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This paper provides a model with which to predict soil ingestion recovery values in soil ingestion studies either retrospectively or prospectively. The predictive equations generated from the model can be used to estimate minimum soil ingestion detection levels from soil ingestion studies which use mass-balance methods. The model is derived from data assessing soil recovery efficiencies in adults using eight different predictive tracer elements. The results constitute a methodology for determining minimum detection levels of soil ingestion and hence have important regulatory significance.
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To assess the contribution of various environmental parameters to the entry of Rn into basements, it is advantageous to simplify and control the important variables present in the field situation. A scale model system, simulating a house in soil, has been constructed to investigate the effect of meteorological parameters and house and soil characteristics on soil gas flow around houses. The house walls and soil are of variable permeability. Wind is simulated by applying a static pressure distribution to the soil surface. The effect of temperature differences and appliances is simulated by depressurizing the model house. Soil gas pressures at various locations around the house are measured under different conditions. The results show that the ratio of wall to soil permeability is the determining factor in soil gas flow patterns. For a wind of 8.94 m s-1 (20 mph), the horizontal pressure gradients are about 99 Pa m-1 in the model when the wall is at least as permeable as the soil. This corresponds to 3.3 Pa m-1 in the field. When the soil is two or more orders of magnitude more permeable than the wall, the gradient is about 19.8 Pa m-1 in the model, or 0.66 Pa m-1 in the field. There is a logarithmic dependence of pressure gradient on the ratio of wall to soil permeability in the range -2 less than log (kw/ks) less than 0. Conversely, it takes a large temperature difference of 27 degrees C to cause a 99 Pa m-1 horizontal pressure gradient in model systems with wall permeability greater than soil permeability. The effects of changes in the model system on soil gas flow patterns are investigated for the cases of lowered soil surface permeability, partial surface capping, and presence of a subfloor gravel bed. Partial surface capping, as would occur with driveways and patios, was found to have a minor effect on soil gas pressures. However, lowered surface permeability, caused by precipitation, can significantly change soil gas flow patterns. The only change in soil pressure gradients or pressure differences in the presence of a gravel bed is in the system with the highest wall-to-soil permeability ratio. In this system, under all conditions (house depressurization, wind, and wind with house depressurization), there is an increase in the absolute value of both upwind and downwind pressure differences and pressure gradients with the addition of a gravel bed.
Microplastics (MPs) have become a pressing global environmental threat, with soils-acting as sinks for MPs from multiple sources-gaining increasing attention. Near-infrared (NIR) spectroscopy offers a promising tool for MPs detection due to its rapid, non-destructive, and field-applicable features. Although previous studies have focused on the effects of individual soil components on the NIR detection performance of MPs, there is still a lack of systematic research on how the complex background-formed by the coupling of multiple physicochemical properties in natural soils-affects detection performance. This study focuses on soil types with different soil-forming processes, selected five representative agricultural soils to systematically evaluate how the combinations of physicochemical properties they represented affect the performance of NIR-based qualitative and quantitative analysis of MPs in soils. The results demonstrated that soil type significantly affected both the spectral response and detection performance of MPs. Brown Pedocals and Brown Earth exhibited clearer characteristic absorption and stronger linear responses, achieving higher identification accuracy under low (<1.5 %) or zero MPs concentrations and the best quantitative performance (R2 ≥ 0.988, prediction set root mean square error (RMSEP) ≤ 0.110 %). In contrast, Phaeozem and Red Soil were more prone to misclassification at low concentrations, while Fluvo-aquic Soil showed the poorest quantitative performance. This study is the first to reveal, at a holistic level, the critical constraints posed by natural soil complexity on the NIR detection of MPs, offering targeted empirical evidence to support the application of NIR technology in real-world soil environments.
Soil was sterilized by various procedures, and then the resident microorganisms were physically separated and concentrated from the soil for viewing by transmission electron microscopy as thin sections and frozen-etched preparation. Remaining cell viability in the soil was tested by conventional plating before and after enrichment culture. The soil proved to be sterile after treatment with 60Co radiation, prolonged autoclaving, prolonged dry heat application at 200C, or glutaraldehyde (if followed by subsequent milk heating), and could be considered sterile after OsO4 treatment. Treatment with glutaraldehyde alone, or 160C dry heat for 3 h, did not sterilize the soil. Cellular fine structure was latered or destroyed by the heat treatments, but was not affected to any extent by any of the other treatments including glutaraldehyde followed by milk heating. These findings are considered in relation to the residual biological information observable by electron microscopy in soil samples which have been sterilized to eliminate possible pathogens before handling of the soil. These findings are also considered with the objective of obliterating the fine structure of the indigenous microorganisms during soil sterilization so that electron microscopy studies can be made of microorganisms inoculated into and grown in the presterilized soil. These findings are considered in relation to the residual biological information observable by electron microscopy in soil samples which have been sterilized to eliminate possible pathogens before handling of the soil. These findings are also considered with the objective of obliterating the fine structure of the indigenous microorganisms during soil sterilization so that electron microscopy studies can be made of microorganisms inoculated into and grown in the presterilized soil.
