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PubMedDate not supplied

Soil solid-phase controls lead activity in soil solution.

Lead pollution of the environment is synonymous with civilization. It has no known biological function, and is naturally present in soil, but its presence in food crops is deemed undesirable. The concern regarding Pb is mostly due to chronic human and animal health effects, rather then phytotoxicity. However, not much is known about the chemistry and speciation of Pb in soils. We determined the activity of Pb2+, in near neutral and alkaline soils, representative of alluvial, desertic and calcareous soils of Egypt, using the competitive chelation method. Lead activity ranged from 10(-6.73) to 10(-4.83) M, and was negatively correlated with soil and soil solution pH (R2 = -0.92, P < 0.01 and R2 = -0.89, P < 0.01, respectively). It could be predicted in soil solution from the equation: log(Pb2+) = 9.9 - 2pH. A solubility diagram for the various Pb minerals found in soil was constructed using published thermodynamic data obtained from the literature, and our measured Pb2+ activities compared with this information. The measured Pb2+ activities were undersaturated with regard to the solubility of PbSiO3 in equilibrium with SiO2 (soil). However, they were supersaturated with regard to the solubilities of the Pb carbonate minerals PbCO3 (cerussite) and Pb3(CO3)2(OH)2 in equilibrium with atmospheric CO2 and hydroxide Pb(OH)2. They were also supersaturated with regard to the solubilities of the Pb phosphate minerals Pb3(PO4)2, Pb5(PO4)3OH, and Pb4O(PO4)2 in equilibrium with tricalcium phosphate and CaCO3. The activity of Pb2+ was not regulated by any mineral of known solubility in our soils, but possibly by a mixture of Pb carbonate and phosphate minerals.

Biological Availability↗
PubMedDate not supplied

Soil variables for predicting potential phosphorus release in Swedish noncalcareous soils.

The accumulation of P in agricultural soils due to fertilization has increased the risk of P losses from agricultural fields to surface waters. In risk assessment systems for P losses, both P release from soil to solution and transport mechanisms need to be considered. In this study, the overall objective was to identify soil variables for prediction of potential P release from soil to solution. Soils from nine sites of the Swedish long-term fertility experiment were used, each with four soil P levels. Phosphorus extractable with CaCl2 was used as an estimate of potential P release from soil to solution. Ammonium lactate-extractable phosphorus (P-AL) or NaHCO3-extractable phosphorus (Olsen P) could not be used alone for prediction of potential P release since soils with high phosphorus sorption capacity (PSC) released less P than soils with low PSC at the same soil test phosphorus (STP) level. Degree of phosphorus saturation (DPS) was calculated as Olsen P or P-AL as a percentage of PSC derived from P sorption isotherms or from Fe and Al extractable in ammonium oxalate. The CaCl2-extractable total phosphorus (CaCl2-TP) was exponentially related to these DPS values (r2 > or = 0.79). The CaCl2-TP was also linearly related to ratios between Olsen P or P-AL and a single-point phosphorus sorption index (PSI; r2 > or = 0.86). These ratios, which are easily determined and gave good correlations with CaCl2-TP, seemed to be the most useful estimates of potential P release for risk assessment systems.

Fertilizers↗
PubMed2005

Fire and grazing effects on wind erosion, soil water content, and soil temperature.

Selective grazing of burned patches can be intense if animal distribution is not controlled and may compound the independent effects of fire and grazing on soil characteristics. Our objectives were to quantify the effects of patch burning and grazing on wind erosion, soil water content, and soil temperature in sand sagebrush (Artemisia filifolia Torr.) mixed prairie. We selected 24, 4-ha plots near Woodward, OK. Four plots were burned during autumn (mid-November) and four during spring (mid-April), and four served as nonburned controls for each of two years. Cattle were given unrestricted access (April-September) to burned patches (<2% of pastures) and utilization was about 78%. Wind erosion, soil water content, and soil temperature were measured monthly. Wind erosion varied by burn, year, and sampling height. Wind erosion was about 2 to 48 times greater on autumn-burned plots than nonburned plots during the dormant period (December-April). Growing-season (April-August) erosion was greatest during spring. Erosion of spring-burned sites was double that of nonburned sites both years. Growing-season erosion from autumn-burned sites was similar to nonburned sites except for one year with a dry April-May. Soil water content was unaffected by patch burn treatments. Soils of burned plots were 1 to 3 degrees C warmer than those of nonburned plots, based on mid-day measurements. Lower water holding and deep percolation capacity of sandy soils probably moderated effects on soil water content and soil temperature. Despite poor growing conditions following fire and heavy selective grazing of burned patches, no blowouts or drifts were observed.

