Search

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.

Uptake of Cd, Zn, Pb and Mn by the hyperaccumulator Thlaspi caerulescens was studied by pot trials in plant growth units and in populations of wild plants growing over Pb/Zn base-metal mine wastes at Les Malines in the south of France. The pot trials utilised metal-contaminated soils from Auby in the Lille area. Zinc and Cd concentrations in wild plants averaged 1.16% and 0.16% (dry weight) respectively. The unfertilised biomass of the plants was 2.6 t/ha. A single fertilised crop with the above metal content could remove 60 kg of Zn and 8.4 kg Cd per hectare. Experiments with pot-grown and wild plants showed that metal concentrations (dry weight basis) were up to 1% Zn (4% Zn in the soil) and just over 0.1% Cd (0.02% Cd in the soil). The metal content of the plants was correlated strongly with the plant-available fraction in the soils as measured by extraction with ammonium acetate and was inversely correlated with pH. Bioaccumulation coefficients (plant/soil metal concentration quotients) were in general higher for Cd than for Zn except at low metal concentrations in the soil. There was a tendency for these coefficients to increase with decreasing metal concentrations in the soil. It is proposed that phytoremediation using Thlaspi caerulescens would be entirely feasible for low levels of Cd where only a single crop would be needed to halve a Cd content of 10 μg/g in the soil. It will never be possible to remediate elevated Zn concentrations within an economic time frame (

Ultramafic (“serpentine”) soils from and adjacent to the Dun Mountain Ophiolitic Belt, South Island, New Zealand were analysed for 11 elements in order to establish to what degree edaphic factors influenced the character of the overlying vegetation. Using principal components analysis with a mutual plot of the first two principal components, involving the total elemental concentrations in the soils, it was possible to divide the soils into 6 virtually non-overlapping fields, each of which represented a specific vegetation community. Component 1 was essentially an “ultramafic plot” with heavy loadings from the elements chromium, cobalt, iron, magnesium, manganese, and nickel. Component 2 was a “non ultramafic” plot with heavy loadings from aluminium, copper and zinc. For elements extracted from the soils at pH 5.9, discrimination was somewhat poorer but confirmed the great importance of magnesium and nickel as controlling elements for the serpentine vegetation. It was concluded that the results indicated the overriding importance of edaphic factors in controlling the serpentine vegetation.

The uptake of Ni, Co, and Cu by the nickel hyperaccumulator Alyssum troodii Boiss and the non-accumulator Aurinia saxatilis (L.) Desv. were studied in pot trials using artificial rooting media with varying concentrations of the metals added as soluble salts, singly and in combination. The ability of five other Ni hyperaccumulating species of Alyssum to hyperaccumulate Co was also investigated. Leaves and stems of A. troodii accumulated Ni to almost the same extent (8000–10 000 μg g-1). In roots, the highest Ni concentration was 2000 μg g-1. In leaves of Au. saxatilis, the maximum Ni concentration was only 380 μg g-1 and the level in roots was even lower. In media containing Co, the maximum concentration of this element in A. troodii (2325 μg g-1) was ten times higher than in the non-accumulator species. Slightly less Co was found in stems and roots of both species. Among the other Ni hyperaccumulators, the maximum concentration of Co in leaves ranged from about 1000–8000 μg g-1. Copper concentrations were the same in all organs of both species when they were grown in copper-rich media and were in the range 40–80 μg g-1, showing that neither plant was capable of taking up Cu at levels comparable to those of Ni and Co. When both plants were grown in media containing equal amounts of both Co and Ni, the Co concentrations in plant organs were the same as for specimens grown in media containing Co only. However, the Ni levels were lower in both species. Uptake of Co therefore appeared to suppress Ni uptake. Pot trials showed that the order of tolerance was Ni>Cu>Co for A. troodii and Ni>Co≈Cu for Au. saxatilis, whereas the seedling tests showed the order to be Co>Ni>Cu. At metal concentrations ≥10 000 μg g-1, the overall tolerance of A. troodii was greater than that of Au. saxatilis which exhibited equally low tolerance to Ni and Cu. We conclude that in A. troodii, A. corsicum Duby, A. heldreichii Hausskn., A. murale Waldstein & Kitaibel, A. pintodasilvae T.R. Dudley, and A. tenium Halacsy, Ni tolerance and hyperaccumulation conveys the same character towards Co. This behaviour should be investigated in other hyperaccumulators of Ni and/or Co.

