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PubMed1996

Percutaneous absorption of 2,4-dichlorophenoxyacetic acid from soil with respect to soil load and skin contact time: in vivo absorption in rhesus monkey and in vitro absorption in human skin.

The herbicide 2,4-dichlorophenoxyacetic acid (2,4-D), used for control of weeds in agriculture, forestry, and rights of way, can accumulate as a residual chemical in soil. The objective was to determine percutaneous absorption of 2,4-D from soil, with emphasis on soil load and skin contact time. With control acetone vehicle, in vivo absorption of 2,4-D in the rhesus monkey was 8.6 +/- 2.1% of the dose, which compared closely to published human absorption of 6.0 +/- 2.4%. Percutaneous absorption from soil loads of 1 and 40 mg/cm2 were 9.8 +/- 4.0 and 15.9 +/- 4.7%, respectively, values similar to acetone vehicle. In vitro absorption in human skin calculated from skin contact accumulation over 24 h was 1.8 +/- 1.7, 1.7 +/- 1.3, and 1.4 +/- 1.2% for soil loads of 5, 10, and 40 mg/cm2, respectively. Thus, soil load did not affect 24-h percutaneous absorption. Current Environmental Protection Agency (EPA) recommended calculated reductions due to soil load are not supported by these results with 2,4-D. Percutaneous absorption of 2,4-D from acetone vehicle for 8 h dosing period was 3.2 +/- 1.0%, one-third the value of 8.6 +/- 2.1% over 24 h. With soil vehicle, absorption for 8 h was only 0.03 +/- 0.02% for 40 mg/cm2 soil load and 0.05 +/- 0/.004% for 1 mg/cm2 soil load. Absorption for 16 h was 2.2 +/- 1.2%. Absorption over time was linear for acetone vehicle, where total dose is deposited on skin, but not linear for soil vehicle, which had an 8-h delay (lag time). This equates with a normal 8-h work day where most of the contaminated soil can be washed off the skin. The apparent partition coefficient of 2,4-D between soil and water changed over time. This suggests there is a "mobility" phase for 2,4-D in soil that will change with time. For soil vehicle, percutaneous absorption of 2,4-D was not linear in respect to soil load or to skin contact time. Calculation based on assumed linearity can falsely estimate potential human health hazard. Clearly, the dermatokinetics with soil and skin represent complex interactive forces that require detailed evaluation before overgeneralizing rules for interpretation in terms of risk assessment.

2,4-Dichlorophenoxyacetic Acid↗

PubMed1997

Bioremediation of pentachlorophenol-contaminated soil by bioaugmentation using activated soil.

The use of an indigenous microbial consortium, pollutant-acclimated and attached to soil particles (activated soil), was studied as a bioaugmentation method for the aerobic biodegradation of pentachlorophenol (PCP) in a contaminated soil. A 125-l completely mixed soil slurry (10% soil) bioreactor was used to produce the activated soil biomass. Results showed that the bioreactor was very effective in producing a PCP-acclimated biomass. Within 30 days, PCP-degrading bacteria increased from 10(5) cfu/g to 10(8) cfu/g soil. Mineralization of the PCP added to the reactor was demonstrated by chloride accumulation in solution. The soil-attached consortium produced in the reactor was inhibited by PCP concentrations exceeding 250 mg/l. This high level of tolerance was attributed to the beneficial effect of the soil particles. Once produced, the activated soil biomass remained active for 5 weeks at 20 degrees C and for up to 3 months when kept at 4 degrees C. The activated attached soil biomass produced in the completely mixed soil slurry bioreactor, as well as a PCP-acclimated flocculent biomass obtained from an air-lift immobilized-soil bioreactor, were used to stimulate the bioremediation of a PCP-impacted sandy soil, which had no indigenous PCP-degrading microorganisms. Bioaugmentation of this soil by the acclimated biomass resulted in a 99% reduction (from 400 mg/kg to 5 mg/kg in 130 days) in PCP concentration. The PCP degradation rates obtained with the activated soil biomass, produced either as a biomass attached to soil particles or as a flocculent biomass, were similar.

