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PubMed2005

Incorporation of carbon originating from CO2 into different compounds of soil microbial biomass and soil organic matter.

In general, soils without the vegetation growing on them are regarded as sources of CO2. However, there are indications that CO2 is also fixed by soil microorganisms. Although this process is not significant from a quantitative point of view, it may change the isotopic composition of soil organic matter. Therefore, we conducted an incubation study with soil and 13C-labeled CO2 to investigate this process. We found that the label was transferred from CO2 into organic compounds in soil. At the end of a 61-day incubation period, 1.3 micromol C g(-1) soil, corresponding to approximately 0.08% of the soil organic carbon, had been fixed. CO2 may, therefore, be an additional source of soil organic carbon. Compound-specific analysis of amino sugars, amino acids, and fatty acids indicated that the label is incorporated into microbial, mainly bacterial, biomass. All groups of microorganisms were involved in the assimilation of CO2, but the relatively high enrichment of mono-unsaturated and mid-chain branched fatty acids indicates that gram negative bacteria and actinomycetes may be slightly more important in this process than other groups of microorganisms.

Bacteria, Anaerobic↗
PubMed1998

Soil ingestion by humans: a review of history, data, and etiology with application to risk assessment of radioactively contaminated soil.

Ingestion of soil by humans has been a documented phenomenon for centuries and still takes place today according to various literature. The literature reviewed here shows that there are two distinct soil ingestion phenomenon: inadvertent and purposeful (geophagia). Certain lifestyles, occupations, and living conditions will likely put different individuals or different groups at risk to these separate, but sometimes related, phenomenon. In particular, reports of geophagia are relatively common for the life stages of adolescence and periods of growth, and during pregnancy and lactation. Geophagia also appears to be relatively common among indigenous peoples on all continents, sometimes taking place to extreme degrees. Because of their high dependence on the land, indigenous peoples are also at highest risk for inadvertent ingestion. Inadvertent intake is more a function of either primitive living conditions or professions that may bring workers into close and continual contact with the soil. It is the purpose of this report to review and summarize literature related to ingestion of soil by humans with emphasis on the relevance of soil ingestion to radiological dose assessment, the etiology of geophagia and its relationship to risk assessment, qualitative observations and quantitative studies of direct soil ingestion by humans with interpretations useful for different lifestyle scenarios, the status of a number of current radiological assessment models in accounting for soil ingestion, and some unresolved issues in modeling the ingestion of soil.

Adolescent↗
PubMed1984

Epidemiology of infection by nontuberculous mycobacteria. V. Numbers in eastern United States soils and correlation with soil characteristics.

Organisms of the Mycobacterium avium, M. intracellulare, and M. scrofulaceum (MAIS) group were recovered in significant numbers from 63 soil samples collected from the floodplains of 4 major rivers in the eastern United States: Hudson (NY), James (VA), Savannah (GA, SC), and Tombigbee (AL, MS). The mean numbers of M. avium-intracellulare, M. scrofulaceum, and MAIS-intermediate biovars recovered increased significantly from the Hudson to the James to the Tombigbee and Savannah soil samples, agreeing reasonably well with previous findings on MAIS distribution in eastern U.S. waters and with the geographic distribution of naval recruits reacting to PPD-B and PPD-G, which is higher in the southeastern United States. From the Savannah and Tombigbee rivers, soils were collected throughout their lengths. The number of total MAIS and biovars recovered from the different soil sites varied widely and showed no obvious trends. However, statistical analysis revealed a highly significant correlation between high numbers of MAIS recovered and high acidity of the soils. Other soil characteristics, such as high total organic matter, high conductivity, and reduced moisture, were only weakly, if at all, correlated with high MAIS numbers. Whereas the general distribution of MAIS in these soils of the Northeast (NY), mid-Atlantic (VA), and Southeast (GA, SC, AL, and MS) might explain the geographic distribution of the naval recruits reacting to PPD-B and PPD-G, the distribution of MAIS in soils along the stretches of the 2 southeastern rivers was not correlated with the county-by-county frequency of PPD-B reactive naval recruits in Georgia, South Carolina, Alabama, and Mississippi.