Animals↗
PubMed2006

Soil microbial and faunal community responses to bt maize and insecticide in two soils.

The effects of maize (Zea mays L.), genetically modified to express the Cry1Ab protein (Bt), and an insecticide on soil microbial and faunal communities were assessed in a glasshouse experiment. Soil for the experiment was taken from field sites where the same maize cultivars were grown to allow comparison between results under glasshouse conditions with those from field trials. Plants were grown in contrasting sandy loam and clay loam soils, half were sprayed with a pyrethroid insecticide (deltamethrin) and soil samples taken at the five-leaf stage, flowering, and maturity. The main effect on all measured parameters was that of soil type and there were no effects of Bt trait or insecticide on plant growth. The Bt trait resulted in more soil nematodes and protozoa (amoebae), whereas insecticide application increased plant Bt concentration and altered nematode community structure. The only significant effects on soil microbial community structure, microarthropods, and larvae of a nontarget root-feeding Dipteran, were due to soil type and plant growth stage. The results indicate that, although there were statistically significant effects of the Bt trait on soil populations, they were small. The relative magnitude of the effect could best be judged by comparison with the insecticide treatment, which was representative of current best practice. The Bt trait had no greater effect than the insecticide treatment. Results from this glasshouse experiment were in broad agreement with conclusions from field experiments using the same plant material grown in the same soils.

Animals↗
PubMed2002

[Ecological benefits of artificial seabuckthorn stands in semi-arid hilly region of Loess plateauion soil- and water conservation and soil moisture].

There is a remarkable function on decreasing runoff and sediment in seabuckthorn and its mixed stands, but the effects on soil- and water conservation are different due to different structure and patterns of seabuckthorn and its mixed stands. The intensity of soil water use by seabuckthorn forest was different along with the month in growing season. In growing season, soil moisture in 0-500 cm layer was 5.1%, the lowest in the end of May and 8.8%, the highest in the end of October. This intensity was also different with forest age. 8 ages seabuckthorn forest consumed 231.2 mm of soil stored water in 0-500 cm layer annually, and soil moisture was 5.6%. Therefore, it should be cut for increasing soil moisture. In end of the third year after cutting, soil moisture in 0-160 cm layer could recover, and the value would be 10.3%-14.6%. Seabuckthorn forest could reduce the effect of slope location on soil moisture. Seabuckthorn and its mixed stands have similar intensity of soil water use, and there was a soil dry layer phenomenon in their stands.

China↗
PubMed2003

[Ecological distribution of soil microorganism in artificial greenbelt in hinterland of Takilimakan Desert and their relations with soil factors].

Studies on the distribution of soil microorganisms in the artificial greenbelt in hinterland of Takilimakan Desert and the effects of soil features on the distribution showed that under saline water irrigation, the activities of soil microorganisms increased sharply, and the soil structure and nutrient status were improved. Among soil microorganisms, bacteria were predominant, actinomyces were the next, and fungi were the least. There were more microorganisms in upper than in deeper soil layers. Soil microorganisms near shelter-forest had a higher activity, and their quantities over 3 m from shelter-forest were almost equal to those in shifting sand. The quantities of soil microorganisms varied with seasons, and there were distinct differences among different sites of forests. Among the measured 11 soil factors, the interactions between pairs of soil available phosphorus-available potassium, organic matter-available potassium, available nitrogen-available potassium, available nitrogen-available phosphorus, organic matter-available phosphorus, available phosphorus-available nitrogen, total nitrogen-available potassium, available potassium-available phosphorus, total nitrogen-available phosphorus, and water contents-available nitrogen were significant, with the correlation coefficients of 1.37-2.58. The direct effects of available phosphorus, available nitrogen, and total nitrogen on the microbial quantity were significant, with the coefficient of 1.01-2.58.

Conservation of Natural Resources↗
PubMed2005

Effect of soil acidification on the growth of Korean pine (Pinus koraiensis) seedlings in a granite-derived forest soil.

