Search

Plants with inordinately high concentrations of heavy metals (‘hyperaccumulators’) can be used for phytoremediation (removal of contaminants from soils) or phytomining (growing a crop of plants to harvest the metals). Pot trials were used to investigate the effects of MgCO3, CaCO3, sulphur, chelating agents (NTA, DTPA, EDTA) and acid mine tailings on nickel and cobalt uptake by the South African nickel hyperaccumulator Berkheya coddii. Plants were grown in a nickel-rich ultramafic (‘serpentine’) soil diluted with pumice. Both MgCO3and CaCO3caused significant decreases in the uptake of both metals, as well as decreasing their solubility in the soil. After the addition of MgCO3,there was a significant increase in soil pH, so the reduction in plant-metal uptake could not be solely attributed to the action of magnesium alone. Since CaCO3had no significant effect on soil pH, this indicated that calcium inhibits the uptake of both cobalt and nickel. All three chelating agents caused a significant reduction in plant uptake of nickel, despite increasing the solubility (plant availability) of these elements in the soil. Cobalt uptake was unaffected. Sulphur, and the addition of acid mine tailings, caused a highly significant increase in nickel and cobalt uptake, relative to the controls. Sulphur could be used as a low-cost soil amendment to enhance the metal uptake of crops grown on ultramafic soils. Thus, land management procedures would enhance phytoremediation and phytomining operations for nickel and cobalt.

Biscutella laevigata and Iberis intermedia were sampled from sites near St Laurent le Minier, Southern France, and B. laevigata was also sampled from Rocca San Silvestro, Tuscany, Italy. Soils associated with the rhizosphere of each plant were also sampled. Both Biscutella laevigata and Iberis intermedia accumulate inordinately high concentrations of thallium (1.94 and 0.4%, respectively) in their above-ground dry tissue. The levels of thallium accumulated by both species were strongly correlated with both the total and extractable concentrations of thallium in the soils. Concentrations of zinc, cadmium, and lead were below the threshold for hyperaccumulation. It is proposed that B. laevigata and/or I. intermedia could be used for phytoremediation or phytomining of thallium-contaminated soils. Such an operation would involve the repeated cropping of either species, until an acceptable level of thallium in the soils was reached. Additionally, the harvested plant material could be burnt and the res...

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.

Following the discovery of the hyperaccumulation of nickel by the Philippine plant Dichapetalum gelonioides subsp. tuberculatum , the nature of the nickel in aqueous plant extracts has been investigated by gel chromatography, ion exchange chromatography, high voltage electrophoresis and GC-MS. The purified extract contained 18% Ni, 24% citric acid and 43% malic acid(mole ratio 1:0.4:1), the remainder consisting of small amounts of Ca, Mg, K, Na and a trace of tartaric acid. Experimental observations are discussed in terms of the stabilities of complexes of citrate and malate with Ni. By using X-ray crystallography it was shown that crystals obtained from a Ni-citrate-malate solution simulating the extract, contain Ni exclusively in the form of an anionic Ni(II)-citrato complex.

Vegetation and soil sampling were carried out in 80 plots located in five different ultramafic (serpentine) sites of Tuscany, central Italy. The physical and chemical features of each plot were determined and the species composition and cover recorded. The exchangeable fraction of soil metals was analysed because it gives a measure of their concentrations available to plants. The plots were classified by cluster analysis and ANOVA was used to compare the environmental variables of the groups of plots. Canonical correspondence analysis was used to detect the principal factors for gradients of species composition within the plant communities. A higher content of exchangeable metals was found under the more evolved and structured plant communities, suggesting that serpentine vegetation of Tuscany is not strongly limited by soil metals, such as chromium, cobalt, nickel and magnesium, typically associated with ultramafic soils. The low nutrient content of the soils and drought stress mainly due to topographical features, appear to have a more significant role in determining the typical scattered vegetation of the Tuscan ultramafics.

The species Peltaria emarginata (Boiss.) Hausskn., from areas of serpentine in northern Greece and Euboea, has been found to accumulate extremely high concentrations of nickel, often exceeding 1% of the dry mass of the plant leaf. Extreme behaviour of this kind is not found in other species of Peltaria, nor in related genera such as Ricotia, even for those plants which have grown on a nickel-rich substrate. Several herbarium specimens labelled Peltaria dumulosa Post have also been shown to have very high nickel levels. P. dumulosa appears never to have been described properly, and the specimens have now been identified as Alyssum samariferum Boiss. & Hausskn., a species in which nickel accumulation has been demonstrated previously.