Humans↗
PubMed2006

Effect of soil properties on copper release in soil solutions at low moisture content.

Copper partitioning at moisture content of 1.2-fold the field moisture capacity (corresponding to a soil water potential of 7.84 J/kg; pF = 1.9) was studied in 11 soils with pH 3.4 to 6.8 and an organic matter content of 4.1 to 233 g C/kg. Soil solutions were separated with the centrifuge method and analyzed to determine pH, Cu2+ activity, dissolved organic carbon, and Cu, Ca, Mg, and Na concentrations. Soil organic matter content, total Cu content, and soil pH were the main variables explaining variation in Cu activity in soil solutions. Based on total Cu, soil organic matter content, and soil solution pH, the Windermere Humic Aqueous Model (WHAM) VI assemblage model provided estimates of Cu2+ activity, {Cu2}, with a root mean square error of the predicted pCu (i.e., -log{Cu2+}) of 0.77.

Copper↗
PubMed2001

Background zinc concentrations in soil affect the zinc sensitivity of soil microbial processes--a rationale for a metalloregion approach to risk assessments.

Soil microbial processes are particularly sensitive to Zn, but great difficulty exists in deriving soil standards based on laboratory toxicity tests. Zinc toxicity data for soil microbial processes were collated from the literature, and their variability with soil properties was assessed. Data were screened for quality and reliability, and analysis was based on the highest metal dose at which no adverse effect was found (HNOAED). The HNOAED values were expressed on a pore-water basis and were found to be positively related to background concentrations of Zn in soil, also expressed on a pore-water basis. This suggests that soil microorganisms acclimate to indigenous concentrations of Zn in soil pore water, and this acclimation affects the subsequent response to Zn added as a pollutant. Thus, regions having low background Zn concentrations in soil pore water will be much more sensitive to Zn pollution than others having high background concentrations. A method to account for effects of background Zn on assessments of Zn toxicity is suggested where metalloregions are defined having common sets of abiotic and biotic factors that affect the toxicity of Zn. This approach could markedly improve regional or continental risk assessments for metals in the environment.

Acclimatization↗
PubMedDate not supplied

Soil microbial communities associated with Bt and non-Bt corn in three soils.

The effects of expression of Cry endotoxin by Bt corn (transgenic corn engineered to express Bacillus thuringiensis toxin) on soil microbial community structure were assessed in a growth chamber experiment. Two lines of transgenic corn expressing different Cry endotoxins were compared with their respective non-transgenic isolines in three soil types with differing textures. Phospholipid fatty acid (PLFA) profiles from bulk soil and community-level physiological profiles (CLPP) from the rhizosphere community were used to assess community structure. Differences in PLFA profiles due to soil type were significant, accounting for 73% of the total variability in the dataset. Differences in bacterial and fungal CLPP profiles due to soil type were statistically significant, but probably not biologically important, accounting for 6.3 and 3.8% of the total variability, respectively. Neither expression of Cry endotoxin nor corn line had a significant effect on microbial profiles, except in the high-clay soil where both factors significantly affected bacterial CLPP profiles (accounting for 6.6 and 6.1% of the variability in that soil, respectively). Expression of Cry endotoxin also significantly reduced the presence of eukaryotic PLFA biomarker in bulk soils, although it is unclear which groups of eukaryotes were affected. We conclude that the effects of transgenic Bt corn in this short-term experiment are small, and longer-term investigations are necessary.

Aluminum Silicates↗
PubMedDate not supplied

Sorption and biodegradability of sludge bacterial extracellular polymers in soil and their influence on soil copper behavior.

