Frank C. Bailey

Mercury speciation and biomagnification in the food web of Caddo Lake, Texas and Louisiana, USA, a subtropical freshwater ecosystem

We studied the biomagnification of total mercury and methylmercury in a subtropical freshwater lake, Caddo Lake, Texas and Louisiana, USA. The present study is unique in that it not only included invertebrates (seven species) and fish (six species) but also an amphibian (one species), reptiles (three species), and mammals (three species). Nonfish vertebrates such as those included in the present study are often not included in assessments of trophic transfer of Hg. Mean trophic position (determined using stable isotopes of nitrogen) ranged from 2.0 (indicative of a primary consumer) to 3.8 (indicative of a tertiary consumer). Mean total Hg concentrations ranged from 36 to 3,292 ng/g dry weight in muscle and whole body and from 150 to 30,171 ng/g dry weight in liver. Most of the Hg in muscle and whole-body tissue was found as methylmercury, and at least 50% of the Hg found in liver was in the inorganic form (with the exception of largemouth bass, Micropterus salmoides). Mercury concentrations were positively correlated with trophic position, indicating that biomagnification occurs in the food web of Caddo Lake. The food web magnification factors (FWMFs; slope of the relationship between mean Hg concentration and trophic position) for both total Hg and methylmercury were similar to those observed in other studies. Because most of the total Hg in consumers was methylmercury, the FWMF for methylmercury was not significantly different from the FWMF for total Hg. Some vertebrates examined in the present study had low Hg concentrations in their tissues similar to those observed in invertebrates, whereas others had concentrations of Hg in their tissues that in previous studies have been associated with negative health consequences in fish.

Effects of silver nanoparticles on zebrafish (Danio rerio) and Escherichia coli (ATCC 25922): a comparison of toxicity based on total surface area versus mass concentration of particles in a model eukaryotic and prokaryotic system.

Silver nanoparticles (Ag NPs) have been classified as the most abundant NP found in commercial products. In the present study, zebrafish (Danio rerio) and bacteria (Escherichia coli; ATCC 25922) were used to test the size-dependent toxicological effects of Ag NPs, the effects of ionic silver versus Ag NPs, and Ag NP effects on mortality using mass concentration (mg/L) compared with total surface area (nm(2) /L). Several diameters of Ag NPs (20, 50, 110 nm) as well as AgNO(3) were chosen as experimental treatments. Treated zebrafish embryos exhibited anomalies of the heart, namely, slower heart rates and pericardial edema. A size-dependent response was not observed in zebrafish when viewing mortality across all Ag NP treatments, although 20 nm elicited the highest incidence of abnormal motility and induced slower development. An Ag NP dose- and size-dependent response was observed in treated bacteria using mass concentration, with 20-nm Ag NP producing the highest mortality rate. In both zebrafish and bacteria, AgNO(3) was shown to be more toxic than Ag NPs at equivalent concentrations. When total surface area of Ag NPs was used to gauge bacterial mortality, a total surface area-dependent, but not size-dependent, response was observed for all three Ag NPs used in the present study, with nearly 100% mortality observed once a total surface area of approximately 1E + 18 nm(2) /L was reached. This trend was not apparent, however, when measuring total surface area for zebrafish mortality.

The use of tetragnathid spiders as bioindicators of metal exposure at a coal ASH spill site

On 22 December 2008, a dike containing coal fly ash from the Tennessee Valley Authority Kingston Fossil Fuel Plant (TN, USA) failed, resulting in the largest coal ash spill in US history. The present study was designed to determine sediment metal concentrations at multiple site locations and to determine whether site-specific bioaccumulation of metals existed in tetragnathid spiders. Selenium and nickel were the only 2 metals to exceed the US Environmental Protection Agency sediment screening levels. Selenium concentrations in spiders were significantly higher at ash-affected sites than in those from reference sites. The ratio of methylmercury to total mercury in spiders was found to be similar to that in other organisms (65-75%), which highlights the potential use of tetragnathid spiders as an indicator species for tracing contaminant transfer between the aquatic and terrestrial ecosystems.

