Publication investigates the implications of forest herbicide applications for aquatic organisms
Forest herbicides are used in many regions
of the US to manage competing vegetation. Forest herbicides have many practical
advantages relative to other vegetation management tools and help reduce the
potential for some environmental impacts such as erosion and nutrient runoff.
Forest herbicides undergo a rigorous
registration process, are used infrequently, are applied at low rates, are
applied to only a small portion of the total forest land base in any given
year, and are applied using state-developed best management practices. Nevertheless,
questions sometimes arise regarding the implications of forest herbicide use for
plant and animal communities, with aquatic communities being of primary interest.
Recently, authors with NCASI, Nutter and
Associates (Athens, Georgia), and the University of Saskatchewan published
results from a study that characterizes concentrations of four forest
herbicides in streamwater during and after aerial application of herbicides in
Oregon’s Coast Range.
The authors also compare maximum
concentrations to traditional toxicity metrics—specifically no observed effect
concentration (NOEC) and no observed adverse effect concentration (NOAEC)—from
a range of laboratory and mesocosm studies to assess the potential for effects
on the site-specific aquatic community.
The authors found very small herbicide
concentrations in streamwater for brief periods following the first few storm events after the application. However, the concentrations were well below the
levels shown to have adverse effects on fish, amphibians, or invertebrates.
The abstract for the publication, which is
in the “Early View” section of the journal Integrated
Environmental Assessment and Management, follows.
“Glyphosate, aminomethylphosphonic acid (AMPA), imazapyr,
sulfometuron methyl (SMM), and metsulfuron methyl (MSM) were measured in
streamwater collected during and after a routine application of herbicides to a
forestry site in Oregon's Coast Range. Samples were collected at 3 stations:
HIGH at the fish-no-fish interface in the middle of the harvest and spray unit,
MID at the bottom of the unit, and LOW downstream of the unit. All herbicides
were applied by helicopter in a single tank mix. AMPA, imazapyr, SMM, and MSM
were not detected (ND) in any sample at 15, 600, 500, and 1000 ng/L,
respectively. A pulse of glyphosate peaking at approximately equal to 62 ng/L
manifested at HIGH during the application. Glyphosate pulses peaking at
115 ng/L (MID) and 42 ng/L (HIGH) were found during the first 2 postapplication
storm events 8 and 10 days after treatment (DAT), respectively: glyphosate was
less than 20 ng/L (ND) at all stations during all subsequent storm events. All
glyphosate pulses were short-lived (4-12 h). Glyphosate in baseflow was
approximately equal to 25 ng/L at all stations 3 DAT and was still
approximately equal to 25 ng/L at HIGH, but ND at the other stations, 8 DAT:
subsequently, glyphosate was ND in baseflow at all stations. Aquatic organisms
were subjected to multiple short-duration, low-concentration glyphosate pulses corresponding to a cumulative time-weighted average (TWA)
exposure of 6634 ng/L × h. Comparisons to TWA exposures associated with a range
of toxicological endpoints for sensitive aquatic organisms suggests a margin of
safety exceeding 100 at the experimental site, with the only potential
exception resulting from the ability of fish to detect glyphosate via
olfaction. For imazapyr, SMM, and MSM the NDs were at concentrations low enough
to rule out effects on all organisms other than aquatic plants, and the low
concentration and (assumed) pulsed nature of any exposure should mitigate this
Louch, J., V. Tatum, G. Allen, V.C. Hale, J.
McDonnell, R.J. Danehy, and G. Ice. 2016. Potential risks to freshwater aquatic
organisms following a silvicultural application of herbicides in Oregon’s Coast
Range. Integrated Environmental
Assessment and Management. http://dx.doi.org/10.1002/ieam.1781