The growth of pine trees has diminished in recent years in industrial areas of Korea. Soil acidification is believed to be responsible. To study its effects, we grew seedlings of three-year-old Korean pine in brown forest soil derived from granite, which had been treated with an acid solution, for 182 days. The anion mol ratio in the solution was SO4(2-):NO3-:Cl-=5:3:2, which is the average in the total precipitation in Korea; six H+ ion concentrations in the soil were studied (0 (control), 10, 30, 60 and 90 mmol H+.kg-1). With increasing amounts of H+ added to the soil, the concentrations of Ca, Mg, K, Al and Mn increased, especially below a soil pH of 3.8. The concentrations of Ca, Mg and K in pine needles and stems increased with increasing H+ added to the soil, whereas their concentrations in the root decreased. Conversely, the concentration of N and P in each organ of the pine plant was higher in all treatments than in controls. Also, the concentrations of Al and Mn increased significantly in all organs of the plant with increasing H+. We also estimated the effect of deliberate soil acidification on tree growth, using the molar ratio (Ca+Mg+K)/Al as an indicator of soil acidification. A strong positive correlation was found between the total dry mass (TDM) of seedlings and the (Ca+Mg+K)/Al molar ratio calculated from the concentrations of water-soluble elements in soil (r=0.99, p<0.001). When the (Ca+Mg+K)/Al molar ratio reached 1.0, the relative TDM had fallen to 40%. These results show that deliberate soil acidification reduces the growth of the Korean pine less than it does the Red pine, which has been the dominant species in Korea.

Acids↗
PubMed2006

Effects of lead contamination on soil enzymatic activities, microbial biomass, and rice physiological indices in soil-lead-rice (Oryza sativa L.) system.

The effect of lead (Pb) treatment on the soil enzymatic activities, soil microbial biomass, rice physiological indices and rice biomass were studied in a greenhouse pot experiment. Six levels of Pb viz. 0(CK), 100, 300, 500, 700, 900 mg/kg soil were applied in two types of paddy soils. The results showed that Pb treatment had a stimulating effect on soil enzymatic activities and microbial biomass carbon (Cmic) at low concentration and an inhibitory influence at higher concentration. The degree of influence on enzymatic activities and Cmic by Pb was related to the clay and organic matter contents of the soils. When the Pb treatment was raised to the level of 500 mg/kg, ecological risk appeared both to soil microorganisms and plants. The results also revealed a consistent trend of increased chlorophyll contents and rice biomass initially, maximum at a certain Pb treatment, and then decreased gradually with the increase in Pb concentration. Pb was effective in inducing proline accumulation and its toxicity causes oxidative stress in rice plants. Therefore, it was concluded that soil enzymatic activities, Cmic and rice physiological indices, could be sensitive indicators to reflect environmental stress in soil-lead-rice system.

Acid Phosphatase↗
PubMed2003

The effect of soil: water ratios on the mineralisation of phenanthrene: LNAPL mixtures in soil.

Contamination of soil by polycyclic aromatic hydrocarbons is frequently associated with non-aqueous-phase liquids. Measurement of the catabolic potential of a soil or determination of the biodegradable fraction of a contaminant can be done using a slurried soil respirometric system. This work assessed the impact of increasing the concentration of transformer oil and soil:water ratio on the microbial catabolism of [(14)C]phenanthrene to (14)CO(2) by a phenanthrene-degrading inoculum. Slurrying (1:1, 1:2, 1:3 and 1:5 soil:water ratios) consistently resulted in statistically higher rates and extents of mineralisation than the non-slurried system (2:1 soil:water ratio; P<0.01). The maximum extents of mineralisation observed occurred in the 1:2-1:5 soil:water ratio microcosms irrespective of transformer oil concentration. Transformer oil concentrations investigated displayed no statistically significant effect on total mineralisation (P>0.05). Soil slurries 1:2 or greater, but less than 1:5 (soil:water), are recommended for bioassay determinations of total contaminant bioavailability due to greater overall mineralisation and improved reproducibility.

Biodegradation, Environmental↗
PubMed2003

Optimization of soil physical and chemical conditions for the bioremediation of creosote-contaminated soil.

