Soil-plant Transfer Coefficients Research Articles

Phytoaccumulation of trace elements (As, Cd, Co, Cu, Pb, Zn) by Nicotiana glauca and Euphorbia segetalis growing in a Technosol developed on legacy mine wastes (Domingo Rubio wetland, SW Spain)

Sulfidic mine wastes have the potential to generate acid mine drainage (AMD) and release acid leachates containing high levels of iron, sulfate and potentially toxic elements (PTEs). Soils receiving AMD discharges are generally devoid of vegetation. Only a few metal-tolerant plant species can survive under such adverse soil conditions. This work investigates two plant species, Nicotiana glauca and Euphorbia segetalis, that have successfully colonized an AMD-impacted wetland area in south-western Spain. The uptake of PTEs from the soil by roots and their transfer and accumulation in the above-ground biomass were quantified. Results showed that these pioneer plants grew in patches of neutral soil within the wasteland despite the high concentrations of PTEs in the rhizosphere soil (up to: 613 mg kg−1 As, 18.7 mg kg−1 Cd, 6370 mg kg−1 Cu, 2210 mg kg−1 Pb and 5250 mg kg−1 Zn). The target organs of As, Cu and Pb accumulation were: root > leaf > stem in N. glauca, and root > stem > leaf in E. segetalis. Zinc and Cd showed a significant decrease in roots relative to aerial parts of N. glauca, and Co was preferentially partitioned in stems of N. glauca and leaves of E. segetalis. The soil–plant transfer coefficient values of PTEs in all parts of both plants were well below unity with the only exception of Cd in leaves of N. glauca (1.254), suggesting that roots acted as a barrier limiting the uptake of PTEs by plants. Interestingly, under the same soil conditions, N. glauca absorbed Cd in considerable proportions from soil and accumulated it in its leaves, while E. segetalis was not effective in transferring PTEs from roots shoots except for Co. In conclusion, soil pH and plant-related factors greatly influence the stabilization of PTE in the rhizospheric soil and produce inconsistencies in PTE phytoavailability. The findings of this study provide criteria to assist in natural remediation in other legacy contaminated sites worldwide.

EVALUATION OF RISK ASSESSMENT FACTORS AMONG SELECTED METALS IN ROADSIDE GROWN CEREALS OF THE SUDAN SAVANNA ECOLOGY OF NIGERIA

Phytoaccumulation of metals (Cd, Cr, Cu, Pb, Zn) in roadside grown wheat and maize varieties ( Pavon-76, Siettecerros, Zea mays L. and Zea mays everta L.) and the toxicity and phytoremediation capability of the plants was investigated. Four sampling sites, roadside (SU 1, SU 3) and distant sites (SU 2 and SU 4) were selected by principle to represent the level of pollution near major traffic routes and were the reference sampling points. Whole plant metal levels of the four crops were determined using the multi-elemental technique- Energy Dispersive X-ray Fluorescent (EDXRF) and double beam AAS at A.B.U Zaria. Plant uptake factor (PUF), soil-plant transfer coefficient (TC) and translocation factor (TF) was computed for each metal. Pearson correlation analyses between the risk assessment factors of the metals were evaluated. Results revealed a positive significant (P<0.05) relationship between PUF/TC and PUT/TF for Cr and Zn in Pavon-76, PUF/TC for Cr and Zn in the two species of Zea mays L. and Cu in Siettecerros indicates atmospheric inputs and special ability or strong selective ability of each of the crops to accumulate certain metals. The inverse correlation between PUF/TC, PUF/TF and TC/TF among the metals indicates the proximity of SU 1 to the major highway, influence of traffic density, atmospheric inputs and geological material and a combination of other factors. This study reveals the potentialities of these varieties of Wheat and Maize which are terrestrial higher plants as accumulators of metallic elements and phytoremediators of roadside soil pollution

Trace metal levels in castor plants growing on refuse dumpsites in wukari metropolis, Nigeria

