Biomedical subjects

David L Parry

Publications and source records attributed to David L Parry.

8 recordsLinked to original sources

PubMed2006

Microbial sulfate reduction under sequentially acidic conditions in an upflow anaerobic packed bed bioreactor.

The aim of this study was to operate an upflow anaerobic packed bed reactor (UAPB) containing sulfate reducing bacteria (SRB) under acidic conditions similar to those found in acid mine drainage (AMD). The UAPB was filled with sand and operated under continuous flow at progressively lower pH and was shown to be capable of supporting sulfate reduction at pH values of 6.0, 5.0, 4.5, 4.0 and 3.5 in a synthetic medium containing 53.5 mmol l(-1) lactate. Sulfate reduction rates of 553-1,052 mmol m(-3) d(-1) were obtained when the influent solution pH was progressively lowered from pH 6.0 to 4.0, under an optimal flow rate of 2.61 ml min(-1). When the influent pH was further lowered to pH 3.5, sulfate reduction was substantially reduced with only about 1% sulfate removed at a rate of 3.35 mmol m(-3) d(-1) after 20 days of operation. However, viable SRB were recovered from the column, indicating that the SRB population was capable of surviving and metabolizing at low levels even at pH 3.5 conditions for at least 20 days. The changes in conductivity in the SRB column did not always occur with changes in pH and redox potential, suggesting that conductivity measurements may be more sensitive to SRB activity and could be used as an additional tool for monitoring SRB activity. The bioreactor containing SRB was able to reduce sulfate and generate alkalinity even when challenged with influent as low as pH 3.5, indicating that such treatment systems have potential for bioremediating highly acidic, sulfate contaminated waste waters.

Acids↗

PubMed2006

Vegetation fires, particulate air pollution and asthma: a panel study in the Australian monsoon tropics.

We examined the relationship between particulate matter (PM) <10 and <2.5 microns in diameter (PM10 and PM2.5) generated by vegetation fires and daily health outcomes in 251 adults and children with asthma over a 7-month period. Data were analysed using generalized estimating equations adjusted for potential environmental confounders, autocorrelation, weekends and holidays. PM10 ranged from 2.6 - 43.3 microg m-3and was significantly associated with onset of asthma symptoms, commencing oral steroid medication, the mean daily symptom count and the mean daily dose of reliever medication. Similar results were found for PM2.5. No associations were found with the more severe outcomes of asthma attacks, increased health care attendances or missed school/work days. These results help fill a gap in the evidence about the population health impacts of lower levels of pollution characteristic of deliberate landscape burning to control fuel loads versus the better documented risks of more intense and severely polluting wildfires.

Adolescent↗

PubMed2005

Evaluation of the stability of arsenic immobilized by microbial sulfate reduction using TCLP extractions and long-term leaching techniques.

An investigation was conducted to evaluate the stability or leachability of arsenic immobilized by microbial sulfate reduction. Anoxic solid-phase samples taken from a bioreactor previously used to treat metal and As contaminated water using sulfate reducing bacteria (SRB) were subjected to the toxicity characteristic leaching procedure (TCLP) and long-term column leaching tests. The results from TCLP experiments showed that the concentration of As leached from solid-phase sulfide material (SSM) samples after an 18 h extraction time was <300 microgl(-1), which is below the current maximum Australian TCLP leachate value for As, and thus would not be characterized as a hazardous waste. In terms of percent total As leached, this was equivalent to <8.5% for SSM samples initially containing 61.3 mgkg(-1) As. The levels of As extracted by the TCLP was found to be significantly lowered or underestimated in the presence of dissolved oxygen, with As concentrations increasing with decreasing headspace-to-leachant volume ratios. The concentration of As was also consistently higher in nitrogen purged extractions compared to those performed in air. This was attributed to the dissolution of Fe-sulfide precipitates and subsequent oxidation of Fe(II) ions and precipitation of ferric(hydr)oxides, resulting in the adsorption of soluble As and corresponding decrease in As concentrations. According to the experimental data, it is recommended that TCLP tests for As leachability should be performed at least in zero-headspace vessels or preferably under nitrogen to minimize the oxidation of Fe(II) to ferric(hydr)oxides. In long-term leaching studies (approximately 68 days), it was found that the low solubility of the SSM ensured that rate of release of As was relatively slow, and the resulting leachate concentrations of As were below the current Australian guideline concentration for arsenic in drinking water.

Air↗

PubMed2004

Adsorption of Pb(II), Cu(II), Cd(II), Zn(II), Ni(II), Fe(II), and As(V) on bacterially produced metal sulfides.

The adsorption of Pb(II), Cu(II), Cd(II), Zn(II), Ni(II), Fe(II) and As(V) onto bacterially produced metal sulfide (BPMS) material was investigated using a batch equilibrium method. It was found that the sulfide material had adsorptive properties comparable with those of other adsorbents with respect to the specific uptake of a range of metals and, the levels to which dissolved metal concentrations in solution can be reduced. The percentage of adsorption increased with increasing pH and adsorbent dose, but decreased with increasing initial dissolved metal concentration. The pH of the solution was the most important parameter controlling adsorption of Cd(II), Cu(II), Fe(II), Ni(II), Pb(II), Zn(II), and As(V) by BPMS. The adsorption data were successfully modeled using the Langmuir adsorption isotherm. Desorption experiments showed that the reversibility of adsorption was low, suggesting high-affinity adsorption governed by chemisorption. The mechanism of adsorption for the divalent metals was thought to be the formation of strong, inner-sphere complexes involving surface hydroxyl groups. However, the mechanism for the adsorption of As(V) by BPMS appears to be distinct from that of surface hydroxyl exchange. These results have important implications to the management of metal sulfide sludge produced by bacterial sulfate reduction.