Bacterial extracellular polymers (BEP) affect the translocation and fate of organic and inorganic pollutants in terrestrial and aquatic ecosystems. In this study, BEP from activated sludge was compared with sludge dissolved organic matter (DOM) in terms of behavior and effects on the mobilization and bioavailability of Cu in a well-aged Cu-contaminated orchard sandy loam. Addition of sludge BEP (10-200 mg dissolved organic carbon [DOC] L(-1)) to the soil resulted in 1.6- to 12.8-fold-higher soil soluble Cu concentration over the control and 1.3- to 2.2-fold over sludge DOM of the same concentration. Consequently, the Cu uptake by the ryegrass (Lolium perenne L., cv. Target) grown in the soil was increased by 31% due to interval watering of 100 mg DOC L(-1) of sludge BEP solution in a 35-d period. The influence of sludge BEP on mobilizing soil Cu could be maintained as long as 60 d or more, depending on BEP biodegradation status. The findings that sludge BEP promoted Cu mobilization and bioavailability could be attributed to less adsorption of BEP by soil, slow degradation, and higher affinity with Cu. For example, after 3 wk of aerobic incubation, the soluble Cu present in the sludge DOM-treated soil was reduced to about the level of the control, while the concentration of soluble Cu in BEP-treated soil was 6.2 times higher than that in the control. Therefore, sludge BEP could act as a facilitated-transport carrier of Cu. The environmental risk of Cu should receive much attention if BEP is incorporated into soils.

Adsorption↗
PubMed2006

Soil electrical conductivity and water content affect nitrous oxide and carbon dioxide emissions in intensively managed soils.

Accumulation of soluble salts resulting from fertilizer N may affect microbial production of N(2)O and CO(2) in soils. This study was conducted to determine the effects of electrical conductivity (EC) and water content on N(2)O and CO(2) production in five soils under intensive cropping. Surface soils from maize fields were washed, repacked and brought to 60% or 90% water-filled pore space (WFPS). Salt mixtures were added to achieve an initial in situ soil EC of 0.5, 1.0, 1.5 and 2.0 dS m(-1). The soil cores were incubated at 25 degrees C for 10 d. Average CO(2) production decreased with increasing EC at both soil water contents, indicating a general reduction in microbial respiration with increasing EC. Average cumulative N(2)O production at 60% WFPS decreased from 2.0 mg N(2)O-N m(-2) at an initial EC of 0.5 dS m(-1) to 0.86 mg N(2)O-N m(-2) at 2.0 dS m(-1). At 90% WFPS, N(2)O production was 2 to 40 times greater than that at 60% WFPS and maximum N(2)O losses occurred at the highest EC level of 2.0 dS m(-1). Differences in the magnitude of gas emissions at varying WFPS were due to available substrate N and the predominance of nitrification under aerobic conditions (60% WFPS) and denitrification when oxygen was limited (90% WFPS). Differences in gas emissions at varying soil EC may be due to changes in mechanisms of adjustment to salt stress and ion toxicities by microbial communities. Direct effects of EC on microbial respiration and N(2)O emissions need to be accounted for in ecosystems models for predicting soil greenhouse gas emissions.

Aerobiosis↗
PubMed2001

Adsorption of chloroacetanilide herbicides on soil (I). Structural influence of chloroacetanilide herbicide for their adsorption on soils and its components.

Adsorption of chloroacetanilide herbicide acetochlor, alachlor, metolachlor and propachlor on soils and soil components was determined, and the structural differences of these herbicides were used to explain the order of sorptivity. Adsorption isotherms for all herbicide-soil combinations conformed to the Freundlich equation, and Ki increased with increasing soil organic carbon content. Kd on soil humic acid was greater than that on clay, but association of humic acid with clay reduced the overall adsorption. On all soils and soil humic acids, herbicide adsorption decreased in the order: metolachlor > acetochlor > propachlor > alachlor. On Ca(2+)-montmorrilonite, the order changed to metolachlor > acetochlor > alachlor > propachlor. FT-IR spectra of herbicide-clay or herbicide-humic acid-clay mixtures showed that H-bonding and charge transfer were the primary interaction pathways between these compounds and the surface of clay or humic acids. The different moieties attached to 2-chloro-acetanilide and their unique arrangement may have influenced the binding mechanisms and thus the sorptivity of these herbicides. This study indicates that the structural difference of pesticides in the same classes may be used as a molecular probe to obtain a better understanding of sorption mechanisms of pesticides on soil.