A preliminary survey of the risk assessment of selected trace metal (Cd, Cr, Cu, Pb and Zn) levels of castor (Ricinus communis L.) plant growing on refuse dumpsites in Wukari Metropolis, Taraba State was investigated. Duplicate samples each of whole castor plants and decomposed remains of the refuse dumpsites were collected from three locations namely Kwararafa 1(Abo prisoners), G.R.A (Barikr) and Marmara 1(Abattior) based on population density and out of the 10 locations surveyed. Triplicates pH readings of the decomposed refuses at the three locations were recorded. Trace metal levels and pH were determined by the flame AAS using acetylene/air and pH meter respectively. Selected risk assessment techniques such as soil-plant transfer coefficient (TC), plant uptake factor (PUF) and translocation factor (TF) were worked out for the castor plants. Results revealed a high TC value (1.405) for whole castor plant above the permissible limits (value >1) than PUF and TF with less than unity value revealing the potential possible transfer of metals into the plant body. Higher levels of Zn and Cd were evident, followed by Cu according to the Joint FAO/WHO Food standards 2006. Health risk assessment of metals from refuse dumpsites is a good technique for predicting potential threat to life.

Toxic elements and energy accumulation in topsoil and plants of spruce ecosystems

The objective of this research was to evaluate trends and relationships of energy and toxic elements accumulation in A-horizon (the depth of 0–5 cm) of soils and in selected plants of the hemioligotrophic (Dystric Cambisols) and oligotrophic (Skeletic-Rustic Podzols) spruce ecosystems situated along transect (750–1110 m a.s.l.) in the NP Slovenský raj (Eastern Slovakia). The results showed that EU limit values of risk elements in agricultural soils were exceeded for Cu and Cd at the altitude of 750–760 m a.s.l., and in case of Cd also above 1000 m a.s.l. Relationship between energy and toxic elements in soils revealed that with an increasing amount of energy, contents of Zn and Cu significantly declined with altitude (r > –0.5 or r > –0.9). The background value of Cu was exceeded in all plants, that of Zn for Dryopteris filix-mas and Rubus idaeus. Furthermore, excessive accumulation of Cd was revealed by all plants. Cu contents in soils were dominant in determining Cu uptake for Vaccinium myrtillus (r > 0.5); Zn and Cd for V. myrtillus (r > 0.6), D. filix-mas (r > 0.5 or r > 0.8) and Fagus sylvatica (r > –0.8 or r > –0.5); Zn also for R. idaeus species (r > 0.4). The soil-plant transfer coefficients higher than 1 hinted R. idaeus on the plots at the altitude of 960 m a.s.l. (Cd 1.1, Cu 1.2, Zn 3.1), which appears as an excellent native indicator of forest ecosystem contamination.

Pb Uptake in Roadside Grown Wheat (Triticum aestivum L.) in the Sudan Savanna, Kano State

Cereal crops grown under irrigation in a semi-arid ecological habitat can be used to assess food quality and safety of agricultural systems at proximity to highways in the Sudan savannah of Northern Nigeria. This study focussed on the risk assessments of Pb transfer, translocation and uptake at selected growth stages (15-, 30-, 45-, 60-, 75- and 90-days representing seedling or germination, tillering, shooting/booting, earing, flowering and ripening stages respectively of two cultivars of Triticum aestivum L. The experimental (SU 1) and control (SU 2) sites were selected based on distances (345 m and 1936 m) from the Kano-Zaria Highway. Pb levels in soils and the two cultivars of Triticum aestivum L. was measured using the double-beam AAS and plant uptake factors (PUF), soil-plant transfer coefficients (TC) and translocation factors (TF) were worked out. Result reveals differences in metal levels of the cultivars of wheat according to growth stages and plant parts. Pb levels was highly significant (P=0.05 and 0.01) in the stems of Siettecerros at the control site indicating selective ability of cultivar to Pb. Pb levels were highest in both cultivars at the 30-days growth stage indicating sensitivity of tillering stage to Pb uptake. A greater than unity value indicate anthropogenic source of Pb. Siettecerros had the highest TF indicating incorporation of higher levels of Pb in the edible plant parts. A higher PUF (45), TC (6.32) and TF (7.66) for Pb in Pavon-76 and Siettecerros respectively, indicates their suitability for bioremediation particularly, phytoextraction of polluted soils from atmospheric pollutants.

