Chemical Movement

D. L. Nofzigfer and A. G. Hornsby, CMES Interactive Simulation of Chemical Movement in Eayered Soils, Institute of Food and Agriculture Sciences, Circular 786, University of Florida, GaiuesviUe, FI., 1986. 

In the area of transport-type models, soil/water systems have been a primary area of development. The Hydrologic Simulation Program (18) described in the paper by Johanson simulates chemical movement and transformation in runoff, groundwater and surface water in contact with soil or sediments. 

In vitro data cannot predict the rate constants for chemical movement between compartments. 

League KM, Green RE, Liu CC, K., et al. 1989. Simulation of organic chemical movement in Hawaii soils with PRZM 1. Preliminary results for ethylene dibromide. Pac Sci 43 67-95. 

Myers, J.L., M.G. Wagger, and R.B. Leidy (1995). Chemical movement in relation to tillage system and simulated rainfall intensity. 

Freeman RA, Schroy JM. 1988. Modeling of chemical movement in soil matrices. Presented at the 195th ACS National Meeting, Toronto, Ontario, Canada, June 5-10, 8. 

The goals of this section are to introduce methods of modeling chemical movement within and between environment compartments, to define specific translocation and transformation processes, to provide a basic understanding of the association among chemical structure, physicochemical properties, and susceptibility to specific translocation and transformation processes, and to provide methods of accessing and estimating physicochemical properties and environmental fate of chemicals. 

The in vitro study did not use adequate controls (e.g., pH, vehicle used, volume of test agent given, and samples taken from sham-operated animals), resulting in artifacts of methods rather than results in vitro data cannot predict the volume of distribution in central or in peripheral compartments in vitro data cannot predict the rate constants for chemical movement between compartments in vitro data cannot predict the rate constants of chemical elimination... 

Thus far the discussion of the transport and reactions of chemicals has predominantly focused on processes occurring in one of two fluids air or water. Of course, the natural environment contains more than these two media furthermore, one medium often contains different phases. For example, the atmosphere contains not only air, but also water and solids (particulate matter) in small, varying amounts surface waters often contain solid particles and gas bubbles. The subsurface medium contains not only solids, but also a substantial volume of water and air. Therefore, a consideration of the principles that determine how a chemical becomes distributed among air, water, and solid phases is necessary, not only to understand chemical movement between media (atmosphere to surface water, soil to atmosphere, etc.), but also to understand the behavior of a chemical within a single environmental medium. 

In the discussion of chemical distribution among phases, it is assumed that chemicals are not transformed (i.e., no chemical bonds are formed or broken). For example, when liquid gasoline evaporates and enters the air in a partially empty gas tank, the bonds within individual molecules of the chemicals that compose gasoline are not being disrupted the molecules are simply moving from a nonaqueous liquid phase to the gas phase without changing their identities. The rate at which this chemical movement occurs from one phase to another, relative to the timescale of interest, determines whether the problem is an equilibrium problem or a kinetics problem. Examples of both types abound in the environment this section, however, refers only to the principles that govern equilibrium. 

Nofziger DL, Hornsby AG. A micro-computer base management tool for chemical movement in soil. Appl Agricul Res 1986 1 50-56. 

Chemical movement at bottoms of ponds, lakes, and quiescent water bodies... 

An example follows that is used to illustrate some of the details of the EC analysis process and its forecasting characteristics. The general reader may skip over this technical section without loss of continuity of the subject. It involves an important and very common EC problem and illustrates the effective use of the flux concept in connecting the interphase chemical movement in a multimedia context. 

Flux is a somewhat abstract entity and does not relate this information directly. It quantifies the chemical movement rate across an interface plane into a receiving media such as the air boundary layer (BL) in the above example. Only when it is coupled with an air dispersion model does it produce concentrations in air. In the case of a large soil surface area source, a simple relationship exists between flux and concentration. For neutral air stability conditions in the atmospheric BL with steady-state wind speed v (m/sec), the concentration in air, c (mg/m ), can be approximated by... 

This is the proceedings from a USA/CiS conference organized by the American Institute of Hydrology. Topics Include nutrient concentrations in ground water and surface runoff, chemical movement through soil, preventing ground water pollution in rural areas, and pesticide volatilization. 

