Synergistic Effects of Organic Contaminants and Soil Organic Matter on the Soil-Water Partitioning and Effectiveness of a Nonionic Surfactant (Triton X-100)

Napthalene- and decane-contaminated soils were treated with Triton X-100 (a nonionic surfactant) to characterize the soil-water partitioning behavior of the surfactant in soils with different organic content. Soil samples with different organic content were prepared by mixing sand-mulch mixtures at different proportions. The experimental results indicated that the amount of surfactant sorbed onto soil increased with increasing soil organic content and increasing surfactant concentration. The effective critical micelle concentration (CMC) also increased with increasing organic content in soil. The CMC of Triton X-100 in aqueous systems without soil was about 0.3 mM and the effective CMC values measured for soil-water-surfactant systems (approximately 1:19 soil/water ratio) with 25%, 50%, and 75% mulch content were 0.9, 1.0, and 1.7 mM, respectively. Sub-CMC surfactant sorption was modeled accurately with both the Freundlich and the linear isotherm. The maximum surfactant sorption onto soil varied from 66% to 82% of added surfactant in the absence of contaminant. The effective CMC values for Triton X-100 increased to some extent in the presence of contaminants, as did the maximum surfactant sorption. The maximum surfactant sorbed onto the soil with 75% mulch content increased from 82% for clean soils, to 95% and 96% for soils samples contaminated with naphthalene and decane, respectively.     

Bioaccumulation of Inorganic Chemicals from Soil by Plants: Spiked Soils vs. Field Contamination or Background

Risk assessors are often cautioned against the use of tests of highly bioavailable salt solutions added to soil to estimate the bioaccumulation of chemicals from waste site soils by plants. In this investigation, a large number of laboratory and field studies that measured the bioaccumulation of inorganic chemicals in plants were reviewed. The objective was to discern whether or not the relationship between the concentration of the element in aboveground vegetation and that in soil was different if the contamination was aged in the field rather than freshly added to soil in salt solution. For two of the eight elements, selenium and cadmium, salt solution experiments were associated with greater soil-plant uptake ratios than field measurements. Thus, these are not reliable data for use in the derivation of plant uptake regressions for screening-level ecological risk assessments at field sites. In contrast, the plant uptake of arsenic, copper, lead, mercury, nickel, and zinc, when added in salt solutions, was generally within the 95% prediction limit of regressions derived from field data. Chemical form, plant taxon, soil type, experimental methodology, and aging may be as important as the source of the chemical in predicting plant uptake of inorganic chemicals from soil.     

Impacts of ISCO Persulfate,Peroxide and Permanganate Oxidants on Soils: Soil Oxidant Demand and Soil Properties

The consumption of in-situ chemical oxidation (ISCO) oxidant by soil oxidizable matter (OM), termed the soil oxidant demand (SOD), is an essential factor when designing treatments for successful remediation at an ISCO site. This study aims to assess the impact of different oxidants on SOD and the soil itself, using the Taguchi experimental design. Five oxidation systems, including persulfate (PS), hydrogen peroxide (HP), permanganate (PM), Fe²⁺ activated PS and Fe²⁺ activated HP, and four factors including oxidant concentration, activator concentration, reaction time, and pH were investigated. The results of the Taguchi analysis in this study show that oxidant concentration had the greatest effect on the SOD. Other factors also affected the SOD and the optimum conditions for achieving a lower SOD were determined using the Taguchi design method. Additionally, original and oxidized soils were analyzed using a scanning electron microscope equipped with an X-ray energy dispersive spectrometer to determine the surface morphology and chemical composition of the samples. Variations in soil organic carbon levels and total soil bacterial counts were recorded and the speciation of soil minerals (Fe, Mn, Cu, and Zn) was analyzed.     

Characteristics of Copper Sorption by Various Agricultural Soils in China and the Effect of Exogenic Dissolved Organic Matter on the Sorption

To explore the effect of exogenic dissolved organic matter (DOM) on Cu(II) sorption in agricultural soils, 26 agricultural soils were collected across China. Exogenic dissolved organic matter, extracting from wheat straw (DOM_W) and swine manure (DOM_S), respectively, were added to the soils to conduct a series of batch sorption and characterization experiments. The solid-liquid partition coefficient (K_d) ranged from 0.02 to 76.46 L g^?1, suggesting different Cu(II) sorption on various soils. PCA analysis indicated that pH, free Fe/Al oxides, carbon, and total Cu content had a significant positive relationship with the Cu(II) sorption, respectively. And the contribution rate of pH was the highest (38.15%). Moreover, DOM markedly inhibited the Cu(II) sorption in alkaline soils while promoted the Cu(II) sorption in acidic soils, which were interacted by the soil properties and DOM characteristics. The effect of DOM_S on Cu(II) sorption were more obvious than DOM_W, which were further confirmed by Fourier transform infrared (FTIR) spectroscopy. FTIR also showed Cu(II) was primarily adsorbed on the specific functional groups, such as CO, OH, and CO, providing direct evidences for the binding of Cu(II) with DOM. This study can guide the rational use of organic fertilizers, and also provide baseline knowledge for the prevention and control of soil pollution.     