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

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

Summary Thirty-two Psychotria species from New Caledonia and 178 from other islands of the Pacific Basin were analyzed for nickel in order to identify hyperaccumulators (> 1000 g/g dry mass) of nickel. P. douarrei was the only taxon which possessed this character and contained a mean concentration of 2.24% nickel in its leaves. This is higher than for any other known hyperaccumulator of nickel. Pot trials showed that P. douarrei can grow in substrates containing up to 1% plant-available nickel. It is suggested that P. dourarrei is a neoendemic taxon possibly derived from P. baillonii which occupies complementary ecological niches on non-nickeliferous soils adjacent to the ultramafic substrates supporting P. douarrei. Evolution may have proceeded via an intermediate nickel-tolerant ecotype of P. baillonii which can still be found growing in association with P. douarrei.

Copper and cobalt were determined in tissue extracts of five metallophytes from Shaba Province, Zaire. About 4O% of the cobalt and copper was extractable into deionized water and a further 4O% was extractable in 0.2M hydrochloric acid. It was concluded that copper and cobalt are bound to several different ligands instead of a single ligand as in the case of nickel hyperaccumulators. Proton microprobe studies on the cobalt accumulator Haumaniastrum robertii showed a strong inverse correlation between the spatial distributions of cobalt and potassium, as well as a direct relationship between cobalt and calcium. It is suggested that some of the cobalt may be immobilized with calcium in oxalate crystals.

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.

The nickel content of herbarium specimens of Californian Streptanthus and Caulanthus has been determined. Serpentine-tolerant species had nickel values of 10-100 ,ug/g (dry mass) except in the case of S. polygaloides Gray which had nickel values in the range 3,300-14,800 ,ug/g (0.33%-1.48%). This is the first hyperaccumulator of nickel found in the Americas. It is suggested that the later classification of S. polygaloides as the monotypic Microsemia polygaloides (Gray) Greene may be justified if the nickel accumulation data are used to reinforce the existing marked morphological differences from other Streptanthus. THE NICKEL CONTENT of most species of vegetation usually does not exceed 10 ,ug/g (dry mass basis) except for taxa growing on nickelrich soils derived from ultrabasic rocks. In such cases, nickel levels of 10-100 ,ug/g are

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 distributions of nickel, copper, zinc, and iron in fresh leaves from four tree species were studied using differential centrifugation of cell homogenates to fractionate the cell organelles and atomic absorption spectrophotometry to measure the concentrations in the various fractions. Results from each species were closely similar. Approximately 90 per cent of the nickel was present in the supernatant fraction while approximately 80 per cent of the iron was present in the chloroplast fraction. Both copper and zinc had subcellular distributions similar to one another and contained appreciable amounts of the elements in both chloroplast and super natant fractions. High-voltage paper electrophoretic separations of the soluble extracts of leaves showed that while copper, zinc, and iron existed principally as anionic complexes, nickel existed as a cationic species. It was considered that this cationic form of nickel was unlikely to be an unchelated aquated cation.

An organometallic complex of nickel has been isolated from nickel-accumulating plants of New Caledonia and has been identified by a combination of infrared spectroscopy, high-voltage paper electrophoresis, gas-liquid chromatography and mass spectrometry. Most of the nickel in Sebertia acuminata, Homalium francii, Homalium guillainii, Homalium kanaliense, Hybanthus austrocaledonicus and Hybanthus caledonicus is found as a negatively-charged citratonickelate (II) complex with Ni(H 2 O) 6 2+ as the major cationic constituent.

A strong correlation has been found between the levels of nickel and citric acid in the leaves of 17 New Caledonian plant species which show a range of nickel-accumulating ability: Sebertia acuminata, Psychotria douarrei, Geissois pruinosa, Hybanthus austrocaledonicus, Hybanthus caledonicus, and 12 species of Homalium. Purified extracts of these plants contain nickel as a citrate complex. Three nickel-accumulating plants from beyond New Caledonia (Alyssum bertolonii, Alyssum serpyllifolium s.sp. lusitanicum and Pearsonia metallifera) do not contain unusually high levels of citrate, nor is citrate present in purified nickel-containing extracts of these species.

The nature of nickel complexes in various Ni accumulating plant species, mainly from New Caledonia, was investigated by techniques including gel chromatography, ion-exchange chromatography, high performance liquid chromatography, and a combination of gas-liquid chromatography and mass spectrometry. Psychotria douarrei contained Ni complexed mainly (63%) as a negatively-charged malate complex balanced by a cationic aquo complex. Phyllanthus serpentinus had anionic Ni bound as 42% citrate and 4O% malate. All other species studied, contained Ni as an anionic citrate complex.

