(1) This "readme" file accompanies software (Window s-based PCs) for the July 2011 version of

the Agency's methodology for assessing impacts of atrazine on aquatic plant communities. This software consists of:
(a) Fortran code and executable files for the progr am "AtrazineLOCPATICalculation", and input files for this program in a zip file.
(b) Fortran code and executable files for the progr am "AtrazineChemographAnalysis".
(2) The executable programs provided here do not re quire an installation routine. They simply need to be copied to a desired directory and run. Each executable runs in a DOS-window, so that user interaction is on a line input/output basis, n ot with a visual interface. The FORTRAN code is provided for review purposes, but, if used to ge nerate new executables, it was developed using Intel Visual Fortran Version 9.1 under Microsoft Vi sual Studio 2005, and uses utilities from the IMSL mathematical library provided with Visual Fortran. (3) The risk assessment methodology embodied in thi s software is described in other posted documents, especially the report Proposed Methodology for Specifying Atrazine Levels of Concern for Protection of Plant Communities in Fres hwater Ecosystems (Erickson 2010) and a 2011 addendum to this report. Briefly, this method ology is a follows:
(a) Information from single-species aquatic plant t oxicity tests with atrazine is used to compute daily "Plant Assemblage Toxicity Index" (PA TI) values for exposures of interest, these daily PATI values being the average reductions in growth rate across a specified assemblage of plant species at each day's concentration.
(b) The daily PATI values are summed to provide a c umulative PATI value that represents the total severity of toxicity in an exp osure of interest. If the exposure is longer than 60 days, this summation is limited to the contiguous 60 days resulting in the highest cumulative PATI value. The use of a cumulative PATI with a 60 day assessment period deviates from Erickson (2010) as explained i n the 2011 addendum to this report.
(c) The relationship of effects of atrazine on aquatic plant communities in experimental ecosystem (microcosm/mesocosm or "cosm") exposures to the cumulative PATI values for these exposures is evaluated to determine what value for the cumulative PATI is a level of concern (LOC PATI ) – based on effects in the experimental systems.
(d) Cumulative PATI values are calculated for fieldexposure time series to determine whether and by how much these exposures exceed the LOC PATI . (e) An LOC based directly on exposure concentration s (rather than PATI) can be developed using the relationship between average co ncentrations and cumulative PATI values in typical field exposures. Such an LOC is not an aspect of the software being provided here, but is discussed elsewhere on the we bsite.(4) The first program, AtrazineLOCPATICalculation_J uly2011, calculates LOC PATI based on the set of experimental ecosystem studies with atrazinedescribed in the memorandum Bibliography of Microcosm and Mesocosm Studies and Criteria Used to Screen Studies for Analysis of Atrazine Risks to Aquatic Plant Communities posted on this website. PATI values for the cosm exposures are based on the overall distributions of toxicity test parameters reported in Erickson (2010). The toxicity distributions are incorporate d into the code, while the cosm data are in the provided zip file. This program will:
(a) Cue the user for an assessment period (in days) , the current choice for this in the Agency's methodology being 60. This input option w as provided for development purposes. (b) Cue the user for a file containing the cosm eff ects data. The file provided in the zip file is "CosmEffects.dat", which reflects the above -cited memorandum. This is an ASCII file with one line for each cosm exposure consistin g of (i) a three character field containing an alphanumeric identification code (lef t justified if less than 3 characters) for the exposure, (ii) a five character field containin g an integer (right justified) designating the exposure duration in days, and (iii) a three ch aracter field containing an integer (right justified) set to 1 if there was a significant adve rse effect and 0 otherwise. In addition, for each cosm exposure, there is a separate file co ntaining a concentration time series for that exposure. Each file is named "Exposure#AAA.tx t", where AAA is the alphanumeric identification code, right truncated if the code is less than three characters. These files must be in the same directory from which the program is executed.
(c) Cue the user for the name of an output file. T he program will then input the cosm data, compute the cumulative PATI for each cosm exp osure, conduct a binary logistic regression of cosm effects versus PATI to determine an LOC PATI , and prepare the output file. The output file will provide the cumulative PATI value for each cosm exposure, information on the regression results, and the fina l LOC PATI value.
(5) The second program, AtrazineChemographAnalyses _July2011, uses the above LOC PATI to evaluate user-provided exposure time series (chemog raphs). Using the same toxicity test parameters as the LOC program, it will calculate th e cumulative PATI for each chemograph and calculate the ratio of this to LOC PATI , this ratio being termed the "effects exceedence f actor" (EEF). It will also compute the maximum running av erage concentration for each chemograph using a user-specified averaging period, a calculat ion which was provided to support development of concentration-based LOCs. The steps in this program are:
(a) Cue the user for the LOC PATI determined in the LOC program.
(b) Cue the user for the assessment period of PATI. This must match what was used to calculate the LOC PATI .(c) Cue the user for the averaging period to derive the maximum running average

concentrations. This need not be the same as the P ATI assessment period
(d) Cue the user for the name of an ASCII file cons isting of names of files containing the concentration time-series for each chemograph. The first line of this file is an integer designating the number of chemographs to be assesse d. Each subsequent line is the name of a concentration time-series file for a particular cosm exposure. If the complete directory path is not given for this file, the file must be in the directory from which the program is being executed. Each of concentration t ime-series files consists of 365 lines, each line consisting of the Julian day (integer) an d the concentration (ug/L) on that day (integer or decimal number). The numbers can be se parated by either spaces or a comma.
(e) Cue the user for the desired name for the outpu t file. The program will then input the chemograph data, calculate the cumulative PATI for each chemograph using the same toxicity distributions as in the LOC program, calcu late the EEFs and the running average concentrations, and prepare the output file. The o utput file consists of one line confirming the LOC PATI

and the assessment period, and then a table showin g each chemograph file name with its running average conce ntration, its cumulative PATI value, and its EEF.