Acetamides↗
PubMed2004

[Effect of crop-residue incorporation on soil CO2 emission and soil microbial biomass].

In a wheat-corn cropping system, the crop residues were crushed and incorporated into soil after harvest. The soil respiration and soil microbial biomass were compared one year later with soil that had doubled amount of residues incorporation or had no incorporated residues. The soil respiration was increased by the residue incorporation and the effect was more apparent when the incorporated residue amount was doubled. The soil microbial biomass was also increased by the residue incorporation. But the effect of the incorporated residue quantity was not significant. Seasonally, the maximum soil respiration appeared earlier than the maximum microbial biomass, but soon turned to decrease. The microbial biomass maintained the high level for a longer period, indicating there was maintenance respiration and biosynthetic respiration as well. The residue incorporation was suggested as a measure to increase the soil fertility, but doubling the amount of residue incorporation seems not necessary.

Biomass↗
PubMed2005

[Temporal variation of soil respiration on sloping pasture of Heihe River basin and effects of temperature and soil moisture on it].

Employing LiCor 6400 gas exchange analyzer and soil respiration chamber attachment (LiCor Inc., Lincoln, NE, USA), this paper continuously measured the soil surface CO2 effluxes on the sloping pasture of Heihe River basin from early April to late October 2003 to investigate the soil CO2 efflux rate and its feedback to the changes of climate and land use. The results showed that from May to October, the diurnal variation of soil respiration was low at night, the lowest at 7:00, 6:30, 5:30, 6:00 and 7:00, raised rapidly at 7:00 - 8:30, and then descended at 16:00 - 18:30. The maximum soil CO2 efflux appeared at 15:00, 14:30, 14:30, 13:30, 14:00 and 15:00. The mean daily soil respiration rate was 0.31 - 6.98 micromol m(-2) s(-1), with the maximum in July and August, the second in May and September, and nearly consistent in April and October. Soil respiration rate had an exponential and power correlation with temperature and soil moisture, respectively.

Carbon Dioxide↗
PubMed2005

[Aging of spiked pyrene in two paddy soils and their particle-size fractions after soil incubation and changes in extractability and bio-availability to earthworm].

Effect of aging on bioavailability and extractability of persistent organic pollutants has recently been paid much attention in environmental studies. This study deals with aging of spiked pyrene, a four-ring polycyclic hydrocarbon, in two paddy soils and their particle-size fractions under laboratory incubation and change in its extractability and bioavailability. The bioavailability of aged pyrene was tested by an assay of exposure to earthworms (Eisenia foetida). The extractability of spiked pyrene was decreased by 15% to 23%, and the bioavailability to earthworm was decreased by 37% to 67% after incubation for 90 d compared to under no incubation. Meanwhile, there was no significant difference in the pyrene extractability between incubation with different size fractions of a single soil. Soil incubation resulted in lower extractability and, thus, lower environmental risk of the organic pollutants after incorporation in paddy soils and their aggregates. The different size fractions of paddy soils may exert different bioavailability when exposure to soil fauna. Thus, content and chemical extractability may not be appropriate index for assessing the potential environmental risk and bioavailability to soil fauna for persistent organic pollutants in paddy soils.

Animals↗
PubMed2025

New insights into soil amendment: Impact of humic acid on typical antibiotic resistance in agricultural soil.

