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Agent Orange in Lake Pend Oreille?

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Plan to contain Eurasian Milfoil engenders controversy. Will it work?

The emails and phone calls are frightening in their intensity. Bonner County's plan to treat Eurasian Milfoil in Lake Pend Oreille in July with three applications of Sonar PR, along with an application of the chemical 2,4-D in late July, have some residents almost frantic with worry. Their concern is that chemical treatment - in particular, treatment with a chemical used in Agent Orange - will prove hazardous for those who use the lake for recreation.

The county's plan is to treat milfoil infestations with Sonar PR, an herbicide whose active ingredient is fluridone. Beginning on July 10 (as of this writing) the treatment will consist of one application at 20 parts per billion, followed by two treatments at 10 ppb each.

According to the pesticide database for the Pesticide Action Network, fluridone is considered "unlikely to be hazardous." In addition, it has been found to be "not acutely toxic" and is "not a likely carcinogen."

Milfoil is particularly susceptible to fluridone and it is theoretically possible to achieve a 100 percent kill with this treatment. If all milfoil is killed by fluridone treatment the only way that milfoil can reinfest the lake is to be reintroduced or to germinate from seeds. Germination by seeds is considered rate.

Washington State has had excellent success using fluridone for milfoil eradication but, they say, "There is no guarantee that every lake group who tries this method will achieve the same results."

Indeed, there is some suggestion it will not. Fluridone, instead of being applied directly to milfoil plants, must be used as a whole-lake treatment. In Minnesota, three lakes were treated with fluridone at 5 ppb - all milfoil was eradicated, but so was 94 percent of the native plant species in the lake. "This damage," reported the Minnesota Department of Natural Resources, "appears to outweigh the benefits of controlling milfoil."

A report by Washington's Department of Ecology states, "In most Washington lakes treated with fluridone, milfoil is found growing in the lake from two to five years later. It is suspected that milfoil is reintroduced via boating activity, since it is often discovered near a public boat launch. However, anecdotal evidence also suggests that milfoil seeds can germinate during dewatering."

While there is no direct toxicity of fluridone to animals, the loss of habitat does cause indirect impacts. The smaller fish lose their hiding places and because the larger fish can find them easily, they have greater chances of being eaten.

The second chemical Bonner County will use to treat milfoil is 2,4-D, what the EPA describes as "a colorless, odorless powder used as an herbicide..." and what some residents call "a chemical found in Agent Orange." That's a little misleading if you think of Agent Orange as something extremely toxic to humans - the problems with Agent Orange arose from a contaminant, Dioxin, in the defoliant.

Exposure to 2,4-D at levels above thee EPA's Maximum Contaminant Level of 70 ppb in drinking water for relatively short periods of time can cause damage to the nervous system.

Additional EPA studies show that lifetime exposure can also include impairment of kidneys and liver.

California's Office of Environmental Health Hazard Assessment lists 2,4-D and related compounds as "developmental toxicants." And the Minnesota Department of Health recommends an MCL of only 6 ppb.

The EPA states, "The short-term effects to exposure of levels much higher than the MCL include dizziness, stiffness of joints, and headache. In terms of chronic effects from long-term exposure to very high levels, one can experience liver and kidney problems and more serious neurotoxic effects. 2,4-D is not a human carcinogen." The EPA lists a reference dose of 0.1 mg/kg/day. That means that a 180-pound person can be exposed to 6 mg of 2,4-D per day for his/her entire life and expect no adverse effects.

According to a report for Connecticut's Plant Science Day, Gregory Bugbee and Dr. Jason White state, "This is far more 2,4-D than could ever be contacted by exposure to a treated lake. The safety of the herbicide has to do with the fact that this is a synthetic plant hormone that has no real mode of toxicity in animals except at extremely high levels."

But is 2,4-D effective? The Minnesota Department of Natural Resources, which has used 2,4-D in an attempt to eradicate milfoil, states, "The MNDNR's experience with attempts to use 2,4-D herbicide to eradicate milfoil is consistent with experience elsewhere, which indicates that efforts to eradicate this exotic are "...rarely, if ever, likely to succeed" (Smith and Barko, 1990:60). Our experience in attempting to prevent the spread of milfoil within a lake is also consistent with the observation by Smith and Barko (1990:60) that efforts to prevent the spread of milfoil within a lake may slow its expansion, but rarely prevent its dispersion within a lake."

If chemicals won't work, what will? That's hard to say. The use of mechanical harvesters is as effective as chemical treatment in the short term, but it must be repeated on a regular basis or milfoil will return.

More disruptive approaches such as dredging or rotovation eliminate or can eliminate all plants, reducing habitat for fish and food for waterfowl, and potentially destabilizing sediments, resulting in murky water.

Biological control methods, such as the use of carp in Washington, are also of limited efficacy. Carp, for example, can decimate native plant populations along with the milfoil. Lack of "host specificity," in fact, is one of the major drawbacks to biological controls.

The greatest biological successes have been seen with weevils, with some declines (though not eradication) in milfoil infestation noted in Wisconsin, Illinois and Minnesota.

It's as unlikely that community protest will prevent the use of chemical poisons to eradicate milfoil in Lake Pend Oreille as it is that the chemical poisons will be successful at the job. Given the lack of a fully successful alternative, however, it's also not likely that the county will be swayed from its chemical path.

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Landon Otis

Tagged as:

Environment, Lake Pend Oreille, milfoil, 24-D

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