Pollution of the aquatic biosphere by arsenic and other elements in the Taupo volcanic zone : a thesis presented in partial fulfilment of the requirements for the degree of Master of Science in Biology at Massey University

An introduction to the Taupo Volcanic Zone and probable sources of polluting elements entering the aquatic environment is followed by a description of collection and treatment of samples used in this study. The construction of a hydride generation apparatus for use with an atomic absorption spectrophotometer for the determination of arsenic and other hydride forming elements is described. Flame emission, flame atomic absorption and inductively coupled plasma emission spectroscopy (I.C.P.-E.S.) were used for the determination of other elements. Determinations of arsenic and other elements were made on some geothermal waters of the area. It was found that these waters contribute large (relative to background levels) amounts of arsenic, boron and alkali metals to the aquatic environment. Some terrestrial vegetation surrounding hot pools at Lake Rotokawa and the Champagne Pool at Waiotapu was found to have high arsenic concentrations. Arsenic determinations made on the waters of the Waikato River and some lakes of the Taupo Volcanic Zone revealed that water from the Waikato River between Lake Aratiatia and Whakamaru as well as Lakes Rotokawa, Rotomahana and Rotoehu was above the World Health Organisation limit for arsenic in drinking water (0.05 µg/mL) at the time of sampling. Arsenic accumulates in the sediments of the Waikato River and Lakes of the Taupo Volcanic Zone. The levels were variable, but characteristically around 100 µg/g. Trout taken from the Waikato River and some lakes in the Taupo Volcanic Zone, had flesh arsenic concentrations of the same order of magnitude as the water from which they were taken. Trout from Lakes Rotorua, Rotoiti and Rotomahana contained average flesh mercury concentrations above the World Health Organisations limit for mercury in foodstuffs (0.5 µg/g). There were positive correlations between weight, length and flesh mercury concentration. Freshwater mussels from Lakes Rotorua and Tarawera had arsenic concentrations above the World Health Organisations limit for arsenic in foodstuffs (2 µg/g). Shellfish taken from the mouth of the Waikato river and from Raglan were below the World Health Organisation's limit for arsenic and mercury. Aquatic macrophytes from the Waikato River had arsenic concentrations many times greater than the water from which they were taken. Some samples of Ceratophyllum demersum had arsenic concentrations above 1000 µg/g dry weight. Water cress from the Waikato River at Broadlands and Orakei Korako contained on average 400 µg/g and 30 µg/g arsenic respectively. An experiment was conducted on the uptake of arsenic by water cress. It was found that water cress does accumulate arsenic if placed in an arsenic solution

Antimony uptake by Zea mays (L.) and Helianthus annuus (L.) from nutrient solution

We investigated the extent of Sb uptake by maize (Zea mays) and sunflower (Helianthus annuus) from nutrient solutions containing concentrations from 3 to 24mg/L of potassium antimonate, with the aim of determining the potential of Sb to enter the food chain. The maximum shoot Sb concentrations in Z.mays and H.annuus were 41mg/kg and 77mg/kg dry weight, respectively. There was no significant difference in Sb uptake between species. The average bioaccumulation coefficients (the plant/solution concentration quotients) were 1.02 and 1.93 for Z.mays and H.annuus, respectively. Phosphate addition did not affect plant growth or Sb uptake. Antimony uptake by both Z.mays and H.annuus is unlikely to pose a health risk to animals and human

Uptake and allocation of plant nutrients and Cd in maize, sunflower and tobacco growing on contaminated soil and the effect of soil conditioners under field conditions

