Robyn Simcock

Phytomining for nickel, thallium and gold

The technique of phytomining involves growing a crop of a metal-hyperaccumulating plant species, harvesting the biomass and burning it to produce a bio-ore. The first phytomining experiments were carried out in California using the Ni-hyperaccumulator Streptanthus polygaloides and it was found that a yield of 100 kg=ha of sulphur-free Ni could be produced. We have used the same technique to test the phytomining potential of the Ni-hyperaccumulators Alyssum bertolonii from Italy and Berkheya coddii from South Africa. The effect of different fertiliser treatments on growth of Alyssum bertolonii was established in situ in Tuscany and showed that the biomass of the plant could be increased by a factor of nearly 3 (4.5 t=ha to 12 t=ha) without significant loss of the Ni concentration (7600 mg=kg) in the plant. Analogous experiments have been carried out on Berkheya coddii where a biomass yield of over 20 t=ha can readily be achieved though the Ni concentration is not as high as in A. bertolonii. The total yield is, however, much greater. We have also been able to induce plants to hyperaccumulate Au by adding ammonium thiocyanate to the substrate. Up to 57 mg=kg Au (dry mass) could be accumulated by Indian mustard (Brassica juncea). Unusual hyperaccumulation (>500 mg=kg dry mass) of Tl has been determined in Iberis intermedia and Biscutella laevigata (Brassicaceae) from southern France. The Iberis contained up to 0.4% Tl (4000 mg=kg) in the whole-plant dry matter and the Biscutella over 1.5%. This unusually high accumulation of Tl has significance for animal and human health, phytoremediation of contaminated soils, and phytomining for Tl. We calculate that using Iberis, a net return of

Harvesting a crop of gold in plants

US 1200=ha (twice the return from a crop of wheat) would be possible with a biomass yield of 10 t=ha containing 0.08% Tl in dry matter. The break-even point (net yield of

Gold Uptake by Plants

US 500=ha) would require 170 mg=kg (0.017%) Tl in dry matter. A model of a phytomining operation and its economics is presented and its advantages and disadvantages discussed.

Emerging threats in urban ecosystems: a horizon scanning exercise

The possibility of turning base metals into gold has intrigued many scientists since the early alchemists, and the discovery of significant gold uptake by plants has long been a ‘philosophers stone’. But background levels of gold in plants are usually very low, rarely exceeding 10 ng per g dry tissue (10 p.p.b.). Hyperaccumulator plants, however, have 100 times the elemental concentrations of normal vegetation, a level of 1 mg per g dry tissue (1 p.p.m.). They can be used in phytoremediation, the in situ improvement of polluted sites. Hyperaccumulation can be induced by adding a chemical amendment, such as EDTA, to a plant substrate to make soluble an otherwise insoluble target metal, such as lead. Here we have induced plants to accumulate gold from ores by treating the substrate with ammonium thiocyanate. This technique might be used as a form of biological mining (phytomining) for gold,.

Quantifying Evapotranspiration Rates for New Zealand Green Roofs

This review covers three aspects of gold uptake by plants: passive uptake by wild plants under natural conditions; hydroponic studies on plants grown in solutions of gold salts; induced hyperaccumulation of gold by plants grown in auriferous substrates using ammonium thiocyanate as a chelating agent. Using induced hyperaccumulation, it is proposed that it would be technically feasible to grow ‘a crop of gold’ usingBrassica juncea or other plant species.

Stormwater mitigation by living roofs in Auckland, New Zealand.

As urbanization intensifies, urban ecosystems are increasingly under pressure from a range of threats. Horizon scanning has the potential to act as an early warning system, thereby initiating prompt discussion and decision making about threat mitigation. We undertook a systematic horizon scanning exercise, using a modified Delphi technique and experts from wide-ranging disciplines, to identify emerging threats in urban ecosystems. The 10 identified threats were generally associated with rapid advances in technology (eg solar panels, light-emitting diode lights, self-healing concrete) or with societal demands on urban nature (eg green prescriptions). Although many of the issues identified are also technological opportunities with recognized environmental benefits, we have highlighted emerging risks so that research and mitigation strategies can be initiated promptly. Given the accelerated rate of technological advancement and the increasing demands of urbanized populations, horizon scanning should be condu...

Hydrology of an extensive living roof under sub-tropical climate conditions in Auckland, New Zealand

Green roofs are an emerging storm-water management tool that has predominantly been analyzed for runoff volume reduction and peak flow mitigation. Little research has been completed on evapotranspiration ET in green roofs. Sedum mexicanum Mexican stonecrop and Disphyma australe New Zealand iceplant in a New Zealand designed, pumice- and zeolite-based substrate were analyzed to determine daily and hourly ET rates under both water-abundant and drought-stressed conditions. Water loss, and thus storage recovery of the substrate, was greatest in the first 9 days. Transpiration T by S. mexicanum contributed up to 48% of total ET 2.19 mm/day and D. australe contributed up to 47% of total ET 2.21 mm/day. After the initial rate of rapid water loss, plants conserved water and ET was not significantly different from evaporation E from unplanted substrate. S. mexicanum had a greater ability to conserve water and thus a greater longevity of life than D. australe under harsh drought conditions.

Modelling the influence of stand structural, edaphic and climatic influences on juvenile Pinus radiata dynamic modulus of elasticity

Living roof technology is emerging as a low impact development method for stormwater management suitable for retrofit in densely developed urban centres. This paper presents results of field monitoring of a 235 m 2 extensive living roof suitable for retrofit installation in Auckland, New Zealand (NZ), to quantify the extent of stormwater control. Comparison in stormwater control is made between living roofs with three different substrate types at two different depths in a side-by-side comparison. No statistically significant differences in runoff response were found between the three substrate types tested. There was no statistically significant additional stormwater benefit found when increasing plot depth from 50–70mm. The overall cumulative retention efficiency of the UoA living roof was 71.6% over the period of 23 October 2008 to 22 October 2009, where 1137.2 mm of rainfall was received. On an individual event basis, the living roof retained a median of 83.6% of rainfall received, with a median peak flow reduction per event of 93.2%. Living roof response cannot be linked to one factor alone; multiple parameters such as rain depth, rain intensity, climatic variables and antecedent dry days all play a role in influencing hydrologic response.