Cistus ladanifer phytostabilizing soils contaminated with non-essential chemical elements

Cistus ladanifer L. is one of the spontaneous species from Iberian Pyrite Belt (IPB) considered promising for phytostabilisation of mining areas. Although the plant–soil relationships of some potentially hazardous elements (e.g. As, Pb, Cu and Zn) are known, for other elements also potentially hazardous and non-essential this information is scarce. However, in soils with multielemental contamination and for landscape rehabilitation processes, these elements should also be considered. The aim of this investigation was to evaluate the potential of C. ladanifer in the phytostabilisation of the soils, developed on different contaminated substrata (e.g. mine wastes, schists and greywackes or their mixtures) and containing non-essential elements (Al, Ag, Ba, Bi, Cd, Sb and Sr), from three Portuguese IPB mining areas (Caveira, Lousal and São Domingos). The uptake, accumulation and translocation of these non-essential elements and their influence on the concentrations of beneficial elements (Co, Na and Se) and major nutrients were studied.Multielemental contaminated soils from the three mining areas had high total concentrations of some non-essential elements (Ba and Sb for the three mines and Se for Caveira and São Domingos). Soil available fraction of the studied elements were usually small (<8.6% of the total concentration) except for Cd whose available fraction was between 10 and 100% of the total concentration (<0.3–1.3mg Cd/kg). In general, C. ladanifer showed significant uptake (biological absorption coefficients indicating strong and intensive uptake) and translocation (translocation coefficients >1) of the studied elements (even the non-essentials), but small accumulation in the shoots (mg/kg−Ag, Bi, Sb and Se: <1.6; Ba, Cd, Co and Sr: 0.05–37.8; Al and Na: 49–2503), independently of the mine area. Elemental concentrations in the shoots were below the limit values indicated for phytotoxicity and toxicity for domestic animals intake. Although the statistical negative influence of Ag, Sb and Sr on the concentrations of the beneficial elements (Na) and nutrients (Ca and Fe) in roots or shoots had been obtained, no visual symptoms was observed in the plants. Cistus ladanifer plants from the studied populations can be considered non-accumulators and excluders of Al, Ag, Ba, Bi, Sr and Sb (soil-plant transfer coefficient≪1) and beneficial elements. Although plants from São Domingos and, in some cases, from Caveira can be accumulators of Cd, the concentrations of Cd in the shoots were small (<0.2mg/kg) and did not represent any environmental risk. Due to its adaptability, tolerance and standard plant behaviours in the three mining areas, C. ladanifer will be a good choice for phytostabilisation of soils contaminated with non-essential elements.

The Determination of Soil-plant Transfer Coefficients of Cesium-137 and Other Elements by γ-Ray Measurement and PIXE Analysis, for use in the Remediation of Fukushima

Edible wild plants growing in the area around the Fukushima Daiichi nuclear power plant remain contaminated. It is important to identify plants with low levels of contamination for the restoration of agriculture in the area. We collected specimens of 10 wild plant species growing in Iitate village which is one of the most highly contaminated areas and also sampled the soil beneath each plant. We measured the specific activity of 137Cs and the concentrations of Na, Mg, Al, Si, P, S, K, Ca, Fe, Zn, Rb and Sr in these samples using a germanium detector and PIXE analysis, respectively. We compared the soil-plant transfer coefficient of 137Cs with those of each element and determined their correlation with 137Cs. It was found that a low Sr transfer coefficient could be used to determine the plants with a low 137Cs transfer coefficient. We suggest that PIXE analysis is a useful analysis technique for agricultural remediation projects in highly contaminated areas around the Fukushima Daiichi nuclear power plant.

The Transfer of Cu, Zn, Mn and Fe between Soils and &amp;lt;i&amp;gt;Allium&amp;lt;/i&amp;gt; Plants (Garlic and Onion), and Tomato in the Southwest of the Buenos Aires Province, Argentina

