LIVE DIRT: Part 2 - Living Contamination
Barbara Kanegsberg, Ed Kanegsberg with Guest Collaborator James Unmack, June 2003
In the context of engineering or chemistry, we tend to think of contamination
as a static, constant problem which can be resolved by filtration or dilution.
Take the contaminate to a de minimis level, and the problem is gone. However,
as explained in last month’s column, bacterial and fungal contamination
present more complex contamination problems; and the consequences more insidious.
Biologists are geared toward the possibility of significant bacterial and fungal
contamination developing from a single spore (like a seed) and creating a situation
that is catastrophic to the process and the product. In general, viable contamination
is a negative force.
There are exceptions, however. Even in industrial processes, bacteria can occasionally be a positive force. For example, bacteria are beneficially used in some aqueous cleaning systems for in-situ or on-board bioremediation of oils. Such processes support hazardous waste minimization.
In bacterial and mold contamination, there are always balances as well
as economic and safety/environmental related trade-offs. Changes
in building and coating
materials, while important for economic and health considerations, are more
supportive of biological growth. (Consider the decreasing use of plaster
relative to that of dry wall. While less costly, dry wall -- basically
paper -- is more
supportive of biological growth.)
In addition, steps taken to protect public health can potentially promote
the growth of interfering biological organisms. Certain inorganic compounds,
notably
lead, copper, and cadmium, are relatively non-supportive of life because
they interfere with enzymes (organic catalysts that operate within the
organism). Because of this, they are hazardous to people. In the
interests of worker
and
community safety, lead pipes and lead-based paints have been replaced.
The replacements, while less hazardous to people, are more supportive
of bio-growth.
Specifically, lead free paint has can support mold. Similarly, cyanide-free
plating processes are promoted to protect workers and to minimize hazardous
wastes. Some cyanide–free plating processes, however, are reported to
have increased problems with growth. An increased potential for increased contamination
by molds and fungi may be an inevitable outgrowth of environmentally-preferred
processes.
Potential consequences of bacterial and fungal growth include compromises
in structural integrity and contamination of product with viable life
forms. Contamination
by secondary, non-viable products such as secretions or non-viable remains
is a potential problem. Bacteria secrete a cement-like material to allow
attachment to surfaces. Molds may send filaments which also release secretions
into pores
of the substrate. For example, Stacchybortyrus mold produces a slimy,
gooey muco-polysaccharide, which may interfere with functionality.
This contamination
is not readily removed with common organic solvents such as perchloroethylene.
Water-based approaches to decontamination are more likely to succeed.
Coolant may deposit fungus or perhaps spores on a part. If the part is
then cleaned in a biodegradable cleaning fluid, the contamination is
then transferred.
Given suitable growth conditions, the level of contamination can increase.
Even with inihibitors, and at high pH, the potential for eventual multiplication
exists. Even resistant additive packages can break down; in fact, one
early warning sign of living contamination is extreme, atypical pH
fluctuation.
Contamination control of viable contaminates is, not unexpectedly,
fairly process-specific. One approach is to adopt conditions where
spores are
not viable. For example,
growth is not likely to occur in classic industrial chlorinated solvents.
In aqueous processes, temperatures of 140° F are sufficient to kill most spores,
although a few will survive 160 to 180° F. In small-scale aqueous processes
that operate at 110° F, there could be a problem.
Thanks to Jim Unmack of Unmack Corporation, Rancho Palos Verdes,
CA. Jim is a Certified Industrial Hygienist and a Certified Safety
Professional
with more
than 30 years experience in protecting workers’ health and safety through
the application of good science to the work environment. He can be reached
at 310-422-4340; jim@unmack.com .
Barbara Kanegsberg and Ed Kanegsberg are independent consultants in critical cleaning, precision cleaning, surface preparation, and contamination control. They are the editors of “Handbook for Critical Cleaning,” CRC Press. Contact them at BFK Solutions LLC., 310-459-3614; info@bfksolutions.com; www.bfksolutions.com.
