Simulation of metals transport and toxicity at a mine-impacted watershed: California Gulch, Colorado

The transport and toxicity of metals at the California Gulch, Colorado mine-impacted watershed were simulated with a spatially distributed watershed model. Using a database of observations for the period 1984-2004, hydrology, sediment transport, and metals transport were simulated for a June 2003 calibration event and a September 2003 validation event. Simulated flow volumes were within approximately 10% of observed conditions. Observed ranges of total suspended solids, cadmium, copper, and zinc concentrations were also successfully simulated. The model was then used to simulate the potential impacts of a 1-in-100-year rainfall event. Driven by large flows and corresponding soil and sediment erosion for the 1-in-100-year event, estimated solids and metals export from the watershed is 10,000 metric tons for solids, 215 kg for Cu, 520 kg for Cu, and 15,300 kg for Zn. As expressed by the cumulative criterion unit (CCU) index, metals concentrations far exceed toxic effects thresholds, suggesting a high probability of toxic effects downstream of the gulch. More detailed Zn source analyses suggest that much of the Zn exported from the gulch originates from slag piles adjacent to the lower gulch floodplain and an old mining site located near the head of the lower gulch.     

Methane bioattenuation and implications for explosion risk reduction along the groundwater to soil surface pathway above a plume of dissolved ethanol

Fuel ethanol releases can stimulate methanogenesis in impacted aquifers, which could pose an explosion risk if methane migrates into enclosed spaces where ignitable conditions exist. To assess this potential risk, a flux chamber was emplaced on a pilot-scale aquifer exposed to continuous release (21 months) of an ethanol solution (10% v:v) that was introduced 22.5 cm below the water table. Despite methane concentrations within the ethanol plume reaching saturated levels (20-23 mg/L), the maximum methane concentration reaching the chamber (21 ppm(v)) was far below the lower explosion limit in air (50,000 ppm(v)). The low concentrations of methane observed in the chamber are attributed to methanotrophic activity, which was highest in the capillary fringe. This was indicated by methane degradation assays in microcosms prepared with soil samples from different depths, as well as by PCR measurements of pmoA, which is a widely used functional gene biomarker for methanotrophs. Simulations with the analytical vapor intrusion model "Biovapor" corroborated the low explosion risk associated with ethanol fuel releases under more generic conditions. Model simulations also indicated that depending on site-specific conditions, methane oxidation in the unsaturated zone could deplete the available oxygen and hinder aerobic benzene biodegradation, thus increasing benzene vapor intrusion potential. Overall, this study shows the importance of methanotrophic activity near the water table to attenuate methane generated from dissolved ethanol plumes and reduce its potential to migrate and accumulate at the surface.     

Modeling the impact of a benzene source zone on the transport behavior of PAHs in groundwater

Aquifers at industrial sites are commonly characterized by a multitude of contaminant source zones. Conceivably, dissolved contaminants originating from an up-gradient residual nonaqueous phase liquid (NAPL) source zone may be transported along the groundwater flow path into another residual NAPL source zone down-gradient. However, if and how contaminants from different zones may affect one another with regard to dissolution and transport has thus far been unknown. To identify and understand such potential interactions, the numerical model BIONAPL3D was applied to simulate the behavior of six dissolved polycyclic aromatic hydrocarbons (PAHs), stemming simultaneously from an up-gradient NAPL source zone, when they encounter a down-gradient NAPL source zone. The down-gradient NAPL source zone was assumed to be a residual benzene phase with a saturation of 10%. When the dissolved PAHs entered the benzene source zone, the aqueous PAH concentrations declined significantly due to their partitioning into the residual benzene phase. As benzene rapidly dissolved intothe aqueous phase,the PAHswere resolubilized with negligible impact due to benzene co-solvency. The degree of resolubilization was much smaller than the initial loss due to partitioning into the benzene phase. Thus, the PAHs formed a new residual NAPL phase that, over time, replaced the original benzene source zone. The new NAPL phase continued to grow even after all of the benzene was dissolved. Our modeling approach is the first theoretical demonstration of a significant interaction of contaminants emanating from multiple source zones. It should be regarded as a starting point to consider source zone interactions at polluted field sites.     

