The Clipper Herbicide label does not specify spray volumes for foliar treatments other than to
apply in sufficient volume of water per acre to ensure adequate coverage. A reasonable high-end
estimate for spray volume could be 50 gallons per acre. Consequently, a high-end estimated level
of adjuvant would be 1.35 mg/L in a 1-ft deep pond as calculated above.
MDAR/MassDEP 3 June 2013
Risk Assessment
As pointed out in the review by Pless (2005), the toxicity of the herbicide/adjuvant mixture is
driven by the surfactant. The risk quotients presented by Pless (2005), based on environmental
concentrations in an estuary scenario, were in the range of 0.13-0.051. The higher value was
determined in association with the adjuvant Hasten. That value marginally exceeded the level of
concern (LOC) of 0.05 for endangered fish. It was pointed out that the highest measured exposure
was extremely conservative in that the pesticide was applied directly to the estuary sediment (mud
flat) without interception by vegetation and measured 3 hours later in the first overflow.
For the consideration of the application in a pond, the estimated environmental concentrations
(EECs) of the Agri-Dex and Hasten adjuvants were calculated above. These two adjuvants
were selected based on the availability of toxicity data for product with adjuvant (Curran et al.,
2003). The highest estimated concentration in a water body with 1-foot depth was 1.35 mg/L.
Based on the 96-hr LC50 of 479 mg/L expressed as adjuvant (Curran et al., 2003) for the product
plus adjuvant mixture, the risk quotient is 0.0028. For the Hasten adjuvant, the risk quotient
would be 0.012. For the limonene-based adjuvants Cide-Kick and Cygnet Plus, the risk quotient
would be 0.016. These values are below levels of concern for aquatic species as established by
USEPA (2011), the most sensitive for endangered species acute risk being 0.05.
Entrix (2003) conducted a risk assessment of four adjuvants that have uses with glyphosate- and
imazapyr-based aquatic herbicides. In addition to Hasten and Agri-Dex, the LI 700 and R-
11 were included in the exposure and risk assessment. Since the spray-volume requirements for
glyphosate-based herbicide are higher compared to imazapyr-based herbicides, the risk quotients
were evaluated as a function of spray volume. The risk quotients were based on the LC50 values
for juvenile rainbow trout as reported by Smith et al. (2004). The same procedure was used here
for the concentrations developed for a pond scenario as described in Section 5.2. Figure 1 shows
that the R-11 adjuvant exceeds the most sensitive Level of Concern (LOC) over the entire
application volume range considered, while the Hasten and Agri-Dex adjuvants do not exceed
the most sensitive LOC even at the highest application volume. In the review by Entrix (2003), it
is pointed out that glyphosate-based herbicides require large application volumes (up to 100
gal/acre for efficacy), while 5 to 20 gal/acre can be used for imazapyr-based herbicides to yield
equivalent results. Consequently, imazapyr-based herbicide applications are associated with lower
adjuvant exposures compared to glyphosate-based herbicides.