Biodegradation, Environmental↗

PubMed2001

Estimating toxic damage to soil ecosystems from soil organic matter profiles.

Concentrations of particulate and total organic matter were measured in upper soil profiles at 26 sites as a potential means to identify toxic damage to soil ecosystems. Because soil organic matter plays a role in cycling nutrients, aerating soil, retaining water, and maintaining tilth, a significant reduction in organic matter content in a soil profile is not just evidence of a change in ecosystem function, but of damage to that soil ecosystem. Reference sites were selected for comparison to contaminated sites, and additional sites were selected to illustrate how variables other than environmental contaminants might affect the soil organic matter profile. The survey was undertaken on the supposition that environmental contaminants and other stressors reduce the activity of earthworms and other macrofauna, inhibiting the incorporation of organic matter into the soil profile. The profiles of the unstressed soils showed a continuous decrease in organic matter content from the uppermost mineral soil layer (0-2.5 cm) down to 15 cm. Stressed soils showed an abrupt decrease in soil organic matter content below a depth of 2.5 cm. The 2.5-5.0 cm layer of stressed soils--such as found in a pine barren, an orchard, sites contaminated with zinc, and a site with compacted soil--had less than 4% total organic matter and less than 1% particulate organic matter. However, damaged soil ecosystems were best identified by comparison of their profiles to the profiles of closely matched reference soils, rather than by comparison to these absolute values. The presence or absence of earthworms offered a partial explanation of observed differences in soil organic matter profiles.

Animals↗

PubMed2005

[Estimation of China soil organic carbon storage and density based on 1:1,000,000 soil database].

Based on 1:1,000,000 soil database, and employing the methods of spatial expression, this paper estimated the soil organic carbon storage (SOCS) and density (SOCD) of China. The database consists of 1:1,000,000 digital soil map, soil profile attribution database, and soil reference system. The digital soil map contained 926 soil mapping units, 690 soil families, and 94 000 or more polygons, while the soil profile attribution database collected 7292 soil profiles, including 81 attribution fields. The SOCDs of soil profiles were calculated and linked to the soil polygons in the digital soil map by the method of "GIS linkage based on soil type", resulting in a vector map of 1:1,000,000 China SOCD. The SOCS of the country or of a soil could be estimated by summing up the SOCS of all polygons or the polygons of a soil, and their SOCD were the SOCS of them derived by their areas. The estimated SOCS and SOCD of the country was 89. 14 Pg (1 Pg = 10(15) g) and 9.60 kg m(-2), respectively, covered all the soils with a total area of 928.10 x 10(4) km2, which might be considered closest to the real value.

Carbon↗

PubMed2000

Mutagenic activity of surface soil and quantification of 1,3-, 1,6-, and 1,8-dinitropyrene isomers in soil in Japan.

To clarify the mutagenic potential of nonagricultural surface soil in Japan, 110 soil samples were collected from five geographically different areas between November 1996 and March 1997, and organic extracts of the soil samples were examined by the Ames/Salmonella assay. Most of the soil extracts showed mutagenicity toward both strains TA98 and TA100 in the presence and/or absence of a mammalian metabolic activation system (S9 mix), suggesting that surface soil is largely contaminated with environmental mutagens. Soil samples collected at Hekinan, Kobe, and Osaka were highly mutagenic toward both strains, and their potencies toward TA98 without S9 mix were extremely high, inducing more than 12 000 revertants per gram of soil. On the other hand, soil samples from Muroran showed strong mutagenicity toward TA100 with S9 mix. Furthermore, 1, 3-dinitropyrene (DNP), 1,6-DNP, and 1,8-DNP in soil samples collected at 10 sampling sites in three metropolitan areas were quantified by fluorometric detection of the corresponding diaminopyrene isomers using high-performance liquid chromatography (HPLC). Three DNP isomers were detected in all soil samples, and the amounts of 1,3-, 1,6-, and 1,8-DNP isomers in the soil samples were 12-3270, 14-5587, and 13-6809 pg/g, respectively. The gross amount of three DNP isomers in surface soil collected at Hekinan was more than 10 ng per gram of soil. The highest contribution ratios of DNP isomers to the mutagenicity of soil extracts were observed for the samples collected at Osaka, and the total of the contribution ratios of three DNP isomers was about 50%. These results suggest that surface soil is largely contaminated with mutagenic compounds and that DNP isomers are one class of major mutagenic and carcinogenic compounds contaminating surface soil.