Chemical extraction methods are generally used to evaluate trace element concentrations in soils. The adequacy of these soil tests is commonly assessed by comparing the extraction results with the metal contents in the plants. In this study, soil and leaf samples were collected in the southwest area of the Buenos Aires Province, Argentina. Garlic (Allium sativum L.), onion (Allium cepa L.) and tomato (Solanum lycopersicum L.) are species of great regional economic importance. These crops need good mineral nutrition for optimum growth and sustainable production. Cu, Zn, Mn and Fe micronutrient uptake by plants was analyzed together with the trace element contents in the soil in which those plants were grown. A single EDTA-extraction procedure was performed to determine soil micronutrients. The amount of extractable-trace elements increased as the concentration of the chelating agent EDTA increased. The range of total element content in soil was: 15.68-31.5 mg·kg-1 for Cu, 75.0-386.3 mg·kg-1 for Zn, 542.5 -1686 mg·kg-1 for Mn and 28,325-32,675 mg·kg-1 for Fe. Micronutrient contents in mature leaf tissue were determined by the acid digestion method. Total and available micronutrient content in soil as well as total content in leaves were measured by flame atomic absorption spectrometry (FAAS). Total micronutrient content and the available extractable-fraction in soils were below the critical values for plant growth. This was in agreement with the amount of micronutrients present in the leaf tissue. A strong relationship between the extraction data and the soil-plant transfer coefficients suggested an appropriate exchange of trace elements from soils to garlic, onion and tomato plants.

Pollution Status of Soils and Vegetation around Busy Motor Parks in Selected Areas of Delta State, Nigeria

Soil and vegetation samples were collected from busy motor parks in selected parts of Delta State and analysed with the aim of ascertaining the potential and environmental impact of the motor park activities on the surroundings. The physicochemical characteristics of the soil samples were investigated using various standard methods while the heavy metal concentrations were determined using Atomic Absorption Spectrophotometric technique. The pH values ranged from 5.59 to 8.52 with a mean value of 7.21 showing that the soils were slightly acidic to slightly alkaline. The electrical conductivity values ranged from 66.54 to 252.9 µs/cm with mean value of 163.48 µs/cm, indicating presence of high level of soluble inorganic salts in the soil samples. The cation exchange capacity values (cmolkg -1 ) ranging from 0.040 to 0.147 with mean value of 0.097 implied that the exchange sites on the soil minerals will be less available for metals retention. The mean percentages of Total Organic Carbon and Total Nitrogen which were 0.488 and 0.107 respectively could be attributed to presence of some biodegradable and compostable materials. The mean concentrations of the heavy metals in the soil samples (mgkg -1 ) were 57.78 for Fe, 1.112 for Pb, 0.482 for Cu, 1.334 for Zn and 0.13 for Cr with the abundance trend of Fe > Zn > Pb > Cu >Cr. The mean metal levels in the vegetation samples ranged from (mgkg -1 ) 0.152 to 12.426 with the abundance trend of Fe > Pb > Zn > Cu > Cr. Soil plant transfer coefficient values for all the metals in all the sites indicate medium accumulation while contamination/pollution index values showed generally very slight contamination. The metal levels in both the soil and vegetation samples in all the sites were relatively higher than the levels recorded in the control sites. The overall results showed evidence of some heavy metals enrichment on the soils and vegetation. This effect could be cumulative over time.

Potentials of Synedrella nodiflora and Sida fallax growing naturally around an abandoned railway station for phytoextraction of heavy metals

Phytoextraction is a non-destructive, cost-effective and safe alternative to conventional cleanup techniques of contaminated soils. In this study, the ability of two plants species Synedrella nodiflora and Sida fallax growing naturally around the abandoned Asafo Railway Station in Kumasi for selective extraction and accumulation of four heavy metals (Pb, Cu, Fe and Zn) were studied using Atomic Absorption Spectroscope. The degree of translocation of these metals by the plants was also calculated. High translocation indices greater than one in the case of Fe and Zn were recorded in S. nodiflora and S. fallax, respectively. However Cu and Pb examined in this study were not effectively extracted nor transported within the plants, hence these plants are excluders of Cu and Pb. The soil plant transfer coefficient for both plant species were calculated for each metal. The highest translocation coefficient value in this study for both plants was recorded for Zn. The translocation coefficient values for Pb and Cu were not significant in both plants, hence these plants can be described as Pb and Cu extruders but potential candidates for Fe bioaccumulation using phytoextraction.

