Microbial communities associated with anaerobic degradation of polybrominated diphenyl ethers in river sediment.

BACKGROUND/PURPOSE: Polybrominated diphenyl ethers (PBDEs) are extensively used as a class of flame retardants and have become ubiquitous environmental pollutants. We aimed to uncover the changes in microbial community with PBDE anaerobic degradation with and without zero-valent iron in sediment from the Erren River, considered one of the most heavily contaminated rivers in Taiwan. METHODS: PBDE anaerobic degradation in sediment was analyzed by gas chromatography with an electron capture detector. Microbial community composition was analyzed by a pyrosequencing-based metagenomic approach. RESULTS: The anaerobic degradation rate of BDE-209 was higher than BDE-28 in sediment; the addition of zero-valent iron enhanced the degradation rates of both. In total, 19 known bacterial genera (4 major genera: Clostridium, Lysinibacillus, Rummeliibacillus, and Brevundimonas) were considered PBDE degradation-associated bacteria (sequence frequency negatively correlated with PBDE remaining percentage) as were four known archaea genera (Methanobacterium, Methanosarcina, Methanocorpusculum, and Halalkalicoccus; sequence frequency positively correlated with PBDE remaining percentage). CONCLUSION: The composition of bacteria and that of archaea affected the anaerobic degradation of BDE-28 and BDE-209. The addition of zero-valent iron further decreased the archaea content to undetectable levels.

Bacterial communities associated with aerobic degradation of polybrominated diphenyl ethers from river sediments.

Polybrominated diphenyl ethers (PBDEs) are persistent organic pollutants and have therefore drawn much environmental concern. We aimed to compare aerobic degradation of different PBDE congeners under various treatments and reveal the bacterial community associated with PBDE degradation in sediment. Results of this study indicate that degradation rates of BDE-15 were enhanced 45.1 and 81.3 % with the addition of suspended and microencapsulated Pseudomonas sp., respectively. However, the degradation rates of BDE-28, BDE-47, BDE-99, and BDE-100 did not differ among experimental treatments. Degradation rates of PBDE congeners were in the order of BDE-15 > BDE-28 > BDE-47 > BDE-99 > BDE-100. Using a pyrosequencing-based metagenomic approach, we found that addition of various treatments altered the microbial community composition in the sediment. Twenty-four bacterial genera associated with degradation of PBDEs; six are the core bacterial genera common among PBDE degraders. The diverse bacterial composition among different PBDE congener degradation indicates different combinations of bacteria involved in degradation of different PBDE congeners.

Influence of blood vessel on the thermal lesion formation during radiofrequency ablation for liver tumors.

PURPOSE: The major obstacles of radiofrequency ablation (RFA) heat treatments are nonuniform heating in the thermal lesion and heat sinks caused by large blood vessels during treatments which could lead to high tumor recurrence in patients. The objective of this study is to help comprehend RFA heat treatment through thermal lesion formation using computer simulation, and thus to provide helpful assistance in planning RFA. METHODS: RFA heat treatment is a popular "minimally invasive" treatment method for both primary and metastatic liver tumors, and the heat treatment is studied by numerical calculation. A finite difference model is used to solve all partial differential equations for a simple three-dimensional cubic geometry model. Maximum tissue temperature is used as a critical index for reaching thermal lesion during RFA. Cylindrical RF cool-tip electrode is internally cooled at constant water temperature. RFA thermal lesion is studied at various impacts by single and countercurrent blood vessel(s) traversing the thermal lesion. Several factors are considered, such as location, diameter, and orientation of the blood vessel(s) to the electrode. RESULTS: Results show the thermal lesion size decreases as the lesion blood perfusion rate increases. And, single large blood vessel which is orthogonal to RF electrode will cause less undercooled volume in the thermal lesion than one which is parallel to RF electrode. Furthermore, convective energy may easily damage parallel vessel and its surrounding normal tissues during RFA. Small blood vessels (or larger vessels with slow blood flow rate) during RFA could form "tail-like" thermal lesion formation, which could damage vessel downstream spots. CONCLUSIONS: Studies suggested that incomplete RF tumor ablation still exists within 1 cm distance between large blood vessel and RF electrode in a liver. This could have significant impact on local tumor recurrence rates. Second, if thermally significant vessel existed inevitably within the lesion, avoiding the RF cool-tip electrode placement next to the parallel large blood vessel would have a better heat treatment during RF heating. Additionally, reduced blood flow rate could help reduce significant cooling by large blood vessel.