Adsorption↗

PubMed2004

Heavy metal speciation in solid-phase materials from a bacterial sulfate reducing bioreactor using sequential extraction procedure combined with acid volatile sulfide analysis.

Heavy metal mobility, bioavailability and toxicity depends largely on the chemical form of metals and ultimately determines potential for environmental pollution. For this reason, determining the chemical form of heavy metals and metalloids, immobilized in sludges by biological mediated sulfate reduction, is important to evaluate their mobility and bioavailability. A modified Tessier sequential extraction procedure (SEP), complemented with acid volatile sulfide (AVS) and simultaneous extracted metals (SEM) measurements, were applied to determine the partitioning of five heavy metals (defined as Fe, Ni, Zn and Cu, and the metalloid As) in anoxic solid-phase material (ASM) from an anaerobic, sulfate reducing bioreactor into six operationally defined fractions. These fractions were water soluble, exchangeable, bound to carbonates (acid soluble), bound to Fe-Mn oxides (reducible), bound to organic matter and sulfides (oxidizable) and residual. It was found that the distribution of Fe, Ni, Zn, Cu and As in ASM was strongly influenced by its association with the above solid fractions. The fraction corresponding to organic matter and sulfides appeared to be the most important scavenging phases of As, Fe, Ni, Zn and Cu in ASM (59.8-86.7%). This result was supported by AVS and SEM (Sigma Zn, Ni and Cu) measurements, which indicated that the heavy metals existed overwhelmingly as sulfides in the organic matter and sulfide fraction. A substantial amount of Fe and Ni at 16.4 and 20.1%, respectively, were also present in the carbonate fraction, while an appreciable portion of As (18.3%) and Zn (19.4%) was bound to Fe-Mn oxides. A significant amount of heavy metals was also associated with the residual fraction, ranging from 2.1% for Zn to 18.8% for As. Based on the average total extractable heavy metal (TEHM) values, the concentration of heavy metals in the ASM was in the order of Cu > Ni > Zn > Fe > As. If the mobility and bioavailability of heavy metals are assumed to be related to their solubility and chemical forms, and that they decrease with each successive extraction step, then the apparent mobility and bioavailability of these five heavy metals in ASM increase in the order of Cu < As < Ni < Fe < Zn. The SEM/AVS ratio was less than one in eight replicate ASM samples, indicating that the ASM was non-toxic with regards to having a low probability of bioavailable metals in the pore water.

Biological Availability↗

PubMed2004

The uptake of uranium by Eleocharis dulcis (Chinese water chestnut) in the Ranger Uranium Mine constructed wetland filter.

Eleocharis dulcis has proliferated in a constructed wetland used to treat uranium mine runoff water, where it rapidly accumulates significant quantities of uranium (U) in its roots and relatively little in its stems. We investigated the mechanism of U uptake and accumulation by E. dulcis using field-sampling techniques and microcosm test work. Results from the microcosm trials and outcomes from statistical tests of field sampled macrophyte, water and sediment indicate that the primary source of U for E. dulcis is the water column. Basipetal translocation of U to the plant's roots was indicated by significant correlations between the U content of stems, taproots and rhizomes and XPS detection of U inside root segments. U sequestering from sediment interstitial water by Fe hydroxides on root surfaces was also evident. No basipetal translocation was evident following the 28-day duration of the microcosm experiments, indicating that it is a longer-term process.

Biodegradation, Environmental↗

PubMed2003

Removal of sulfate and heavy metals by sulfate reducing bacteria in short-term bench scale upflow anaerobic packed bed reactor runs.

Mildly acidic metal (Cu, Zn, Ni, Fe, Al and Mg), arsenic and sulfate contaminated waters were treated, over a 14 day period at 25 degrees C, in a bench-scale upflow anaerobic packed bed reactor filled with silica sand and employing a mixed population of sulfate-reducing bacteria (SRB). The activity of SRB increased the water pH from approximately 4.5 to 7.0, and enhanced the removal of sulfate and metals in comparison to controls not inoculated with SRB. Addition of organic substrate and sulfate at loading rates of 7.43 and 3.71 kg d(-1) m(-3), respectively, resulted in >82% reduction in sulfate concentration. The reactor removed more than 97.5% of the initial concentrations of Cu, Zn and Ni, while only >77.5% and >82% of As and Fe were removed, respectively. In contrast, Mg and Al levels remained unchanged during the whole treatment process. The removal patterns for Cu, Zn, Ni and Fe reflected the trend in their solubility for their respective metal sulfides, while As removal appeared to coincide with decreasing Cu, Zn, Ni and Fe concentrations, which suggests adsorption or concomitant precipitation with the other metal sulfides.

Adsorption↗

PubMed2003

Monitoring of labile metals in turbid coastal seawater using diffusive gradients in thin-films.

Diffusive gradients in thin-films (DGT) have been investigated for in situ monitoring of labile metals in north Australian coastal seawater. Field and experimental data showed that DGT devices provided adequate detection limits, accuracy and precision for monitoring of near-pristine levels of labile Mn, Co, Cu, Cd and Pb when deployed for periods of 3 days. However, Zn could not be adequately determined due to high blank levels. The ratio of DGT-labile to 0.45 microm-filtered metal levels in natural seawater ranged from 0.44-0.63 for Cu but was close to unity for Co and Cd. Elevated levels of suspended particulate matter up to 57.3 mg l(-1) did not have an adverse effect on the performance of DGT.

Diffusion↗