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Plymouth, MI, United States

Brusseau M.L.,University of Arizona | Matthieu III D.E.,University of Arizona | Carroll K.C.,University of Arizona | Mainhagu J.,University of Arizona | And 4 more authors.
Journal of Contaminant Hydrology | Year: 2013

The objective of this study was to characterize the temporal behavior of contaminant mass discharge, and the relationship between reductions in contaminant mass discharge and reductions in contaminant mass, for a very heterogeneous, highly contaminated source-zone field site. Trichloroethene is the primary contaminant of concern, and several lines of evidence indicate the presence of organic liquid in the subsurface. The site is undergoing groundwater extraction for source control, and contaminant mass discharge has been monitored since system startup. The results show a significant reduction in contaminant mass discharge with time, decreasing from approximately 1 to 0.15 kg/d over five years. Two methods were used to estimate the mass of contaminant present in the source area at the initiation of the remediation project. One was based on a comparison of two sets of core data, collected 3.5 years apart, which suggests that a significant (~ 80%) reduction in aggregate sediment-phase TCE concentrations occurred between sampling events. The second method was based on fitting the temporal contaminant mass discharge data with a simple exponential source-depletion function. Relatively similar estimates, 784 and 993 kg, respectively, were obtained with the two methods. These data were used to characterize the relationship between reductions in contaminant mass discharge (CMDR) and reductions in contaminant mass (MR). The observed curvilinear relationship exhibits a reduction in contaminant mass discharge essentially immediately upon the initiation of mass reduction. This behavior is consistent with a system wherein significant quantities of mass are present in hydraulically poorly accessible domains for which mass removal is influenced by rate-limited mass transfer. The results obtained from the present study are compared to those obtained from other field studies to evaluate the impact of system properties and conditions on mass-discharge and mass-removal behavior. The results indicate that factors such as domain scale, hydraulic-gradient status (induced or natural), and flushing-solution composition had insignificant impact on the CMDR-MR profiles and thus on underlying mass-removal behavior. Conversely, source-zone age, through its impact on contaminant distribution and accessibility, was implicated as a critical factor influencing the nature of the CMDR-MR relationship. © 2013 Elsevier B.V. Source


Tate P.T.,Conestoga Rovers and Associates | Shin W.S.,Kyungpook National University | Pardue J.H.,Louisiana State University | Jackson W.A.,Texas Tech University
Water, Air, and Soil Pollution | Year: 2012

The massive oil release from the Deep Water Horizon disaster has reemphasized the need to remediate oil impacted marshes. Due to the physically fragile nature of salt water marshes, bioremediation is often proposed as an appropriate technology and nutrient amendment is often proposed as a means of accelerating biodegradation of crude oil. However, no information is currently available concerning the efficacy of in situ nutrient amendments in Gulf Coast salt marshes. An experimental crude oil spill (142 l over 100 m2) was conducted to evaluate the efficacy of nitrogen amendment to stimulate bioremediation in a Spartina alterniflora dominated Louisiana salt marsh. A randomized complete block design with replication (n=10) was utilized to test the hypothesis that additions of fast-release ammonium nitrate (60 g N/m 2) and slow-release urea (30 gN/m 2) fertilizers could enhance biodegradation of selected crude oil components in the marsh. Crude oil degradation was monitored by analyzing sediment samples for branched and unbranched alkanes over the 180-day study period. The compound/hopane ratio was used to correct for nonbiological losses. No consistent statistically significant effect of fertilizer addition on degradation rates was observed, despite success in increasing the porewater ammonium and NaCl-extractable ammonium over the time frame of the trial. Intrinsic pseudo-first order degradation rates of alkanes in all plots were substantial (0.003-0.008 day -1). Existing, background levels of N did not appear to limit biodegradation rates in Spartinadominated salt marshes. These results suggest that nutrient amendments will not be successful in stimulation biodegradation of crude oil in these systems. © Springer Science+Business Media B.V. 2011. Source


Marino D.J.,Conestoga Rovers and Associates
Journal of Toxicology and Environmental Health - Part A: Current Issues | Year: 2012