Trace elements tolerance, accumulation and translocation in Cistus populifolius, Cistus salviifolius and their hybrid growing in polymetallic contaminated mine areas

Plants from Cistus genus show a great plasticity and are able to grow both in contaminated and non-contaminated soils. Cistus salviifolius L. was identified in several mines from Portuguese Iberian Pyrite Belt (PIPB) while Cistus populifolius L. was collected in 2009 in Chança and Caveira mines for the first time. In these mine areas, a hybrid of both species Cistus×hybridus Pourr. was also collected being this its first report from those areas. This study aimed to compare the biogeochemical behavior of the three Cistus species growing in the polymetallic mine areas of Caveira, Chança and São Domingos (PIPB). Their possible use in phytoremediation programs of multielemental contaminated soils was evaluated.Soils from Caveira and São Domingos presented high concentrations of various chemical elements and were considered seriously contaminated with As (13–3030mg/kg), Cu (159–1750mg/kg), Pb (932–9210mg/kg) and Sb (23–486mg/kg), and with severe contamination of Zn (33–1010mg/kg). Chança soils presented the lowest trace elements contamination.The three species showed tolerance to moderate acid soils (4.2<pH<6.1), with low fertility and high multielemental contamination. Cistus×hybridus, C. populifolius and C. salviifolius growing in the same mine area are not significantly different for elemental concentration, except for Fe and Sb. Similar behavior was observed for C. populifolius and hybrid growing in different mine areas (Caveira and Chança). Besides the different concentration of each chemical element in Cistus plants, no significant differences were observed in the translocation capacity from roots to shoots for all species: non essential elements and Fe were stored in roots (translocation coefficient: 0.1–0.9) and macro- and micronutrients were transported to the aerial part (translocation coefficient: 1.0–7.7) due to their metabolic functions.All Cistus populations can be considered Mn accumulators, and non-accumulators of As, Cu, Fe, Pb and Sb as well as Caveira plants for Zn (soil-plant transfer coefficient <1). Chança and São Domingos plant populations showed both, accumulators and non-accumulators behavior for Zn. The studied plant species did not show significant ecological variability intra or inter-population and can contribute to the rehabilitation of mining areas with semiarid characteristics.

Risk Element (As, Cd, Cu, Pb, and Zn) Contamination of Soils and Edible Vegetables in the Vicinity of Guixi Smelter, South China

Risk element (As, Cd, Cu, Pb, and Zn) contamination in soils and in two edible vegetables (Solanum melongena L. and Capsicum annum L.) was investigated in the vicinity of Guixi Smelter, South China. Soil As concentrations averaged 23.9 mg/kg. Sites near the smelter tailings recorded the highest levels of As and heavy metals in soils. The concentration order of heavy metals in soils was Cd < Pb < Zn < Cu. Cu and Cd in soils were abundant in the exchangeable and bound to carbonate fraction, while Pb and Zn were in the residual fraction, limiting their potential toxicity as pollutants. The proportions of the metals in the mobile fraction followed the order Pb < Zn < Cu < Cd. In Solanum melongena L. and Capsicum annum L., Zn concentration was the highest, followed by Cu, Cd, and Pb, different from that in soils and in the mobile fraction. Concentrations of heavy metals in the labile fractions in soils and in vegetables presented significant correlation (p < 0.05). Both of the two vegetables are not the Cu and Zn accumulators. As for Cd and As, Capsicum annum L. poses a higher risk to animal and human health than Solanum melongena L., with soil-plant transfer coefficients more than three. Root-stem is the main barrier for most of the heavy metals and As in the two vegetables, resulting in higher metal concentrations in roots relative to other plant tissues. The low stem-fruit transfer coefficients for Zn in Solanum melongena L. and for Pb in Capsicum annum L. suggested that very few of them could reach the fruits.

Utilization of optimized BCR three-step sequential and dilute HCl single extraction procedures for soil–plant metal transfer predictions in contaminated lands