Humic acid (HA) addition can improve agricultural soil, but little is known about how it affects the soil resistome. In this study, we used selective agar plate combined with quantitative PCR (qPCR) and 16S rRNA gene sequencing to investigate how HA influences antibiotic resistant bacteria (ARB) and antibiotic resistant genes (ARGs) in soil contaminated with erythromycin and kanamycin. 0.1 % HA reduced the abundance of culturable erythromycin-resistant bacteria (ERB), while promoting the growth of kanamycin-resistant bacteria (KRB). Lysinibacillus and Paenibacillus were the dominant genera in ERB and KRB, respectively, governing the changes in their abundances. At this concentration, the Lysinibacillus abundance in ERB decreased from 96.74 % to 70.57 %. Meanwhile, that of Paenibacillus in KRB increased from 33.40 % to 77.44 %. The copy number of ermF decreased after HA addition, while that of ermB increased. Furthermore, 0.1 % HA significantly reduced the copy number and relative abundance of aadA1 and aac(6')-Ib (aka aacA4)-03 in the soil. Changes in these two types of ARB and ARGs were primarily driven by shifts in the microbial community structure. Soil physicochemical properties, particularly increased organic matter (OM), altered the absolute abundance of ermB. Meanwhile, changes in intI1 abundance determined the risk associated with aadA1 and aac(6')-Ib (aka aacA4)-03. These findings emphasize the dual role of HA in the dissemination of antibiotic resistance in agricultural soils and highlight the necessity of considering dose-dependent effects when applying HA as a soil amendment.

Soil Microbiology↗
PubMed2005

A comparative study of adsorption of an anionic and a non-ionic surfactant by soils based on physicochemical and mineralogical properties of soils.

In the present work we performed a comparative study on the adsorption of the surfactants sodium dodecyl sulphate (SDS) (anionic), and octylphenoxypolyethoxyethanol (Triton X-100) (non-ionic) to 18 soils with organic matter (OM) and clay fraction contents varying over a broad range. The objective of the study was to gain further insight into the influence of the physicochemical and mineralogical properties of soils on the adsorption of surfactants by soils. Adsorption isotherms were obtained using concentrations below the critical micellar concentration (cmc) of the surfactants. The adsorption coefficients, Kf, determined from the Freundlich equation were lower for SDS (range 1.77-82.1, mean value 36.3) than for Triton X-100 (range 0.01-913, mean value 257). Simple and multiple correlation coefficients were obtained between Kf values and soil characteristics. The results obtained indicate the influence of the OM content on the adsorption of SDS (r=0.64, p<0.01) and of the clay fraction content on that of Triton X-100 (r=0.83, p<0.001). Additionally, we observed a preferential adsorption of SDS by the 1:1 mineral kaolinite (r=0.54, p<0.05), while Triton X-100 was adsorbed mainly by the 2:1 minerals, montmorillonite (r=0.66, p<0.01) and illite (r=0.87, p<0.001). According to the influence of different soil parameters on adsorption, different mechanisms of adsorption are proposed for each surfactant. Our findings point to the interest of considering the physicochemical properties of soils and also the mineralogy of the soil clay fraction when selecting a surfactant in technologies involving enhanced solubilization and removal of contaminants from soils and sediments.

Adsorption↗
PubMed2004

Effects of soil amendments on lead uptake by two vegetable crops from a lead-contaminated soil from Anhui, China.

Previous studies have documented that phosphate compounds of lead (Pb) [e.g., pyromorphite Pb5(PO4)3-(X), where X=OH, F or Cl] are comparatively insoluble, and their formation in Pb-contaminated soil may be a means of reducing the bioavailability and chemical lability of Pb in soil. In this study, the effect of phosphate compound amendments on the bioavailability of Pb in a polluted alkaline soil was examined. A Pb-contaminated soil was treated with hydroxyapatite (HA), phosphate rock (PR), water-soluble P fertilizer (single superphosphate, SSP) and the combination of HA with SSP. The bioavailability of Pb was determined in plant uptake studies with vegetables (Brassica campetris L. var. communis, BC) and Brassica oleracea L. var. acephala, BO) and sequential extraction. The results indicated that the Pb concentrations in both shoots and roots of two vegetable plants decreased with increasing quantities of added P compound, and the HA treatment had the best effect at the level of 5000 mg of P kg(-1)as compared with other treatments in which the Pb concentrations in shoots of BO and BC decreased 51.9% and 65.5%, respectively, and the Pb concentrations in roots of BO and BC decreased 67.3% and 57.2%, respectively, as compared with the control treatment. The SSP treatment had little effect on the Pb concentrations in plant tissues. Sequential extraction results indicated that the addition of soil amendments transform soil Pb from nonresidual fractions to residual fraction substantially. The effect of treatments followed this order at the equivalent P addition: HA>PR>HA+SSP>SSP. The results suggested that HA amendments can lower the bioavailability and increase the geochemical stability of soil Pb, so it has the potential for in situ remediation in Pb-contaminated soils.

