Bacteria and protozoa are virtually ubiquitous. What is the estimated
mass in kilograms of microorganisms a person might ingest through
breathing, eating, and drinking in a lifetime of say, 70 years? This
is not a health issue question, only quantitative.

Thank you very much for accepting my comment as an answer.  I'm
repeating in this field:  it is estimated that bacteria in the gut
have a total weight of 3-4
pounds. Here is a description of some of our many "guests":
http://www.hsc.wvu.edu/som/microguide/humanmicro.htm (from the
Department of Pathology, West Virginia University).

Still, its comforting to know that most of them are beneficial or
neutral.  Bet you're glad you didn't ask about tapeworms and other
parasites...

Search strategy: A search combining "ingest" or "ingestion" with
"human" and "microorganisms" or "bacteria" did not provide useful
results.  I knew that bacteria form the largest part of the microbial
load in humans, and thought that an indication of how many bacteria
are present in or on humans would provide a partial answer, so I
searched on "bacterial load" and "human"

What a fascinating question! Although I haven't been able to find any
good data on this, I can recommend a book that might help: "Life on
Man," by Theodor Rosebury (ISBN: 0670427934). I read this book while I
was in college, more than thirty years ago, and have long since lost
my copy, but it is a terrific source of information about
microorganisms as they relate to human beings. It's out of print, but
used copies are not hard to find:

http://dogbert.abebooks.com/servlet/BookDetailsPL?bi=62881084

http://dogbert.abebooks.com/servlet/BookDetailsPL?bi=190399440

http://dogbert.abebooks.com/servlet/BookDetailsPL?bi=181538162

Not an answer to your question, but related, is the estimate that
bacterial in the gut are estimated to have a total weight of 3-4
pounds.

Here is a description of some of our many "guests":
http://www.hsc.wvu.edu/som/microguide/humanmicro.htm

Another "fun" source for you would be _The Lives of a Cell_ by Lewis Thomas.

tehuti: Thanks for the info. The website you mentioned told me more
than I really wanted to know. I'm beginning to regret asking the
question...getting a bit queasy. You may post your comment as an
answer if you wish.
Thanks,
knowitall22

HELLO FRIEND IT SHOULD BE FIRST CLEAR THAT YOU ARE TALKING ABOUT TOTAL
MICROBES PRESENT ON HUMAN BODY OR THE TOTAL MICROBES PRESENT ON HUMAN
BODY OR INTAKE OF MICROBES IN HUMAN BODT BOTH ARE DIFFERENT THINGS. IF
WE ARE TALKING ABOUT THE TOATAL MICROBES THAT MAY BE ENTER IN TO BODY.
THE HUMAN BODY HAS CERTAIN BARRIER WHICH CAN BE DISINGUISHED IN TO
THREE PARTS. PHYSICAL BARRIER ,CHEMICAL BARRIER AND BIOLOGICAL
BARRIER.THIS BARRIER STOPS THE MICROBIAL INTAKE IN HUMAN BODY.BUT MANY
ORGANISMS ARE PRESENT IN OUR BODY WHICH IS CALLED AS NORMAL FLORA.THIS
NORMAL FLORA ARE PRESENT IN DIFFERENT ORGANS OF HUMAN BODY.SO NOW WE
CAN ENUMERATE TOTAL NUMBER OF NORMAL FLORA PRESENT IN HUMAN BODY BUT
WE CANT QUANTIFY THE ORGS WHICH TRIES TO ENTER IN HUMAN BODY.
        BECAUSE IT DEPENDS ON THE SEVERAL PARAMETERS.IT EFFECTS ON
HUMAN INTAKE OF MICROBES. THAT IS PHYSICAL,ENVIRONMENTAL,PERSONAL
HYGEN,CLIMATIC CONDITION,SOCIAL STATUS, GEOGRAPHICAL PARAMETERS,ETC...
        MICROBIAL INVASION IS DEPENDING ALL THIS PAPAMETERS.LIKE SOME
PERSON PRESENT IN HOT ENVIRONMENTAL CONDITION HAVE DIFFERENT MICROBIAL
INTAKE THEN PRESON IN RAIN FOREST. SUCH LIKE THAT THE WATER PURITY,
THE FOOD VARIATION IS IS ALSO PLAYS VITAL ROLE IN INTKE OF MICROBES.
        JUST THINK THAT THERE SHOULD BE A VAS DIFFERANCE IN AFRICAN
AND PRESON IN USA.THERE LIVING STANDERD IS SO MUTCH DIFFERENT.SO THERE
MICROBIAL INTAKE IS SO MUTCH DIFFERENT.
          SO THE QUANTATIVE ANLYSIS OF NORMAL FLORA PRESENT AT HUMAN
BODY IS POSSIBLE BUT THE FLORA THAT ENTERS IN HUMAN BODY AT EVERY
SECOND IS NOT FEASIBLE.
   THANK YOU

ash22: You are of course correct...my question was oversimplified,
which I did not realize at the time I wrote it. I thank you and others
for their efforts.
In any event you have enlightened this person greatly, and I thank you
for it.
knowitall22