Amino acid racemization and its relation to geochronology and archaeometry.

Amino acid racemization, used as a method of relative and quantitative dating of fossils, evaluates the degree of postmortem conversion of l to d amino acid enantiomers. While extensively utilized, this method has garnered confusion due to controversial age estimates for human fossils in North America in the 1970s. This paper explains the age controversy and aftermath, current chromatographic methods used in research, mathematical calibration models, and a short synopsis of other dating techniques in geochronology and archaeometry.

Ritual drinks in the pre-Hispanic US Southwest and Mexican Northwest.

Chemical analyses of organic residues in fragments of pottery from 18 sites in the US Southwest and Mexican Northwest reveal combinations of methylxanthines (caffeine, theobromine, and theophylline) indicative of stimulant drinks, probably concocted using either cacao or holly leaves and twigs. The results cover a time period from around A.D. 750-1400, and a spatial distribution from southern Colorado to northern Chihuahua. As with populations located throughout much of North and South America, groups in the US Southwest and Mexican Northwest likely consumed stimulant drinks in communal, ritual gatherings. The results have implications for economic and social relations among North American populations.

Survival, Reproduction and Growth of the Marine Amphipod, Leptocheirus plumulosus, Following Laboratory Exposure to Copper-Spiked Sediment.

Leptocheirus plumulosus was exposed for 28 days to Cu-spiked sediment at mean concentrations ranging from 44.4 to 605 mg Cu/kg dry sediment in a sediment/water test system designed to simulate natural conditions. The NOEC (no observed effect concentration)-LOEC (lowest observed effect concentration) range for the most sensitive endpoint of growth was 199-414 mg Cu/kg sediment. An IC50 for reproduction was estimated at 187 mg Cu/kg sediment. Mean Cu concentrations in pore water (PW) where significant effects were observed were 25.8 and 59.0 µg/L, while their respective concentrations in overlying water (OW) were 22.1 and 28.0 µg Cu/L. Copper concentrations were ≤19.1 and <16.6 µg/L in PW and OW, respectively, at lower exposures where effects were not evident. Concentrations of Cu in marine sediment lower than sediment quality guidelines based on geochemical factors of acid volatile sulfide, organic carbon content (f OC), and sediment grain size (i.e., silt + clay) would appear not to result in adverse effects toward L. plumulosus.

Survival and Growth of the Marine Polychaete, Neanthes arenaceodentata, Following Laboratory Exposure to Copper-Spiked Sediment.

Juvenile marine polychaetes, Neanthes arenaceodentata, were exposed for 28 days to copper (Cu)-spiked sediment at six concentrations ranging from 48.3 to 2380 mg Cu/kg dry sediment, plus control. Survival was reduced (p ≤ 0.05) at concentrations ≥1190 mg Cu/kg. Growth was inhibited at Cu concentrations ≥506 mg Cu/kg. Dose-response relationships yielded LC10 and LC50 estimates of 514 and 1230 mg Cu/kg, respectively. The growth effect EC50 estimate was 409 mg Cu/kg. Ranges for the no observable effect concentration and lowest observable effect concentration were 506-1190 mg Cu/kg for survival, and 230-506 mg Cu/kg for growth. Pore water concentrations of Cu were 38.7-65.8 µg Cu/L in exposures where toxic effects were observed, compared to a range of 15.1-22.4 µg Cu/L in exposures where significant effects were not evident. The results of the study were compared with empirical and mechanistic sediment quality guidelines for the protection of benthic organisms.

Adsorption and degradation of neonicotinoid insecticides in agricultural soils.

The adsorption and degradation of seven commercially available neonicotinoid insecticides in four types of agricultural soils from three states (Mississippi, Arkansas, and Tennessee) in the USA were studied. The adsorptions of all the neonicotinoids fit a linear isotherm. The adsorption distribution coefficients (Kd) were found to be below 2.0 L/kg for all the neonicotinoids in all the soils from Mississippi and Arkansas. Only in the Tennessee soil samples, the Kd ranged from 0.96 to 4.21 L/kg. These low values indicate a low affinity and high mobility of these insecticides in the soils. The soil organic carbon-water partitioning coefficient Koc ranged from 349 to 2569 L/kg. These Kd values showed strong positive correlations with organic carbon content of the soils. The calculated Gibbs energy change (ΔG) of these insecticides in all the soils ranged from - 14.6 to - 19.5 kJ/mol, indicating that physical process was dominant in the adsorptions. The degradations of all these neonicotinoids in the soils followed a first-order kinetics with half-lives ranging from 33 to 305 days. The order of the insecticides with decreasing degradation rate is as follows: clothianidin > thiamethoxam > imidacloprid > acetamiprid > dinotefuran > thiacloprid > nitenpyram. The moisture content, clay content, and cation exchange capacity showed positive effects on the degradation rate of all the neonicotinoids. The Groundwater Ubiquity Score (GUS) calculated from the adsorption distribution coefficient, organic content, and half-life indicates that, except for thiacloprid, all the neonicotinoids in all the soils are possible leachers, having potentials to permeate into and through groundwater zones.

