Ecological risk of methylmercury in Everglades National Park, Florida, USA.

Dramatic declines in mercury levels have been reported in Everglades biota in recent years. Yet, methylmercury (MeHg) hot spots remain. This paper summarizes a risk assessment of MeHg exposure to three piscivorous wildlife species (bald eagle, Haliaeetus leucocephalus; wood stork, Mycteria americana; and great egret, Ardea albus) foraging at a MeHg hot spot in northern Everglades National Park (ENP). Available data consisted of literature-derived life history parameters and tissue concentrations measured in 60 largemouth bass (Micropterus salmoides), 60 sunfish (Lepomis spp.), and three composite samples of mosquitofish (Gambusia holbrooki) collected from 2003 to 2005. To assess risk, daily MeHg intake was estimated using Monte Carlo methods and compared to literature-derived effects thresholds. The results indicated the likelihood was very high, ranging from 98-100% probability, that these birds would experience exposures above the acceptable dose when foraging in northern ENP. Moreover, the likelihood that these birds would experience exposures above the lowest-observed-adverse-effect level (LOAEL) ranged from a 14% probability for the wood stork to 56% probability for the eagle. Data from this study, along with the results from several other surveys suggest that biota in ENP currently contain the highest MeHg levels in South Florida and that these levels are similar to or greater than other known MeHg hot spots in the United States. Given these findings, this paper also outlines a strategic plan to obtain additional measured and modeled information to support risk-based management decisions in ENP.

Extreme spatial variability and unprecedented methylmercury concentrations within a constructed wetland.

We began monitoring concentrations of both total mercury (THg) and methylmercury (MeHg) in surface water at Stormwater Treatment Area-2 (STA) on July 20, 2000. This 2602 hectare STA was constructed with three independent marshes to remove phosphorus from agricultural runoff and reduce eutrophication in the northern Everglades. However, there was concern that in doing so, STA-2 might inadvertently worsen the existing mercury problem in the Everglades. Accordingly, operating permits stipulated that flow-through operation of these treatment cells could not begin until concentrations of THg and MeHg in the interior marsh were not significantly greater than corresponding concentrations in the supply canal. Cells 2 and 3 quickly met the start-up criteria in the fall of 2000. In contrast, Cell 1 exhibited anomalously high MeHg concentrations in the fall of 2000 and 2001, and the summer of 2002. During the last such event, water-column concentrations in Cell 1 reached 32 ng THg/L and an unprecedented 20 ng MeHg/L. Tissue Hg in resident fishes reached levels as high as 430 ng/g in mosquitofish, Gambusia holbrooki, 930 ng/g in sunfish, Lepomis spp., and 2000 ng/g in largemouth bass, Micropterus salmoides. Guided by results from the monitoring program, flow rate and water depth were managed as a means to alter sulfur biogeochemistry and, thereby, reduce in situ mercury methylation. This adaptive management strategy likely played a role in the decline in water-column concentrations of THg and MeHg in Cell 1 by late 2002 and the subsequent declines in tissue Hg levels in resident fishes. Cell 1 finally met formal start-up criteria on November 26, 2002.

Levels of mercury in alligators (Alligator mississippiensis) collected along a transect through the Florida Everglades.

As part of a multi-agency study of alligator health, 28 American alligators (Alligator mississippiensis) were captured along a transect through the Florida Everglades in 1999. Liver and tail muscle tissues were sampled and analyzed on a wet weight basis for total mercury (THg) using cold-vapor atomic absorption spectrophotometry. All tissues had detectable concentrations of THg that ranged from 0.6 to 17 mg/kg in liver and from 0.1 to 1.8 mg/kg in tail muscle. THg was more concentrated in liver tissue than tail muscle, but levels were highly correlated between tissues. THg concentrations in tissue differed significantly among locations, with animals from Everglades National Park (ENP) having mean concentrations of THg in liver (10.4 mg/kg) and tail muscle (1.2 mg/kg) that were two-fold higher than basin-wide averages (4.9 and 0.64 mg/kg, respectively). The reasons for higher contamination of ENP alligators were unclear and could not be explained by differences in sex, length, weight or animal age. While delta15N values were positively correlated with THg concentrations in tail muscle, spatial patterns in isotopic composition did not explain the elevated THg levels in ENP alligators. Therefore, it appears that ENP alligators were more highly exposed to mercury in their environment than individuals in other areas. Comparisons to a previous survey by Yanochko et al. [Arch Environ Contam Toxicol 32 (1997) 323] suggest that mercury levels have declined in some Everglades alligators since 1994.

Biomonitoring environmental contaminants near a municipal solid-waste combustor: a decade later.

During the 1999 nesting season, eggs and nestlings of anhingas (Anhinga anhinga) and white ibises (Eudocimus albus) were collected from a colony located on the site of a municipal solid-waste (MSW) combustor and analyzed for residues of chemicals potentially released from this facility. Concentrations of most residues, including tetrachlorodibenzo-p-dioxin (TCDD). tetrachlorodibenzofuran (TCDF), arsenic, beryllium, cadmium and lead, were at levels comparable to those found during a similar survey done in 1989, prior to facility start-up. Nickel residues were detected only sporadically in anhingas and in eggs from ibises, and decreased significantly in concentration in ibis nestlings in 1999 compared to 1989. While concentrations of mercury in anhinga nestlings and in eggs of both species were comparable to 1989 levels, its concentration was significantly greater in ibis nestlings in 1999. However, levels of mercury in the ibises remained relatively low when compared to birds from other areas of Florida and did not appear to represent a health threat. While lead did not increase in 1999, its concentration in ibis nestlings remained a concern. The most notable temporal trend observed in birds at this site was a general monotonic decrease in levels of selenium residues during the 10-year monitoring period.