The prediction of soil metal phytoavailability using the chemical extractions is a conventional approach routinely used in soil testing. The adequacy of such soil tests for this purpose is commonly assessed through a comparison of extraction results with metal contents in relevant plants. In this work, the fractions of selected risk metals (Al, As, Cd, Cu, Fe, Mn, Ni, Pb, Zn) that can be taken up by various plants were obtained by optimized BCR (Community Bureau of Reference) three-step sequential extraction procedure (SEP) and by single 0.5 mol L −1 HCl extraction. These procedures were validated using five soil and sediment reference materials (SRM 2710, SRM 2711, CRM 483, CRM 701, SRM RTH 912) and applied to significantly different acidified soils for the fractionation of studied metals. The new indicative values of Al, Cd, Cu, Fe, Mn, P, Pb and Zn fractional concentrations for these reference materials were obtained by the dilute HCl single extraction. The influence of various soil genesis, content of essential elements (Ca, Mg, K, P) and different anthropogenic sources of acidification on extraction yields of individual risk metal fractions was investigated. The concentrations of studied elements were determined by atomic spectrometry methods (flame, graphite furnace and hydride generation atomic absorption spectrometry and inductively coupled plasma optical emission spectrometry). It can be concluded that the data of extraction yields from first BCR SEP acid extractable step and soil–plant transfer coefficients can be applied to the prediction of qualitative mobility of selected risk metals in different soil systems.

Exposure and bioavailability of arsenic in contaminated soils from the La Parrilla mine, Spain

Arsenic derived from mining activity may contaminate water, soil and plant ecosystems resulting in human health and ecotoxicological risks. In this study, exposure assessment of arsenic (As) in soil, spoil, pondwater and plants collected from the areas contaminated by mine tailings and spoils in and around the La Parrilla mine, Caceres province, Spain, was carried out using AAS method. Water solubility, bioavailability and soil–plant transfer coefficients of As and phytoremediation potential of plants were determined. Arsenic concentrations varied from 148 to 2,540 mg/kg in soils of site 1 and from 610 to 1,285 mg/kg in site 2 exceeding the guideline limit for agricultural soil (50 mg/kg). Arsenic concentrations in pond waters varied from 8.8 to 101.4 μg/l. High concentrations of water-soluble As in the soils that ranged from 0.10 to 4.71 mg/kg in site 1 and from 0.46 to 4.75 mg/kg in site 2 exceeded the maximum permitted level of water-soluble As (0.04 mg/kg) in agricultural soils. Arsenic concentrations varied from 0.8 to 149.5 mg/kg dry wt in the plants of site 1 and from 2.0 to 10.0 mg/kg in the plants of site 2. Arsenic concentrations in plants increased in the approximate order: Retama sphaerocarpa < Pteridium aquilinum < Erica australis < Juncus effusus < Phalaris caerulescens < Spergula arvensis in site 1. The soil–plant transfer coefficients for As ranged from 0.001 to 0.21 in site 1 and from 0.004 to 0.016 in site 2. The bioconcentration factor based on water-soluble As of soil varied from 3.2 to 593.9 in the plants of site 1 whereas it varied from 2.1 to 20.7 in the plants of site 2. To our knowledge, this is the first study in Europe to report that the fern species P. aquilinum accumulates extremely low contents of As in its fronds despite high As levels in the soils. Therefore, the S. arvensis, P. caerulescens and J. effusus plant species grown in this area might be used to partly remove the bioavailable toxic As for the purpose of minimization of mining impacts until hypothetical hyperaccumulating and/or transgenic plants could be transplanted for the phytoremediation of As contaminated soils.

Genotype x environment interaction in the uptake of Cs and Sr from soils by plants

