              Summary of Modifications and New Features in
   
                MINTEQA2 and PRODEFA2 Versions 3.10, 3.11
                              (UPDATE.TXT)
        
                             December 1991


             Center for Exposure Assessment Modeling (CEAM)
                  U.S. Environmental Protection Agency
                   Office of Research and Development
                    Environmental Research Laboratory
                          College Station Road
                       Athens, Georgia  30613-0801

                     (404) 546-3549 / (FTS) 250-3549

 

Introduction
____________

MINTEQA2 and PRODEFA2 version 3.10 includes several new features and
modifications to existing version 3.00 features.  Version 3.10 was 
released in September 1991.  Version 3.11 was released in December
1991 and is identical to 3.10 except for a modification in the
composite ligand sub-model (described below) that results in much
faster execution for problems with several metals that compete for
the ligand.  The new features in versions 3.10 and 3.11 include:	
	

 -  A new sub-model for computing the complexation of various metals
    with natural dissolved organic matter is included.  This model is 
    based on the work of Dobbs et al. (1989) which treats dissolved
    organic matter as a complex material consisting of many different
    types of monoprotic acid sites.  The concentration of these 
    ligand sites is normally distributed with respect to their log K 
    values for protons or metals.  Assuming a known mean log K value
    for metals (Perdue, 1984), the mean log K values for various metals 
    with dissolved organic matter from the Suwannee River have been 
    determined by lanthanide ion probe spectroscopy (Susetyo et al.,
    1991).  A database of trace metal reactions with Suwannee River 
    dissolved organic matter and their mean log K values is included 
    with version 3.10 (file COMPLIG.DBS).  The incorporation of these 
    reactions in standard equilibria calculations is accomplished by 
    including a separate subroutine (COMPOSIT).  In addition, PRODEFA2 
    has been modified to assist the user in defining new composite ligand
    reactions not in COMPLIG.DBS.  To use this sub-model the user should
    note the following:

    1.  The composite ligand component DOM (component id 145) represents
        dissolved organic matter.  There is no distinction between humic 
        and fulvic fractions in this model.  Component CLIG2 (id number 146)
        is a general component for user-defined reactions between 
        other substances that, like dissolved organic matter, are best 
        represented as a complex mixture of ligands having a 
        continuous distribution of log K values characterized by a
        mean log K and standard deviation.  

    2.  The particular continuous distribution used in MINTEQA2 is
        Gaussian.  Other distributions are possible but not without
        modifying the source code (COMPOSIT.FOR).
    
    3.  The concentration of the composite ligand component is ALWAYS
        specified in moles of sites per liter (regardless of the setting 
        for units of concentration).   

    4.  For the Suwannee River samples, the site density was 5.0E-04
        moles of sites per gram organic matter.  The organic matter
        found to contain 48.79% carbon.

    5.  The database of mean log K values and the reactions to which 
        they pertain is in file COMPLIG.DBS.  This file has the same 
        format as THERMO.DBS except that the entry that is used for
        standard enthalpy of reaction in THERMO.DBS represents the 
        standard deviation of log K in COMPLIG.DBS.

    6.  The concept of composite ligands, that is, ligands that are  
        complex mixtures of various sub-ligands that display a continuous
        spectrum of binding affinities, is separable from the concept that 
        dissolved organic matter is such a substance.  Therefore, the 
        composite ligand model is implemented in the general sense; the
        only link to organic matter is the database COMPLIG.DBS that 
        gives specific reactions and their mean log K values for a specific
        substance: Suwannee River dissolved organic matter.  The user can
        use the composite ligand model for other substances if the user has
        the specific reactions and constants.        
   
    7.  References and Bibliography:

        Grimm, D.M., L.V. Azarraga, L.A. Carreira, and W. Susetyo (1991) 
        Envir. Sci. Tech.,25,1427-1431.

        Susetyo, W., L.A. Carreira, L.V. Azarraga, and D.M. Grimm (1991)
        Fresenius J. Anal. Chem.,339,624-635.

        Dobbs, J.C., W. Susetyo, L.A. Carreira, L.V. Azarraga (1989b) Anal.
        Chem.,61,1519-1524.

        Perdue, E.M., J.H. Reuter, R.S. Parrish (1984) Geochim. Cosmochim.
        Acta,48,1257-1263.

        Dobbs, J.C., W. Susetyo, F.E. Knight, M.A. Castles, L.A. Carreira,
        L.V. Azarraga (1989a). Anal. Chem.,61,483-488.
                         
        Susetyo, W., J.C. Dobbs, L.A. Carreira, L.V. Azarraga, D.M. Grimm
        (1990) Anal. Chem.,62,1215-1221.       

 
       
Other Modifications Released in Version 3.10
____________________________________________
                                      
 -  Initial activity guesses made by PRODEFA2 are optionally improved 
    in MINTEQA2 prior to the first iteration.  This feature, which can
    optionally be disabled for any component, uses acid-base and redox 
    chemistry relations to provide improved activity guesses for key 
    components.	 The result is faster convergence once iterations
    begin and reduced likelihood of non-convergence.

 -  The auxiliary output option for components has been expanded to 
    include species.  Equilibrium results for up to six components or 
    species can be output to a special file for import into a spreadsheet
    program.                           

 -  On-screen display during MINTEQA2 execution has been improved.

 -  PRODEFA2 menus and screens have been improved.

 -  All oxidation-reduction half-reactions have been re-written
    as reductions where the reduced form is the product and has 
    negative stoichiometry.  The seven-digit ID numbers of these
    reactions are composed with the three-digit component ID
    of the reduced form in the three leftmost positions.  These
    changes aid interpretation of results.



Special Note
____________

Input files (*.INP) for version 3.00 can be used in versions 3.10
and 3.11 if the following minor modifications are made:

Using a text editor that saves files in ASCII text (non-binary) format,
edit the line that contains program option flags.  This is usually the
fourth line in the input file and consists of a series of 13 digits
separated by single spaces.  Most of the digits are zero or 1.  Make
the following changes:

 -  If this run was previously designed to incorporate a sweep,
    set the 11th digit to 1.  If this is not a sweep run, set the 11th
    digit to zero.

 -  Set the 12th digit to the number of components flagged for special
    output (for import to a spreadsheet or graphing program).  Set to 
    zero if this run did not incorporate special output.

 -  Set the 13th digit to 1 if the 12th digit is now greater that zero.
    If the 12th digit is zero, set the 13th to zero as well.

The only other change that may be necessary is to make any TYPE 3
redox couples listed in the users input file be consistent with the new
redox couple rules (see above).  The user can do this by making sure the 
three leftmost digits of the seven-digit ID represent the reduced form.
Also, because some reactions may have been reversed relative to earlier
versions, BLANK OUT ALL ENTRIES TO THE RIGHT OF THE SEVEN-DIGIT ID.
MINTEQA2 will obtain the correct values from the database.  This applies
only to redox couples.  If the users input file has no redox couples
specified, no action is required.

Once these modifications are complete, the user can use this file in
PRODEFA2 for further modifications or use it as an input data file for
MINTEQA2.

                       #########################

JA/ja/dwd - December 1991 - E:\MINTEQA2\UPDATE.TXT