Characterizing dependence of pesticide load in surface water on precipitation and pesticide use for the Sacramento River watershed

Transport of pesticides by surface runoff during rainfall events is a major process contributing to pesticide contamination in rivers. This study presents an empirical regression model that relates pesticide loading over time in the Sacramento River with the precipitation and pesticide use in the Sacramento River watershed. The model closely simulated loading dynamics of diazinon, simazine, and diuron during 1991-1994 and 1997-2000 winter storm seasons. The coefficients of determination for regression ranged from 0.168 to 0.907, all were significant at <0.001. The results of this study provide strong evidence that precipitation and pesticide use are the two major environmental variables dictating the dynamics of pesticide transport into surface water in a watershed. The capability of the statistical model to provide time-series estimates on pesticide loading in rivers is unique and may be useful fortotal maximum daily load (TMDL) assessments.     

Effect of free stall surface on daily activity patterns in dairy cows with relevance to lameness prevalence

Differences in behavior of nonlame cows, slightly lame cows, and moderately lame cows in 6 free stall barns with sand bedding (SAND) vs. 6 free stall barns with rubber-crumb geotextile mattress surfaces (MAT) were documented in Wisconsin dairy herds. All lactating cows in the 12 herds were observed and given a locomotion score based on a 4-point scale: 1 = nonlame, 2 = slightly lame, 3 = moderately lame, and 4 = severely lame. Herd least square means +/-SE for prevalence of clinical lameness (locomotion scores = 3 and 4) were 11.1 vs. 24.0 +/- 1.7% for herds using SAND vs. MAT surfaces, respectively. Subsets of 10 cows per herd with locomotion scores of 1 to 3 were observed via video cameras for 24-h periods. Cows in MAT herds spent more time standing in free stalls per day than cows in SAND herds. Differences in standing times were 0.73 h/d for cows that were not lame, 2.32 h/d for cows that were slightly lame, and 4.31 h/d for cows that were moderately lame in MAT herds compared with equivalent cows in SAND herds. In MAT herds, the increase in time spent standing in the stall in moderately lame cows was associated with a significant reduction in stall use sessions per day, which impacted daily lying time. Although cause and effect are not clear, these findings have implications for housing, comfort, and care of cows in dairy herds with different types of free stall surfaces.     

高剪切混合罐内物料流场的可视化与结构改进

为研究新型高剪切混合罐内的物料流场分布,应用计算流体力学商业软件对混合罐内物料流场进行数值模拟.分析了高剪切混合罐内的物料混合机理,采用标准模型与滑移网格法对新型高剪切混合罐内的物料流场进行可视化研究.初步得出高剪切混合罐内物料的流动情况,湍流静能与能量耗散率的分布,流量与转速的关系.     

Effects of daily exogenous oxytocin on lactation milk yield and composition

Eighty-four Holstein cows were used to determine effects of exogenous oxytocin on 305-d milk production and health. Cows were assigned at parturition by parity group to treatments: 1) oxytocin group, animals received an injection of 1 ml (20 IU) of oxytocin at each milking throughout lactation and 2) control group, animals received no injection. Oxytocin injections were given in the thigh region within 3 min following the initiation of udder preparation and immediately prior to machine attachment. Udder preparation consisted of forestripping and manual cleaning (10 to 20 s) and drying (5 to 10 s) of teats. Cows were milked in a parlor, and milk yield was recorded at each milking. Milk samples were collected from each cow biweekly for milk fat, protein, and somatic cell count determination. Individual lactations were modeled using Woods' lactation equation; resulting coefficients were analyzed using ANOVA. The oxytocin group produced 849 kg more milk during the lactation than the control group, with a significant difference occurring after peak milk yield. This suggests that exogenous oxytocin maintained greater persistency during lactation. No significant differences existed for milk fat or protein percentages. The use of exogenous oxytocin at milking increased lactation milk production with no apparent effect on health.     

Determination of ammonium turnover and flow patterns close to roots using imaging optodes

The physical effect of nitrogen upon plants has been studied thoroughly; however, direct studies of nitrogen turnover close to roots have been limited by analytical techniques with low spatial and temporal resolution. Thus, little is known about differences in turnover taking place along and between intact root structures over time as well as how root arrangement, root cell type, plant age, microbial activity, and the dark/light cycle influence uptake and supply of nutrients to root structures. In this study an imaging (planar) optode was used to quantify ammonium over time close to an intact root system of a large fruit bearing tomato plant (Lycopersicon esculentum). Images throughout the experiment made it possible to define the ammonium depletion zone and active turnover potential as well as determine turnover rate and flow patterns around the root system over time. The results indicated that ammonium uptake for tomato plants proceeds over the entire root structure but transverse thin peripheral roots are about twice as efficient as the main root and that the uptake process might influence nutrient availability. The flow patterns close to the root structure revealed that apical regions seem to have a central role in ammonium acquisition.     

