Granite Bacteria Issues
This topic is a surprise to many readers, that granite can harbor living
organisms. Yet in fact, all that is needed for life to thrive is a protected spot
to live, moisture and something to eat. Granite provides all three of these
Since a sealer cannot completely block out water, thus moisture will be
available. Even deep underground, with no sunlight or nutrients, bacteria
thrive. One type of bacteria turns minerals into food, while another type uses
the waste products left over and so on.
However, in a counter top, there is food available, grease, crumbs, all manner
of proteins, sugars, and carbohydrates smeared around and ground down into
a paste by use and cleaning, then forced into crevices and pores.
Do a Google search on shopping carts and bacteria, see how long they last
with only moisture from hands and nutrients from skin oils. Countertops are a
haven for bacteria, which is why sanitation is so important.
This is a sore point with stone shops - the bacterial aspects of granite.
Studies have proven the susceptibility of granite to bacterial colonization and
other studies have shown the rapid increase in food borne illness, yet no one
has done a study to find any correlation between the two. That will be done in
the near future, first a paper study to bring together what has been done
already, then food borne illness records will be checked to see what
percentage have granite countertops in the home. Denying scientific proof
that granite is unsanitary is just trying to justify a purchase or trying to sell
more stone tops.
One study on granite and bacteria was very thorough, yet it has been
attacked by the granite industry. If you do the math on the results of the study
you see why they are worried about the impact on their product. Here is a
short version of what NASA found and why a homeowner would want to know.
Imagine, NASA's findings of over 100,000 bacteria per gram of granite, plus
many, many bacteria spore. Here is the math, stone averages about 16
pounds per square foot (3 cm) x 453.6 grams per pound = 7257.6 grams per
7257.6 x 100,000 bacteria per gram (NASA's figure)= 725,760,000 bacteria
per square foot of countertop. Average top is around 75 square foot, so
725,760,000 bacteria per square foot x 75 average square foot top =
54,432,000,000 bacteria per countertop.
Over 54 Billion bacteria, just in the cracks and crevices alone, not counting
what is on the surface. If a 5 log reduction could be done reliably, there would
still be over a half million bacteria left in the cracks and crevices after
disinfection. Twenty minutes after disinfection, the bacteria would have
doubled to one million, forty minutes, two million, an hour later four million, and
so on. In about four hours, the bacteria have multiplied to 2,229,534,720. In
seven hours, the bacteria will have multiplied to 150 billion bacteria.
Keep in mind that these NASA figures were for rock taken from a desert
environment, with little food and water available for the bacteria. Imagine the
average stone top, soaking in moisture from cleaning the top surface, and
humidity from the bottom and edges.
On the studies page, there is a Brazillian/Portugese study that showed up to
590% more bacteria retained on a granite surface than a plastic surface such
as polypropylene or polyethylene. The study concluded that granite was more
prone to colonization by bacteria and that sanitizing granite countertops was
This thread was from a stone fabrication site: Smelly granite, bacteria or mold?
And while they didn't mention bacteria or mold, the advice to use bleach left
no doubt as to what was causing the problems.
Another study showed Salmonella bacteria thriving in granite outcroppings,
even surviving desiccation for extended periods. Prior to this study, it was
thought that Salmonella were present in human and mammal intestinal tracts
and were spread by poor practices in slaughter houses. Now it is know that
regardless of the source, from the stone when it was mined or from meat juice
contamination, the granite provides a suitable home for the bacteria to thrive.
Another study shows the danger of bacteria found in the soil because of the
natural antibiotics secreted by plants and other bacteria. Some will say that
the natural bacteria that normally colonizes granite will keep the quantity of
dangerous bacteria down by competition, yet this study shows that sometimes
it makes the dangerous bacteria more resistant to drugs.
The Marble Institute has two studies that it relies on when claiming that granite
is a safe material for a countertop. Both are riddled with errors and omissions.
Both are discussed on the Studies page of this site.
Granite is a proven habitat for bacteria,despite other claims. Sanitizing granite
countertops must be done on a regular basis to keep the population of
bacteria down to a level that a healthy human immune system can handle.
This is easily done, yet the harsh sanitizing solutions quickly strip any sealer
present on the surface of the granite as well as degrading any resins used to
fill pits and fissures in the slabs during polishing. So you have a choice,
unsanitary countertops or easily stained countertops.