AbstractThe soil‐plant transfer factors for Cs and Sr were analyzed in relationship to soil properties, crops, and varieties of crops. Two crops and two varieties of each crop: lettuce (Lactuca sativa L.), cv. Salad Bowl Green and cv. Lobjoits Green Cos, and radish (Raphanus sativus L.), cv. French Breakfast 3 and cv. Scarlet Globe, were grown on five different soils amended with Cs and Sr to give concentrations of 1 mg kg–1 and 50 mg kg–1 of each element. Soil‐plant transfer coefficients ranged between 0.12–19.10 (Cs) and 1.48–146.10 (Sr) for lettuce and 0.09–13.24 (Cs) and 2.99–93.00 (Sr) for radish.Uptake of Cs and Sr by plants depended on both plant and soil properties. There were significant (P ≤ 0.05) differences between soil‐plant transfer factors for each plant type at the two soil concentrations. At each soil concentration about 60 % of the variance in the uptake of the Cs and Sr was due to soil properties. For a given concentration of Cs or Sr in soil, the most important factor effecting soil‐plant transfer of these elements was the soil properties rather than the crops or varieties of crops. Therefore, for the varieties considered here, soil‐plant transfer of Cs and Sr would be best regulated through the management of soil properties.At each concentration of Cs and Sr, the main soil properties effecting the uptake of Cs and Sr by lettuce and radish were the concentrations of K and Ca, pH and CEC. Together with the concentrations of contaminants in soils, they explained about 80 % of total data variance, and were the best predictors for soil‐plant transfer. The different varieties of lettuce and radish gave different responses in soil‐plant transfer of Cs and Sr in different soil conditions, i.e. genotype x environment interaction caused about 30 % of the variability in the uptake of Cs and Sr by plants. This means that a plant variety with a low soil‐plant transfer of Cs and Sr in one soil could have an increased soil‐plant transfer factor in other soils.The broad implications of this work are that in contaminated agricultural lands still used for plant growing, contaminant‐excluding crop varieties may not be a reliable method for decreasing contaminant transfer to foodstuffs. Modification of soil properties would be a more reliable technique. This is particularly relevant to agricultural soils in the former USSR still affected by fallout from the Chernobyl disaster.

Availability of Cd, Ni and Zn to Ryegrass in Sewage Sludge-Treated Soils at Different Temperatures

A pot experiment to compare the availability of Cd, Ni and Znto ryegrass (Lolium perenne L.) was conducted at 15 and 25 °C. For this purpose, three ratesof sewage sludge (0, 10 and 50 t ha-1) were applied in aloamy sand (LS) and a clay loam (CL). Heavy metal availabilityassessed by soil extractions with 0.05 M CaCl2 and the organic matter content were monitored during a period of twoyears, while uptake by ryegrass was monitored over one year after addition of the sludge. The concentrations of Cd and Ni in both the ryegrass and the soil extracts increased significantly, during the first year, especially at 50 t ha-1. However, in the second year metal availability reached a plateau. During the first year, in the ryegrass Znconcentrations did not show an increase, but in the soil CaCl2-extracted Zn increased. During the same period,the organic matter content decreased rapidly, especially at25 °C, in the first year and much more slowly in thesecond, giving a total decrease of 16%. Temperature had a marked effect on metal availability; both soil extracts andplant samples from the 25 °C treatment had greater concentrations of Cd, Ni and Zn than those at 15 °C. This may be attributed to the organic matter, which decomposedmore rapidly at 25 °C. Moreover, soil-plant transfercoefficients (Tc) of the metals were significantly higher at 25 °C than at 15 °C, with Cd showing the greatest difference, followed in decreasing order by Zn and Ni.

Mobility and plant availability of radioactive Cs in natural soil in relation to stable Cs, other alkali elements and soil fertility

The mobility and plant availability of radioactive Cs from the Chernobyl accident in natural soil-plant systems of varying fertility were studied at three sampling locations situated in subalpine areas of central Norway. The soil samples included litter, humus (0–2 cm and 2–5 cm depth), and mineral soil (8–12 cm and 20–30 cm depth), and the plant species studied were Betula nana, Empetrum hermaphroditum and Juncus trifidus. The lichen Cetraria nivalis was also sampled. The sampling took place in the middle of the growth season during the period 1987–1989. The soil and vegetation samples werw analysed with respect to total radiocaesium ( 137Cs and 134Cs), Rb, stable Cs and exchangeable 137Cs (in soil only), K, Ca and Mg. The radiocaesium activity in the vascular plants and lichen decreased by at least 40% during the sampling period. The decrease in activity of E. hermaphroditum and C. nivalis is explained by growth of new low-activity material in 1988 and 1989, diluting material directly contaminated by the fallout in 1986. For B. nana and J. trifidus the decrease was caused by lower radiocaesium uptake by the root system. The uptake of radiocaesium in the latter two species seemed to be connected primarily with the radiocaesium content in the soil humus layer. Only in J. trifidus radiocaesium showed clear connection with the other soil parameters studied. Calculations of specific activities and soil-plant transfer coefficients showed that radioactive caesium in the soil was more available to plants than total stable caesium. Comparison of 137Cs/ 134Cs ratios in soil and plants indicated that the radiocaesium content in the soil is still influenced by 137Cs from nuclear weapons fallout.