Mispah type soil (FAO : Lithosol) contaminated with > 250 000 mg kg(-1) creosote was collected from the yard of a creosote treatment plant. The soil's carbon, nitrogen and phosphorus contents were determined. Due to creosote contamination, the carbon content of the soil was found to be 130,000 mg C kg(-1). This concentration was found to greatly affect the nitrogen content (0.08%). The phosphorus content was less affected (4.5%). It was estimated that a nutrient amendment to bring the soil to a C : N 10 : 1 would be adequate to stimulate microbial growth and creosote degradation. The soil was amended with a range of C : N ratios below and above the estimated ratio. In one of the treatments, the phosphorus content was amended. Sterile and natural controls were also set up. The soil was incubated at 30 +/- 2 degrees C on a rotary shaker at 150 rpm in the dark for six weeks. Water content was maintained at 70% field capacity. The lowest nitrogen supplementation (C : N = 25 : 1) was more effective in enhancing microbial growth (3.12E + 05) and creosote removal (68.7%) from the soil. Additional phosphorus was not very effective in enhancing the growth of microorganisms and removal of creosote. The highest nitrogen supplementation (C : N = 5 : 1) did not enhance microbial growth and creosote removal. Phenolics and lower molecular mass polycyclic aromatic hydrocarbons (PAHs) were observed to be more susceptible to microbial degradation than higher molecular mass compounds. Nutrient concentration, moisture content and pH were thus observed to play very significant roles in the utilization of creosote in soil. These results are being used for the development of a bioremediation technology for the remediation of creosote contaminated soils in a treatment plant in South Africa.

Bacteria↗
PubMed2006

Comparison of microbial pyrene and benzo[a]pyrene mineralization in liquid medium, soil slurry, and soil.

The microbial degradation of 14C-pyrene and 14C-benzo[a]pyrene by a bacterial mixed culture was studied within a mixture of the PAHs phenanthrene, anthracene, pyrene, fluoranthene, and benzo[a]pyrene as sole carbon source in the different culture systems: (i) liquid medium, (ii) soil slurry (surface and grinding influence), and (iii) soil. The fate of these two labeled compounds was followed in these systems with an emphasis on mineralization to carbon dioxide, extractability, and adsorption to humic materials and formation of unextractable residual. Mineralization showed the most obvious differences: soil slurries achieved the best results both concerning the extent of mineralization and the time required. The highest extent of pyrene mineralization (54% within 21 days) was observed in soil slurries; in liquid media, pyrene mineralization was slower, but reached approximately the same extent (54% in 150 days); in soils, mineralization reached only 36% of added pyrene after 160 days. Benzo[a]pyrene was mineralized in a mixture of PAHs in soil slurries to an extent of 34% within 70 days, whereas mineralization in liquid medium and soil occurred in the range of 5% (70 days). Mineralization of benzo[a]pyrene in sand slurries was lower compared to soil slurries (19% in sand slurries vs. 32% in soil slurries within 50 days).

Adsorption↗
PubMed2005

Toxicity of cadmium to soil microbial biomass and its activity: effect of incubation time on Cd ecological dose in a paddy soil.

Cadmium (Cd) is ubiquitous in the human environment and has toxic effect on soil microbial biomass or its activity, including microbial biomass carbon (C(mic)), dehydrogenase activity (DHA) and basal respiration (BR), etc., C(mic), DHA, BR were used as bioindicators of the toxic effect of Cd in soil. This study was conducted to determine the effects of Cd on soil microbial biomass and its activity in a paddy soil. The inhibition of microbial biomass and its activity by different Cd concentrations was described by the kinetic model (M1) and the sigmoid dose-response model (M2) in order to calculate three ecological doses of Cd: ED(50), ED(10) and ED(5). Results showed that M2 was better fit than M1 for describing the ecological toxicity dose effect of cadmium on soil microbial biomass and its activity in a paddy soil. M2 for ED values (mg/kg soil) of C(mic), DHA, BR best fitted the measured paddy soil bioindicators. M2 showed that all ED values (mg/kg) increased in turn with increased incubation time. ED(50), ED(10) and ED(5) of C(mic) with M2 were increased in turn from 403.2, 141.1, 100.4 to 1000.7, 230.9, 144.8, respectively, after 10 d to 60 d of incubation. ED(50), ED(10) and ED(5) of DHA with M2 increased in turn from 67.6, 6.2, 1.5 to 101.1, 50.9, 41.0, respectively, after 10 d to 60 d of incubation. ED(50), ED(10) and ED(5) of BR with M2 increased in turn from 149.7, 6.5, 1.8 to 156.5, 50.8, 35.5, respectively, after 10 d to 60 d of incubation. So the ecological dose increased in turn with increased incubation time for M2 showed that toxicity of cadmium to soil microbial biomass and its activity was decreased with increased incubation time.

Biomass↗
PubMed1990

Dissipation of s-triazines and thiocarbamates from soil as related to soil moisture content.