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 ‘philosopher's stone’. But background levels of gold in plants are usually very low, rarely exceeding 10 ng per g dry tissue (10 p.p.b.)1. Hyperaccumulator plants2, 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 phytoremediation3, 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 lead4. 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 gold5,6.

Automotive emissions are by far the most serious source of environmental lead pollution because of their ubiquitous nature. Their effects on humans have been extensively studied during the past decade and have been reviewed by BROOKS (1977). Blood lead levels are generally considered to be the best indices of the lead burden of humans (LUDWIG et al. 1965) and of domestic animals (BLOOM et al. 1976, WARD et al. 1977).

Orpanoxin, a nonsteroidal anti-inflammatory drug (NSAID) lacking gastric ulcerogenic effects in the therapeutic dose range in rats, was compared with six reference NSAIDs for oral activity in the rat paw carrageenin-induced edema assay. Tested NSAIDs were ranked on the basis of oral mg/kg ED50 values: piroxicam, 0.55; orpanoxin, 35.6; diflunisal, 59.6; benoxaprofen, greater than 300; tolmetin sodium, greater than 300; and sulindac, greater than 300. Zomepirac sodium was inactive. Only the three most potent compounds produced greater than 60% inhibition of edema. Inhibition was generally greater at 4 h than at 6 h post carrageenin for all compounds. Oral activity of orpanoxin was also demonstrated in the guinea-pig u.v.-induced erythema model (ED50 = 24.2 mg/kg p.o. when given 1 h before irradiation) and in the mouse ear croton oil induced edema test (ED50 value = 131 mg/kg p.o.). Topical activity of orpanoxin was assessed in both the guinea-pig and mouse models. In the guinea-pig u.v.-induced erythema model, application (1 h after u.v.) of 1, 5, and 10% (w/v) orpanoxin creams (containing 10% urea) significantly inhibited erythema at 2, 3, and 4 h post-irradiation. Orpanoxin, mefenamic acid, and indomethacin as 1% creams inhibited total erythema scores 70, 92 and 74%, respectively. Evidence for topical activity in the mouse ear assay was also obtained for orpanoxin in diethyl ether or 10% urea cream, but not in dimethylsulfoxide. It was concluded that orpanoxin has anti-inflammatory activity comparable to reference NSAIDs in the rat paw edema test, is active orally in rat, mouse, and guinea-pig models, and shows topical activity in the guinea-pig and the mouse.

Pot trials were carried out on plants ofHaumaniastrum katangense, Haumaniastrum robertii andAeolanthus biformifolius. These metallophytes from Zaire were grown in substrates containing from 0–10,000 μg/g (0–1%) copper or cobalt. The tolerance of each species was determined and for cobalt was highest inH. robertii (4000 μg/g) and for copper was highest inAeolanthus biformifolius (9000 μg/g). Discontinuities in the plant-soil curves for each element indicate an exclusion mechanism operating for all three species at lower concentrations of the element in the soil. All species would grow in soils containing only traces of cobalt or copper and this indicated that uptake of heavy metals was not linked to a physiological requirement for either element. The plant-soil relationship for cobalt (P

Plant and soil sampling was carried out across scheelite-bearing ore-bodies at six areas of different geological, vegetational, climatic and topographical environments in the South Island of New Zealand. The feasibility of using the concentration of tungsten in plants and soils to locate the scheelite was investigated for all the areas. These regions may be classified into two main groups according to their lithology and vegetation. The first group, comprising Clenorchy, Paradise, Macrae's Flat and Top Valley, is underlain by the schists of the New Zealand geosyncline, has a low rainfall and a predominantly shallow-rooted vegetation such as tussock grass and bracken. In these areas soil sampling was generally more effective than plant sampling, although the latter sometimes gave sharper anomalies. The areas of the second group, Barrytown and Canaan, are both underlain by predominantly granitic material, have a high rainfall, rugged topography and a predominantly beech forest vegetation. In these areas, although soil sampling was in general satisfactory, tree-trunk sampling was found to have certain advantages in locating extensions of known scheelite-bearing reefs.

