Reference values of maximum walking speed among independent community-dwelling Danish adults aged 60 to 79 years: a cross-sectional study.

OBJECTIVES: To establish reference values for maximum walking speed over 10 m for independent community-dwelling Danish adults, aged 60 to 79 years, and to evaluate the effects of gender and age. DESIGN: Cross-sectional study. SETTING: Danish companies and senior citizens clubs. PARTICIPANTS: Two hundred and fifty-two adults (167 women, 85 men) with a mean age of 70 [standard deviation (SD) 4] years. INTERVENTIONS: Not applicable. MAIN OUTCOME MEASURE: Results for the 10-m walk test (10 MWT) were used to establish reference values. RESULTS: The mean reference value for maximum walking speed over 10 m for all participants was 1.94 (SD 0.31) m/second. Reference values for women aged 60 to 69 years and 70 to 79 years were 1.96 (SD 0.26) and 1.81 (SD 0.29) m/second, respectively. Reference values for men aged 60 to 69 years and 70 to 79 years were 2.10 (SD 0.35) and 2.01 (SD 0.30) m/second, respectively. Significant differences (P<0.01) were observed in the age and gender categories. Men were found to walk faster than women, and individuals aged 60 to 69 years walked faster than individuals aged 70 to 79 years. CONCLUSIONS: This study established the reference values for maximum walking speed over 10 m among independent community-dwelling Danish adults aged 60 to 79 years. The study results showed significant differences in maximum walking speed for different ages and between men and women.

Dynamics of reductive TCE dechlorination in two distinct H(2) supply scenarios and at various temperatures.

Anaerobic microbial dechlorination of trichloroethene (TCE) by a mixed, Dehalococcoides containing culture was investigated at different temperatures (4-60 degrees C) using propionate and lactate as a slow- and fast-releasing hydrogen (H(2)) source, respectively. Distinct temperature-dependent dynamics of substrate fermentation and H(2) levels could explain observed patterns of dechlorination. While varying the temperature caused changes in rate, the overall pattern of dechlorination was characteristic of the supplied electron donor. Feeding cultures with a rapidly fermentable substrate such as lactate generally resulted in high H(2) concentrations and fast and complete dechlorination accompanied by rapid methanogenesis. In contrast, low H(2) release rates resulting from fermentation of propionate were associated with 2 to 3-fold longer time frames necessary for complete dechlorination at intermediate temperatures (15-30 degrees C). A lag-phase prior to dechlorination of cis-dichloroethene (cDCE), together with a characteristic build-up of H(2) and methane, was consistently observed at slow H(2) supply. At temperatures of 10 degrees C and lower, the system remained in this lag phase and no dechlorination past cDCE was observed within the experimental time frame. However, when lactate was the substrate, complete dechlorination of TCE occurred within 74 days at 10 degrees C, accompanied by methane production. The choice of fermentable substrate decisively influenced the rate and degree of dechlorination at an electron donor/TCE ratio as high as 666:1. Temperature-dependent H(2) levels resulting from fermentation of different substrates could be satisfactorily explained through thermodynamic calculations of the Gibbs free energy yield assuming a constant metabolic energy threshold of -20 kJ/(mol reaction).

Dechlorination after thermal treatment of a TCE-contaminated aquifer: laboratory experiments.