Half-lives (t1/2) of two soil incorporated s-triazines (atrazine and prometon) and two thiocarbamate (EPTC and triallate) herbicides were determined in relation to soil moisture content in two California soils. Treated soils were incubated at three moisture levels in aerated glass vials at 25 +/- 1 degree C and were analyzed at 0, 7, 16, 28, 56 and 112 day intervals. Loss of herbicides in all treatments followed first-order kinetics. The t1/2-values of all herbicides decreased with increasing soil moisture and followed an empirical equation, t1/2 = aM(-b) (where t1/2 is half-life; M the moisture content; and a and b are constants). Soil moisture had a greater effect on carbamates than on s-triazines . Prometon exhibited the longest half-life in both soils, whereas EPTC was least persistent in one soil and atrazine in another. The t1/2-values for atrazine, prometon, EPTC, and triallate with medium moisture levels and 10 microg/g concentration were 34.6, 43.2, 25.4 and 38.1 days in sandy loam and 26.5, 44.4, 44.1 and 25.9 days in loamy sand, respectively. Disappearance of 50% of the applied concentrations of most of the herbicide-soil combinations (except EPTC and triallate in one soil) took longer for lower initial concentrations (1 microg/g) than for higher concentrations (10 microg/g).

Journal Article↗
PubMed2006

Competitive sorption and desorption of heavy metals in mine soils: influence of mine soil characteristics.

Many mine soils are chemically, physically, and biologically unstable and deficient. They are sometimes amended with sewage sludge and ashes but often contain heavy metals that increase the already high mine soils' heavy metal contents. Cd, Cr, Cu, Ni, Pb, and Zn in mutual competition were added to five mine soils (Galicia, Spain). Soil capacities for heavy metal sorption and retention were determined by means of distribution coefficients and selectivity sequences among metals. Influence of soil characteristics on sorption and retention was also examined. Retention selectivity sequences indicate that, in most of the soils, Pb is the preferred retained metal, followed by Cr. The last metals in these sequences are Ni, Cd, and Zn. Soil organic matter content plays a fundamental role in control of Pb sorption. Gibbsite, goethite, and mica influence Cr retention. Soil organic matter, oxides, and chlorite contents are correlated with K(d sigma sp medium). Heavy metals are weakly adsorbed by soils and then desorbed in high amounts. To recover these soils it is necessary to avoid the use of residues or ashes that contain heavy metals due to their low heavy metal retention capacity.

Journal Article↗
PubMed1995

Capacity for methane oxidation in landfill cover soils measured in laboratory-scale soil microcosms.

Laboratory-scale soil microcosms containing different soils were permeated with CH(inf4) for up to 6 months to investigate their capacity to develop a methanotrophic community. Methane emissions were monitored continuously until steady states were established. The porous, coarse sand soil developed the greatest methanotrophic capacity (10.4 mol of CH(inf4) (middot) m(sup-2) (middot) day(sup-1)), the greatest yet reported in the literature. Vertical profiles of O(inf2), CH(inf4), and methanotrophic potential in the soils were determined at steady state. Methane oxidation potentials were greatest where the vertical profiles of O(inf2) and CH(inf4) overlapped. A significant increase in the organic matter content of the soil, presumably derived from methanotroph biomass, occurred where CH(inf4) oxidation was greatest. Methane oxidation kinetics showed that a soil community with a low methanotrophic capacity (V(infmax) of 258 nmol (middot) g of soil(sup-1) (middot) h(sup-1)) but relatively high affinity (k(infapp) of 1.6 (mu)M) remained in N(inf2)-purged control microcosms, even after 6 months without CH(inf4). We attribute this to a facultative, possibly mixotrophic, methanotrophic microbial community. When purged with CH(inf4), a different methanotrophic community developed which had a lower affinity (k(infapp) of 31.7 (mu)M) for CH(inf4) but a greater capacity (V(infmax) of 998 nmol (middot) g of soil(sup-1) (middot) h(sup-1)) for CH(inf4) oxidation, reflecting the enrichment of an active high-capacity methanotrophic community. Compared with the unamended control soil, amendment of the coarse sand with sewage sludge enhanced CH(inf4) oxidation capacity by 26%; K(inf2)HPO(inf4) amendment had no significant effect, while amendment with NH(inf4)NO(inf3) reduced the CH(inf4) oxidation capacity by 64%. In vitro experiments suggested that NH(inf4)NO(inf3) additions (10 and 71 (mu)mol (middot) g of soil(sup-1)) inhibited CH(inf4) oxidation by a nonspecific ionic effect rather than by specific inhibition by NH(inf4)(sup+).

