Adjuvants and surfactants were also considered in human health and ecological effects risk
assessments of imazapyr use for controlling vegetation in riparian corridors (AMEC, 2009). The
most frequently used adjuvants were identified to be Agri-Dex, Dyne-Amic, Class-Act and
R-11. It should be noted that the assessment did not consider direct applications to water.
Reference was made to a study by Smith et al. (2004), which was cited above. While toxicity data
were reviewed, the document did not include a formal exposure and risk assessment for the
adjuvants.
Additional adjuvants that have been reported to being used by applicators in Massachusetts
include Cide-Kick and Cygnet Plus. These adjuvants contain d-limonene as the major surfactant.
Limonene is slightly toxic to fish and aquatic invertebrates with LC50 values of 80 mg/L and 39
mg/L, respectively (USEPA, 1994).
Exposure Assessment
Pless (2005) considered several adjuvants as used in tank mixes in the ecological risk
assessment. The environmental properties and toxicity of adjuvants were also considered with
the assessment of imazapyr herbicide use in estuaries in Washington State (Entrix, 2003). Both
reviews considered estimated adjuvant concentration in water in an estuary scenario. For the
purpose of this special review presented here, the environmental concentration of two adjuvants
Agri-Dex and Hasten was estimated in a pond scenario as described below.
It was assumed that the adjuvant was used in a 1% v/v concentration in the tank mix (the label
requires >0.25%). It was further assumed that the application volume was 50 gallons per acre
(label requirement is >5 gal for ground applications). A 1% v/v adjuvant concentration in the 50
gal spray volume would correspond to a 1.89 L adjuvant volume per acre. Based on the density
of Agri-Dex (0.879 kg/L, Agri-Dex MSDS), this volume corresponds to 1.66 kg Agri-Dex
adjuvant per acre. The peak concentration of Agri-Dex in a 1-acre water body with a 1-foot
depth can be calculated as follows: 1.66 × 106 mg / (4047 m2 × 0.3048 m × 1000 L/m3) = 1.35
mg/L. For the 6.56-feet (2-meter) and 3-feet depths the concentrations are 0.21 mg/L(mg/L) and
0.45 mg/L(mg/L), respectively. The values for the adjuvants Hasten, Cide-Kick and Cygnet
Plus are very similar for the same adjuvant concentration given that the density of these
adjuvants are very similar compared to Agri-Dex (0.87-0.9 kg/L). It should be noted that these
calculations assumed no interception by target vegetation and no sorption to sediment. The
adjuvant concentrations calculated above are slightly lower than the values for adjuvant
concentrations that were reported in Entrix (2003). Those calculations assumed a density of 1
kg/L, whereas the actual density of the adjuvant products Agri-Dex and Hasten is less than 1
kg/L.