Mass balance studies

Baker 11, RA Hites (2000) Is combustion the major source of polychlorinated dibenzo-/ - dioxins and diben-zofurans to the environment A mass balance study. Environ Sci Technol 34 2879-2886. 

Geochemical mass balance studies (also known as input-output budgets) invoke a simple conservation-of-mass principle. If the flux of any element leaving a watershed (e.g., via streams), and the flux of that element into the watershed (e.g., via atmospheric precipitation) are known, the difference between the two can be calculated, and this difference must be due to the sum of all reactions and transformations involving that element which took place within the watershed. Pioneering mass balance studies on weathering profiles and/or small watersheds include those of Garrels and Mackenzie (,51, 52) and Cleaves and Bricker and their... 

Many mass balance studies which report weathering rates as a function of unit area of landscape surface do not permit comparison of those rates with laboratory dissolution rates, and cannot, therefore, contribute to the objectives of this paper. Only two published studies have thus far attempted to renormalize such calculated rates to mineral surface area. Discussion of these studies therefore forms the basis for comparisons of laboratory rates with natural weathering rates. 

Rates estimated in the above studies are shown in Table I. Watershed-scale geochemical mass balance studies yield calculated feldspar weathering rates one to three orders of magnitude slower than rates determined in laboratory experiments. 

The permeability of the drug substance can be determined by different approaches such as pharmacokinetic studies in humans (fraction absorbed or mass balance studies) or intestinal permeability studies (in vivo intestinal perfusion studies in humans or suitable animal models or in vitro permeation studies using excised intestinal tissue or epithelial cell culture monolayers like CaCo-2 cell line). In order to avoid misclassification of a drug subject to efflux transporters such as P-glycoprotein, functional expression of such proteins should be investigated. Low- and high-permeability model... 

Braun, J. J., Pagel, M., Herbillon, A. Rosin, C. 1993. Mobilization and redistribution of REEs and thorium in a syenitic lateritic profile A mass balance study. Geochimica et Cosmochimica Acta, 57, 4419-4434. 

Figure 2. Schematic of sampling probe used for mass balance study...

Aastrup et al. (71) found in a Swedish study that about 80% of the Hg deposited in a catchment was retained in the mor (organic surface soil), but noted that an unknown proportion of the retained Hg might be lost to the atmosphere. Similarly, in a mass-balance study of three catchments around Harp Lake in central Ontario, Mierle (63) estimated that 84-92% of Hg deposition was retained. 

Viral detection assays based on infectivity suffer from significant variability, which necessitates the use of statistical evaluation. Polymerase chain reaction-based assays are currently being developed and validated for viral clearance. With PCR assays, there is a potential to distinguish between inactivation and physical removal, perform mass balance studies, evaluate more than one vims at a time for a given process step, reduce the time for completing clearance studies, and accurately quantitate the amount of vims bound to such surfaces as chromatography resins. Table 5 compares the assay precision between an infectivity assay and a quantitative PCR assay. 

Setoyama, T., Drijfhout, W. J., van de Merbel, N. C., Humphries, T. J., and Hasegawa, J. (2006). Mass balance study of [14C] rabeprazole following oral administration in healthy subjects. Int. J. Clin. Pharmacol. Ther. 44 557-565. 

There have been a few large-scale field studies of PCBs in the food webs of the lakes. These include two EPA mass balance studies, the Green Bay Mass Balance Study and the Lake Michigan Mass Balance Study. The field data collected for these studies was used to calibrate the complex contaminant models, which were developed as the primary goal of the studies. The ultimate objective of these mass balance studies was to predict concentrations of PBTs in top predator fish from only knowing the external loadings of the PBTs. Thus the models linked food web models to fate and transport, hydro-logic, and nutrient models. To calibrate the food web models, an extensive collection of all major trophic levels over both space and time was done and analyzed for PCBs and other selected analytes. 

Fig. 14 Lipid-normalized PCB concentrations in the Lake Michigan food web, showing 95th, 90th, 75th, 50th, 25th, 10th, and 5th percentiles (data from the Lake Michigan Mass Balance study)...

McCarty HB, Schofield J, Miller K, Brent RN, Van Hoof P, Eadie B (2004) Results of the Lake Michigan mass balance study polychlorinated biphenyls and trans-nonachlor data report. US EPA... 

US EPA (2005) Lake Michigan Mass Balance Study loadings report... 

The increased input of nutrients and other pollutants to rivers and estuaries may have been exacerbated by the destruction of large areas of fresh and salt water wetlands, often for agriculture (Figs 2 and 3). For example, in the United States, in 1950 there were over 100,000,000 acres (over tOx I0 > hectares) of wetlands being drained (Shaw and Fredine, 1956). The impact of wetlands on water quality is difficult to quantify (Nixon, 1980), but the few annual mass balance studies that are available indicate that these environments serve as sinks (though of widely varying strength) for nutrients (Fig. 4) and a number of... 

Fig. 4. The results of annual mass balance studies for a number of fresh and salt water wetland areas receiving different levels of nutrient input. From Nixon and Lee (in press).

The steady-state volume of distribution is 12 1/kg. Donepezil hydrochloride is approximately 96% bound to human plasma proteins. The distribution of donepezil hydrochloride in various body tissues has not been definitively studied. However, in a mass balance study conducted in healthy male volunteers, 240 h after the administration of a single 5 mg dose of 14C-labeled donepezil hydrochloride, approximately 28% of the label remained unrecovered. This suggests that donepezil and/or its metabolites may persist in the body for more than 10 days. 

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