Air Pollutants↗

PubMed2002

Effects of agronomical measures on the microbial diversity of soils as related to the suppression of soil-borne plant pathogens.

The diversity of soil microbial communities can be key to the capacity of soils to suppress soil-borne plant diseases. As agricultural practice, as well as directed agronomical measures, are known to be able to affect soil microbial diversity, it is plausible that the soil microflora can be geared towards a greater suppressivity of soil-borne diseases as a result of the selection of suitable soil management regimes. In the context of a programme aimed at investigating the microbial diversity of soils under different agricultural regimes, including permanent grassland versus arable land under agricultural rotation, we assessed how soil microbial diversity is affected in relation to the suppression of the soil-borne potato pathogen Rhizoctonia solani AG3. The diversity in the microbial communities over about a growing season was described by using cultivation-based--plating on different media--and cultivation-independent--soil DNA-based PCR followed by denaturing gradient gel electrophoresis (DGGE) community fingerprinting--methods. The results showed great diversity in the soil microbiota at both the culturable and cultivation-independent detection levels. Using cultivation methods, various differences between treatments with respect to sizes of bacterial and fungal populations were detected, with highest population sizes generally found in rhizospheres. In addition, the evenness of eco-physiologically differing bacterial types was higher in grassland than in arable land under rotation. At the cultivation-independent level, clear differences in the diversities of several microbial groups between permanent grassland and arable land under rotation were apparent. Bio-assays that assessed the growth of R. solani AG3 hyphae through soil indicated a greater growth suppression in grassland than in arable land soils. Similarly, an experiment performed in the glasshouse showed clear differences in both microbial diversities and suppressiveness of R. solani growth in soil, depending on the presence of either maize or oats as the crop. The significance of these findings for designing soil management strategies is discussed.

Agriculture↗

PubMed2003

Soil ingestion by sheep grazing the metal enriched floodplain soils of mid-Wales.

Floodplain soils within and downstream from the mineralised and mined areas of mid-Wales, are contaminated by metals, especially Pb, because of historical and contemporary fluvial pollution. Rates of soil ingestion by sheep grazing these sites have been quantified to establish the relative importance of the soil-plant-animal and soil-animal pathway of metals. The highest rates of soil ingestion occurred during the winter/spring period. During March, soil ingestion exceeded 30% of the D.M. intake at 2 of the 11 sites investigated. The total daily intake of metals by sheep reflects the degree of soil metal enrichment, and is elevated during the winter/spring period, coincident with the higher rates of soil ingestion and the generally higher pasture herbage metal concentrations. Because the soil-plant transfer of Pb is low, ingested soil is often the major pathway of this metal to sheep. This is especially evident in March and May when on average 80.0 and 82.9%, respectively of the Pb intake was via soil ingestion. At one site in May, 97% of the Pb intake was attributable to ingested soil. Even when soil-plant transfers are not so low, as found for Cu and Zn, ingested soil can occasionally supply greater than 60% of these metals to the animal. However, despite the potential importance of soil ingestion, little is known about the availability to and absorption of soil-borne metals by animals.

Adsorption↗

PubMed2001

Significance of soil properties in the adsorption and mobility of the fungicide metalaxyl in vineyard soils.