Klebsiella pneumoniae clinical isolates with features of both multidrug-resistance and hypervirulence have unexpectedly low virulence.

Klebsiella pneumoniae has been classified into two types, classical K. pneumoniae (cKP) and hypervirulent K. pneumoniae (hvKP). cKP isolates are highly diverse and important causes of nosocomial infections; they include globally disseminated antibiotic-resistant clones. hvKP isolates are sensitive to most antibiotics but are highly virulent, causing community-acquired infections in healthy individuals. The virulence phenotype of hvKP is associated with pathogenicity loci responsible for siderophore and hypermucoid capsule production. Recently, convergent strains of K. pneumoniae, which possess features of both cKP and hvKP, have emerged and are cause of much concern. Here, we screen the genomes of 2,608 multidrug-resistant K. pneumoniae isolates from the United States and identify 47 convergent isolates. We perform phenotypic and genomic characterization of 12 representative isolates. These 12 convergent isolates contain a variety of antimicrobial resistance plasmids and virulence plasmids. Most convergent isolates contain aerobactin biosynthesis genes and produce more siderophores than cKP isolates but not more capsule. Unexpectedly, only 1 of the 12 tested convergent isolates has a level of virulence consistent with hvKP isolates in a murine pneumonia model. These findings suggest that additional studies should be performed to clarify whether convergent strains are indeed more virulent than cKP in mouse and human infections.

Photodegradation of clothianidin and thiamethoxam in agricultural soils.

Presented in this paper is a study on the photodegradation of two widely used neonicotinoid insecticides clothianidin and thiamethoxam in three soils and in solid phase. The effects of light with differing wavelengths were examined using the natural sunlight and single ultraviolet A (UVA) and ultraviolet B (UVB) light sources. The results indicated that UVB played a key role in the photodegradation of clothianidin and thiamethoxam while the effects of visible and UVA lights were negligible. The degradations of clothianidin and thiamethoxam under all the light sources followed the first-order kinetics, and the half-lives of clothianidin and thiamethoxam in the three soils under the sunlight ranged from 97 to 112 h and 88 to 103 h, respectively. When clothianidin and thiamethoxam were directly exposed to the sunlight without soil, the degradation rates were remarkably higher with half-lives being 13 and 10 h, respectively. Therefore, the insecticides fallen on the surface of soils would be degraded under sunlight much faster than those that enter the soils. The examination of the degradation products revealed four compounds from the photodegradation of clothianidin and three from thiamethoxam, and clothianidin was one of the photodegradation products of thiamethoxam.

Chronic toxicity of silver to the sea urchin (Arbacia punctulata).

The chronic toxicity of silver to the sea urchin (Arbacia punctulata) was determined in 30 per thousand salinity seawater during a three-part study: A fertilization test (1-h sperm exposure), a 48-h embryo test, and a 30-d adult test. Combined data from the three tests resulted in a lowest-observed-effect concentration of 19 microg/L, a no-observed-effect concentration of 8.6 microg/L, and a maximum acceptable toxicant concentration of 13 microg/L, based on measured concentrations of dissolved silver. The 96-h median effective concentration was 40 microg/L, and the acute to chronic toxicity ratio was 3.1. During the tests, measured concentrations of free ionic silver (Ag+) were only 0.0027 to 0.0046% of dissolved silver concentrations, as predicted by ion-speciation theory. Some measured Ag+ concentrations were lower than predicted, indicating the presence of other ligands in the seawater test media. These strong sulfide ligands were exuded by the exposed sea urchins into the seawater (where Ag-sulfide complexes formed) in amounts that increased in direct proportion to the silver concentration during the toxicity test. This suggests a toxicity-defense mechanism that functioned by modifying the chemistry of the surrounding external medium.

Influence of salinity and organic carbon on the chronic toxicity of silver to mysids (Americamysis bahia) and silversides (Menidia beryllina).