A microcosm study was conducted to evaluate dechlorination of trichloroethene (TCE) to ethene and survival of dechlorinating bacteria after a thermal treatment in order to explore the potential for post-thermal bioremediation. Unamended microcosms containing groundwater and aquifer material from a contaminated site dechlorinated TCE to cis-1,2-dichloroethene (cDCE), while lactate-amended microcosms dechlorinated TCE to cDCE or ethene. A thermal treatment was simulated by heating a sub-set of microcosms to 100 degrees C for 10d followed by cooling to 10 degrees C over 150 d. The heated microcosms demonstrated no dechlorination when unamended. However, when amended with lactate, cDCE was produced in 2 out of 6 microcosms within 300 d after heating. Dechlorination of TCE to cDCE thus occurred in fewer heated (2 out of 12) than unheated (10 out of 12) microcosms. In unheated microcosms, the presence of dechlorinating microorganisms, including Dehalococcoides, was confirmed using nested PCR of 16S rRNA genes. Dechlorinating microorganisms were detected in fewer microcosms after heating, and Dehalococcoides were not detected in any microcosms after heating. Dechlorination may therefore be limited after a thermal treatment in areas that have been heated to 100 degrees C. Thus, inflow of groundwater containing dechlorinating microorganisms and/or bioaugmention may be needed for anaerobic dechlorination to occur after a thermal treatment.

The need for bioaugmentation after thermal treatment of a TCE-contaminated aquifer: Laboratory experiments.

A microcosm study was conducted to evaluate the need for bioaugmentation after a thermal treatment to anaerobically dechlorinate trichloroethene (TCE) to ethene. The microcosms were either: heated to 100 degrees C and slowly cooled to simulate thermal remediation while bioaugmenting when the declining temperature reached 10 degrees C; or kept at ambient groundwater temperatures (10 degrees C) and bioaugmented for comparison. Aquifer samples from three sediment locations within a TCE-polluted source zone were investigated in duplicate microcosms. In biostimulated (5 mM lactate) and heated microcosms, no conversion of TCE was observed in 4 out of 6 microcosms, and in the remaining microcosms the dechlorination of TCE was incomplete to cDCE (cis-dichloroethene). By comparison, complete TCE dechlorination to ethene was observed in 4 out of 6 heated microcosms that were bioaugmented with a highly enriched dechlorinating mixed culture, KB-1, but no electron donor, and also in 4 of 6 microcosms that were augmented with KB-1 and an electron donor (5 mM lactate). These data suggest that electron donor released during heating, was capable of promoting complete dechlorination coincident with bioaugmentation. Heated microcosms demonstrated less methanogenesis than unheated microcosms, even with elevated H2 concentrations and addition of KB-1, which contains methanogens. This suggests that the heating process suppressed the native microbial community, which can decrease competition with the bioaugmented culture and increase the effectiveness of dechlorination following a thermal treatment. Specifically, cDCE removal rates were four to six times higher in heated than unheated bioaugmented microcosms. This study confirms the need for bioaugmentation following a laboratory thermal treatment to obtain complete dechlorination of TCE.

Anaerobic dechlorination and redox activities after full-scale Electrical Resistance Heating (ERH) of a TCE-contaminated aquifer.

The effects of Electrical Resistance Heating (ERH) on dechlorination of TCE and redox conditions were investigated in this study. Aquifer and groundwater samples were collected prior to and after ERH treatment, where sediments were heated to approximately 100 degrees C. Sediment samples were collected from three locations and examined in microcosms for 250 to 400 days of incubation. Redox activities, in terms of consumed electron acceptors, were low in unamended microcosms with field-heated sediments, although they increased upon lactate-amendment. TCE was not dechlorinated or stalled at cDCE with field-heated sediments, which was similar or lower compared to the degree of dechlorination in unheated microcosms. However, in microcosms which were bioaugmented with a mixed anaerobic dechlorinating culture (KB-1) and lactate, dechlorination past cDCE to ethene was observed in field-heated sediments. Dechlorination and redox activities in microcosms with field-heated sediments were furthermore compared with controlled laboratory-heated microcosms, which were heated to 100 degrees C for 10 days and then slowly cooled to 10 degrees C. In laboratory-heated microcosms, TCE was not dechlorinated and redox activities remained low in unamended and lactate-amended sediments, although organic carbon was released to the aqueous phase. In contrast, in field-heated sediments, high aqueous concentrations of organic carbon were not observed in unamended microcosms, and TCE was dechlorinated to cDCE upon lactate amendment. This suggests that dechlorinating microorganisms survived the ERH or that groundwater flow through field-heated sediments carried microorganisms into the treated area and transported dissolved organic carbon downstream.