Adsorption and mobility of the fungicide metalaxyl were studied in 16 vineyard soils from the La Rioja region (Spain), with organic matter (OM) contents in the 0.31--1.37% range, and in 7 natural soils with OM contents in the 3.30--8.24% range. Adsorption isotherms were obtained using the batch equilibrium technique, and mobility was studied by soil thin-layer chromatography (soil-TLC). In all cases, the adsorption isotherms fit the Freundlich equation. The values of the K(f) constants were low in the vineyard soils (0.01--0.64) and increased in the natural soils (1.05--2.83). The n(f) values were in general lower than unity. K(f) constants were significantly correlated (p < 0.001) with the OM content when all of the soils were considered. According to the determination coefficient, r(2), OM would account for 88% of the variance in adsorption. When the vineyard soils alone were considered, a significant correlation was seen between K(f) and the OM and clay contents; both parameters, varying simultaneously, explain 80% of the variance in adsorption. Study of the mobility of metalaxyl with soil-TLC indicated that in vineyard soils the fungicide has the potential for being highly mobile in 19% of the soils and mobile in 81% of them. In natural soils, the fungicide has the potential for being moderately mobile or mobile in 86 and 14% of the soils, respectively. This type of behavior of metalaxyl indicates that in vineyards soils of the La Rioja region (Spain) with low OM contents, where application of the compound is continuous, a leaching of the fungicide from the soil to groundwaters could potentially occur. These results should be borne in mind when metalaxyl is to be used in the soils of this region.

Absorption↗

PubMedDate not supplied

Relationship of soil test phosphorus and sampling depth to runoff phosphorus in calcareous and noncalcareous soils.

A study was initiated to investigate the relationship between soil test P and depth of soil sampling with runoff losses of dissolved molybdate reactive phosphorus (DMRP). Rainfall simulations were conducted on two noncalcareous soils, a Windthorst sandy loam (fine, mixed, thermic Udic Paleustalf) and a Blanket clay loam (fine, mixed, thermic Pachic Argiustoll), and two calcareous soils, a Purves clay (clayey, smectitic, thermic Lithic Calciustoll) and a Houston Black clay (fine, smectitic, thermic Udic Haplustert). Soil (0- to 2.5-, 0- to 5-, and 0- to 15-cm depths) and runoff samples were collected from each of the four soils in permanent pasture exhibiting a wide range in soil test P levels (as determined by Mehlich III and distilled water extraction) due to prior manure applications. Simulated rain was used to produce runoff, which was collected for 30 min. Good regression equations were derived relating soil test P level to runoff DMRP for all four soil types, as indicated by relatively high r2 values (0.715 to 0.961, 0- to 5-cm depth). Differences were observed for the depth of sampling, with the most consistent results observed with the 0- to 5-cm sampling depth. Runoff DMRP losses as a function of the concentration of P in soil were lower in calcareous soils (maximum of 0.74 mg L(-1)) compared with noncalcareous soils (maximum of 1.73 mg L(-1)). The results indicate that a soil test for environmental P could be developed, but it would require establishing different soil test P level criteria for different soils or classes of soils.

Calcium↗

PubMed2002

Speciation and fractionation of heavy metals in soil experimentally contaminated with Pb, Cd, Cu and Zn together and effects on soil negative surface charge.