The California Site Mitigation Decision Tree Manual, 1985, was developed by the California Department of Health Services to provide a detailed technical basis for managing uncontrolled hazardous waste sites. The Decision Tree describes a process that relies on criteria, Applied Action Levels (AALs) to evaluate and, if necessary, mitigate the impact of uncontrolled hazardous waste sites on the public health and the environment. AALs are developed for individual substances, species, and media of exposure. AALs have been routinely developed for the media of air and water; however, an approach for developing AALs for soil contact was lacking. Given that the air pathway for soil contact is addressed in AALs for air, two routes of exposure, ingestion and dermal contact, are addressed in developing AALs for soil contact. The approach assumes a lifetime of exposure to soil in a residential setting. Age-related changes in exposure are included in the scenario. Exposure to soil due to ingestion and dermal contact are quantitated independently and then integrated in the final exposure scenario. A mass balance approach using four elements is employed to quantitate soil ingestion for a young child. Changes in soil ingestion with age are based on age-related changes in blood lead concentration and mouthing behavior. Dermal exposure to soil was determined from studies that reported skin soil load and from estimates of exposed skin surface area. Age-related changes in the dermal exposure to soil are also based on changes with age of blood lead concentration and mouthing behavior. The estimates of exposure to soil due to ingestion and dermal contact are integrated, and an approach for developing AALs is advanced. AALs are derived by allocating the Maximum Exposure Level as described in the Decision Tree to the average daily exposure to soil. Toxicokinetic considerations for the two routes of exposure must be included in deriving AALs for the soil medium of exposure.
Axenic, washed conidia of Fusarium solani f. sp. phaseoli, Aspergillus flavus, and Verticillium albo-atrum were placed on washed Difco purified agar discs along with an inorganic salt solution containing various levels of carbon and nitrogen substrates. These discs were exposed to volatiles from six soils (pH 5.1-8.6). Fusarium solani macroconidial germination was inhibited mostly by volatiles from soils of pH 5.1, 6.1, 7.0, and 7.5, but high levels of glucose and NH4Cl reversed this inhibition, raising germination to that of no-soil, no-carbon or nitrogen controls. Conidial germination of A. flavus was inhibited mainly by volatiles from high pH (7.0, 7.8, and 8.6) soils, and increased levels of glucose plus an amino acid mixture nullified this inhibition. Volatiles from soils of pH 5.1, 6.1, and 7.5 stimulated A. flavus conidial germination. Assays after the removal of CO2 from the air above soil of pH 5.1 demonstrated that volatiles inhibitory to A. flavus were produced by this soil. Assays indicated that a KOH-soluble compound was a fungistatic soil volatile to F. solani macroconidial germination. The nullification by carbon and nitrogen substrates of F. solani and A. flavus inhibition caused by soil volatiles parallels that for soil fungistasis. Conidial germination of V. albo-atrum was markedly stimulated by volatiles in all soils tested, and was not affected by removal of CO2. Inhibitory soil volatiles may increase the nutritional requirements for spore germination of certain fungi.
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The effects of three soil pH's, three soil temperatures, and three soil moistures on [14C]isofenphos degradation were investigated. All three factors interacted strongly and significantly affected the persistence of isofenphos as well as the formation of the degradation products (p less than 1%). Isofenphos degradation was greatest at the higher temperatures 35 degrees C greater than 25 degrees C greater than 15 degrees C (except under alkaline pH's), medium moisture 25% greater than 30% greater than 15%, and in both alkaline (pH = 8) and acidic soils (pH = 6) compared with neutral soil (pH = 7). Isofenphos oxon formation was greatest at higher temperatures 35 degrees C compared with 25 degrees C and 15 degrees C, in acidic soil greater than neutral soil greater than alkaline soil, and under high moisture (30%) compared with the 15% and 22.5% moistures. The formation of soil-bound residues was greatest at higher temperatures 35 degrees C greater than 25 degrees C greater than 15 degrees C, higher moisture 30% compared with 15% and 22.5%, and in alkaline soil compared with neutral and acidic soils.
Survival of Rhizoctonia solani in precolonized tablebeet seed was greater in a light-textured sandy loam (SL 1) than in a heavy-textured silty clay loam (SiCL). Reduction in survival as well as competitive saprophytic activity of the pathogen resulted when clays (kaolinite and montmorillonite) were added to SL to prepare soils of heavier texture. Survival and activity of R. solani, however, were not increased when sand was added to SiCL (suppressive to R. solani survival) to make this soil lighter in texture. In natural soils of different textures, activity of R. solani was maintained longer in two light-textured sandy loam soils than in a light-textured loamy sand or loam. During investigation of soil chemical and biological influences on R. solani survival, high K2O content in soil was significantly correlated with low saprophytic activity of the pathogen. In all instances where soil microbial activity as determined by a dehydrogenase assay was high, low saprophytic activity was found. Since high microbial activity or K2O content in soil were not associated with any particular soil type, biological or chemical factors may be more important than soil texture in influencing survival and activity of R. solani in soil.