Effects of humic substances on precipitation and aggregation of zinc sulfide nanoparticles

Nanoparticulate metal sulfides such as ZnS can influence the transport and bioavailability of pollutant metals in anaerobic environments. The aim of this work was to investigate how the composition of dissolved natural organic matter (NOM) influences the stability of zinc sulfide nanoparticles as they nucleate and aggregate in water with dissolved NOM. We compared NOM fractions that were isolated from several surface waters and represented a range of characteristics including molecular weight, type of carbon, and ligand density. Dynamic light scattering was employed to monitor the growth and aggregation of Zn-S-NOM nanoparticles in supersaturated solutions containing dissolved aquatic humic substances. The NOM was observed to reduce particle growth rates, depending on solution variables such as type and concentration of NOM, monovalent electrolyte concentration, and pH. The rates of growth increased with increasing ionic strength, indicating that observed growth rates primarily represented aggregation of charged Zn-S-NOM particles. Furthermore, the observed rates decreased with increasing molecular weight and aromatic content of the NOM fractions, while carboxylate and reduced sulfur content had little effect. Differences between NOM were likely due to properties that increased electrosteric hindrances for aggregation. Overall, results of this study suggest that the composition and source of NOM are key factors that contribute to the stabilization and persistence of zinc sulfide nanoparticles in the aquatic environment.     

Effects on groundwater microbial communities of an engineered 30-day in situ exposure to the antibiotic sulfamethoxazole

Effects upon microbial communities from environmental exposure to concentrations of antibiotics in the μg L(-1) range remain poorly understood. Microbial communities from an oligotrophic aquifer (estimated doubling rates of only once per week) that were previously acclimated (AC) or unacclimated (UAC) to historical sulfamethoxazole (SMX) contamination, and a laboratory-grown Pseudomonas stutzeri strain, were exposed to 240-520 μg L(-1) SMX for 30 days in situ using filter chambers allowing exposure to ambient groundwater, but not to ambient microorganisms. SMX-exposed UAC bacterial communities displayed the greatest mortality and impairment (viable stain assays), the greatest change in sensitivity to SMX (dose-response assays), and the greatest change in community composition (Terminal Restriction Fragment Length Polymorphism; T-RFLP). The sul1 gene, encoding resistance to SMX at clinically relevant levels, and an element of Class I integrons, was not detected in any community. Changes in microbial community structure and SMX resistance over a short experimental period in previously nonexposed, slow-growing aquifer communities suggest concentrations of antibiotics 2-3 orders of magnitude less than those used in clinical applications may influence ecological function through changes in community composition, and could promote antibiotic resistance through selection of naturally resistant bacteria.     

Effects of non-fermented tea extracts on in vitro digestive hydrolysis of lipids and on cholesterol precipitation

Extracts of non-fermented teas precipitated cholesterol and decreased dialysability of lipids in an in vitro model that simulated digestion in humans. The efficiency of tea extracts was affected by catechins and mainly by EGCG, ECG, GCG and CG. Total amounts and concentrations of individual catechins in extracts depended strongly on the tea brands. There were significant relationships between amounts of dialysable products of triglyceride hydrolysis, amounts of precipitated cholesterol, and concentrations of individual catechin gallates in tea brews. Dialysability of lipids was effectively reduced by tea extracts high in GCG and CG. Dialysability of lipids was strongly correlated with the sum of GCG and CG (R ² = 84.64%) whereas precipitation of cholesterol was highly correlated with total amounts of catechin gallates in the tea extracts (R ² = 89.59%).     