Speciation and fractionation of heavy metals in soil subsamples experimentally loaded with Pb, Cd, Cu and Zn in orthogonal design was investigated by sequential extraction, and operationally defined as water-soluble and exchangeable(SE), weakly specific adsorbed(WSA), Fe and Mn oxides-bound(OX) and organic-bound(ORG). The results showed that fractions of heavy metals in the soil subsamples depended on their speciation. About 90% of Cd and 75% of Zn existed in soil subsamples in the SE fraction. Lead and Cu existed in soil subsamples as SE, WSA and OX fractions simultaneously, although SE was still the major fraction. Organic-bound heavy metals were not clearly apparent in all the soil subsamples. The concentration of some heavy metal fractions in soil subsamples showed the good correlation with ionic impulsion of soil, especially for the SE fraction. Continuous saturation of soil subsamples with 0.20 mol/L NH4Cl, which is the first step for determination of the negative surface charge of soil by the ion retention method, resulted in desorption of certain heavy metals from the soil. It was found that the percentage desorption of heavy metals from soil subsamples depended greatly on pH, the composition and original heavy metal content of the soil subsamples. However, most of the heavy metals in the soil subsamples were still be retained after multiple saturation. Compared with the parent soil, the negative surface charge of soil subsamples loaded with heavy metals did not show difference significantly from that of the parent one by statistical analysis. Heavy metals existed in the soil subsamples mainly as exchangeable and precipitated simultaneously.

Ammonium Chloride↗

PubMed2004

Toxicity testing of heavy-metal-polluted soils with algae Selenastrum capricornutum: a soil suspension assay.

A small-scale Selenastrum capricornutum (Rhapidocelis subcapitata) growth inhibition assay was applied to the toxicity testing of suspensions of heavy-metal-polluted soils. The OECD 201 standard test procedure was followed, and algal biomass was measured by the fluorescence of extracted chlorophyll. The soils, which contained up to (per kilogram) 1390 mg of Zn, 20 mg of Cd, and 1050 mg of Pb were sampled around lead and zinc smelters in northern France. The water extractability of the metals in suspensions (1 part soil/99 parts water w/v) was not proportional to the pollution level, as extractability was lower for soil samples that were more polluted. Thus, the same amount of metals could be leached out of soils of different levels of pollution, showing that total concentrations of heavy metals in soil (currently used for risk assessment purposes) are poor predictors of the real environmental risk via the soil-water path. Despite high concentrations of water-extracted zinc (0.6-1.4 mg/L of Zn in the test), exceeding by approximately 10-fold the EC(50) value for S. capricornutum (0.1 mg Zn/L), 72-h algal growth in the soil extracts was comparable or better than growth in the standard control OECD mineral medium. The soil suspension stimulated the growth of algae up to eightfold greater than growth using the OECD control medium. Growth stimulation of algae was observed even when soil suspensions contained up to 12.5 mg Zn/L and could not be explained by supplementary nitrogen, phosphorous, and carbonate leached from the soil. However, if the growth of algae in suspensions of clean and polluted soils was compared, a dose-dependent inhibitory effect of metals on algal growth was demonstrated. Thus, as soil contains nutrients/supplements that mask the adverse effect of heavy metals, a clean soil that has properties similar to the polluted soils should be used instead of mineral salt solution as a control for analysis of the ecotoxicity of soils.

Cadmium↗

PubMed2006

Effect of 2,4-D contamination on soil functional stability evaluated using the relative soil stability index (RSSI).

Soil functional stability is the capacity of soil functions to resist and recover from an environmental perturbation and can be used to evaluate soil health. It can be influenced by the presence of xenobiotics such as herbicides. The impact of a fresh 2,4-D contamination (36 mg kg(-1) dry soil) on soil functional stability was evaluated by comparing the capacity of soil enzyme activities to resist and recover from a heat perturbation for both a clean and 2,4-D-contaminated soil. The functional stabilities of the soils (uniform sands, pH 6.9, 7% (w/w) organic matter) were calculated using the relative soil stability index (RSSI). The RSSI scores indicate the proportion of potential enzyme activity the soil retains after a perturbation compared to the potential activity of an unperturbed soil. Six extra-cellular enzyme activities (acid and alkaline phosphatases, arylsulfatase, urease, protease and beta-glucosidase) were monitored in soil microcosms during a 15-day period. During this period, a 60 degrees C heat perturbation was applied to the soil for 24 h. The activities of arylsulfatase and protease were found to be the most stable following heat perturbation obtaining the highest RSSI scores (87% and 77%, respectively). Urease activity showed the lowest RSSI score (38%). Although all enzyme activities were inhibited by the presence of 2,4-D, the RSSI results indicated that contamination lowered the stability of only three enzyme activities (arylsulfatase, beta-glucosidase and urease). The RSSI adequately described resistance, recovery and recovery rate parameters and enabled differentiation between functional stabilities of clean and contaminated soil and between different soil types.

