Download Water fogging and misting systems are they a risk to human

Water fogging and misting systems
– are they a risk to human health?
ISSUE
NUMBER:
2001/5
Thousands of nursery workers have been, and continue to be, exposed to the fine
aerosols of water from both fogging and misting systems. Does this exposure put these
workers at risk of contracting Legionnaire’s disease or other water-borne human
diseases? Dr David Douglas, a consultant in occupational and environmental health,
reports that good quality water (that is treated town water, clean rain water or water
that has been disinfected properly) will not contain bacteria, fungi or viruses that are
harmful to either plants or humans.
The
Australian
horticultural
industry has, for several decades,
been using water-fogging systems to
assist in temperature control, and
water-misting systems for watering
seedlings.
Both systems produce fine aerosols
of water, with droplet sizes usually
less than 60 microns. Such droplets
are too large to be inhaled into the
deep lungs of humans, but can
readily reach the upper airways and
bronchial passages.
To date, there have been no written
or anecdotal reports of adverse
human health effects attributed to
such exposure. Nevertheless, the
Nursery & Garden Industry
Australia (NGIA) has received
inquiries about the potential for
fogging and misting systems to
cause Legionnaire’s disease or other
human diseases.
Fogging and misting systems will not cause human health problems
as long as the water being used does not contain bacteria, fungi or
viruses and/or is disinfected properly.
water-borne
Legionnaire’s disease, which is a pneumonia-like
illness, was first recognised when a serious
outbreak occurred at an American Legionnaires’
Convention in Philadelphia in 1978, but it was
not a new disease at that time.
© NGIA – The Nursery Papers – Issue no 2001/5 – Page 1
The causative organism (Legionella pneumophila) is
widespread in the environment as a common
contaminant of water sources. Outbreaks of Legionella
pneumonia in Australia have mostly been associated
with contaminated water in cooling towers and spa
baths, with case reports also implicating exposure to
potting mixes.
It is possible that the water used in fogging and
misting systems could contain Legionella bacteria,
especially if: (i) drawn from surface supplies such as
dams, creeks and rivers; (ii) drawn from recycled
water sources, or (iii) drawn from water stored at
20-45˚C.
Similarly, it is possible that the fogging and misting
systems could contain other bacteria harmful to
humans, such as E. coli, that may result in
gastrointestinal diseases.
However, the probability of bacteria contaminating
fogging and misting systems can be eliminated if the
quality of the water delivered by the fogging and
misting systems is maintained so as to provide optimal,
disease-free, growing conditions for plants. The best
water for plants, that is, water that is free of plant
pathogens (bacteria, fungi and viruses), will also be
free of human pathogens.
The need for good quality water, and detailed
information on the many different ways of achieving
it, has been well documented. Keith Bodman, director
of horticulture, environmental sciences and rural
studies, Challenger TAFE, WA, claims: “The quality of
your water will determine what crops can be
successfully grown, the methods of cropping; and the
types of treatment needed to make it suitable for use,
re-use, or discharge from the site.”
The provision of good quality water is a fundamental
but potentially complex issue. The reader is advised to
refer to the publications listed below and consult with
the relevant Nursery and Garden Industry associations
and/or state authorities.
Periodic testing of water being used in fogging and
misting systems for plant and human pathogens can
also help determine the water quality and/or the
effectiveness of the water treatment.
Further reading
Rolfe, Chris, et al. (2000), Managing water in plant
nurseries, second edition. NSW Agriculture.
Bodman K. (1997), ‘Improving water quality’.
Ornamental Update (Volume 12 number 3),
Queensland Department of Primary Industries.
‘Using ultra violet radiation and chlorine dioxide to
control fungal plant pathogens in water’, The Nursery
Papers, 1996 #05.
‘Water disinfestation – chloro-bromination and ozone
systems get the thumbs up!’ The Nursery Papers, 1997
#08.
‘Slow Sand Filtration (SSF) for water treatment in
nurseries and greenhouses’, The Nursery Papers, 1999
#03.
The bottom line
Town water that has been treated and used for
domestic household purposes (not ‘Grey Water’) is not
likely to cause any plant or human health problems.
Surface water (dam, river, creek or recycled water)
should be treated for plant pathogens to ensure
optimum plant growth. This treatment, assuming it is
regularly monitored and effective, will also prevent
possible human diseases.
Acknowledgements
The author, Dr David Douglas, Douglas Consulting
Australia, is grateful for the assistance provided by Mr
D. Randall of Floranda Flowers, Cabariah,
Queensland; and by Ms C. Lane of GrowSearch,
Department of Primary Industries, Queensland.
If there remain any doubts about the quality of the
water being delivered by fogging or misting systems,
then the water should be tested for Legionella bacteria
and other human water-borne pathogens by the
relevant state public health laboratories.
Page 2 – © NGIA – The Nursery Papers – Issue no 2001/5