Ecological half-life of radiocesium in white-tailed deer on the Department of Energy's Savannah River Site: What can a half century of field monitoring tell us?

This paper estimates the 137Cs ecological half-life of white-tailed deer inhabiting the Department of Energy's Savannah River Site (SRS) based on sex and age using data collected over a 51-year time-period. With a physical half-life of 30.2 yr, the biological half-life for the deer herd is considerably shorter because of the isotope's biochemical mimicry of K+ inside the body. Leveraging this long-term dataset and robust sample size, we compared the long-term half-century estimates to shorter decadal increments. The simple exponential decay model for the entire 51-year sampling period predicted an ecological half-life of 23.15 years. When breaking the sample data into decadal increments 137Cs body burden had complex temporal dynamics with predicted half-lives ranging from 9.25 to 32.33 years. Exponential decay for the entire 51-year sampling period for models evaluated by sex, age, sex*age to determine how these variables influence the predictability in the mean depuration rate, the ecological half-lives were between 21 and 23 years for all permutations, except for fawns that had a half-life no different than the physical half-life of the isotope itself. Differential habitat use and competition most likely explains why both yearling and adult females consistently had higher body burdens than males over the 51-year time period, showing how dynamic this radioisotope is in biological systems. This study is one of the most robust long-term datasets in the world (n = 42,412) that is specifically focused on monitoring the uptake and depuration of 137Cs in a wild species.

The development and use of a spatially explicit model for river otters to evaluate environmental hazards: a case study on the Department of Energy's Savannah River Site.

The Department of Energy's (DOE) Savannah River Site (SRS) faces a legacy of radionuclide and metal contamination from industrial processes that occurred throughout the site. Northern river otters (Lontra canadensis) are appropriate receptors for studying the effects of long-term, low-level contamination because they are long-lived, higher trophic level organisms susceptible to accumulating high levels of pollutants. The purpose of this study was to use latrine surveys to examine patterns of wetland latrine usage; explicitly model northern river otter resource selection on the landscape level; and utilize the model results within an ecological risk assessment (ERA) framework to assess potential effects of metals and radiocesium (137Cs) on the population for the SRS as a case study. River drainages and associated wetlands were surveyed for latrine sites and scats were collected and analyzed for 137Cs activity to validate model results. The spatially explicit resource model predicted otter drainage reach use and was used in an ERA to develop exposure models for nine heavy metals as well as 137Cs on the SRS population of river otters. The evaluation predicted that the only contaminant occurring at high enough levels to cause population effects was mercury and that the observed concentrations were probably not high enough to cause significant impairment. However, multiple metals were above action level thresholds. The field validation process showed an unexpected preference for one man-made treatment wetland that was heavily contaminated, showing that the ERA process is complex and must be approached using multiple scales.

Microbial community structure of a freshwater system receiving wastewater effluent.

Despite our dependency on treatment facilities to condition wastewater for eventual release to the environment, our knowledge regarding the effects of treated water on the local watershed is extremely limited. Responses of lotic systems to the treated wastewater effluent have been traditionally investigated by examining the benthic macroinvertebrate assemblages and community structure; however, these studies do not address the microbial diversity of the water systems. In the present study, planktonic and benthic bacterial community structure were examined at 14 sites (from 60 m upstream to 12,100 m downstream) and at two time points along an aquatic system receiving treated effluent from the Charleston Wastewater Treatment Plant (Charleston, IL). Total bacterial DNA was isolated and 16S rRNA sequences were analyzed using a metagenomics platform. The community structure in planktonic bacterial communities was significantly correlated with dissolved oxygen concentration. Benthic bacterial communities were not correlated with water quality but did have a significant geographic structuring. A local restructuring effect was observed in both planktonic and benthic communities near the treated wastewater effluent, which was characterized by an increase in abundance of sphingobacteria. Sites further downstream from the wastewater facility appeared to be less influenced by the effluent. Overall, the present study demonstrated the utility of targeted high-throughput sequencing as a tool to assess the effects of treated wastewater effluent on a receiving water system, and highlighted the potential for this technology to be used for routine monitoring by wastewater facilities.

Atrazine and glyphosate dynamics in a lotic ecosystem: the common snapping turtle as a sentinel species.