Contaminated land may in many cases still be used for agriculture, provided that crops are chosen appropriately, as the accumulation of contaminants varies greatly among cultivars and also plant parts. We aimed to determine whether maize (Zea mays), sunflower (Helianthus annuus) and tobacco (Nicotiana tabaccum) grown on a heavy-metal contaminated soil containing copper (540mg Cu kg−1), zinc (680mg Zn kg−1) and cadmium (1.4mg Cd kg−1) could be used to gradually remediate the soil, while producing valuable biomass. The soil was treated with either a normal fertiliser regime (control), elemental sulphur (S), or the biodegradable chelant NTA (nitrilotriacetic acid), to test how soil acidification or chelating organic compounds would affect the uptake and allocation of selected elements (Ca, Cd, Cu, Fe, K, Mg, Mn, P, S and Zn). The highest concentrations of Cd, Cu and Zn occurred in the leaves and/or roots, while seeds and grains contained much lower concentrations of these elements. All these concentrations, however, were still in the ranges considered normal for the respective plant parts grown on uncontaminated soil. While sunflower and maize could be safely used as food and feed, tobacco would better be used for bioenergy than for cigarette production because of its relatively high foliar Cd concentration. The two treatments (S and NTA) had only slight effects on the uptake and allocation of plant nutrients and Cd. Thus, there was little benefit of these treatments for phytoextraction purposes at this sit

Antimony uptake and toxicity in sunflower and maize growing in SbIII and SbV contaminated soil

Using pot experiments, we investigated the uptake of antimony (Sb) by sunflower (Helianthus annuus L. cv. Iregi), and maize (Zea mays L. cv. Magister) in two different soils, a potting mix and an agricultural soil. In one treatment Sb was added to the experimental soils as KSb(OH)6 ("SbV-treatment”) and in the other as Sb2O3 ("SbIII-treatment”). Soluble soil Sb concentrations were linearly related to the applied Sb rates, ranging from 0.02 (controls) to 175mgL−1 soil solution. Accumulation of Sb tended to be slightly higher in the SbV treatment in sunflower, while no difference in Sb uptake between the two Sb treatments was found in maize. The half maximal effective concentration (EC50) values derived from the dose-response curves were higher for the SbV than for the SbIII treatment when they were related to soluble soil Sb concentrations, but differences became insignificant when they were related to shoot Sb concentrations. Maize was substantially more sensitive to Sb toxicity than sunflower, indicating physiological differences in Sb tolerance between the two plant species. Our results show that on soils with high Sb contamination, as often found in shooting ranges, plants may suffer from Sb toxicit

Response of Populus tremula to heterogeneous B distributions in soil

Background: Poplars accumulate inordinate amounts of B in their leaves and are candidate plants for the remediation of B contaminated soil. We aimed to determine the effect of heterogeneous B distribution in soil by comparing the growth and B accumulation of young Populus tremula trees growing in soil with heterogeneous and homogeneous B distributions. Methods: The first of two experiments focused on the tolerance and B accumulation of P. tremula under heterogeneous soil B distributions, while the second was designed to study fine root growth under such conditions in detail. Results: Growth and B accumulation of P. tremula were unaffected by the spatial distribution of B. Root and shoot growth were both reduced simultaneously when leaf B concentrations increased above 800mgkg−1. In the heterogeneous soil B treatments, root growth was more reduced in spiked soil portions with B concentrations >20mgkg−1. Fine root length growth was stronger inhibited by B stress than secondary growth. Conclusions: The root growth responses of P. tremula to B are primarily a systemic effect induced by shoot B toxicity and local toxicity effects on roots become dominant only at rather high soil B concentrations. Local heterogeneity in soil B should have little influence on the phytoremediation of contaminated site

Thermal Runaway of a Li-Ion Battery Studied by Combined ARC and Multi-Length Scale X-ray CT

