Traditional agricultural practices enable sustainable remediation of highly polluted soils in Southern Spain for cultivation of food crops.

This study relates elemental content of a range of edible crops grown in soils severely polluted by metals and metalloids as affected by traditional smallholder management practices. Five agricultural plots close to a sulfidic waste dump were monitored. Soil analysis demonstrated elevated concentrations of As, Cu, Pb and Zn that were greatly in excess of maximum statutory limits for agricultural soils in the studied region. The main vegetables (lettuce, chard, onion, potatoes) and lemon, together with their associated soils, were measured for elemental content. Extractable soil element concentrations were very low. There were differences in elemental accumulation between crops, but none exceeded statutory concentrations in edible parts. Soil-plant transfer factors were uniformly low for all elements and crops. It is concluded that traditional soil management practices (annual liming and application of animal manures) have created conditions for sustainable long-term safety use, with potential for multiple end-use, of these highly polluted soils.

Factors affecting accumulation of thallium and other trace elements in two wild Brassicaceae spontaneously growing on soils contaminated by tailings dam waste.

Thallium is a scarce, highly toxic element. There are several investigations that report Tl accumulation in plants of the family Brassicaceae. These plants could pose a risk in areas where Tl is present at higher concentrations than normal soils. The present study reports analyses of two wild Brassicaceae, Hirschfeldia incana and Diplotaxis catholica, growing spontaneously at five sampling sites moderately polluted with Tl and other trace elements in the Green Corridor of the Guadiamar river, Seville, S. Spain. In general, trace element content was unremarkable in all part plants, despite the concentrations present in soil. Thallium was the only element whose concentration in both plant species was above normal for plants (maximum values of 5.00 mgkg(-1) in H. incana flowers). There were significant positive correlations between total Tl in soil and Tl in both plant species. Transfer Coefficients (TC) for all elements were, in general, <1 for both species, except for Tl in flowers and fruits at some sites. The highest Enrichment Factor (EF) was found for Tl in H. incana fruits (EF = 607) and D. catholica flowers (EF = 321). H. incana was studied in a previous growing season (2004) in the same area, although the rainfall was 3 times more than in the year of the present study (2005), giving a maximum Tl content of 46.5 mgkg(-1) in H. incana flowers. The data presented here show that Tl content of plants growing in semi-arid conditions can be significantly influenced by precipitation. In dry years, plant Tl accumulation may be significantly reduced.

Field trials to assess the uptake of arsenic by vegetables from contaminated soils and soil remediation with iron oxides.

The uptake of arsenic (As) by plants from contaminated soils presents a health hazard that may affect the use of agricultural and former industrial land. Methods for limiting the hazard are desirable. A proposed remediation treatment comprises the precipitation of iron (Fe) oxides in the contaminated soil by adding ferrous sulfate and lime. The effects on As bioavailability were assessed using a range of vegetable crops grown in the field. Four UK locations were used, where soil was contaminated by As from different sources. At the most contaminated site, a clay loam containing a mean of 748 mg As kg(-1) soil, beetroot, calabrese, cauliflower, lettuce, potato, radish and spinach were grown. For all crops except spinach, ferrous sulfate treatment caused a significant reduction in the bioavailability of As in some part of the crop. Application of ferrous sulfate in solution, providing 0.2% Fe oxides in the soil (0-10 cm), reduced As uptake by a mean of 22%. Solid ferrous sulfate was applied to give concentrations of 0.5% and 1% Fe oxides: the 0.5% concentration reduced As uptake by a mean of 32% and the 1% concentration gave no significant additional benefit. On a sandy loam containing 65 mg As kg(-1) soil, there was tentative evidence that ferrous sulfate treatment up to 2% Fe oxides caused a significant reduction in lettuce As, but calabrese did not respond. At the other two sites, the effects of ferrous sulfate treatment were not significant, but the uptake of soil As was low in treated and untreated soils. Differences between sites in the bioavailable fraction of soil As may be related to the soil texture or the source of As. The highest bioavailability was found on the soil which had been contaminated by aerial deposition and had a high sand content.