Influence of Temperature and Oil Content on the Soil/Air Partition Coefficient for Hexachlorobenzene in Oil-Contaminated Rice Paddy Field Soil

The soil/air partition coefficients (K _SA ) for hexachlorobenzene (HCB) in oil-contaminated (crude oil and diesel) rice paddy field soils were measured in a solid fugacity meter at different oil concentrations over the temperature range of 5 to 30°C at 100% relative humidity. The results showed that values of K _SA increased with a decrease of temperature. As for oil content, there is a critical separate phase concentration (CSPC) above which K _SA increased with increasing of oil content. When oil content is above CSPC, oil plays a role as a separate phase that enhances the sorption capacity of the soil. At a given temperature (20°C) values of CSPC depended on the natural organic matter (NOM) contents of the soil, while for a given oil concentration they depended on the temperature. The normalized oil/air partition coefficients ) for HCB deduced from K _SA for oils and experimentally determined with crude oil/quartz sand system were similar and 0.7–7 times higher than the normalized organic/air partition coefficient ), which implied that oil was a super sorbent. The enthalpies (ΔH_SA) for crude oil and diesel were 64.9 and 55.7 kJ mol^?1, respectively.     

The Nature and Longevity of Agricultural Impacts on Soil Carbon and Nutrients: A Review

Since the domestication of plant and animal species around 10,000 years ago, cultivation and animal husbandry have been major components of global change. Agricultural activities such as tillage, fertilization, and biomass alteration lead to fundamental changes in the pools and fluxes of carbon (C), nitrogen (N), and phosphorus (P) that originally existed in native ecosystems. Land is often taken out of agricultural production for economic, social, or biological reasons, and the ability to predict the biogeochemical trajectory of this land is important to our understanding of ecosystem development and our projections of food security for the future. Tillage generally decreases soil organic matter (SOM) due to erosion and disruption of the physical, biochemical, and chemical mechanisms of SOM stabilization, but SOM can generally reaccumulate after the cessation of cultivation. The use of organic amendments causes increases in SOM on agricultural fields that can last for centuries to millennia after the termination of applications, although the locations that provide the organic amendments are concurrently depleted. The legacy of agriculture is therefore highly variable on decadal to millennial time scales and depends on the specific management practices that are followed during the agricultural period. State factors such as climate and parent material (particularly clay content and mineralogy) modify ecosystem processes such that they may be useful predictors of rates of postagricultural biogeochemical change. In addition to accurate biogeochemical budgets of postagricultural systems, ecosystem models that more explicitly incorporate mechanisms of SOM loss and formation with agricultural practices will be helpful. Developing this predictive capacity will aid in ecological restoration efforts and improve the management of modern agroecosystems as demands on agriculture become more pressing.     

The Influence of Soil Properties on the Mobility of Metals Following a Single Application of Polluted Sewage Sludge to Seventy Agricultural Topsoils: A Laboratory Column Study

The main aim of this study was to examine the influence of soil properties on the leaching of Cd, Cr, Cu, Ni, Pb, and Zn following the application of polluted sewage sludge to contrasting topsoils. Seventy agricultural soil samples from different parts of Spain were amended with a single dose of sewage sludge (equivalent to 50 t dry weight ha^?1) and a column study was performed under controlled conditions. After two, four, and six months of incubation, 283 ml of distilled water (equivalent to a rainfall event of 25 l m^?2) was applied. The leachates were then collected and analyzed for metals. For all of the soils considered, the pH was the most important parameter for the control of mobility metals (except for Cu, determined by the sand and soil organic carbon and only to a lesser extent by the soil pH r² = 0.604, p < 0.001) and was negatively related to all of the studied metals. For Pb and Zn, soil pH was the single soil property explaining their mobility (r² = 0.411, p < 0.001 for Pb; r² = 0.713, p < 0.001 for Zn) while for Cd, Cr and Ni, EC, sand and silt also appeared in the statistical models (r² = 0.753, p < 0.001 for Cd; r² = 0.366, p < 0.001 for Cr; r² = 0.784, p < 0.001 for Ni). In the basic soils, soil texture was the most important soil property controlling the mobility of metals (except for that of Pb, which it only weakly predicted). For the acidic-neutral soils, the soil pH was the most important soil property controlling metal mobility (except for that of Cr, which was mainly determined by the pseudo-total Cr content).     

Arctic Soil Respiration: Effects of Climate and Vegetation Depend on Season

Arctic ecosystems are important in the context of global climate change because the most rapid rises in air temperature are expected at high northern latitudes during winter. The presence of extensive soil carbon reserves in the Arctic suggests that substantial feedbacks to CO₂-induced climate change could occur if warming alters carbon cycling belowground. Characterization of the controls on regional patterns of belowground CO₂ release through the annual cycle is an important step towards evaluating potential feedbacks from arctic ecosystems to climate change. In this study, we assess seasonal control over the influences by climate and vegetation-type on CO₂ efflux from belowground in the Alaskan tundra. Our results indicate that climate had strong effects on belowground CO₂ release in both seasons. By contrast, vegetation-type had little impact on CO₂ efflux from belowground in winter but was the principal control in summer. Together, these results demonstrate that seasonality is a critical factor regulating climate and vegetation-type effects on belowground CO₂ release, which should be included in regional models of net carbon balance in arctic ecosystems. Received 8 December 1998; accepted 2 April 1999.