Atrazine and glyphosate are two of the most common pesticides used in the US Midwest that impact water quality via runoff, and the common snapping turtle (Chelydra serpentina) is an excellent indicator species to monitor these pesticides especially in lotic systems. The goals of this study were to (1) quantify atrazine, the atrazine metabolite diaminochlorotriazine (DACT), and glyphosate burdens in common snapping turtle tissue from individuals collected within the Embarras River in Illinois; (2) quantify atrazine, DACT, and glyphosate loads in water from the aquatic habitats in which common snapping turtles reside; and (3) investigate tissue loads based on turtle morphology and habitat choice. Concentrations of atrazine, DACT, and glyphosate in tissue did not show any relationship with lake habitat, carapace length, width, or mass. Both atrazine and glyphosate tissue samples varied as a function of site (river vs. lake), but DACT did not. Atrazine and glyphosate concentrations in water samples showed a linear effect on distance from the reservoir spillway and a deviation from linearity. Water column concentrations of all three contaminants varied across capture sites, but atrazine water concentration did not influence DACT water concentration nor did it exhibit a site interaction. Water atrazine and glyphosate concentrations were greater than tissue concentrations, whereas DACT water and tissue concentrations did not differ. This study showed that turtles are useful in long-term pesticide monitoring, and because DACT as a metabolite is less sensitive to variation, it should be considered as a preferred biomarker for pesticide runoff.

Toxicodynamic modeling of 137Cs to estimate white-tailed deer background levels for the Department of Energy's Savannah River Site.

The U.S. Department of Energy's (USDOE) Savannah River Site (SRS) is a former nuclear weapon material production and current research facility adjacent to the Savannah River in South Carolina, USA. The purpose of this study was to determine the background radiocesium ((137)Cs) body burden (e.g., from global fallout) for white-tailed deer (Odocoileus virginianus) inhabiting the SRS. To differentiate what the background burden is for the SRS versus (137)Cs obtained from SRS nuclear activities, data were analyzed spatially, temporally and compared to other off-site hunting areas near the SRS. The specific objectives of this study were: to compare SRS and offsite deer herds based on time and space; to interpret comparisons based on how data were collected as well as the effect of environmental and anthropogenic influences; to determine what the ecological half-life/decay rate is for (137)Cs in the SRS deer herd; and to give a recommendation to what should be considered the background (137)Cs level in the SRS deer herd. Based on the available information and analyses, it is recommended that the determination of what is considered background for the SRS deer herd be derived from data collected from the SRS deer herd itself and not offsite collections for a variety of reasons. Offsite data show extreme variability most likely due to environmental factors such as soil type and land-use patterns (e.g., forest, agriculture, residential activities). This can be seen from results where samples from offsite military bases (Fort Jackson and Fort Stewart) without anthropogenic (137)Cs sources were much higher than both the SRS and a nearby (Sandhills) study site. Moreover, deer from private hunting grounds have the potential to be baited with corn, thus artificially lowering their (137)Cs body burdens compared to other free-ranging deer. Additionally, sample size for offsite collections were not robust enough to calculate a temporal decay curve with an upper confidence level to determine if the herds are following predicted radioactive decay rates like the SRS or if the variability is due to those points described above. Using mean yearly values, the ecological half-life for (137)Cs body burdens for SRS white-tailed deer was determined to be 28.79 years--very close to the 30.2 years physical half-life.

Trophic dynamics of U, Ni, Hg and other contaminants of potential concern on the Department of Energy's Savannah River Site.

The Department of Energy's Savannah River Site is a former nuclear weapon material production and current research facility located in South Carolina, USA. Wastewater discharges from a fuel and nuclear reactor target manufacturing facility released depleted and natural U, as well as other metals into the Tims Branch-Steed Pond water system. We investigated the current dynamics of this system for the purposes of environmental monitoring and assessment by examining metal concentrations, bioavailability, and trophic transfer of contaminants in seven ponds. Biofilm, detritus, and Anuran and Anisopteran larvae were collected and analyzed for stable isotopes (δ (15)N, δ (13)C) and contaminants of potential concern (COPC) with a focus on Ni, U, and Hg, to examine metal mobility. Highest levels of Ni and U were found in biofilms U (147 and 332 mg kg(-1) DW, respectively), while highest Hg levels were found in tadpoles (1.1 mg kg(-1) DW). We found intraspecific biomagnification of COPCs as expressed through stable isotope analysis. Biofilms were the best indicators for contamination and Anuran larvae with the digestive tract removed were the best indicators of the specific bioavailability of the focal metals. Monitoring data showed that baseline δ (15)N values differed between ponds, but within a pond, values were stable throughout tadpole Gosner stage, strengthening the case to use this species for monitoring purposes. It is likely that there still is risk to ecosystem integrity as COPC metals are being assimilated into lower trophic organisms and even low levels of this mixture has shown to produce deleterious effects to some wildlife species.

Assessing multiple endpoints of atrazine ingestion on gravid Northern Watersnakes (Nerodia sipedon) and their offspring.

