Environmental transport

The CESARS database contains comprehensive environmental and health information on chemicals. It provides detailed descriptions of chemical toxicity to humans, mammals, aquatic and plant life, as well as data on physical chemical properties, and environmental fate and persistence. Each record consists of chemical identification information and provides descriptive data on up to 23 topic areas, ranging from chemical properties to toxicity to environmental transport and fate. Records are in English. Available online through CCINFOline from the Canadian Centre For Occupational Health and Safety (CCOHS) and Chemical Information System (CIS) on CD-ROM through CCIN-FOdisc. 

These various broad research observations generated questions about the influence of chemical environments in aquatic systems upon plutonium and what chemical species might be present. The oxidation states of plutonium, its associations with DOC, and its complexation by inorganic ions all seemed interrelated and important to the understanding of environmental transport. 

Silver Environmental Transport, Eate, Effects, and Models ... 

Ryan PA (1985) Multimedia modelling of environmental transport. MS Thesis, University of Califomiain Los Angeles... 

Swackhamer, D.L. and L.L. McConnell. 1993. Workgroup report on environmental transport and fate. Chemosphere 27 1835-1840. 

No studies on the environmental transport and partitioning of endrin aldehyde could be found in the available literature. Values of the estimated log Kow for endrin aldehyde vary widely, ranging from 3.1 to 5.6 (see Table 3-2). Based on the lowest estimated log Kow, the Koc value for endrin aldehyde can be estimated to be approximately 1,000 (Lyman 1990), indicating a low mobility in soil (Swann et al. 1983). Using the higher estimated values of log Kow (4.7-5.6), the K00 value for endrin aldehyde can be estimated to range from 8,500 to 380,000 (Lyman 1990), indicating that this compound will be virtually immobile in most soils (Swann et al. 1983). Because of its low vapor pressure of... 

Similarly, little information could be found in the available literature on the environmental transport and partitioning of thiocyanate in the environment. At near ambient temperatures ( 30 °C), it appears that sorption and volatilization are not significant partitioning processes for thiocyanate in soil, with thiocyanate losses due primarily to microbial degradation (see Section 5.3.2.3) (Brown and Morra 1993). 

Jaber HM, Mabey WR, Liu AT, et al. 1984. Data acquisition for environmental transport and fate screening for compounds of interest to the Office of Emergency and Remedial Response. Washington, D.C. US Environmental Protection Agency. EPA-600/6-84-011. NTIS no. PB84-245281, 147. 

Ashton D, Hilton M, Thomas KV (2004) Investigating the environmental transport of human pharmaceuticals to streams in the United Kingdom. Sci Total Environ 333 167-184... 

In this section, two types of data are briefly summarized 1) environmental transport and persistence, and (2) monitoring. The discussion Is chemical specific. Some Interesting concepts relevant to some of the chemical characteristics are developed later In the Discussion section. Results from this section are also used In the Conclusion section to derive some generalizations about pesticides leaching to ground water. 

The key results of the environmental transport and persistence analyses for these 12 pesticides are summarized In Table IV. The processes Included In soil dissipation half-lives could be biodegradation, hydrolysis, oxidation, reduction, soil photolysis, and volatilization. Note that biodegradation may be other than first-order, whereas the other processes are usually first order or pseudo-first-order. 

EHC monographs examine the physical and chemical properties and analytical methods sources of environmental and industrial exposure and environmental transport kinetics and meta-bohsm including absorption, distribution, transformation, and elimination short- and long-term effects on animals, carcinogenicity, mutagenicity, and teratogenicity and finally, an evaluation of risks for human health and the effects on the environment. 

An important concept for environmental transport is resistances. The inverse of a rate parameter is a resistance to chemical transport. Or, in equation form ... 

Now, if R is much greater than R2, we can assume that R2 is zero without compromising the accuracy of the rate calculation. In electric circuits, two resistances applied in series are simply added together in calculating the line resistance. The same is true for resistance to chemical transport. If is 1,000 resistance units and R2 is 1 resistance unit, we can ignore R2 and still be within 99.9% of the correct answer. For most environmental transport and fate computations, it is sufficient to be within 99.9% of the correct answer. 

In this chapter, we have discussed some of the topics in the bulk of the text, where the physics of mass transport - rather than the mathematics of the diffusion equation - are essential. We will return to these and similar engineering concepts throughout the text in an attempt to develop models in the environmental transport and fate of chemicals that are realistic but can be solved, even if that solution is approximate. 

Mean values are important in environmental transport and fate because the environment is not well mixed. To address various applications in the most effective manner, we often consider mean values and the variations from the mean values separately. We will be predominantly using two types of mean values temporal means and cross-sectional means. 

When working with a computational transport code, there is httle reason to simplify equation (2.14) further. Our primary task, however, is to develop approximate analytical solutions to environmental transport problems, and we will normally be assuming that diffusion coefficient is not a function of position, or x, y, and z. We can also expand the convective transport terms with the chain rule of partial differentiation ... 

Similar concerns involving turbulent transport of chemicals occur in the air environment, except it is difficult to conhne the problem to two dimensions. Example 5.5 is a demonstration of the application of equation (5.20) to environmental transport in the air. 

Solving the diffusion equation in environmental transport can be challenging because only specihc boundary conditions result in an analytical solution. We may want to consider our system of interest as a reactor, with clearly defined mixing, which is more amenable to time dependent boundary conditions. The ability to do this depends on how well the conditions of the system match the assumptions of reactor mixing. In addition, the system is typically assumed as one dimensional. The common reactor mixing assumptions are as follows ... 

We could operate our computational transport model with only numerical dispersion (i.e., as a tanks-in-series model). It is often inconvenient to do so in environmental transport applications, however, because the cross-sectional mean velocity, U, can... 

SC 64-17 Uncertainty in Environmental Transport in the Absence of Site Specific Data... 

Environmental transport, distribution and transformation Environmental levels and human exposure Kinetics and metabolism in laboratory animals and humans Effects on laboratory mammals and in vitro test systems Effects on humans... 

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