Journal Article↗
PubMed2006

Spatial stratification of soil bacterial populations in aggregates of diverse soils.

Most soil microbial community studies to date have focused on homogenized bulk soil samples. However, it is likely that many important microbial processes occur in spatially segregated microenvironments in the soil leading to a microscale biogeography. This study attempts to localize specific microbial populations to different fractions or compartments within the soil matrix. Microbial populations associated with macroaggregates and inner- versus total-microaggregates of three diverse soils were characterized using culture-independent, molecular methods. Despite their relative paucity in most surveys of soil diversity, representatives of Gemmatimonadetes and Actinobacteria subdivision Rubrobacteridae were found to be highly abundant in inner-microaggregates of most soils analyzed. By contrast, clones affiliated with Acidobacteria were found to be relatively enriched in libraries derived from macroaggregate fractions of nearly all soils, but poorly represented in inner-microaggregate fractions. Based upon analysis of 16S rRNA, active community members within microaggregates of a Georgian Ultisol were comprised largely of Gemmatimonadetes and Rubrobacteridae, while within microaggregates of a Nebraska Mollisol, Rubrobacteridae and Alphaproteobacteria were the predominant active bacterial lineages. This work suggests that microaggregates represent a unique microenvironment that selects for specific microbial lineages across disparate soils.

Actinobacteria↗
PubMed1991

A guide to interpreting soil ingestion studies. II. Qualitative and quantitative evidence of soil ingestion.

Four major studies have attempted to qualitatively and quantitatively assess the extent of soil ingestion in children using the soil tracer methodology. The validity of the estimates of soil ingestion in each study was reevaluated in light of the inherent strengths and limitations of study design and/or execution, as well as via a novel methodology for estimating the soil recovery variance for each tracer, which then led to the estimation of soil ingestion detection limits for each tracer for studies performing mass-balance analyses. Based on these analyses it is concluded that the Binder et al. (1986, Arch. Environ. Health 41, 341-345) and Van Wijnen et al. (1990, Environ. Res. 51, 147-162) studies provide no convincing evidence to support qualitative and quantitative estimates of soil ingestion due to inherent limitations in their respective study designs. The Davis et al. (1990, Arch. Environ. Health 45, 112-122) and Calabrese et al. (1989, Regul. Toxicol. Pharmacol. 10, 123) studies displayed convincing qualitative evidence of soil ingestion. However, the results indicate that the median soil ingestion estimates of Davis et al. were less reliable than those of Calabrese et al. The range of detection limits vary according to the tracer and the assumption of acceptable precision in recovery estimation. The minimum detection level of soil ingestion in children in the Calabrese et al. study, with a variance in recovery of 100% +/- 20%, was 21 mg/day based on Zr.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed2004

Seasonal changes of redox potential and microbial activity in two agricultural soils of tropical Australia: some implications for soil-to-plant transfer of radionuclides.

Very little is known of the factors controlling soil-to-plant transfer of radionuclides in tropical environments. As part of an IAEA/FAO coordinated research project (CRP) designed to elucidate some of those factors, near-surface samples of two agricultural red-earth soils (Blain and Tippera) were collected from a study site in the Northern Territory. The climate is tropical monsoonal with crops being grown over the wet season from December to March/April. It is important to understand soil variables that may be related to this dramatic seasonality. In this investigation, soil redox state and microbial populations were assessed before and after the growing season with a view to generating hypotheses for future evaluation. The X-ray absorption near edge structure (XANES) technique was used to determine overall changes in the solid-state redox speciation of Fe and Mn in soils across the growing period. Fe speciation did not change but approximately 10% of the total Mn was oxidised from Mn(II) to Mn(III) and Mn(IV) in both soils between October 1999 and April 2000. An apparent disconnect between Fe and Mn was not unexpected given the >10 times higher concentration of Fe in the soils compared with Mn. These results have implications for the bioavailability of redox sensitive radionuclides such as Tc and Pu. Similarly, microbial population estimates were derived before and after the growing period. Total bacterial populations did not vary from 10(6) to 10(7) colonies per gram. Fungal populations increased over the growing season from 3-6 x 10(5) to 1-4 x 10(6) colonies per gram of soil. Fungi have the potential to decrease soil pH and hence increase the bioavailability of radionuclides such as Cs. In addition, fungi act to facilitate plant nutrition. This could lead to enhanced accumulation of nutrient analogues (e.g. Sr and Ra for Ca; Tc for Mn), but this effect may be masked by improved biomass production.

Agriculture↗