Developmental effects of siloxane exposure in zebrafish: A comparison study using laboratory-mixed and environmental water samples.

Siloxanes are used in personal care, biomedical, and industrial products. Their worldwide use and persistence in the environment cause consistent exposure for both humans and aquatic animals. Two siloxane congeners, decamethylcyclopentasiloxane (D5; CAS 541-02-6) and octamethylcyclotetrasiloxane (D4; CAS 556-67-2), are among the most prevalent, with measurable levels in air, sediment, water, and biological samples. However, few studies have examined the impact of developmental (embryo/larva) exposure. To address this gap, we performed parallel experiments using wildtype zebrafish (Danio rerio). One set of experiments used laboratory-mixed individual solutions containing either D4, D5, or 2,4,6,8-tetramethylcyclotetrasiloxane (D4 H ; CAS 2370-88-9); the other used environmental water samples containing a mixture of siloxanes, including D4 and D5. These samples were collected from Bladensburg Waterfront Park (BWP) a site along the Anacostia River, Washington, DC. In both experiments, zebrafish (24-48 h postfertilization, hpf) were exposed until 7 or 14 days (d)pf. Chronic exposure to D4, D5, or BWP water until 7 dpf caused stress-like behaviors and reduced swim velocities; anatomical differences were noted only in BWP-exposed larvae. At 14 dpf, BWP-treated larvae still showed slower swimming velocities and increased immobility; anatomical differences were no longer evident and thigmotactic behavior was reduced. D4 and D5-exposed larvae did not survive after 10 dpf. Larvae exposed to D4 H showed no decreases in behavior or growth at either age. These results suggest early developmental sensitivity to siloxane exposure and point to the need to consider embryonic/larval endpoints when assessing aquatic contaminants.

Bacterial community profiles from sediments of the Anacostia River using metabolic and molecular analyses.

UNLABELLED: BACKGROUND AIM AND SCOPE: Though the tidal Anacostia River, a highly polluted riverine system, has been well characterized with regard to contaminants, its overall resident bacterial populations have remained largely unknown. Improving the health of this system will rely upon enhanced understanding of the diversity and functions of these communities. Bacterial DNA was extracted from archived (AR, year 2000) and fresh sediments (RE, year 2006) collected from various locations within the Anacostia River. Using a combination of metabolic and molecular techniques, community snapshots of sediment bacterial diversity and activity were produced. RESULTS: Employing Biolog EcoPlates, metabolic analysis of RE sediments from July revealed similar utilization of amines, amino acids, carbohydrates, carboxylic acids, and polymers at all sites. Normalized optical density measurements demonstrated that for most compounds, utilizations were similar though when differences did occur, the downstream site was enhanced compared to one or both of the upstream sites. Using denaturing gradient gel electrophoresis, bacterial diversity fingerprints of operational taxonomic units (OTUs) were obtained. Dendograms of the banding patterns revealed qualitative relationships as well as differences between replicate samples from similar sites. Replicates from the AR sites shared several common OTUs, while RE sites were more varied. Species richness and Shannon diversity indices generally increased with increasingly downstream locations, and were significant for the AR sediments (analysis of variance, P < 0.0001). Carbon and nitrogen content and concentration of fine grain sediment (<63 µm) were positively correlated with OTU richness (r (2) = 0.37, P = 0.0008; r (2) = 0.45, P < 0.0001; r (2) = 0.48, P = 0.001, respectively). CONCLUSIONS: This study demonstrated that the bacterial communities from all regions sampled were not only metabolically active with the capacity to utilize several different compounds as energy sources but also were genetically diverse. This study is the first to focus on the overall bacterial community, providing insight into this vital component of stream ecosystems. Understanding the bacterial components of aquatic systems such as the Anacostia River will increase our knowledge of the overall structure and function of the ecological communities in polluted systems, subsequently enhancing our ability to improve the health of this important tidal river.

Nutrients, oxygen dynamics, stable isotopes and fatty acid concentrations of a freshwater tidal system, Washington, D.C.

The Anacostia River in Washington, D.C., USA is an urban waterway contaminated with PAHs, PCBs, metals and sewage. Although several studies have examined the heavy metal geochemistry within the river, no studies have examined basic biogeochemical processes within the Anacostia river system. This study examines nutrients, bacterial biomarkers, organic material, and carbon, nitrogen and sulfur sources in the system. High biological oxygen demand and low nitrogen (0.33-0.56 mg L(-1)) and phosphorus (0.014-0.021 mg L(-1)) concentrations were observed in three areas of the river. Downstream sites had higher nutrient concentrations and dissolved organic matter (up to 13.7 mg L(-1)). Odd-chain length and branched fatty acids (FAs) in the sediments indicated bacterial sources, but long chain FAs indicative of terrestrial primary production were also abundant in some sediments. Sediment carbon stable isotope analyses showed a mix of autochthonous and allochthonous derived materials, but most carbon was derived from terrestrial sources (-23.3 to -31.7 per thousand). Sediment nitrogen stable isotopes ranged from -5.4 to 5.6 per thousand, showing nitrate uptake by plants and also recycling of nitrogen within the river. Sulfur sources were generally between 3 and -5 per thousand, reflecting local sulfate sources and anaerobic sulfate reduction.

Correlation of metabolism with tissue carbon and nitrogen turnover rate in small mammals.

Stable isotopes have proven to be a useful tool for deciphering food webs, examining migration patterns and determining nutrient resource allocation. In order to increase the descriptive power of isotopes, an increasing number of studies are using them to model tissue turnover. However, these studies have, mostly by necessity, been largely limited to laboratory experiments and the demand for an easier method of estimating tissue turnover in the field for a large variety of organisms remains. In this study, we have determined the turnover rate of blood in mice and rats using stable isotope analysis, and compared these rates to the metabolic rates of the animals. Rats (Rattus norvegicus) (n=4) and mice (Mus musculus) (n=4) were switched between isotopically distinct diets, and the rate of change of delta(13)C and delta(15)N in whole blood was determined. Basal metabolic rates (as CO(2) output and O(2) consumption per unit time, normalized for mass) were determined for the rats and mice. Rats, which were an order of magnitude larger and had a slower metabolic rate per unit mass than mice (0.02 vs. 0.14 O(2)/min/g), had a slower blood turnover than mice for (13)C (t (1/2 )=24.8 and 17.3 days, respectively) and (15)N (t (1/2 )=27.7 and 15.4 days, respectively). A positive correlation between metabolic rate and blood isotopic turnover rate was found. These are the only such data for mammals available, but the literature for birds shows that mass and whole-body metabolic rates in birds scale logarithmically with tissue turnover. Interestingly, the mammalian data graph separately from the bird data on a turnover versus metabolic rate plot. Both mice and rat tissue in this study exhibited a slower turnover rate compared to metabolic rate than for birds. These data suggest that metabolic rate may be used to estimate tissue turnover rate when working with organisms in the field, but that a different relationship between tissue turnover and metabolism may exist for different classes of organisms.