Predicting effects of blood flow rate and size of vessels in a vasculature on hyperthermia treatments using computer simulation.

BACKGROUND: Pennes Bio Heat Transfer Equation (PBHTE) has been widely used to approximate the overall temperature distribution in tissue using a perfusion parameter term in the equation during hyperthermia treatment. In the similar modeling, effective thermal conductivity (Keff) model uses thermal conductivity as a parameter to predict temperatures. However the equations do not describe the thermal contribution of blood vessels. A countercurrent vascular network model which represents a more fundamental approach to modeling temperatures in tissue than do the generally used approximate equations such as the Pennes BHTE or effective thermal conductivity equations was presented in 1996. This type of model is capable of calculating the blood temperature in vessels and describing a vasculature in the tissue regions. METHODS: In this paper, a countercurrent blood vessel network (CBVN) model for calculating tissue temperatures has been developed for studying hyperthermia cancer treatment. We use a systematic approach to reveal the impact of a vasculature of blood vessels against a single vessel which most studies have presented. A vasculature illustrates branching vessels at the periphery of the tumor volume. The general trends present in this vascular model are similar to those shown for physiological systems in Green and Whitmore. The 3-D temperature distributions are obtained by solving the conduction equation in the tissue and the convective energy equation with specified Nusselt number in the vessels. RESULTS: This paper investigates effects of size of blood vessels in the CBVN model on total absorbed power in the treated region and blood flow rates (or perfusion rate) in the CBVN on temperature distributions during hyperthermia cancer treatment. Also, the same optimized power distribution during hyperthermia treatment is used to illustrate the differences between PBHTE and CBVN models. Keff (effective thermal conductivity model) delivers the same difference as compared to the CBVN model. The optimization used here is adjusting power based on the local temperature in the treated region in an attempt to reach the ideal therapeutic temperature of 43 degrees C. The scheme can be used (or adapted) in a non-invasive power supply application such as high-intensity focused ultrasound (HIFU). Results show that, for low perfusion rates in CBVN model vessels, impacts on tissue temperature becomes insignificant. Uniform temperature in the treated region is obtained. CONCLUSION: Therefore, any method that could decrease or prevent blood flow rates into the tumorous region is recommended as a pre-process to hyperthermia cancer treatment. Second, the size of vessels in vasculatures does not significantly affect on total power consumption during hyperthermia therapy when the total blood flow rate is constant. It is about 0.8% decreasing in total optimized absorbed power in the heated region as gamma (the ratio of diameters of successive vessel generations) increases from 0.6 to 0.7, or from 0.7 to 0.8, or from 0.8 to 0.9. Last, in hyperthermia treatments, when the heated region consists of thermally significant vessels, much of absorbed power is required to heat the region and (provided that finer spatial power deposition exists) to heat vessels which could lead to higher blood temperatures than tissue temperatures when modeled them using PBHTE.

Reconstruction of the temperature field for inverse ultrasound hyperthermia calculations at a muscle/bone interface.

An inverse algorithm with Tikhonov regularization of order zero has been used to estimate the intensity ratios of the reflected longitudinal wave to the incident longitudinal wave and that of the refracted shear wave to the total transmitted wave into bone in calculating the absorbed power field and then to reconstruct the temperature distribution in muscle and bone regions based on a limited number of temperature measurements during simulated ultrasound hyperthermia. The effects of the number of temperature sensors are investigated, as is the amount of noise superimposed on the temperature measurements, and the effects of the optimal sensor location on the performance of the inverse algorithm. Results show that noisy input data degrades the performance of this inverse algorithm, especially when the number of temperature sensors is small. Results are also presented demonstrating an improvement in the accuracy of the temperature estimates by employing an optimal value of the regularization parameter. Based on the analysis of singular-value decomposition, the optimal sensor position in a case utilizing only one temperature sensor can be determined to make the inverse algorithm converge to the true solution.