Effects of feed withdrawal and transport on cecal environment and Campylobacter concentrations in a swine surgical model

The objective of the present study was to evaluate how feed withdrawal and transportation influenced the cecal environment and cecal populations of Campylobacter in swine. Four miniature Yucatan gilts (8.8 kg), naturally infected with Campylobacter jejuni, were surgically implanted with cecal cannulas. The gilts were fasted for 48 h. Samples of cecal contents were collected for 7 days prior to and for 7 days after the fast, and mean values were determined for pH, volatile fatty acids (VFA), and CFU enumeration of C. jejuni. This was replicated three times. In another trial, gilts (full-fed) were transported in a livestock trailer for 4 h and cecal samples were collected before and after transport and analyzed for pH, VFA, and CFU. Following a 48-h fast, cecal pH increased (P < 0.05) by 1 unit; acetic and propionic acids decreased (P < 0.05) by 61% and 71%, respectively; and there was a twofold log10 increase (P < 0.05) in CFU/g cecal content of C. jejuni. Values of pH, VFA, and CFU of C. jejuni did not change in cecal samples from gilts following transportation. These data are important for food safety considerations because feed withdrawal, commonly associated with shipping and slaughter, can increase Campylobacter concentrations in the pig intestinal tract.     

Effects of two transport systems on lamb welfare and meat quality

The aim of this study was to analyse the effect of a direct transport system (DTS) versus transport with a logistic stopover system (TLS) on lamb welfare and meat quality at two seasons. A total of 96 lambs were sampled in a 2 × 2 × 2 factorial design, testing two transport systems and two seasons (summer and winter), with two replicates in each season. Significant interactions (P ≤ 0.05) between transport system and season in both welfare and meat quality were found. In general, lambs subjected to direct transport and logistic stopover during winter had a more intense stress response and poorer meat quality than lambs transported during summer. However, direct transport during the cold season seemed to be the most stressful, compared to the rest of the groups, which was reflected in significantly higher levels of cortisol, lactate, glucose, ratio of N/L, higher pH24 and darker and tougher meat.     

Effects of two transport systems on lamb welfare and meat quality

The aim of this study was to analyse the effect of a direct transport system (DTS) versus transport with a logistic stopover system (TLS) on lamb welfare and meat quality at two seasons. A total of 96 lambs were sampled in a 2×2×2 factorial design, testing two transport systems and two seasons (summer and winter), with two replicates in each season. Significant interactions (P≤0.05) between transport system and season in both welfare and meat quality were found. In general, lambs subjected to direct transport and logistic stopover during winter had a more intense stress response and poorer meat quality than lambs transported during summer. However, direct transport during the cold season seemed to be the most stressful, compared to the rest of the groups, which was reflected in significantly higher levels of cortisol, lactate, glucose, ratio of N/L, higher pH24 and darker and tougher meat.     

Effects of solvent and alkaline earth metals on the heat-induced precipitation process of sodium caseinate

The precipitation temperatures of sodium caseinate in H₂O and D₂O in the presence of Mg²⁺, Ca²⁺, Sr²⁺ and Ba²⁺ were investigated through fluorescence, turbidity and conductivity experiments.     

Adsorption of transgenic insecticidal Cry1Ab protein to silica particles. Effects on transport and bioactivity

Bt crops are genetically modified to be resistant against insect pests by expressing insecticidal Cry proteins. The processes governing the fate and bioavailability of the expressed transgenic Cry proteins in soils are poorly understood. We studied adsorption of Cry1Ab to negatively charged silica (SiO(2)) particles, a major soil constituent and a model for negatively charged mineral surfaces, at pH 5 to 10 and ionic strengths I = 10 mM to 250 mM, both in solution depletion and saturated column transport experiments. Cry1Ab-SiO(2) interactions were dominated by patch-controlled electrostatic attraction (PCEA), as evident from increasing Cry1Ab attraction to SiO(2) with decreasing I at pH at which both Cry1Ab and SiO(2) were net negatively charged. Experimental and modeling evidence is provided that the surface heterogeneity of SiO(2) particles modulated PCEA, leading to a fraction of adsorption sites with slow Cry1Ab desorption kinetics. Desorption rates from these sites increased upon increasing the solution pH. In toxicity bioassays, we demonstrated that Cry1Ab retained insecticidal activity when adsorbed to SiO(2), suggesting high protein conformational stability during adsorption-desorption cycles. Models predicting Cry1A protein adsorption in soils therefore need to account for combined effects of the nonuniform protein surface charge distribution and of sorbent surface heterogeneity.