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Use of herbicides to kill native vegetation on Utah's public land will soar by 34 percent, according to a final environmental impact statement issued by the Bureau of Land Management.

A few of the herbicides are assumed to be carcinogenic, sometimes because studies are not complete. But the statement says all will be used with safeguards at least as strict as indicated by standards on the chemicals' labels. Also, herbicide applications are scheduled and designed to minimize impacts on non-target plants and animals."The rates of application depend on the target species, presence and condition of non-target vegetation, soil type, depth to the water table, presence of other water sources, and the requirements of the label," the statement says.

The study of BLM vegetation treatment throughout the 13 Western states says the agency's proposed alternative on the issue would destroy present vegetation on 371,640 acres a year throughout the West. This is the greatest acreage to be treated, among five alternatives studied.

"Treating vegetation is necessary to develop or restore a desired plant community, create biological diversity, increase forage or cover for animals, protect buildings and other facilities, manage fuels to reduce wildlife hazard, manage vegetation community structure, rejuvenate decadent vegetation, enhance forage/browse quality, or remove noxious weeds or poisonous plants," the statement says.

Often, when controversies erupt over vegetation treatment projects in Utah, such as "chaining" to rip out pinyon and juniper forests, the cause is the destruction of trees so that livestock ranching operations can be enhanced by planting grasses that cattle eat.

Under Alternative 1, the proposed option, total acreage treated in the West would go from the present 242,505 acres to 371,640 acres per year. Chemical treatment - herbicides sprayed by helicopter and aircraft, and distributed by vehicle and hand - would increase from today's 37,475 to 141,515 acres.

In Utah, chemical treatment of land is supposed to go up from 7,505 acres to 10,100 acres. Total acres treated would go from 23,875 to 28,450.

Rejected alternatives were: no aerial application of herbicides, no use of herbicides, no use of pre-scribed burning, and continuing current management practices.

Other than "slight" or "very slight" toxicity, negative characteristics cited for specific herbicides include:

- Atrazine. Moderately to highly toxic to fish, highly toxic to immature fish and amphibians; a possible human mutagen. It can be an eye irritant. Kidney changes have been found in rats fed the chemical, and the Environmental Protection Agency classifies atrazine as a possible uman carcinogen. - Bromacil. Classified as a possible human )carcinogen.

- Chlorsulfuron. Nothing worse than low toxicity to birds.

- Clopyralid. Severe eye irritant.

- 2,4-D. Moderately toxic to mammals, and a severe eye irritant. "Ingestion or skin exposure to 2,4-D by humans may produce many different symptoms, including irritation of the gastro-intestinal tract, chest pain, and muscle twitching." May be carcinogenic. Moderately to highly toxic for aquatic species, with crustaceans and snails among the most sensitive. Moderately toxic to some birds.

- Dicamba. Very slight skin irritant; severe eye irritant. Moderately toxic to insects.

- Diuron. Although listed as slightly toxic to mammals, "with sufficient exposure, however, diuron facilitates nervous system depression, and the resulting symptoms include slowed respiration and heart rate, weakness, and lethargy." Moderately toxic to fish, highly toxic to ome aquatic invertebrate species.

- Glyphosate. Carcinogenicity not determined. One formulation can be more dangerous to fish and aquatic invertebrates than other formulations of the chemical. - Hexazinone. Nothing cited beyond slight toxicity.

- Imazapyr. Slightly irritating to eyes and skin. Further study needed on whether it is carcinogenic.

- Mefluidide. Nothing beyond slightly toxic.

- Picloram. A slight eye irritant, very slight skin irritant. Assumed to be carcinogenic.

- Simazine. Possible human carcinogen.

- Sulfometuron methyl. Slightly irritating to eyes and skin. "Decreased reproductive success has been noticed in rats."

- Tebuthiuron. Nothing beyond slight toxicity to wildlife.

- Triclopyr. Slightly to moderately toxic to mammals. Moderate eye irritant, slight skin irritant. One formulation is highly toxic to fish.