Microscopic analysis of longitudinal sections of feeder roots of apple seedlings from soil with experimentally prepared different degrees of soil sickness led to the following results: 1. A colonization of root-barks by actinomycetes could be pointed out in injured and in macroscopic not visible injured feeder roots of apple seedlings from sick soil. 2. The frequency of the colonization of root-pieces of the two highest root classes was in the sick soil at 47.3% and in the two soils with a less degree of soil sickness at 32.4%. In the non-sick soil the root were at a frequency of 0.3% nearly free from actinomycetes. 3. Feeder roots colonizated by actinomycetes showed injuries in the cell-bandage. Increasing injuries of the roots were obtained with increasing intensity of colonization by actinomycetes. In heavy injured feeder roots the proof of actinomycetes was difficult or no more possible. As the share of heavy injured roots was increasing with increasing degree of soil sickness can be supposed that the real frequency of root colonization by actinomycetes is substantially higher than it was observed in roots seeming to be healthy macroscopically. 4. The results obtained support our hypothesis that soil sickness of apple trees is caused by actinomycetes. The injuries of the roots appearing as a consequence of the colonization may explain both, the soil sickness in the case of replanting and the development of soil sickness in growing apple plantations. 5. Since until now there is no proof that actinomycetes cause injuries in roots of fruit-trees further examinations have to be aspired to confirm our results.
The disappearance of the herbicide, Avadex (40% diallate), from five agricultural soils (differing in either pH, carbon content, or nitrogen content), incubated under sterile and non-sterile conditions, was followed for a period of 20 weeks. Avadex was rapidly lost from microbiologically active soils, with over 50% of the applied (2.5 ppm) dosage disappearing within four weeks; losses from sterile soils were much slower with recoveries of over 50% after 20 weeks. Incubation of soil with Avadex to which 14C-labeled diallate had been added resulted in rapid formation of 14CO2 from microbiologically active samples and only very slow 14CO2 formation from sterile samples. Substantial quantities of radioactivity were retained as unextractable residues in both sterile and non-sterile soils after senven days incubation. From these data it was concluded that the disappearance of the herbicide from non-sterile soils was mainly due to microbial degradation and to binding of diallate or its metabolites as residues to undefined soil components. Losses from sterile soils were attributed to both binding of residues and to a slow chemical degradation. Avadex degradation by pure cultures was studied using representative fungi isolated from the five soils. Of the fungi tested, Phoma eupyrena, Penicillium janthinellum, and Trichoderma harzianium coudl degrade at least 20% of the applied (2.5 ppm) herbicide after ten days incubation. Degradation of Avadex in soil cultures of T. harzianum was found to be slower than degradation in liquid nutrient cultures.
Urban soils can play a significant role in climate change mitigation due to their capacity to store carbon (C) and support microbial biodiversity. In this context, this study evaluated the effects of different fertilization strategies on soil quality, greenhouse gas emissions, and microbial communities in two urban green areas located in the Campania region (Southern Italy) over a three-year period. Mineral fertilization (MIN), micronized vermicompost (CMP), micronized biochar (BCH), vermicompost plus biochar (CMP + BCH) were compared to an unfertilized control (CNT). The results showed that soil physicochemical properties were mainly influenced by site-specific conditions and temporal variability, whereas cation exchange capacity was the soil parameter most responsive to fertilization treatments. The QBS-ar index, used as an indicator of soil biological quality based on soil arthropods, was primarily affected by seasonality, with higher values recorded during spring-summer and no significant effects attributable to fertilization treatments. Vermicompost, BCH, and their combination were associated with lower net soil-vegetation CO2 fluxes and smaller temporal increases in the measured flux compared with the control and mineral fertilization treatments. All treatments exhibited a negative estimated annualized net C balance, indicating that, under the adopted temporal upscaling procedure, the estimated gaseous exchanges exceeded the annual increase in soil organic carbon stocks. Nevertheless, BCH showed the least negative estimated annualized balance. Analyses of microbial diversity revealed that bacterial and fungal communities were mainly shaped by temporal and seasonal factors, while fertilization treatments had limited effects on microbial diversity and community composition. Overall, the findings indicate that biochar showed the most favorable estimated carbon balance and the lowest measured net CO2 fluxes under the conditions investigated. However, its effects on soil biological and microbial properties were limited in the short term, and none of the tested treatments achieved net carbon sequestration. These results suggest that biochar may contribute to climate change mitigation as part of long-term, site-specific management strategies rather than as a standalone solution for improving soil multifunctionality.