Synthetic zeolites as amendments for sewage sludge-based compost.

The effects of incorporating a synthetic zeolite (Zeolite P) in a range of concentrations (0.1-1.0 w:w) into an experimental horticultural compost, derived from sewage sludge, have been investigated. The impact of zeolite treatment on time-related changes of the labile zinc, copper, iron and manganese pools within the compost was compared to lime incorporation (5% w:w) and to a proprietary unamended peat-based compost. Addition of 0.5% and 1.0% zeolite significantly reduced labile zinc over a 90 day period. The highest zeolite treatment was more effective than liming; 0.5% zeolite was as effective as lime. Plant growth trials measuring transfer of metals to ryegrass (Lolium perenne L. cv Elka) in successive harvests demonstrated that both 1.0% zeolite and 5% lime treatment caused significant reduction in total metal transfer from soil-plant over a 116 day growth period. It is concluded that the use of synthetic zeolite as an amendment for compost of this type significantly reduces potential for soil metal mobility and soil-plant transfer.

A field study of the ecotoxicology of copper to bryophytes.

The impact of particulate copper, emitted from a copper rod-rolling plant, on the distribution of common grassland bryophytes has been investigated. Several areas of managed grassland, differing in total and water-extractable soil copper content, surrounding the factory were surveyed to establish species composition and distribution of the bryophyte flora. Clear differences emerged in the distribution patterns of the main acrocarpous (upright/tufted growth form) and pleurocarpous (horizontal/spreading growth form) species present, with some species being more or less confined to soils with elevated copper (Pohlia nutans), whilst others were absent from such sites. The distribution of acrocarpous species was not related to increasing soil copper concentrations, whereas pleurocarpous species showed considerable sensitivity. This may not be a simple reflection of sensitivity to copper; ecological factors such as differences in patterns of water and soluble copper uptake between the different growth forms may be significant factors, as may be changes in the vascular plant flora giving rise to differences in population densities of potential competitors between sites. Pleurocarpous species are absent from grassland where total soil copper >550 microg g(-1) dry weight, whilst the less sensitive acrocarpous species occur at total soil copper levels in excess of 2000 microg g(-1) dry weight.

Patterns of soil copper contamination and temporal changes in vegetation in the vicinity of a copper rod rolling factory.

Patterns of soil copper contamination have been examined in the vicinity of a copper rod rolling plant in Prescot, Merseyside, UK. The site, established in 1975, was found to possess clear patterns of soil copper contamination, with the highest levels of HNO3 and water-extractable fractions encountered in the factory grounds adjacent to the location of the furnace chimney. The majority of the copper had accumulated in the upper soil horizons. The site is surrounded by planted lawns, established at different times after the commissioning of the plant. The species composition of the extant grassland communities, found at sites with differing soil copper levels, was compared to the composition of the original seed mixtures sown at each of ten sites. These surveys clearly showed that different levels of soil copper contamination had produced significant changes in grassland composition with time. At the most polluted site, copper tolerant Agrostis capillaris clones were the main grasses present only two years after the area was sown with a four-species mixture of non-tolerant grass seed. Lolium perenne possessed extreme sensitivity to copper. A number of dicotyledonous species, normally considered sensitive to elevated copper levels, were found to be unaffected where such conditions had arisen after plants had established from seed.

Accumulation and egestion of dietary copper and cadmium by the grasshopper Locusta migratoria R & F (Orthoptera: Acrididae).