Sixteen elements were determined in 156 specimens of 47 species of New Caledonian Flacourtiaceae including the genera Casearia, Homalium, Lasiochlamys and Xylosma. The data were used to study inter-elemental relationships, particularly those involving nutrient elements, magnesium and phytotoxic elements such as chromium, cobalt and nickel. Phytotoxic chromium was not accumulated to any marked degree by any taxon. Cobalt was inversely correlated with boron and sodium, and nickel with both nutrients as well as manganese. The data seemed to indicate the overriding controlling factor of reduced nutrient uptake caused by elements present in high concentrations in serpentinic substrates. It would seem that this reduced uptake is a major factor in the ‘serpentine problem’, at least as far as the Flacourtiaceae and the New Caledonian environment is concerned. By contrast, the toxic effects of elements such as nickel, cobalt and chromium seems less important.

Elemental concentrations were studied in two New Caledonian hyper-accumulators of nickel and in the soils supporting these plants. The nickel content of Hybanthus austrocaledonicus was directly related to the total nickel content of the soil, and this species may therefore be used for biogeochemical prospecting. Nickel was correlated well with other elements of the iron family in non-lateritic ultrabasic soils but not in laterites. Both H. austrocaledonicus and Homalium kanaliense contained adequate amounts of potassium despite very low concentrations in the supporting soils. These low nutrient levels were further aggravated by antagonism to potassium uptake caused by other soil elements. Because of the paucity of relationships between nickel in H. kanaliense and elements in the soil, it is suggested that the high nickel levels in this plant may be controlled by organic constituents in this species. re]19760504

A small shrub Hybanthus floribundus (Lindl.) F. Muell. Violaceae growing in Western Australia accumulates nickel and cobalt to a very high degree. Values of up to 23% nickel in leaf ash may represent the highest relative accumulation of a metal on record. The high accumulation of nickel poses interesting problems in plant physiology and plant biochemistry.

Leptospermum scoparium plants cultured in solutions containing Na2 (51)CrO4 accumulated most of the absorbed radioactivity in the roots. About one third of the root radioactivity was soluble in 80% ethanol in the form of three (51)Cr-complexes, the predominant one being identified as trioxalatochromate (III) ion. These complexes were also present in stem and leaf extracts. (51)Cr distribution was examined in various chemical fractions; protein and nucleic acids were especially low in radioactivity.

Cadmium, copper, lead, silver and zinc were determined in bryophytes from two mining areas in New Zealand. Background concentrations of all, except copper in Hypnum cupressiforme Hedw., were lower than in the lowest background values obtained for Swedish specimens of this species. Near the dusty treatment plant at Te Aroha, all bryophytes had high metal concentrations when compared with the substrate, which indicated foliar uptake of airborne contaminants when compared with uptake by bryophytes in mineralized areas due presumably to passive ion-exchange at the rhizoid-soil interface. Uptake of silver near a treatment plant at Maratoto and uptake of heavy metals by the aquatic bryophyte Fissidens rigidulus Hook. f. et. Wils were also investigated.

Although plant indicators or accumulators of copper are well represented in the literature (Duvigneaud 1958; Duvigneaud & Denaeyer de Smet 1963; Cole, Provan & Tooms 1968; Howard-Williams 1970), the list of nickel indicators or accumulators is considerably smaller. The term 'accumulator' is here defined as a plant whose mean content of a particular element (expressed on an ash-weight basis) is greater than the content of the same element in the fine earth fraction of the substrate. Table 1 lists all the known nickel