2,4-Dichlorophenoxyacetic Acid↗

PubMed2000

Analysis of the dynamics of fungal communities in soil via fungal-specific PCR of soil DNA followed by denaturing gradient gel electrophoresis.

A molecular method for profiling of fungal communities in soil was applied in experiments in soil microcosms, with two objectives, (1) to assess the persistence of two selected fungal species in soil, and (2) to analyze the response of the natural fungal community to a spill of sulphurous petrol in the same soil. To achieve the aims, two soil DNA extraction methods, one originally designed for the direct extraction of bacterial community DNA and the other one aimed to obtain fungal DNA, were tested for their efficiency in recovering DNA of fungal origin from soil. Both methods allowed for the efficient extraction of DNA from introduced Trichoderma harzianum spores as well as Arthrobotrys oligospora mycelial fragments, at comparable rates. Several PCR amplification systems based on primers specific for fungal 18S ribosomal RNA genes were tested to design strategies for the assessment of fungal communities in soil. The PCR systems produced amplicons of expected size with DNA of most fungi studied, which included members of the Ascomycetes, Basidiomycetes, Zygomycetes and Chytridiomycetes. On the other hand, the 18S rRNA genes of Oomycetes (including key plant pathogens) were poorly amplified. Plant (Solanum tuberosum), nematode (Meloidogyne sp.) and bacterial DNA was not amplified. For studies of soil fungal communities, a nested PCR approach was selected, in which the first PCR provided the required specificity for fungi, whereas the second (nested) PCR served to produce amplicons separable on denaturing gradient gels. Denaturing gradient gel electrophoresis (DGGE) allowed the resolution of mixtures of PCR products of several different fungi, as well as products resulting from mixed-template amplifications, into distinct banding patterns. The persistence of fungal species in soil was assessed using T. harzianum spores and A. oligospora hyphal fragments added to silt loam soil microcosms. Using PCR-DGGE, these fungi were detectable for about 14 days and 2 months, respectively. Both singly-inoculated soils and soils that had received mixed inoculants revealed, next to bands resulting from indigenous fungi, the expected bands in the DGGE profiles. The A. oligospora specific amplicon, by virtue of its unique migration in the denaturing gradient, was well detectable, whereas the T. harzianum specific product comigrated with products from indigenous fungi. PCR-DGGE analysis of DNA obtained from the silt loam soil treated with dibenzothiophene-containing petrol showed the progressive selection of specific fungal bands over time, whereas this selection was not observed in untreated soil microcosms. Cloning of individual molecules from the selected bands and analysis of their sequences revealed a complex of targets which clustered with the 18S rDNA sequences of the closely-related species Nectria haematococca, N. ochroleuca and Fusarium solani. Fungal isolates obtained from the treated soil on PDA plates were identified as Trichoderma sp., whereas those on Comada agar fell into the Cylindrocarpon group (anamorph of Nectria spp).

Base Composition↗

PubMed2003

Relating soil solution Zn concentration to diffusive gradients in thin films measurements in contaminated soils.