Herbarium specimens of the genus Haumaniastrum (mainly from Shaba Province Zaire) were analysed for copper and cobalt.H. homblei showed elevated copper levels and indicated its tolerance to mineralized ground.H. robertii (previously-known as a “copper flower”) showed the expected high copper concentrations, but contained abnormally high concentrations of cobalt (av. 4304 μg/g dry weight) far exceeding those of copper. This species has the highest cobalt content of any phanerogam and its distribution may be controlled by cobalt rather than by copper. re]19761220

Cretaceous-Tertiary boundary clays rich in iridium from five sites in Europe and New Zealand were investigated. The clays are found to be 100-10,000-fold-enriched in elemental carbon (mainly soot), which is isotopically uniform and apparently comes from a single global fire. The soot layer coincides with the iridium layer, suggesting that the fire was triggered by meteorite impact and began before the ejecta had settled.

Experiments were carried out on the tolerance to and uptake of copper and cobalt by three members of a phylogenetic series of taxa within the genusSilene from Zaire which were reputed to represent a progression of increasing adaptation to metalliferous soils. Plants studied were the widespread and presumably non-tolerantSilene burchelli var.angustifolia (B), a more tolerant variant of this taxon (E) designated an ecotype, and the metallophyteS. cobalticola (C). Studies on the effects of both metals, singly and in combination, on seed germination, seedling and plant performance and yield, and metal uptake from soil cultures, confirmed in general the sequence B

A study was made of soil factors controlling the distribution of five species from a serpentine flora in the Dun Mountain area, South Island, New Zealand. Samples of soil were taken from sites of each of the species and each sample was analysed for calcium, chromium, cobalt, copper, magnesium, manganese, nickel, potassium, and zinc. On the basis of the species growing on them, the soil samples were divided into five groups: group 1,Pimelea suteri; group 2,Myosotis monroi; group 3,Hebe odora; group 4,Cassinia vauvilliersii- group 5,Leptospermum scoparium. Discriminant analysis was used to characterise each group of soils on the basis of chemical composition. The results showed that the two endemic plants (P. suteri andM. monroi) were much more commonly found in localities of highest magnesium concentration. These two species were strongly differentiated by the potassium and copper levels in their soils. No strong elemental discrimination was found among the non-endemic species.

Pot trials onLychnis alpina, L. alpina var. serpentinicola, andSilene dioica were carried out on these ‘kisplanten’ (pyrite plants) to determine their uptake and tolerance of copper, lead, nickel and zinc. The tolerance and uptake of all four heavy metals was far greater for both varieties ofL. alpina than forS. dioica thus casting doubt onS. dioica being a true ‘kisplante’. There were no detectable differences between both varieties ofL. alpina indicating that var. serpentinicola may only be a stunted form ofL. alpina possibly not warranting varietal ranking. Uptake of copper, lead and nickel was very great in the case ofL. alpina. Plant-soil correlations for nickel were very highly significant in the case of both varieties ofL. alpina so that this taxon has an obvious role in biogeochemical prospecting. To describeL. alpina as a ‘copper flower’ is an oversimplification of a complex situation. The species is probably a true pyrite plant with tolerance to all of the major components of sulphide ore deposits.

Herbarium specimens of 17 species of Geissois were analysed for nickel, cobalt, chromium and iron with a view to discovering further hyperaccumulators of nickel (>1000 μg/g on a dry mass basis) in addition to the previously recordedG. pruinosa. A further six hyperaccumulators were discovered, all from New Caledonia. Unlike 90% of hyperaccumulators, Geissois is in Subclass Rosidae of the Magnioliate which it shares with three other hyperaccumulators (two species ofArgophyllum andPearsonia metallifera. The work highlights the remarkable concentration of hyperaccumulators in New Caledonia.

