One of the major concerns for human health in the past decade is the potential dangers posed by increased concentrations of steroidal hormones in soils and water. These hormones are considered to be endocrine disrupting compounds (EDCs), which may harm human health when exposed to high concentrations, or in the case of long term exposure to lower concentrations. In a 3 year study, two steroids, estrone and testosterone, were measured in lettuce plants irrigated with wastewater effluents and freshwater and treated with several types of biosolids. The relative contribution of the different factors, mainly irrigation water and biosolids, to the hormone levels in the lettuce plants was determined. It was found that irrigation water, which contained significant amounts of hormones, had the most substantial effect, whereas biosolids had only minor influence on hormone levels in the lettuce. The hormone levels in the plants were compared to the FDA recommendation for daily consumption in food, and were found to exceed the recommended level (when consumed by a typical individual), and therefore could have negative physiological impacts. Overall this study shows that biosolids have little effect on hormone uptake by lettuce, and it emphasizes the negative impact of irrigation water on these levels, which is of concern to public health.
The physical processes governing advective and diffusive gas movement and distribution in dry soils are, in general, well understood and quantified. In this study, we derived and applied analytical and numerical models to describe these processes under different conditions and scenarios and conducted gas flow experiments in 200‐L barrels packed with dry quartz sand in a temperature‐controlled laboratory. We used either pure N2 (0% O2) or atmospheric air (20.9% O2) injection or gas extraction from (or into) buried point sources (or sinks) to examine the effects of (a) source depth, (b) source discharge rate, and (c) injection cycle period on gas concentration and pressure distribution. We further quantified the contribution of diffusion from the atmospheric soil surface for the different scenarios, made possible by injecting N2 and tracking the complementary O2 concentration [i.e. the difference between atmospheric (20.9%) and the measured soil O2 concentration]. An analytical solution for steady air flow from a point source in a finite, cylindrical domain is presented. The main findings are that air injection, and air extraction, are efficient at aerating the soil volume above the buried gas source or sink. On the other hand, air injection increases the aeration's effectiveness, especially below the source. Shortening the cycle period of gas injection increases gas‐use efficiency (i.e., increases the injected gas concentration) in most of the soil domain. The measurements were in good agreement with the results computed by the models’ analytical and numerical solutions.
Soil aeration (i.e., soil air content and composition) is of major importance in agricultural and environmental practices. Poor aeration reduces plant growth, development, yield, and resistance to diseases and other abiotic stresses (e.g., salinity). In many soils contaminated with hydrocarbons, low O 2 supply limits the rate of contaminant decomposition and prolongs remediation. Soil aeration is governed by diffusion of O 2 from the atmosphere and countercurrent diffusion of CO 2 to the atmosphere. Injection of air (with an atmospheric O 2 concentration of 20.9%) into poorly aerated soils is expected to improve soil aeration by enriching it with O 2 and extracting CO 2. In addition, air flow causes redistribution of soil water. Water redistribution is affected by operational (discharge rate, frequency, duty cycle) and geometrical (depth and distance between sources) air injection parameters, soil parameters (e.g., water retention and conductivity), and irrigation geometry and scheduling. We studied forced oneand three-dimensional air (or N 2) and water injection into packed wet sand and analyzed the effect of air injection on soil aeration and water redistribution in granular media. The study demonstrates the applicability of the Darcy-Buckingham law to air flow at different degrees of water saturation and for a large relevant range of capillary numbers. We also suggest a simple method to measure the soil's conductivity to air (Darcy's constant) for different air contents and use a simple analytical solution to estimate O 2 diffusion from the atmosphere. We discuss the effect of operational air injection parameters on aeration's effectiveness and efficiency. 1 INTRODUCTION Soil aeration refers to the portion of air-filled porosity and/or the composition of the soil air, mainly the concentrations of O 2 and CO 2 (as well as other toxic gases) (Ben-Noah & Friedman, 2018). Soil aeration processes and their ability to satisfy soil respiration demand are of major concern in both agricultural and environmental practices.
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