Lithium ion battery failure occurs across multiple length scales. In this work, the properties of thermal failure and its effects on electrode materials were investigated in a commercial battery using a combination of accelerating rate calorimetry (ARC) and multi-length scale X-ray computed tomography (CT). ARC measured the heat dissipated from the cell during thermal runaway and enabled the identification of key thermal failure characteristics such as onset temperature and the rate of heat generation during the failure. Analysis before and after failure using scanning electron microscopy (SEM) and X-ray CT were performed to reveal the effects of failure on the architecture of the whole cell and microstructure of the cathode material. Mechanical deformations to the cell architecture were revealed due to gas generation at elevated temperatures (>200 °C). The extreme conditions during thermal runaway caused the cathode particles to reduce in size by a factor of two. Electrode surface analysis revealed surface deposits on both the anode and cathode materials. The link between electrode microstructure and heat generation within a cell during failure is analysed and compared to commercially available lithium ion cells of varying cathode chemistries. The optimisation of electrode designs for safer battery materials is discussed

Effects of Increasing Dosages of Acid Mining Wastes in Metal Uptake by Lygeum spartum and Soil Metal Extractability

Mine tailings are an environmental problem in southern Spain because wind and water erosion of bare surfaces results in the dispersal of toxic metals over nearby urban or agricultural areas. Revegetation with tolerant native species may reduce this risk. We grew the grass Lygeum spartum under controlled conditions in pots containing a mine tailings mixed into nonpolluted soil to give treatments of 0%, 25%, 50%, 75%, and 100% mine tailings. We tested an acidic (pH3) mine tailings which contained high concentrations of Cd, Cu, Pb, and Zn. Electrical conductivity and pH of the control soil were dramatically affected by the addition of the acid tailings (pH 2dS m−1 in all treatments). Water extractable metal concentrations increased in proportion to the amount of tailings added (up to 1,000mg kg−1 Zn). L. spartum survived, but only in the 25% treatment. In all treatments and for all metals, the plants accumulated higher concentrations in the roots than in shoot

Examining the Cycling Behaviour of Li-Ion Batteries Using Ultrasonic Time-of-Flight Measurements

Diagnostic systems for Li-ion batteries have become increasingly important due to the larger size, and cost of the batteries being deployed in increasingly demanding applications, including electric vehicles. Here, ultrasound acoustic time-of-flight (ToF) analysis is conducted under a range of operating conditions. Measurements are performed on a commercial pouch cell during varying discharge rates to identify a range of effects that influence the acoustic ToF measurements. The cell was examined using X-ray computed tomography to ensure no significant defects were present and to confirm the layered structure in the region being investigated, validating the signal pattern observed. Analyses of the acoustic signals obtained suggest that stresses are generated in the electrodes during both the charge and discharge of the cell with the magnitude of Young's modulus for the component materials being both a function of the state-of-charge and applied current. Characteristic responses for both electrodes during the charge/discharge cycle highlight the potential application of the technique as a real-time diagnostic tool

Battery state-of-charge estimation using machine learning analysis of ultrasonic signatures

The potential of acoustic signatures to be used for State-of-Charge (SoC) estimation is demonstrated using artificial neural network regression models. This approach represents a streamlined method of processing the entire acoustic waveform instead of performing manual, and often arbitrary, waveform peak selection. For applications where computational economy is prioritised, simple metrics of statistical significance are used to formally identify the most informative waveform features. These alone can be exploited for SoC inference. It is further shown that signal portions representing both early and late interfacial reflections can correlate highly with the SoC and be of predictive value, challenging the more common peak selection methods which focus on the latter. Although later echoes represent greater through-thickness coverage, and are intuitively more information-rich, their presence is not guaranteed. Holistic waveform treatment offers a more robust approach to correlating acoustic signatures to electrochemical states. It is further demonstrated that transformation into the frequency domain can reduce the dimensionality of the problem significantly, while also improving the estimation accuracy. Most importantly, it is shown that acoustic signatures can be used as sole model inputs to produce highly accurate SoC estimates, without any complementary voltage information. This makes the method suitable for applications where redundancy and diversification of SoC estimation approaches is needed. Data is obtained experimentally from a 210 mAh LiCoO2/graphite pouch cell. Mean estimation errors as low as 0.75% are achieved on a SoC scale of 0–100%