Trophic status and metal bioaccumulation differences in multiple fish species exposed to coal ash-associated metals.

On December 22, 2008 a dike containing coal fly ash from the Tennessee Valley Authority Kingston Fossil Plant near Kingston Tennessee USA failed and resulted in the largest coal ash spill in U.S. history. Coal ash, a by-product of coal combustion, is known to contain multiple contaminants of concern, including arsenic and selenium. The purpose of this study was to investigate species differences in the bioaccumulation of arsenic and selenium and potential factors contributing to these differences (i.e., trophic dynamics and gut pH) in the vicinity of the Kingston coal ash spill. Elevated levels of arsenic and selenium were observed in various tissues of largemouth bass, white crappie, bluegill and redear sunfish from sites associated with the Kingston coal ash spill. Highest concentrations of selenium were found in redear sunfish with liver concentrations as high as 24.83mg/kg dry weight and ovary concentrations up to 10.40mg/kg dry weight at coal ash-associated sites. Investigations into the gut pH and trophic dynamics of redear sunfish and bluegill demonstrated a large difference in the gut physiology between these two species. Redear sunfish stomach and intestinal pH was found to be 1.1 and 0.16 pH units higher than in bluegill, respectively. In addition, fish from coal ash-associated sites showed enrichment differences ((15)N and (13)C) compared to no ash sites, indicating differences in food web dynamics between sites. These results imply the incorporation of coal ash-associated compounds into local food webs and/or a shift in diet at ash sites compared to the no ash reference sites. Based on these results, further investigation into a broader food web at ash-associated sites is warranted.

Adrenocortical Effects of Human Encounters on Free-Ranging Cottonmouths (Agkistrodon piscivorus)

Abstract The increased encroachment of humans into natural areas is typically viewed as stressful for many wildlife species. A common stress response of many animals, including snakes, is the elevated release of the adrenal hormone, corticosterone. To test whether human encounters elicited a stress response in snakes, we monitored the levels of circulating corticosterone in free-ranging Cottonmouths (Agkistrodon piscivorus) during staged interactions. When exposed to a high-level disturbance (i.e., capture and confinement in a bag) for 30 min, Cottonmouths exhibited a significant corticosterone stress response as predicted. This response was four times that of the control treatment (i.e., immediately bled snakes) and shows that Cottonmouths exhibit strong corticosterone responses to confinement. Conversely, blood corticosterone values for low-level disturbance (i.e., nearby human presence for 30 min) did not differ significantly from the control treatment. The lack of a strong stress response to low-level disturbance indicates that Cottonmouths possess a seemingly adaptive mechanism of not being overly alarmed by the mere presence of a potential predator. This suggests that the occasional foot-path encounters humans commonly have with snakes may not be stressful for some snake species.

Asparagine362 is essential for zinc binding and catalysis in the peptidase reaction of Saccharomyces cerevisiae leukotriene A4 hydrolase

Zinc metallopeptidases are ubiquitous enzymes with diverse cellular functions that can be found in most organisms. Leukotriene A₄ hydrolase (LTA4H; E.C. 3.3.2.6) is an unusual zinc metallopeptidase of the M1 family that also possesses an epoxide hydrolase activity; however, the role of its peptidase activity remains unknown. To further characterize the peptidase activity of LTA4H and other closely related metallopeptidases, a multiple sequence alignment and predicted structure were used to target three amino acid residues of yeast LTA4H for mutagenesis: Asn362, Trp365, and Asp399. Although mutating Trp365 and Asp399 had little effect on catalysis, altering Asn362 had varying effects on catalysis, depending on the replacement residue. Mutation of Asn362 to glutamine (N362Q) caused minor catalytic defects, while mutation to leucine (N362L) or glutamate (N362E) caused large reductions in activity. Both N362L and N362E also exhibited an altered pH dependence of catalysis, reduced chloride activation, and reduced zinc affinity and content, indicating that Asn362 may interact with the nearby zinc coordinating residue His344, and possibly with Glu363 as well, to polarize and/or orient these residues.