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How clean is your lake?

Two years ago, I was involved in preparing chemical hazard assessments for the Ontario Ministry of the Environment (MOE). Chemical substances deemed hazardous were placed on the Effluent Monitoring Priority Pollution List (EMPPL). Part of the scoring criteria used was the degree of partitioning a species exhibits among four different phases (air, soil, water and sediment). A fugacity program developed by Dr. Mackay of the University of Toronto was used to calculate the partition data. Recently, I obtained a copy of Toxfate, an organics toxic contaminants fate model, developed by Efraim Halton and written by David S Brendon, both of the National Water Research Institute (NWRI).

Toxfate, a contaminant fate model uses information about the lake topography and the physical-chemical characteristics of a contaminant, and predicts its fate in the lake and in biota. Toxfate incorporates such processes as chemical volatization, sorption on suspended solids, biological ingestion, sedimentation and resuspension. A finite section approach describes the lake, and each section is assumed completely mixed. Within each volume the differential equations describing the distribution of the contaminant are then solved. A paper describing the model in more detail was included: E. Halfon and Barry G. Oliver, 'Simulation and data analysis of four chlorobenzenes in a large lake system (Lake Ontario) with Toxfate, a contaminant fate model, Modelling in Ecotoxicology', S.E. Jorgenson, Ed., Elsevier Science Publishers BV, Amsterdam, (1990) 197-214.

Toxfate was originally written in Fortran 77 in 1984 for use on a mainframe. Today there are two parts to Beta Version 3.6, one called Toxfate (the modelling program), and the other is Toxshell. Toxshell is a user-friendly interface written for microcomputer users. The diskette comprised of four files. The READ.ME file contains the Documentation and User Guide. For best results the program should be installed on a hard disk; however, it may be run from a floppy drive. An item not mentioned in the User Guide is the current instruction on how to install the program on to your hard disk. The user should be in the drive containing the floppy disk. At the DOS prompt type Install C: or Install D:, for installation to your C: or D: drive. From here on, the batch program does the rest of the work for you, unravelling compressed format files and creating a Toxfate directory with four subdirectories containing data and program files.

The program is loaded from the Toxfate directory, by typing the command Toxshell. This brings the user into the shell program which has a professional-looking screen with dropdown menus. The main menu at the top of the screen contains the headings: Lake Input, Chemical Input, Toxfate, Output, Help and Quit. The Lake Input submenu gives you a choice of loading an existing lake file, editing a lake file or creating your own lake file. The Chemical Input submenu has similar options. However, if you decide to create a lake or chemical file of your own, you must have a complete set of data entered before you can get out of the panel. The program will only run if you have chosen a lake and a chemical file.

Halfon conveniently includes a complete set of data for Lake Ontario, 19 sets of steady-state chemical files and five sets of dynamical data for which yearly loadings are available from 1909 to 1987 and extrapolated to 1992. This information is very useful on its own. It is similar to having a small database of lake data, chemical property data, and fate data for some common hazardous chlorinated organics.

The program can be run two different ways: steady-state (one loading) or dynamical (yearly loadings) depending on how the Chemical Input file is set up. When the Lake and Chemical Inputs are chosen the next step is to choose Toxfate and select Run. A panel pops up telling the user how long the run will take in minutes and if the user stills wants to do that particular run. At this point you may go back to the chemical input file and edit it by adjusting the number of hours per integration step. By increasing this number, you decrease the time it takes to run the model. As a test run, I ran PCB data with Lake Ontario data, this took about two minutes using an IBM PS/2-80286 system. Halfon gives other examples in the READ.ME file for modifications the user may wish to make to existing data files including a smaller lake simulation or how to start the simulation for a particular year.

The program's output creates four files; PARAMS.DAT, WAT.DAT, SED.DAT, and CHART.DAT. A batch file then renames the files to the output file of your choice, (the program has asked you for this at the end of the run) with the extensions;.PRM,.WAT, .SED, AND .CHT. The output can be viewed either on-screen graphically, where you have a choice of looking at the Water Column and Mass Balance or created output files can be imported into a spreadsheet program. The spreadsheet program used was Lotus 1-2-3. I was only able to import two of the files, the first input line for file .WAT was greater than 240 characters and could not be imported. An advanced user can overcome this problem by adjusting the output lines in the program. The .CHT file is not meant to be imported into a spreadsheet program. It is only used for checking the mass balance or debugging the software.

A Quit submenu offers two choices. You may either quit or temporarily Exit to DOS and load a spreadsheet program to import recently made files. When finished with the spreadsheet program, enter Exit to re-enter the Toxfate program at a point where they left off. This function allows the user to make slight changes to Lake or Chemical Input files recently used without having to re-enter, or re-select those files. There are many uses for the data files once imported into a spreadsheet program. The example shown indicates the predicted PCB concentrations versus sediment depth over 50 years.

This fate model is currently being used in courses at the University of Minnesota. Halfon is very interested in collaborating with other scientists in order to improve this model. In fact, this is just what some scientists at the University of Minnesota are doing. They are improving the sediment part of the program based on extensive research done in that area. Fate models such as Toxfate, can be very useful for regulating agencies in predicting the long-term fate of undesirable contaminants. From examining the results of the model it becomes apparent the lengths the government and industry will have to take toward reducing toxic emissions in our precious waterways.

In the version of Toxfate reviewed (3.6), the Help menu was not available yet; so, it was necessary to rely on the READ.ME file. I found the model easy to use and also discovered a new source for chemical fate and loading information on-disk for Lake Ontario. Halfon was easy to contact and happy to answer any questions. Those interested in receiving a free copy of this program may contact him directly.

Carola F. Serwotka currently works at Gore & Storrie, Ltd., Consulting Engineers, as an intermediate project engineer. She has been the Secretary for the Toronto Section of the CSChE for the past three years, and the Ottawa Office Liaison for the Toronto Section of the CIC for the last year. Serwotka graduated from a four-year chemical engineering programme at Ryerson in 1988.
COPYRIGHT 1991 Chemical Institute of Canada
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Copyright 1991 Gale, Cengage Learning. All rights reserved.

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Title Annotation:computer software being used in the determination and monitoring of toxins in lakes
Author:Serwotka, Carola F.
Publication:Canadian Chemical News
Date:Aug 1, 1991
Previous Article:Policy on women in chemical engineering.
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