The technique of diffusive gradients in thin films (DGT) has been suggested to sample an available fraction of metals in soil. The objectives of this study were to compare DGT measurements with commonly measured fractions of Zn in soil, viz, the soil solution concentration and the total Zn concentration. The DGT technique was used to measure fluxes and interfacial concentrations of Zn in three series of field-contaminated soils collected in transects toward galvanized electricity pylons and in 15 soils amended with ZnCl2 at six rates. The ratio of DGT-measured concentration to pore water concentration of Zn, R, varied between 0.02 and 1.52 (mean 0.29). This ratio decreased with decreasing distribution coefficient, Kd, of Zn in the soil, which is in agreement with the predictions of the DGT-induced fluxes in soils (DIFS) model. The R values predicted with the DIFS model were generally larger than the observed values in the ZnCl2-amended soils at the higher Zn rates. A modification of the DIFS model indicated that saturation of the resin gel was approached in these soils, despite the short deployment times used (2 h). The saturation of the resin with Zn did not occur in the control soils (no Zn salt added) or the field-contaminated soils. Pore water concentration of Zn in these soils was predicted from the DGT-measured concentration and the total Zn content. Predicted values and observations were generally in good agreement. The pore water concentration was more than 5 times underpredicted for the most acid soil (pH = 3) and for six other soils, for which the underprediction was attributed to the presence of colloidal Zn in the soil solution.

Colloids↗

PubMed2005

Percutaneous absorption of 4-cyanophenol from freshly contaminated soil in vitro: effects of soil loading and contamination concentration.

Despite the skin's excellent barrier function, dermal exposure to soil contaminated with toxic chemicals can represent a significant health hazard (e.g., via multiple work related contacts in the farming and waste disposal industries). The development of environmental standards or limits for chemical levels in soil has been impeded because quantification of percutaneous uptake from this medium has not been well-defined. The objective of the research described here, therefore, was to better characterize the rate and extent of dermal penetration as a function of soil loading and degree of soil contamination. The absorption of a model compound (4-cyanophenol, CP) across hairless mouse skin in vitro has been determined at four different soil loadings (5, 11, 38 and 148 mg cm-2) and at six levels of soil contamination (concentrations ranging from 0.19 to 38 mg/g soil). Following 8 h of exposure, the amount of CP absorbed was independent of soil loading when CP concentration was constant, implying that the quantity of soil presentwas always sufficientto provide atleast a single layer of tightly packed particles. At the lowest loadings, however, with increasing times of exposure, the CP transport rate fell off due to depletion of chemical from the soil. At constant soil loading (38 mg cm(-2)), CP flux (Jss) across the skin was linearly proportional to the level of contamination (C(o)soil) over the range 0.19 to 23.5 mg of CP per gram of soil: Jss (micorg cm(-2) h(-1)) = (1.1 x 10(-5) g cm(-2) h(-1)) x Csoil (microg/g soil). At the highest CP contamination concentration, however, the transport rate was about an order of magnitude higher than expected, possibly due to the presence of pure CP crystals. In conclusion, these results provide new quantifications of the characteristics of dermal uptake from chemically contaminated soils and important information with which to develop and verify predictive models of dermal absorption.

Administration, Cutaneous↗

PubMed2003

Effects of soil amendments at a heavy loading rate associated with cover crops as green manures on the leaching of nutrients and heavy metals from a calcareous soil.

