 (29) | 6.5 ± 0.9 (23) |
| Sodium (mmol/L) | 110–170 mmol/L | 159 ± 0.5 (10) | 159.3 ± 11.6 (30) | 163.1 ± 9.5 (24) |
| Uric Acid (mg/dL) | 0.3–25 mg/dL | 0.5 ± 0.3 (6) | 0.6 ± 0.3 (27) | 0.3 ± 0.2 (24) |
| Significant differences compared to other sites or correlations with Hg are indicted in bold | ||||
Methyl mercury bioaccumulation in aquatic environments is driven in part by atmospheric deposition of mercury from anthropogenic sources, however numerous local factors influence the degree to which MeHg bioaccumulates in biota. The results of our analysis show that American alligators in coastal North Carolina are subject to widespread exposure to mercury. The elevated concentrations of blood Hg found in alligators at the Lake Waccamaw site suggest that bioavaliable levels of MeHg are high, and that factors related to the extensive wetlands surrounding this site are likely increasing the bioavailability and bioaccumulation of Hg. Similar to previous studies, we found that alligator populations from sites in close geographical proximity may have very different levels of Hg contamination that is likely dependent on complex natural and anthropogenic differences in hydrology and ecologic influences on the aquatic environment (Nilsen et al., 2017a). We recommend that ongoing biomonitoring studies be expanded across additional sites that include various ecological and hydrological conditions found throughout the range of American alligators. Further, expanded biomonitoring studies are needed to better understand the impacts of contaminants on alligator populations, and possible risks to humans from consuming contaminated alligator meat. Only by implementing rational and affective biomonitoring plans that take into account changing anthropogenic impacts on aquatic ecosystem will it be possible to understand the impacts of toxic contaminants on alligator populations, or predict and avoid potential adverse health effects on humans consuming alligator meat.
AST
aspartate aminotransferase (U/L)
CFR
Cape Fear River
CK
creatine kinase
CV
coefficient of variation
F
female
LW
Lake Waccamaw
LOD
limit of detection
M
male
MeHg
methyl mercury
SJR
St Johns River
SRM
standard reference material
SVL
snout to vent length
tHg
total mercury
[tHg] total Hg concentration
Acknowledgments:
We are indebted to our many volunteers and advisors including Frank Robb and Russ Lowers, Deborah and Stephen Burke, Kathy Sykes, and our NC State students and lab members of the lab who assisted with field sampling. We would also like to thank the staff of North Carolina Wildlife Resource Commission, especially Alicia Davis, Christopher Kent, and John Henry Harrelson, and Arnold Brunell of the Florida Fish and Wildlife Conservation Commission. We are especially grateful for the help and tolerance received from the residents of Wilmington, Lake Waccamaw, NC.
Funding
Research reported in this publication was supported by the National Institute of Environmental Health Sciences of the National Institutes of Health under Award Number P42ES031009. The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Institutes of Health.
Competing Interests
The authors have no relevant financial or non-financial interests to disclose.
Author Contributions
Conceptualization: SMB, FR
Methodology: SMB, MPG, KDR
Investigation: SMB, MPG, KDR, FR
Visualization: SMB
Funding acquisition: SMB
Project administration: SMB
Supervision: SMB
Writing – original draft: SMB
Writing – review & editing: SMB, MPG, KDR, FR
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No competing interests reported.