Since the early 1970s, the National Cancer Institute (NCI) and National Toxicology Program (NTP) have conducted carcinogenesis and toxicology studies on several hundred chemicals using the B6C3F1 mouse. A number of publications have examined growth, survival, and tumor incidence over time, including the impact of changes in housing and diet. However, no reports have been published to date examining the variation in organ weights over time, especially in light of reported body weight effects associated with housing and diet changes. Therefore, all available absolute and relative organ weight data for untreated control B6C3F1 mice were collected from 2-wk, 3-mo, and 15-mo NCI/NTP investigations with report dates through August 2010 in order to examine organ weight changes over time and by study type. Study data were grouped into 5-yr intervals by initiation date. Body weights in males increased over time except in 2-wk studies, while body weights in females rose through 1993 and remained constant or declined thereafter. Higher body weights were noted in individually housed mice, and in drinking water studies compared to feed or inhalation studies. Elevated organ weights were typically associated with increased body weights except that lower organ weights were evident as early as 2-wk on study with the introduction of the NTP-2000 diet in 1994. Relative organ weights decreased over time in males and females. Finally, organ weight coefficients of variation (standard deviation/mean) declined over time in 2-wk, 3-mo, and 15-mo studies, which may reflect improved data collection methods or reduced interlaboratory variability. © 2012 Copyright Taylor and Francis Group, LLC. Source


Marino D.J.,Conestoga Rovers and Associates
Journal of Toxicology and Environmental Health - Part A: Current Issues | Year: 2012

The B6C3F1 mouse is the standard mouse strain used in toxicology studies conducted by the National Cancer Institute (NCI) and the National Toxicology Program (NTP). While numerous reports have been published on growth, survival, and tumor incidence, no overall compilation of organ weight data is available. Importantly, organ weight change is an endpoint used by regulatory agencies to develop toxicity reference values (TRVs) for use in human health risk assessments. Furthermore, physiologically based pharmacokinetic (PBPK) models, which utilize relative organ weights, are increasingly being used to develop TRVs. Therefore, all available absolute and relative organ weight data for untreated control B6C3F1 mice were collected from NCI/NTP studies in order to develop age-specific distributions. Results show that organ weights were collected more frequently in NCI/NTP studies at 2-wk (60 studies), 3-mo (147 studies), and 15-mo (40 studies) intervals than at other intervals, and more frequently from feeding and inhalation than drinking water studies. Liver, right kidney, lung, heart, thymus, and brain weights were most frequently collected. From the collected data, the mean and standard deviation for absolute and relative organ weights were calculated. Results show age-related increases in absolute liver, right kidney, lung, and heart weights and relatively stable brain and right testis weights. The results suggest a general variability trend in absolute organ weights of brain < right testis < right kidney < heart < liver < lung < spleen < thymus. This report describes the results of this effort. © 2012 Copyright Taylor and Francis Group, LLC. Source


Marino D.J.,Conestoga Rovers and Associates
Journal of Toxicology and Environmental Health - Part A: Current Issues | Year: 2012

The Fischer 344 (F344) rat has been the standard rat strain used in toxicology studies conducted by the National Cancer Institute (NCI) and the National Toxicology Program (NTP). However, the numerous reports published to date on growth, survival, and tumor incidence have not included an overall compilation of organ weight data. Notably, dose-related organ weight effects are endpoints used by regulatory agencies to develop toxicity reference values (TRVs) for use in human health risk assessments. In addition, physiologically-based pharmacokinetic (PBPK) models, which utilize relative organ weights, are increasingly being used to develop TRVs. Because a compilation of organ weights for F344 rats could prove beneficial for TRV development and PBPK modeling, all available absolute and relative organ weight data for untreated control F344 rats were collected from NCI/NTP feed, drinking-water, and inhalation studies in order to develop age-specific distributions. Results showed that organ weights were collected more frequently at 2-wk (59 studies), 3-mo (148 studies), and 15-mo (38 studies) intervals than at other intervals and more frequently from feeding and inhalation than from drinking-water studies. Liver, right kidney, lung, heart, thymus, and brain weights were most frequently collected. From the collected data, the mean and standard deviation for absolute and relative organ weights were calculated. Findings showed age-related increases in absolute weights and decreases in relative weights for brain, liver, right kidney, lung, heart, thyroid, and right testis. The results suggest a general variability trend in absolute organ weights of brain < right testis < heart < right kidney < liver < lung < thymus < thyroid. © 2012 Copyright Taylor and Francis Group, LLC. Source

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