Tests were conducted with mysids (Americamysis bahia) and silversides (Menidia beryllina) to evaluate the influence of salinity and organic carbon on the chronic toxicity of silver. During 7- and 28-d tests conducted at 10, 20, and 30% per hundred salinity, higher concentrations of dissolved silver generally were required to cause a chronic effect as the salinity of the seawater was increased. The 28-d mysid and silverside 20%-effective concentration values (expressed as dissolved silver) ranged from 3.9 to 60 and from 38 to 170 microg/L, respectively, over the salinity range. This pattern was not observed when the same test results were evaluated against the concentrations of free ionic silver (measured directly during toxicity tests), as predicted by the free-ion activity model. Increasing the concentration of dissolved organic carbon from 1 mg/L to the apparent maximum achievable concentration of 6 mg/L in seawater caused a slight decrease in chronic toxicity to silversides but had no effect on the chronic toxicity to mysids. The possible additive toxicity of silver in both food and water also was investigated. Even at the maximum achievable foodborne concentration, the chronic toxicity of silver added to the water was not affected when silver was also added to the food, based on the most sensitive endpoint (growth). However, although fecundity was unaffected at all five tested concentrations during the test with silver in water only, it was significantly reduced at the two highest waterborne silver concentrations (12 and 24 microg/L) during the test with silver dosed into food and water.

Evolution of cadmium resistance in Daphnia magna.

A diverse laboratory population of Daphnia magna Straus was established by combining individuals from eight sources. Artificial selection for increased resistance to the acute toxic effects of cadmium was performed, and after eight generations, the average median effective concentration increased from 61 to 180 microg/L. No differences in life span, offspring production, time to first brood, number of offspring in the first brood, or intrinsic rate of population increase (r) were observed between the cadmium-adapted population and the controls under ideal conditions or under conditions of temperature or feeding ration stress, but cadmium-adapted daphnids were smaller. Control and cadmium-adapted populations were equally sensitive to copper and malathion, but the cadmium-adapted population was less sensitive to lead and more sensitive to phenol. Analysis of amplified fragment-length polymorphisms indicated a significant decrease in genetic diversity in the cadmium-adapted population. Although the evolved cadmium resistance would allow adapted populations to exist in areas where cadmium concentrations would be toxic to unadapted populations, the decreased genetic diversity, smaller size, and increased sensitivity to at least one other toxicant could reduce the probability of long-term survival even in the absence of future cadmium exposure.

The influence of subterranean termites on the hydrological characteristics of a Chihuahuan desert ecosystem.

Rainfall simulation at an average intensity of 124 mm·h-1 was used to compare infiltration and run off on arid areas where subterranean termites had been eliminated four years prior to the initiation of the study (termite free) with adjacent areas populated by subterranean termites (termites present). Infiltration rates on termite free plots with less than 5% perennial plant cover were significantly lower 51.3±6.8 mm·h-1 than rates on comparable termites present plots 88.4±5.6 mm·h-1. On plots centered on Larrea tridentata shrubs, there were no differences in infiltration rates with or without termites. Plots with shrub cover had the highest infiltration rates 101±6 mm·h-1. Highest run-off volumes were recorded from termite free <5% grass cover plots and the lowest from plots with shrubs. There were no differences in suspended sediment concentrations from termites present and termite free plots. Average bed load concentration was more than three times greater from termite free, <5% cover plots than from termites present, <5% cover plots.The reduction in infiltration, high run-off volumes and high bedloads from termite free areas without shrub cover is related to increased soil bulk density resulting from the collapse of subterranean galleries of the termites that provide avenues of bulk flow into the soil. Subterranean termites affect the hydrology of Chihuahuan desert systems by enhancing water infiltration and retention of top soil. The presence of a shrub canopy and litter layer cancels any effect of subterranean termites on hydrological parameters. Since approximately 2/3 of the area is not under shrub canopies, subterranean termites are considered to be essential for the maintenance of the soil water characteristics that support the present vegetation.

Apparent toxicity resulting from the sequestering of nutrient trace metals during standard Selenastrum capricornutum toxicity tests.