The potential risk of groundwater contamination by the excessive leaching of N, P and heavy metals from soils amended at heavy loading rates of biosolids, coal ash, N-viro soil (1:1 mixture of coal ash and biosolids), yard waste compost and co-compost (3:7 mixture of biosolids to yard wastes), and by soil incorporation of green manures of sunn hemp (Crotalaria juncea) and sorghum sudangrass (Sorghum bicolor x S. bicolor var. sudanense) was studied by collecting and analyzing leachates from pots of Krome very gravelly loam soil subjected to these treatments. The control consisted of Krome soil without any amendment. The loading rate was 205 g pot(-1) for each amendment (equivalent to 50 t ha(-1) of the dry weight), and the amounts of the cover crops incorporated into the soil in the pot were those that had been grown in it. A subtropical vegetable crop, okra (Abelmoschus esculentus L.), was grown after the soil amendments or cover crops had been incorporated into the soil. The results showed that the concentration of NO3-N in leachate from biosolids was significantly higher than in leachate from other treatments. The levels of heavy metals found in the leachates from all amended soils were so low, as to suggest these amendments may be used without risk of leaching dangerous amounts of these toxic elements. Nevertheless the level of heavy metals in leachate from coal ash amended soil was substantially greater than in leachates from the other treatments. The leguminous cover crop, sunn hemp, returned into the soil, increased the leachate NO3-N and inorganic P concentration significantly compared with the non-legume, sorghum sudangrass. The results suggest that at heavy loading rates of soil amendments, leaching of NO3- could be a significant concern by application of biosolids. Leaching of inorganic P can be increased significantly by both co-compost and biosolids, but decreased by coal ash and N-viro soil by virtue of improved adsorption. The leguminous cover crop, sunn hemp, when incorporated into the soil, can cause the concentration of NO3-N to increase by about 7 fold, and that of inorganic P by about 23% over the non-legume. Regarding the metals, biosolids, N-viro soil and coal ash significantly increased Ca and Mg concentrations in leachates. Copper concentration in leachate was increased by application of biosolids, while Fe concentration in leachates was increased by biosolids, coal ash and co-compost. The concentrations of Zn, Mo and Co in leachate were increased by application of coal ash. The concentrations of heavy metals in leachates were very low and unlikely to be harmful, although they were increased significantly by coal ash application.

Abelmoschus↗

PubMed2007

Strong impact on the polycyclic aromatic hydrocarbon (PAH)-degrading community of a PAH-polluted soil but marginal effect on PAH degradation when priming with bioremediated soil dominated by mycobacteria.

Bioaugmentation of soil polluted with polycyclic aromatic hydrocarbons (PAHs) is often disappointing because of the low survival rate and low activity of the introduced degrader bacteria. We therefore investigated the possibility of priming PAH degradation in soil by adding 2% of bioremediated soil with a high capacity for PAH degradation. The culturable PAH-degrading community of the bioremediated primer soil was dominated by Mycobacterium spp. A microcosm containing pristine soil artificially polluted with PAHs and primed with bioremediated soil showed a fast, 100- to 1,000-fold increase in numbers of culturable phenanthrene-, pyrene-, and fluoranthene degraders and a 160-fold increase in copy numbers of the mycobacterial PAH dioxygenase gene pdo1. A nonpolluted microcosm primed with bioremediated soil showed a high rate of survival of the introduced degrader community during the 112 days of incubation. A nonprimed control microcosm containing pristine soil artificially polluted with PAHs showed only small increases in the numbers of culturable PAH degraders and no pdo1 genes. Initial PAH degradation rates were highest in the primed microcosm, but later, the degradation rates were comparable in primed and nonprimed soil. Thus, the proliferation and persistence of the introduced, soil-adapted degraders had only a marginal effect on PAH degradation. Given the small effect of priming with bioremediated soil and the likely presence of PAH degraders in almost all PAH-contaminated soils, it seems questionable to prime PAH-contaminated soil with bioremediated soil as a means of large-scale soil bioremediation.

Arthrobacter↗

PubMed2004

Microbial diversity in soil: selection microbial populations by plant and soil type and implications for disease suppressiveness.

An increasing interest has emerged with respect to the importance of microbial diversity in soil habitats. The extent of the diversity of microorganisms in soil is seen to be critical to the maintenance of soil health and quality, as a wide range of microorganisms is involved in important soil functions. This review focuses on recent data relating how plant type, soil type, and soil management regime affect the microbial diversity of soil and the implication for the soil's disease suppressiveness. The two main drivers of soil microbial community structure, i.e., plant type and soil type, are thought to exert their function in a complex manner. We propose that the fact that in some situations the soil and in others the plant type is the key factor determining soil microbial diversity is related to the complexity of the microbial interactions in soil, including interactions between microorganisms and soil and microorganisms and plants. A conceptual framework, based on the relative strengths of the shaping forces exerted by plant and soil versus the ecological behavior of microorganisms, is proposed.

Agriculture↗