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 potential.”  

Contact information 

Reference 

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