Aquatic bryophytes growing in streams were used for biogeochemical prospecting for uranium in the Buller Gorge area of New Zealand. Alpha radioactivity was found to bear an inverse relationship to the uranium content of many bryophytes. The concentration of this element in the bryophytes gave an approximately quantitative indication of mineralization in the area and correlated well with the uranium content of the waters. Bryophytes have sometimes been used in the search for minerals but they have been used mainly as geobotanical indicators using such plants as the well known "copper mosses" which are said to grow preferentially over copper deposits. (Shacklette, 1967; Hartman, 1969). Biogeochemical prospecting (the chemical analysis of plant material) is seldom feasible for bryophytes since their rhizoids are always superficial and cannot give evidence of mineralization at depth. This objection does not apply to aquatic bryophytes which are constantly washed by their environment and which might be expected to concentrate trace elements from the streams that pass over them by adsorption on their leaves. The accumulation of uranium by nonaquatic bryophytes has been observed by Grodzinskii (1959) and Samoilova (1961), but as far as is known the aquatic forms have never been previously used for prospecting purposes. During the past decade, extensive studies involving geochemical and biogeochemical methods of prospecting have been carried out in the Hawks Crag Breccia, a uraniferous area in the South Island of New Zealand. Studies involving the analysis of stream waters for uranium (Wodzicki, 1959) have shown that this method is not reliable since not only are flow rates extremely variable but often uranium levels are close to the limits of detection of the analytical method. In the work reported in this paper, we have examined the possibility of using aquatic bryophytes as indicators of uranium mineralization in the watersheds of the streams in which they were found. The reasoning behind this approach was that bryophytes, which approximate in some degree to simple ion exchangers (Puustjiirvi, 1956), have a long lifetime of up to several decades and might afford an indication of the mean uranium content of stream waters over a long period. Furthermore, analysis would be much easier than for stream waters since it is known that bryophytes have 1 This research was supported by grants from the Mineral Resources Subcommittee of the New Zealand University Grants Committee. The assistance of Dr. P. J. Peterson and Dr. G. A. M. Scott is also gratefully acknowledged. 2 Department of Chemistry and Biochemistry, Massey University, Palmerston North, New Zealand. This content downloaded from 207.46.13.128 on Tue, 06 Sep 2016 06:06:43 UTC All use subject to http://about.jstor.org/terms 502 THE BRYOLOGIST [Volume 72 the capability of absorbing relatively large amounts of elements (Oho, Kawai & Kawai, 1959). The alpha activity of the bryophytes and their uranium content were compared with known mineralization in the watersheds concerned and were also compared with analysis of stream waters carried out indirectly by concentration of uranium on to peat samples contained in finely-woven cotton bags placed in the streams (Lopatkina, 1967). Description of the Buller Gorge Locality.-The area of uranium mineralization is located in the Lower Buller Gorge on the West Coast of the South Island some 15 miles east of the township of Westport. The mineralization is found in a formation known as the Hawks Crag Breccia (Beck, Reed & Willett, 1958). Primary uranium minerals are coffinite and uraninite whereas secondary minerals such as autunite, gummite and torbernite occur extensively wherever weathering has occurred. The rainfall of the area averages 80-100 inches per year. The region is extremely rough and dissected with numerous steep, swift streams which often provide the only practical access to the region, which is covered with dense indigenous forest. A map of the area (Fig. 1) shows the streams (numbered 1-14) from which bryophytes were collected. MATERIALS AND METHODS Bryophytes in streams of this region grow as closely-entwined, small clumps that contain as many as seven or eight species, including Bryum blandum Hook. f. & Wils., Dicranella vaginata (Hook.) Card., Distichophyllum pulchellum (Hook. f. & Wils.) Mitt., Fissidens rigidulus C. Miill., Lophocolea planiuscula (Tayl.) Gott., Lindenb. & Nees, Plagiochila deltoides Lindenb., Pterogophyllum dentatum (Hook. f. & Wils.) Mitt., Riccardia sp., and Thamnium pandum (Hook. f. & Wils.) Jaeg. Initially, attempts were made to identify the species and to collect and analyze them separately. An average of five species were collected from each of 14 streams draining the Hawks Crag Breccia, but the separation and identification of the species was difficult and time-consuming. Later, the species composition of a sample was ignored altogether and composite samples of mixed bryophytes were gathered from the streams. Samples were prepared by washing in order to separate the plants from the trapped sedimentary material, which was also retained for analysis, and were then dried at 10?C and ashed at 450?C before final determination of the trace constituents. In order to sample stream waters, New Zealand Hauraki peat was washed successively in tap water, distilled water, ethyl alcohol, and benzene as recommended by Horvath (1960) and was dried at 110?C. Ten-gram samples of this material were sealed in finely-woven cotton bags and were anchored in stream beds for one week. The samples were then collected, dried at 10?C, and ashed at 450?C for subsequent analysis. The alpha activity of ashed bryophytes and of sediment samples was measured by use of a Beckman Lowbeta II counter. Uranium was determined fluorimetrically (Brooks & Whitehead, 1968). Full details of the experimental procedure have been reported elsewhere (Whitehead & Brooks, 1969). Gamma spectrometry was carried out on selected samples by use of a lithium-drifted germanium detector attached to a 256 multichannel analyzer at the Institute of Nuclear Sciences D.S.I.R. Lower Hutt. Samples were also analyzed for beryllium, copper, and lead by emission spectrography since these elements have been shown to be geochemically associated with uranium in the Hawks Crag Breccia (Cohen, Brooks & Reeves, 1969). The significance of the data was tested by computer calculation of correlation coefficient for various pairs of variables. RESULTS AND DISCUSSION The Alpha Activity and Uranium Content of Bryophytes.-Statistical analysis of the uranium content (ppm) and alpha activity (counts/100 min./50 mg) for 36 samples This content downloaded from 207.46.13.128 on Tue, 06 Sep 2016 06:06:43 UTC All use subject to http://about.jstor.org/terms 1969] WHITEHEAD & BROOKS: BRYOPHYTES AND URANIUM 503