Copper and cadmium budgets were studied for a model insect herbivore/host plant system comprising the oligophagous leaf-chewing grasshopper (Locusta migratoria) feeding on Zea mays (Gramineae). Fifth instar larvae were fed, for between 5 and 20 days, on maize foliage contaminated with either copper, cadmium or on control foliage containing no excess metal. Male and female locusts fed on copper-treated maize retained 45 and 42% of ingested copper respectively, figures not significantly different from the 41 and 33% retained on untreated maize. Remaining copper was egested with the faeces. Locusts fed on copper-treated maize showed an increase of 27% in body copper burden compared with those on the control diet: the increase was independent of time on the diet. Female locusts retained 33% and males 21% of ingested cadmium. Faecal cadmium levels were elevated, and accumulation in both sexes was proportional to time on the Cd-enriched diet. For both copper and cadmium, some ingested metal probably passed directly through the locust gut, bound to undigested food material. Results suggest that grasshoppers may effectively regulate excess dietary copper, but are unable efficiently to regulate cadmium.

The effects of feeding by the black bean aphidAphis fabae Scop. (Homoptera: Aphididae) on copper and cadmium accumulation in broad bean (Vicia faba L.).

Broad beans (Vicia faba L.), cultured hydroponically were supplied with 100 µg mL(-1) copper or 50 µg mL(-1) cadmium in nutrient solution. Samples of plant material from both nutrient regimes were analysed before and after infestation by the black bean aphid (Aphis fabae Scop.). Heavy aphid infestation resulted in a significant reduction in copper content of shoots in comparison with uninfested plants. A similar, but less well- defined, situation occurred in the case of cadmium.Further investigations examined the effects of different levels of aphid infestation on the above phenomena. In all cases the presence of feeding aphids reduced elemental accumulation in plant shoots. Long term infestation with population densities as low as three adult aphids showed a reduction in shoot copper and cadmium content.

Lead and potential health risks from subsistence food crops in urban Kenya.

Lead, zinc and cadmium were analysed in a range of subsistence crops cultivated in and around Nairobi city centre. Lead was found to be the only contaminant of concern, being widely dispersed with elevated levels found in crops and soils from both suburban and city centre areas. Extremely high concentrations were recorded in the edible portions of a variety of crops, and high soil Pb levels were recorded within 30m of busy roads. Based on these data, it is estimated that subsistence on a diet of crops cultivated in and around Nairobi could increase Pb intake by 10-100 times the FAO/WHO maximum tolerable levels, potentially contributing substantially to existing health problems.

A role forAmanita muscaria L. in the circulation of cadmium and vanadium in a non-polluted woodland.

The sporophore of the fungusAmanita muscaria L. contains greatiy elevated levels of cadmium (29.9 µg g(-1) dwt) and vanadium (344.9 µg g(-1) dwt) in comparison with the soil in a birch woodland (total (HNO3-extractabie Cd 0.4 µg g(-1) dwt, V 11.7 µg g(-1) dwt). The significance of this remarkable concentration of normally rare and dispersed elements in terms of their circulation in the woodland has been investigated. Both elements are released from sporophore tissue in a form which can be taken up by a test plant (lettuce), cultivated in the woodland soil amended with different quantities of sporophore tissue, Cadmium levels in all plant tissues were elevated in comparison to the non-amended controls; only root vanadium levels responded to the amendment of the soil. The results are discussed in terms of their significance for the natural cycling of both elements. It is calculated that an abundant population of sporophores could circulate 1.4% of the total cadmium and 0.65% of the total vanadium pool found in the litter layer and 0-5 cm soil horizon in the sampled woodland over a period of 14 days (mean life span of a sporophore).

Vanadium uptake by higher plants: Some recent developments.

The occurrence of vanadium in the biosphere, and the possible roles this element may play in the metabolism of living organisms, especially higher plants, are discussed. The aqueous chemistry of the element is reviewed, and the chemical properties of the element are related to those of soils and plants. Evidence is present for a biotransformation of vanadium from vanadate (VO 3 (-) ) to vanadyl (VO(2+)) during uptake by plants, based on tissue analysis and ESR spectra. The significance of this process on the potential impact of vanadium in the biosphere is discussed.

Studies on the behaviour of lead in wood binding of free and complexed 210Pb to xylem tissue.