Biological Availability↗
PubMed2004

Modeling soil organic matter dynamics as affected by soil water erosion.

Soil organic carbon (SOC) stock is an important component of the global carbon (C) cycle, which has the potential to influence global climate. In this paper we presented an overview of soil organic matter (SOM) models in the context of soil erosion and discussed basic processes driving erosion-induced SOC loss. Although the mechanism of this loss is poorly understood, erosion influences SOC in two ways: redistribution of C within the watershed or ecosystem, and loss of C to the atmosphere. Erosion disperses soil, altering its microbiological activity as well as water, air and nutrient regimes. This, along with sediment enrichment, has an impact on greenhouse gas emission from soil. For most of agricultural settings, field studies suggest that cultivation along with soil erosion are the primary reasons for SOC loss. Tracing the fate of eroded C is a challenging task. Modeling is the approach taken most often. In this paper we discuss approaches used in various SOC models to assess erosion-induced C loss from soil in agricultural ecosystems. An example with Century model applied to meadow and corn-soybean rotation under chisel-till demonstrated the model's ability to respond well to different erosion scenarios. It was estimated that at soil loss rate of 10 t ha(-1) year(-1) (value often considered a threshold for maintaining productivity) 19% of the total SOC loss would be attributed to erosion after 90 years of cultivation.

Agriculture↗
PubMed2005

Establishing principal soil quality parameters influencing earthworms in urban soils using bioassays.

Potential contamination at ex-industrial sites means that, prior to change of use, it will be necessary to quantify the extent of risks to potential receptors. To assess ecological hazards, it is often suggested to use biological assessment to augment chemical analyses. Here we investigate the potential of a commonly recommended bioassay, the earthworm reproduction test, to assess the status of urban contaminated soils. Sample points at all study sites had contaminant concentrations above the Dutch soil criteria Target Values. In some cases, the relevant Intervention Values were exceeded. Earthworm survival at most points was high, but reproduction differed significantly in soil from separate patches on the same site. When the interrelationships between soil parameters and reproduction were studied, it was not possible to create a good model of site soil toxicity based on single or even multiple chemical measurements of the soils. We thus conclude that chemical analysis alone is not sufficient to characterize soil quality and confirms the value of biological assays for risk assessment of potentially contaminated soils.

Animals↗
PubMed2005

Assessing soil ecotoxicity of methyl tert-butyl ether using earthworm bioassay; closed soil microcosm test for volatile organic compounds.

An earthworm bioassay was conducted to assess ecotoxicity in methyl tert-butyl ether (MTBE)-amended soils. Ecotoxicity of MTBE to earthworms was evaluated by a paper contact method, natural field soil test, and an OECD artificial soil test. All tests were conducted in closed systems to prevent volatilization of MTBE out of test units. Test earthworm species were Perionyx excavatus and Eisenia andrei. Mortality and abnormal morphology of earthworms exposed to different concentrations of MTBE were examined. MTBE was toxic to both earthworm species and the severity of response increased with increasing MTBE concentrations. Perionyx excavatus was more sensitive to MTBE than Eisenia andrei in filter papers and two different types of soils. MTBE toxicity was more severe in OECD artificial soils than in field soils, possibly due to the burrowing behavior of earthworms into artificial soils. The present study demonstrated that ecotoxicity of volatile organic compounds such as MTBE can be assessed using an earthworm bioassay in closed soil microcosm with short-term exposure duration.

Air Pollutants↗