The water accommodated fractions (WAFs) of aqueous mixtures of three lubricant additives showed significant apparent toxicity to the freshwater alga, Selenastrum capricornutum, and experiments were conducted to investigate the hypothesis that toxicity resulted from the removal of one or more essential nutrients from the test medium by the lubricant additives. Algal growth effects were noted at ashless dispersant A concentrations as low as 0.5 x mg l(-1) and growth was completely inhibited at 100 mg x l(-1). Algal cells transferred from the 100 mg x l(-1) WAF of ashless dispersant A to fresh medium at the end of a standard 96-h toxicity test resumed growing at a rate similar to growth in undosed algal medium, indicating that the effect was algistatic rather than algicidal. Fortifying the iron (Fe) and disodium ethylenediaminetetraacetic acid (EDTA) concentrations of the WAF with 200% of the concentrations used in the formulation of algal medium after 24 h of exposure caused a resumption of algal growth at a rate comparable to the control growth, and a resulting EL50 value above 100 mg x l(-1). Similar effects were observed when the two other lubricant additives were tested at WAF concentrations that completely inhibited algal growth during standard toxicity tests: fortification of a 50 mg x l(-1) WAF of ZnDTP with 1000% of the Fe and EDTA used in the formulation of algal medium caused a resumption of growth at a rate statistically identical to the control growth, and the fortification of a 2800 mg x l(-1) WAF of ashless dispersant B with 700% of the entire complement of nutrients used in the formulation of algal medium caused a resumption of growth at a rate comparable to the control. The indirect toxic effect of these lubricant additives to algae results from the sequestration of one or more nutrient metals essential for algal growth. Standard algal toxicity tests with these lubricant additives may, therefore, have little environmental relevance because the complex chemistry of natural waters differs greatly from the nutrient limited algal medium, and the sequestration effect observed in these static tests could be absent under real world conditions.

An open source software project for obstetrical procedure scheduling and occupancy analysis.

Increases in the rate of births via cesarean section and induced labor have led to challenging scheduling and capacity planning problems for hospital inpatient obstetrical units. We present occupancy and patient scheduling models to help address these challenges. These patient flow models can be used to explore the relationship between procedure scheduling practices and the resulting occupancy on inpatient obstetrical units such as labor and delivery and postpartum. The models capture numerous important characteristics of inpatient obstetrical patient flow such as time of day and day of week dependent arrivals and length of stay, multiple patient types and clinical interventions, and multiple patient care units with inter-unit patient transfers. We have used these models in several projects at different hospitals involving design of procedure scheduling templates and analysis of inpatient obstetrical capacity. In the development of these models, we made heavy use of open source software tools and have released the entire project as a free and open source model and software toolkit.

Collection and preparation of sensor network data to support modeling and analysis of outpatient clinics.

Simulation studies of outpatient clinics often involve significant data collection challenges. We describe an approach for data collection using sensor networks which facilitates the collection of a large volume of very detailed patient flow data through healthcare clinics. Such data requires extensive preprocessing before it is ready for analysis. We present a general data preparation framework for sensor network generated data with particular emphasis on the creation and analysis of patient path strings. Several examples of the analysis of sensor network data are also presented. Our approach has been used in two large outpatient clinics in the United States.

Silver speciation during chronic toxicity tests with the mysid, Americamysis bahia.

A 28-day chronic toxicity test and two 7-day chronic estimation toxicity tests were conducted with silver nitrate (AgNO(3)) and the marine invertebrate, Americamysis bahia, in 20 per thousand (parts-per thousand) salinity seawater. One 7-day test was initiated with 7-day-old mysids and the second was initiated with <24-h-old mysids. There was very good agreement between the three toxicity tests. The no-observed-effect concentration (NOEC) values from the 28-day test, the 7-day test initiated with 7-day-old mysids, and the 7-day test initiated with <24-h-old mysids were 34, 65 and 38 microg/l silver, respectively. The 96-h LC50 values from the 28-day toxicity test and the 7-day toxicity test initiated with 7-day old mysids were 260 microg/l, and the 96-h LC50 value from the 7-day toxicity test initiated with <24-h-old mysids was 280 microg/l. Free ionic silver, Ag(+), concentrations measured with a silver electrode were in good agreement with concentrations calculated using total dissolved silver and chloride concentrations. Mean measured concentrations of Ag(+) in the test solutions ranged from 0.99 to 25 ng/l for the dissolved silver concentrations that ranged from 34 to 410 microg/l silver, indicating that free ionic silver varied from 0.003 to 0.006% of the silver dissolved in the 20 per thousand salinity seawater. Understanding the relationship of salinity and silver speciation, and the effect of this relationship on chronic invertebrate toxicity, will be useful for development of a marine biotic ligand model (BLM) and a water quality criterion for silver. This model could provide an important tool for improving the relationship of laboratory toxicity test results and predicted effects in natural environments, where variations in salinity may act to modify the toxicity of silver and other metals.