Ecotoxicological studies that focus on a single endpoint might not accurately and completely represent the true ecological effects of a contaminant. Exposure to atrazine, a widely used herbicide, disrupts endocrine function and sexual development in amphibians, but studies involving live-bearing reptiles are lacking. This study tracks several effects of atrazine ingestion from female Northern Watersnakes (Nerodia sipedon) to their offspring exposed in utero. Twenty-five gravid N. sipedon were fed fish dosed with one of the four levels of atrazine (0, 2, 20, or 200 ppb) twice weekly for the entirety of their gestation period. Endpoints for the mothers included blood estradiol levels measured weekly and survival more than 3 months. Endpoints for the offspring included morphometrics, clutch sex ratio, stillbirth, and asymmetry of dorsal scales and jaw length. Through these multiple endpoints, we show that atrazine ingestion can disrupt estradiol production in mothers, increase the likelihood of mortality from infection, alter clutch sex ratio, cause a higher proportion of stillborn offspring, and affect scale symmetry. We emphasize the need for additional research involving other reptile species using multiple endpoints to determine the full range of impacts of contaminant exposure.

Evaluating the Illinois Stream Valley segment model as an effective management tool.

Stream habitat assessments are conducted to evaluate biological potential, determine anthropogenic impacts, and guide restoration projects. Utilizing these procedures, managers must first select a representative stream reach, which is typically selected based on several criteria. To develop a consistent and unbiased procedure for choosing sampling locations, the Illinois Department of Natural Resources and the Illinois Natural History Survey have proposed a technique by which watersheds are divided into homogeneous stream segments called valley segments. Valley segments are determined by GIS parameters including surficial geology, predicted flow, slope, and drainage area. To date, no research has been conducted to determine if the stream habitat within a valley segment is homogeneous and if different valley segments have varying habitat variables. Two abutting valley segments were randomly selected within 13 streams in the Embarras River watershed, located in east-central Illinois. One hundred meter reaches were randomly selected within each valley segment, and a transect method was used to quantify habitat characteristics of the stream channel. Habitat variables for each stream were combined through a principal components analysis (PCA) to measure environmental variation between abutting valley segments. A multivariate analysis of variance (MANOVA) was performed on PCA axes 1-3. The majority of abutting valley segments were significantly different from each other indicating that habitat variability within each valley segment was less than variability between valley segments (5.37 ≤ F ≤ 245.13; P ≤ 0.002). This comparison supports the use of the valley segment model as an effective management tool for identifying representative sampling locations and extrapolating reach-specific information.

High levels of fluctuating asymmetry in populations of Apodemus flavicollis from the most contaminated areas in Chornobyl.

Random deviations from the perfect symmetry of normally bilaterally symmetrical characters for an individual with a given genotype occur during individual development due to the influence of multiple environmental factors. Fluctuating asymmetry (FA) is often used as a measure of developmental instability, and can be estimated as the variance of the distribution of differences between the left and right sides. We addressed the question of whether levels of FA were elevated in radioactively contaminated populations living around Chornobyl compared to those in reference populations of the yellow-necked mouse (Apodemus flavicollis). In addition, we studied amounts of directional asymmetry (DA) when one side is larger than the other on average. There was a significant difference among populations, including reference populations, in the amount of both FA and DA. A higher level of FA was documented for the contaminated populations in close proximity to the failed Chornobyl reactor for both the asymmetry of size and shape. The FAs of size and shape were highest in populations from the most contaminated locations in the Chornobyl exclusion zone. Although the directional asymmetry of shape was also highest in the contaminated populations, it was not significantly different from those in most of the reference populations. Populations from less contaminated areas inside the Chornobyl exclusion zone did not express FA values different from those of the reference populations outside the affected area. FA of skulls of A. flavicollis may indicate the degree to which the level of radioactive contamination affects the development of animals at Chornobyl. However, the mechanisms leading to these effects are not clear and probably vary from population to population. There were significant correlations between the overall right to left differences for the Procrustes aligned shape configurations, centroid sizes, and intramuscular (137)Cs. Detectable effects of radiation on developmental stability probably start to occur between 0.132 and 0.297 microGy/h.

FOOD QUALITY, HETEROZYGOSITY, AND FITNESS CORRELATES IN PEROMYSCUS POLIONOTUS.

Oldfield mice (Peromyscus polionotus) that are more heterozygous utilize food and maintain body weight under varying degrees of dietary stress better than their less heterozygous counterparts. Mice were collected in southern Florida and fed diets of three qualities. During each dietary treatment, body weight, amount of food eaten, amount of food absorbed, and feeding efficiency were determined. Body weights for all mice decreased during the experiment. More heterozygous mice maintained their weight better during periods of dietary stress than those that were less heterozygous. Mice with different levels of genetic variability had essentially the same mean feeding efficiency with high quality diets. Mice with high heterozygosities maintained the same efficiency with low quality diets, but those with lower heterozygosities had decreased feeding efficiencies. A slight increase in available energy for mice of different heterozygosities can dramatically change fitness correlated characters, such as growth rates, body weights, energy stores, and reproductive rates.