The binding of lead to xylem tissue has been studied using an isolated segmentperfusion technique. The results show that free lead ions bind more readily to xylem tissue than does lead in the form of a lead-glycine complex. A small, but significant proportion of the applied lead moves laterally from wood to bark. Both binding and lateral movement of lead are shown to be time-dependant. The results are discussed in terms of using trees and the chemical analysis of their annual growth rings to date heavy metal pollution histories.

Studies on lateral movement of 210Pb in woody stems : Patterns observed in dormant and non-dormant stems.

Evidence has been obtained for lateral transport of bark applied 210Pb from bark to wood in a range of tree species. This lateral redistribution was found to be independant of cambial reactivation, Lead being recovered from bark and wood in the same proportions from dormant and non-dormant shoots. The results are discussed in relationship to naturally-occurring uptake of Lead by stems.

Distribution of growth regulators and sugars by the tangential and radial transport systems of stem segments of Willow.

The tangential transport of labelled growth regulators and sugars, through the bark of isolated stem segments of Willow (Salix viminalis L.), has been studied. It has been shown that these compounds have distinct patterns of distribution, particularly in the case of plant growth regulators. IAA moves preferentially into the lower half of a horizontal stem, kinetin into the upper half when these substances are applied via a bark abrasion made on the side of the stem. Distribution patterns of sugars were more variable, in some instances upward movement occurred, in others downward. The distinctness of the distribution patterns was accentuated by pretreatment of the stem segments in a horizontal position for 7 days prior to experimentation. Radial movement of labelled IAA and kinetin, centrifugally from the centre of the xylem to the bark, showed no difference in distribution between the upper and lower portions of the stem.

Patterns of translocation and metabolism of (14)C-labelled IAA in the phloem of Willow.

When 2-(14)-C-labelled IAA was applied to an isolated segment of Willow via a bark abrasion the pathway of transport of this compound was found to be located in the sieve elements as evidenced by the pattern of activity found in honeydew excreted by individuals of Tuberolachnus salignus (Gmelin) feeding on the segment.Further experiments have established that polarity of transport of (14)C-IAA occurs in a basipetal direction when isolated segments of willow are orientated in a vertical position, with the morphological apex uppermost. No polarity was found when segments were orientated in a vertical position with the morphological base uppermost, or when the segments were orientated in a horizontal position. The metabolism of (14)C-IAA was also studied with respect to orientation. It was shown that the conversion rate of IAA to IAA aspartate was influenced by the orientation of the segment. It is considered that this is not a direct effect of orientation on the rate of metabolism of IAA.

Influence of IAA upon the longitudinal and tangential movement of labelled sugars in the phloem of Willow.

Using a bark abrasion technique, the influence of IAA upon patterns of sugar translocation in isolated stem segments of Willow (Salix viminalis L.) has been studied. IAA was found to exert a considerable influence over translocation in both a longidutinal and tangential direction. Studies on longitudinal movement have led to the postulation of two possible effects of IAA on this system. Firstly a stimulation of sugar loading from the storage parenchyma into the sieve elements as described by Lepp and Peel (1970), and secondly a direct effect upon, the longitudinal transport process. The situation with regard to the tangential transport system is not as clear in all its aspects, though once again it is postulated that IAA may have a direct effect upon the movement of sugars in the tangential transport system.

Some effects of IAA and kinetin upon the movement of sugars in the phloem of willow.

Isolated bark strips of willow were sealed on to polythene tubes having three compartments. Colonies of the aphid Tuberolachnus salignus Gmelin were established on the bark at each end of the strip. IAA or kinetin at a concentration of 10(-5)M was applied to the cambial surface of the strip in one of the end compartments, whilst either (14)C-labeled sucrose or (86)RbCl was applied in the centre compartment.Both IAA and kinetin caused the activity from the (14)C-Sucrose to move away from the area of their application, as measured by the specific activity of the honeydew collected from the aphid colonies. No effect of these hormones was demonstrated on the movement of (86)Rb.The results from further experiments in which sieve element exudate was collected via the severed stylets of the aphid, indicate that IAA and kinetin increase the rate of loading of sugars into sieve elements, i.e. the source capacity of the bark to which they are applied.