Consultant's Report - Minnesota State Legislature

• Development ofLTso and LT99 (exposure time required for 50 % and 99 % mortality)
at the maximum permitted exposure to Cutrine®-Ultra on 24-h old larval mussels (see
Appendix 4).
• Recommendations regarding use of Cutrine®-Ultra to control D. polymorpha in Lake
Ossawinnamakee, MN. Data presented in Appendices 1 - 4 shall be used to address
the problem statement. In addition, we present an explicit statement of areas of
uncertainty, and recommendations regarding further options to limit spread of D.
polymOlpha.
Recommendations Regarding Use of Cutrine®-Ultra to Control D. polymorpha in
Lake Ossawinnamakee, MN
Toxicity ojCutrine@-Ultra to larval and adult D. polymOlpha
Laboratory trials indicate that Cutrine®-Ultra can be used to control larval D.
polymorpha at permitted concentrations. We estimate 99 % control of larval D.
polymorpha by 24-h exposure to 0.027 - 0.081 mg CulL Cutrine®-Ultra (from the LC99
range of Cutrine®-Ultra, Experiment 1, Appendix 2) in Lake Ossawinnamakee water at
18 D C. MN DNR have communicated that control measures have used a weekly treatment
with 1 mg CulL as Cutrine®-Ultra, which attenuated to as low as 0.2 mg CulL prior to
reapplication (Montz, pers. comm.). We therefore conclude that the current weekly
treatment employed by MN DNR is at least approximately lOx that required for 99 %
efficacy, a factor that is likely to provide adequate control provided that water residence
time in the treated area is not significantly less than 24 h. We also estimate 99 % control
of D. polymorpha larvae following 52-minute exposure to Cutrine®-Ultra concentrations
as low as 0.331 mg CulL (Appendix 4).
In addition, Appendix 2 indicates that this Cutrine®-Ultra concentration is likely
to prevent fertilization of released gametes, due to a toxic action other than that of the
chelated Cu, and possibly due to the surfactantlpenetrant combination in Cutrine®-Ultra.
Adult D. polymOlpha were significantly more resistant to Cutrine®-Ultra than
were larval stages. Estimates for 99 % adult control were dependent upon exposure time,
and ranged from 1.7 mg CulL (96-h exposure) to 8.8 mg CulL (48-h exposure) in Lake
Ossawinnamakee water at 18 DC. We conclude that exposure to the current Cutrine®­
Ultra treatment regime for up to 96 h is insufficient to contral adults. However, since our
96-h data do suggest 99 % adult control in 1.7 mg CulL, it is likely that longer exposures
to Cu at I mg CulL might provide adequate adult control in Lake Ossawinnamakee
water. Although the data are not sufficient to support this theory, MN DNR might
consider whether to treat Lake Ossawinnamakee at 1 mg CulL for a single prolonged
period as a control measure for the entire adult D. polymorpha population.
Areas ojuncertainty
4