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pesticide mixtures to aquatic life. Int. Env. Assessment and Manag. 3:364-372.
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validation of approaches for predictive hazard assessment of realistic pesticide mixtures.
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pesticide mixtures. Ecology and Society 9:1-15.
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MDAR/MassDEP 1 June 2013
Risk Assessment of Adjuvants Used with Aquatic Herbicides
The Clipper Herbicide label indicates that treatment of emergent or floating vegetation requires
the addition of an adjuvant in the tank mix. The label suggests the use of nonionic surfactants at
recommended manufacturer’s rates.
The risk assessment of several adjuvant products that are commonly used with the application of
aquatic herbicides is presented below.
The toxicity of adjuvants was considered in risk assessments of herbicide applications in estuaries
in Washington State (Entrix, 2003) and San Francisco (Pless, 2005). Commonly used adjuvants
included non-ionic alkylphenol ethoxylates and/or fatty acids (e.g., R-11, X-77), and crop-oil
based concentrates (e.g., Agri-Dex, Hasten). On the basis of EPA toxicity criteria, the nonionic
alkylphenol ethoxylates (e.g., R-11, X-77) are moderately acutely toxic to aquatic
species. The crop-oil based surfactants would be considered practically non-toxic. Smith et al.
(2004) characterized the toxicity of four surfactants to juvenile rainbow trout and implications for
their use over water. The 96-h LC50 values were 6.0 mg/L for R-11, 17 mg/L for LI 700, 74
mg/L for Hasten, and 271 mg/L for Agri-Dex. The 96-h EC50s (on-bottom gilling behavior)
were 4.4 mg/L for R-11 and 17 mg/L for LI 700.
Curran (2003) determined the toxicity of formulated herbicide product Arsenal Herbicide (a.i.,
imazapyr) with and without the adjuvants Agri-Dex and Hasten using juvenile rainbow trout.
The 96-h LC50 value for Arsenal Herbicide without adjuvant was 77,716 mg/L. In systems
containing Arsenal plus adjuvant, the 96-h LC50 was expressed as mg/L surfactant and were
reported to be 113 mg/L for Hasten and 479 mg/L for Agri-Dex. These values were compared
with the LC50 values for the surfactants alone which were 74 mg/L for Hasten and 271 mg/L for
Agri-Dex. Since this source of information was a meeting abstract, no further evaluation of data
was possible for the review presented here. The authors concluded that the data suggest that the
Arsenal Herbicide formulation has low toxicity to juvenile rainbow trout, the toxicity the tank
mixes is driven by the surfactants, and depending on the type of surfactant and its percentage in
the tank mix, surfactants may pose greater hazard to non-target species than Arsenal Herbicide.
MDAR/MassDEP 2 June 2013