Identification and prioritization is used to rank chemicals, movements, and other factors for escalation, which may result in more detailed risk analysis. The components of a prioritization process can be included in a company-specific process and may consist of ... 

Table 4.4 summaries the results of the qualitative risk analysis. Three of the raw materials operations (chlorine, butadiene, and acrylonitrile) and three of the products/wastes (chlorine cylinders, herbicides, and aqueous HCl) were screened out for further risk analysis. Therefore, four chemical movements were escalated for a more detailed semi-quantitative risk analysis... 

Before each chemical/movement was evaluated by the team, the route was reviewed and segmented based on a coarse-level evaluation of the population density. Then, the corporate lead categorized the population as high, medium, or low, based on levels predefined for these worldwide risk analyses. A graphic developed by the team representing the routes is depicted in Figure 4.6. 

Using the consequence and likelihood categories, risk matrix, and risk evaluation criteria, the team reviewed three release scenarios (small, medium, and large) for the segments identified for each of the chemical movements. The result of the semi-quantitative risk estimation for this facility s hazardous material transportation operation is detailed in Table 4.12. From this results table, the following are determined ... 

Even though higher-level risks were identified for two of the chemical movements, this level of analysis lends itself to recommending and evaluating risk reduction strategies, as warranted. In this continuing example, the bulk pesticide is escalated for quantitative analysis (Chapter 5) and the chlorine containers risk reduction options are the focns of Chapter 7. 

Compared to fixed-facility QRAs, transportation QRAs can be even more variable in terms of resource requirements because a study can cover a single chemical movement or many such movements within a single analysis. In addition, each time an alternate transportation option is included for evaluation, it is comparable to evaluating a whole new processing unit at a fixed facility. 

No one prioritization factor is intended to escalate an issue to a full TSVA however, it is recommended that a multistep process be developed to identify the specific chemicals, movements, and segments that may require further evaluation. An example prioritization process is illustrated in Figure 6.1, consisting of the following steps ... 

Step 5—Security Evaluation Each of the chemical movements screened out through the prioritization process shotrld be analyzed by a general security review before closing these items. Section 6.5 discusses basehne security elements. All issues that make it through the prioritization process should be reviewed using a TSVA methodology (Section 6.4). 

Step 6—Periodic Review It is important to periodically review the security of the transportation network to ensure that the baseline program elements are still in place, recommended coimtermeasures have been implemented, and vulnerabilities reassessed. Additionally, this process should be reinitiated if there is specific intelligence or tlueat information pertaining to your supply chain, mode of transport, or specific chemical movement. 

An increase in carrier accident rates Problems identified dining inspections Violations of management practices Changes in the nnmber of movements New cnstomers New chemical movements Changes in rentes or modes Specific threat information... 

Semi- Quantitative Risk Analysis (Chapter 4) Faciiity Levei Qualitative risk analysis resulted in the escalation of four of the nine chemical/ mode transportation operations from the Asian facility Increased detail resulted in screening out two of the chemical movements Bulk chlorine and pesticide recommendations developed Rerouting Repackaging... 

Moore PA, Atema J, Gerhardt GA (1991) Fluid dynamics and microscale chemical movement in the chemosensory appendages of the lobster, Homarus americanus. Chem Senses 16 663-674... 

Describe an experiment to measure the rate of a chemical movement into a cell, given that the rate cannot be measured directly. What assumptions must be made ... 

The way forward is either legal or chemical. The legal constrains by the prospect of punishment the chemical avoids by elimination at source. The latter, always the better mode of action, depends on developments of chemistry itself and has inspired the politico-environmento-chemical movement of green chemistry. In broad terms, green chemistry aims to minimize the impact of chemical manufacturing processes on the environment by strict guidelines about the use of materials and the elimination of waste. 

Diffusion A process in which a chemical moves from regions of higher concentration to regions of lower concentration. The process is called molecular diffusion if the chemical movement is due to the random walk of the molecules within the phase, and eddy diffusion if the chemical movement is due to the turbulent movement of the phase. 

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