Flumioxazin has a number of positive environmental fate characteristics. It degrades relatively
quickly, progressively through more polar, water soluble degradates. However, there seems to be
a lack of knowledge of the fate of the major degradates (see section in the review on
Uncertainties and Data Gaps). There is a general concern with aquatic herbicide uses for
contamination of groundwater underlying treated ponds. However, water column fate data
indicate that water concentrations of flumioxazin and its degradates over shorter and longer term
durations would be below levels of human health concern for drinking water. Therefore
concentrations potentially reaching groundwater would be even less given degradation processes
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that would work on the parent and degradates as they pass though sediments and travel with
groundwater. Flumioxazin has relatively high, non-selective predicted aquatic toxicity to a
range of aquatic organisms. Our evaluation focused on fish and invertebrates. Included are high
risks of concern to endangered species in some cases and to other non-endangered species in
other cases after both short and long-term exposures. Flumioxazin has a high, non-selective,
acute toxicity to all plants (including endangered species) from terrestrial to planktonic unicellular
to vascular aquatic plants.
For threatened and endangered species, flumioxazin has a high, non-selective, acute toxicity and
poses a high risk to all plants from terrestrial to planktonic unicellular to vascular aquatic plants.
The toxicological database for flumioxazin has a number of data gaps and most importantly lacks
toxicity studies conducted under natural light conditions which would permit the full expression
of the photo-induced toxicity that the flumioxazin class of compounds is known for. For this
reason, the risk estimates derived in the review with existing data are likely underestimates of the
risks to aquatic organisms.
Given these considerations, we are recommending that the herbicide Clipper®, containing the
active ingredient flumioxazin be allowed for control of nuisance aquatic vegetation in the
Commonwealth with a number of restrictions which either are in addition to those on the product
label or supersede those on the label:
· The maximum permissible application concentration should be 200 ug/L.
· In order to limit the spatial extent of non-target damage from the toxicity of flumioxazin,
no more that ¼ of the water body may be treated in any one year. This will allow for
subsequent repopulation of damaged areas from adjacent untreated waters.
· Applications taking place within ¼ of the water body should be staggered around and
within the basin to ensure that natural recolonization of native plants may occur. Repeat
treatments within a year should be limited to targeted treatments around shoreline
structures (e.g., boat launches, docks, swimming beaches, dams, water intake pipes, etc.).
· Treated areas may not be retreated with flumioxazin or any herbicide with a similar mode
of action (i.e., light dependent peroxidizing herbicide) in consecutive years in order to
prevent the development of herbicide resistance in treated plants. The exception to this
restriction is repeat targeted treatments in consecutive years around shoreline structures
(e.g., boat launches, docks, swimming beaches, dams, water intake pipes, etc.).
· Flumioxazin should be excluded from use in State-listed aquatic species habitats, unless
otherwise authorized in writing on a case-by-case basis by the MA Division of Fisheries
and Wildlife pursuant to MA Endangered Species Act (321 CMR 10.14 or 10.18).
· Given concerns for the toxicity of flumioxazin to mussels and the absence of knowledge
about the effects of flumioxazin on these organisms, we recommend that applicators
survey for native freshwater mussels in lakes being treated during the first year of use of
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flumioxazin-containing products and implement a monitoring program if mussels are
present to determine if any impacts to survival or growth occur after treatment. The MA
Division of Fisheries & Wildlife Natural Heritage & Endangered Species Program is
available to consult with applicators about the design and implementation of such
programs. Permits are necessary to collect and kill freshwater mussels in Massachusetts.