January 17, 1997
Lawn Herbicides Tracked Indoors
Residues of widely used lawn herbicides may be tracked into
homes and deposited on indoor carpet surfaces or in household
dust, according to a recent study in the journal
Environmental Science and Technology. The study, which
examined transport of 2,4-D and dicamba, concluded that 3% of
dislodgeable turf residues (i.e. the portion of a pesticide
formulation that does not adhere to the turf) were
transported to carpet dust and that 0.3% of turf residues
were transported to the carpet surface. The authors reported
that once on carpet surfaces the residues can come into
contact with skin.
According to the study, previous research has suggested that
transport of pesticides into homes presents significant risks
of human exposure, particularly for children who may ingest
residues through hand-to-mouth behavior. Once indoors,
carpets, dust and furnishings may become long-term reservoirs
for pesticides because common environmental degradation
factors such as sunlight, wind, rain or soil microbes are
absent.
In the study, researchers applied a pesticide formulation
containing 2,4-D, dicamba and mecoprop (X-Gro Broadleaf Weed
Killer) to sections of a lawn that had not been treated with
pesticides for at least 10 years. Participants then walked on
the treated plots, staggering their times and walking in
different areas so that most of the treated ground was
covered. They then either wiped their feet on a mat or walked
directly onto indoor carpeting, both of which had never been
used before. Researchers analyzed residues tracked onto the
carpets at four hours, eight hours and one day after
pesticide application. In addition, they measured levels of
turf dislodgeable residues on the lawn at these times and
over the course of several days.
For the first three days after application, the researchers
estimated a potential track-in rate of 4.5 micrograms of 2,4-
D per day. Use of entryway mats reduced the level of
pesticide residues on carpet surfaces by 25% and reduced
carpet dust residues by 33%. The researchers estimated that
2,4-D residues could remain in household carpet dust for up
to one year after turf application at concentrations of
approximately 0.3 micrograms/square meter. The authors stated
that this level is consistent with levels of 2,4-D that they
found in household dust of nine suburban homes.
A range of health and environmental impacts have been
associated with exposure to 2,4-D, including endocrine
disruption, reproductive effects, cancer and toxicity to
birds and fish; impacts associated with exposure to dicamba
include neurological effects, non Hodgkins' lymphoma (cancer)
and mutagenicity.
The authors described a recent study of 2,4-D in children's
urine that compared children from a town containing a 2,4-D
manufacturing plant to children from a town without such a
plant. The study found 2,4-D in 18% of children from the town
with the 2,4-D plant and 23% of children from the town
without the plant, implying that the presence of 2,4-D was
due to some factor or factors other than the manufacturing
plant. The authors of the track-in study stated that "Given
the fact that children's hand-to-mouth activity promotes
ingestion of contaminated carpet dust, we might assume that
chronic indoor exposure will follow a lawn application and
may result in measurable urinary levels."
The authors also pointed out that their control lawn, an area
to which no herbicide was applied, offered information about
spray drift levels. The study found that eight hours after
application turf dislodgeable residues on the untreated plot
were 2-3% of the levels found on treated turf plots at the
same time. Detectable levels were also present in the carpet
dust after track-in from the unsprayed plot. The authors
surmised that their application gun may produce a finer
aerosol than some commercial sprayers, which could result in
more drift. They pointed out that previous agricultural drift
studies have found drift levels up to 8% of the application
loading rate.
Sources: Measuring Transport of Lawn-Applied Herbicide Acids
from Turf to Home: Correlation of Dislodgeable 2,4-D Turf
Residues with Carpet Dust and Carpet Surface Residues. Marcia
Nishioka et. al. Environmental Science and Technology, Volume
30, Number 11, November 1996.
National Coalition Against the Misuse of Pesticides (NCAMP)
Technical Report, Volume 12, Number 1, January 1997.
2,4-D. Extension Toxicology Network, September 1993.
Dicamba. Caroline Cox. Journal of Pesticide Reform, Volume
14, Number 1, Spring 1994.
Contact: PANNA
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