Hyperaccumulators (here defined as species containing at least 500 μg/g dryweight of either copper or cobalt in leaves), are of interest for the fields of mineral exploration and phytochemistry. Reported hyperaccumulation of copper inAeolanthus biformifolius and the presence of two other species on copper/cobalt mineralization in Shaba (Zaire) led to a survey of these elements in 49 species of the African genusAeolanthus Mart.A. biformifolius appears to be also a hyperaccumulator of Co (2520 μg/g in leaves, 4300 μg/g in corms). Cobalt levels for most species ofAeolanthus were considerably above typical values for phanerogams and indicate the favorable potential of the genus for further study.

The distribution and dynamics ofHaumaniastrum katangense (S. Moore) duvign. et Plancke (‘copper flower’) in southern Shaba Province, Zaire have been studied. In the course of 20 years, this species has spread well beyond its original distribution. It is a successful coloniser of manmade environments containing mineralized substrates: i.e. disturbed or non-disturbed copper/cobalt deposits; copper/cobalt mining sites; sites of precolonial smelters; verges of dirt roads dressed with mine waste; along railways carrying ore wagons.

The trace element content of ashed specimens of a New Zealand serpentine flora and the associated soils was investigated. Six species (Myosotis monroi Cheesem.,Notothlaspi australe Hook. f.,Pimelea suteri Kirk,Cassinia vauvilliersii (Homb. et Jacq.) Hook. f. varserpentina Ckn. et Allan,Hebe odora (Hook. f.) Ckn. andLeptospermum scoparium J. R. et G. Forst.) were analysed for cobalt, chromium, copper and nickel by emission spectroscopy. The significance of the experimental data was evaluated by calculation of the correlation coefficients by a computer.C. vauvilliersii showed highly significant correlation between plant ash and soil concentration for chromium, cobalt and nickel.H. odora andL. scoparium showed similar but less pronounced correlations. Relative concentrations varied considerably among the species studied.P. suteri is a strong accumulator of nickel and cobalt andL. scoparium of chromium. Good correlations were observed for certain pairs of elements in the plant ash of individual species and in the soils alone. Data for uptake by plants were compared with soil extractabilities. Calcium-magnesium ratios were also determined, and were found to be much lower than in the same species growing on non-serpentinized soils. It was concluded that the above species, particularlyC. vauvilliersii will be useful in biogeochemical prospecting.

The uptake of tungsten by the New Zealand silver beech (Nothofagus menziesii) was investigated by pot trials with seedlings of this species in order to obtain information on the mode of their accumulation of this element as a preliminary to further field studies involving biogeochemical prospecting. Tungsten accumulation was most pronounced in the roots. Under controlled glasshouse conditions, the concentrations of this element in the roots, stems and leaves, were all related to levels in the soil.

Differences have been shown in molybdenum uptake by microorganisms from the rhizosphere and soil sampled away from the roots, of the radish,Raphanus sativus L., grown in market garden soils from Napier and Hastings (New Zealand).

The determination of osmium content and isotopic abundances in geological materials has received increasing attention in recent years following the proposal of Alvarez et al.1 that mass extinctions at the end of the Cretaceous period were caused by the impact of a large (∼10km) meteorite which left anomalously high iridium levels as a geochemical signature in the boundary shales. Here we report a new and simple method for measuring osmium in geological materials, involving fusion of the sample with sodium peroxide, distillation of the osmium as the tetroxide using perchloric acid, extraction into chloroform, and absorption of the chloroform extract onto graphite powder before instrumental neutron activation analysis. In a variant of this technique, the chloroform extract is back-extracted into an aqueous phase and the osmium isotopes are determined by plasma-source mass spectrometry (ICPMS). We have used this method on the Woodside Creek (New Zealand) Cretaceous/Tertiary boundary clay and have obtained the first osmium content (6g ng g−1) for this material. The 187Os/186Os ratio is 1.12±0.16, showing a typical non-crustal signature. This combined distillation–extraction–ICPMS method will prove to be useful for measuring osmium isotopes in other geological materials.