Mercury in eggs and feathers of great egrets (Ardea albus) from the Florida Everglades.

Great egret (Ardea albus) eggs and nestling feathers were collected for total mercury (THg) and methylmercury (MeHg) analysis from two colonies in the Florida Everglades in 1999 and 2000. THg was present in all eggs at a mean concentration of 0.39 +/- 0.19 microg/g fresh weight (n = 33, range = 0.08-0.86 microg/g). Egg-THg levels did not differ significantly between colonies or years. MeHg concentration in eggs was 0.35 +/- 0.18 microg/g fresh weight (n = 20, range = 0.05-0.82 microg/g,), and on average represented 85% of the THg found in the egg. Concentration of THg in feathers from egret nestlings, age 11-31 days, ranged from 1.4 to 8.6 microg/g dry weight. Feather-THg levels also did not differ significantly between colonies or years. THg concentrations in feathers, normalized based on bill length, were positively correlated to THg concentrations in eggs from the same clutch. Levels of THg in both eggs and feathers were lower in 1999 and 2000 than values reported for similar samples collected in 1993-95, indicating that MeHg exposure has decreased in the southern Everglades since the mid-1990s. THg levels in eggs and nestling feathers for the period of this study were below levels associated with toxic reproductive effects. Clutch size, fledging success, and brood size observed in this study were consistent for this species in the Everglades. Collectively, these results suggest that MeHg was not adversely affecting the reproductive performance of this population during the study.

Evaluation of bioassays to monitor surface microlayer toxicity in tropical marine waters.

Bioassays were developed, using embryos of: coral,Montastraea faveolata; graysby, Epinephelus cruentatus;grouper, Epinephelus adscensionis x gruttatus (hybrid); queenconch, Strombus gigas; rock-boring urchin, Echinodermatalucunter; spotted seatrout, Cynoscion nebulosus; variegatedurchin, Lytechinus variegatus; winged pearl oyster, Pteriacolymbus; and yellowtail snapper, Ocyurus chrysurus. Relativesensitivities and precison of various species-endpoint combinations wereevaluated using three reference toxicants: copper, sodium dodecyl sulfate,and Dibrom(R). The 24-h P. colymbus embryo test had the best overallsensitivity and exhibited a high degree of precision. However, oyster embryoswere difficult to obtain and did not aggregate at the air-water interface.Therefore, the P. colymbus embryo test was deemed unsuitable for useas a bioassay for monitoring sea-surface microlayer (SSML) toxicity. Testsbased on normal development of L. variegatus to the early pluteus 3stage and percent normal-live C. nebulosus larvae at 48 h wererelatively sensitive and exhibited good replicability and repeatability. TheL. variegatus urchin embryo test was also found to be highlyreproducible. The results of this comparative study indicated that L.variegatus and C. nebulosus were suitable surrogates forcoral-reef species in toxicity assessments of the SSML.

Biomonitoring environmental contaminants near a municipal solid-waste combustor.

Tetrachlorodibenzo-p-dioxin (TCDD), tetrachlorodibenzofuran (TCDF) and selected metal concentrations were measured in eggs and nestlings of anhingas (Anhinga anhinga) and white ibises (Eudocimus albus) collected from a colony next to a municipal solid-waste (MSW) combustor and ash landfill. Most of the measured residues, including TCDD, TCDF, arsenic, beryllium, cadmium and nickel, remained at pre-operational levels during the first five years of facility operation. Selenium (in anhingas) and mercury (in both anhingas and ibises) occurred at their lowest concentrations in samples collected during the fifth year of facility operation (Year-5). Alternatively, concentrations of lead in ibis nestlings were highest in Year-1 and Year-5 compared to Year-0. The MSW combustor could neither be ruled out nor confirmed as the source of this lead.

Absorption line parameter measurements using laser spectroscopy.

An analytical method is described for obtaining the precise location of an absorption line and the pressure broadening coefficients due to self-broadening or foreign gas broadening from experimental measurements using a laser operating on a single line near the absorption line. These absorption line characteristics are obtained from the pressure dependence of the transmittance of the laser radiation for the gas of interest, the analysis involving a least squares fit to a family of Lorentz curves. The method includes a computer search for the region of best fit to the Lorentz profile and provides both the values of and errors in the above coefficients. The pressure broadening coefficient obtained is the same as for the more general Voigt curve. The method is applied to the absorption line of vinyl chloride near 27.972 microm and of methane near 3.392 microm and the results compared with a graphical fit to a Voigt profile. The self-broadening coefficients obtained were alpha = 0.15 x 10(-3) +/- 0.97 x 10(-4) cm(-1) Torr(-1) for vinyl chloride and alpha = 0.14 x 10(-3) +/- 0.46 x 10(-4) cm(-1) Torr(-1) for methane. The separation between the helium-neon laser line at 2947.903 cm(-1) and the methane absorption line at 2947.888 +/- 0.015 cm(-1) was found to be 0.21 x 10(-2) +/- 0.15 x 10(-2) cm(-1).