Redox processes and release of organic matter after thermal treatment of a TCE-contaminated aquifer.

Redox conditions in heated and unheated microcosm experiments were studied to evaluate the effect of thermal remediation treatment on biogeochemical processes in subsurface environments. The results were compared to field-scale observations from thermal treatments of contaminated sites. Trichloroethene-contaminated aquifer material and groundwater from Ft. Lewis, WA were incubated for 200 days at ambient temperature (i.e., 10 degrees C) or heated to 100 degrees C for 10 days and cooled slowly over a period of 150 days to mimic a thermal treatment. Increases of up to 14 mM dissolved organic carbon were observed in the aqueous phase after heating. Redox conditions did generally not change during heating in the laboratory experiment, and only minor changes occurred as an effect of heat treatment in the field. The conditions were slightly manganese/iron-reducing in two sediments and possibly sulfate-reducing in the third sediment based on production of up to 0.20 mM dissolved iron and 0.15 mM dissolved manganese and consumption of 0.08 mM sulfate. The calculated energy gain of less than -20 kJ/mol H2 for iron and sulfate reduction as well as methane production indicated that these processes were thermodynamically favorable. Sulfate reduction and methane production occurred in the unheated microcosms upon lactate amendment. Little or no reduction of the redox level was identified in heated lactate-amended microcosms, possibly because of limited microbial activity. Because the redox conditions, pH, and alkalinity remained within normal aquifer levels upon heating, bioaugmentation may be feasible for stimulating anaerobic dechlorination in heated samples or in future field applications.

Influence of Bacillus subtilis cell walls and EDTA on calcite dissolution rates and crystal surface features.

This study investigates the influence of EDTA and the Gram-positive cell walls of Bacillus subtilis on the dissolution rates and development of morphological features on the calcite [1014] surface. The calcite dissolution rates are compared at equivalent saturation indicies (SI) and relative to its dissolution behavior in distilled water (DW). Results indicate that the presence of metabolically inactive B. subtilis does not affect the dissolution rates significantly. Apparent increases in dissolution rates in the presence of the dead bacterial cells can be accounted for by a decrease of the saturation state of the solution with respect to calcite resulting from bonding of dissolved Ca2+ by functional groups on the cell walls. In contrast, the addition of EDTA to the experimental solutions results in a distinct increase in dissolution rates relative to those measured in DW and the bacterial cell suspensions. These results are partly explained by the 6.5-8 orders of magnitude greater stability of the Ca-EDTA complex relative to the Ca-B. subtilis complexes as well as its free diffusion to and direct attack of the calcite surface. Atomic force microscopy images of the [1014] surface of calcite crystals exposed to our experimental solutions reveal the development of dissolution pits with different morphologies according to the nature and concentration of the ligand. Highly anisotropic dissolution pits develop in the early stages of the dissolution reaction at low B. subtilis concentrations (0.004 mM functional group sites) and in DW. In contrast, at high functional group concentrations (4.0 mM EDTA or equivalent B. subtilis functional group sites), dissolution pits are more isotropic. These results suggest that the mechanism of calcite dissolution is modified by the presence of high concentrations of organic ligands. Since all the pits that developed on the calcite surfaces display some degree of anisotropy and dissolution rates are strongly SI dependent, the rate-limiting step is most likely a surface reaction for all systems investigated in this study. Results of this study emphasize the importance of solution chemistry and speciation in determining calcite reaction rates and give a more accurate and thermodynamically sound representation of dead bacterial cell wall-mineral interactions. In studies of natural aquatic systems, the presence of organic ligands is most often ignored in speciation calculations. This study clearly demonstrates that this oversight may lead to an overestimation of the saturation state of the solutions with respect to calcite and thermodynamic inconsistencies.