Krenite (ammonium ethyl carbamoylphosphonate) is a new and promising chemical formulation for brush control which appears to be considerably safer than other formulations. To assess its suitability as a brush control agent, a laboratory study was undertaken by B.C. Research to determine the maximum concentration of Krenite that does not harm salmon and trout which may be resident in watersheds nearby spray operations.
Coho salmon and rainbow trout were transiently exposed (for 4 or 12 days) to a range of Krenite concentrations at several sensitive stages of development. These Included three stages of egg development, newly-hatched alevins (yolk-sac fry), swim-up (feeding) fry, fingerlings, pre-smolts and smolts (salmon only). All mortaiities were recorded during and subsequent to Krenite exposures. Lethal threshold-effect concentrations of Krenite were calculated from these data for each specified stage of development. Survivors from egg and fry stages which had been exposed to Krenite concentrations less than the lethal threshold level were returned to fresh running water lor further study. They were reared to actively growing fingerling size and compared to like groups which had been held in freshwater only (controls) in order to determine the effects of transient Krenite exposures on their subsequent development, growth and condition. Additional studies were conducted with rainbow trout swim-up fry and fingerlings to determine whether the toxicity of Krenite was affected by temperature, pH, hardness, alkalinity and other variations in receiving-water characteristics which might be encountered during spray operations.
For both salmonid species it was found that newly-hatched alevins or yolk..sac fry were most sensitive to Krenite. Egg stages on the other hand were highly tolerant of Krenite. Other post-hatched stages were somewhat more tolerant to Krenite than the newly-hatched alevin stage. Generally coho salmon were more tolerant to Krenite than rainbow trout. No latent effects were found in the development, growth or condition of survivors previously exposed as eggs or fry to Krenite concentrations less than the lethal threshold level. Therefore, the threshold-effect concentrations for Krenite and salmonld fish were based on the lethal threshold concentrations found for the most sensitive developmental stage, yolk-sac fry. These values were 618 (coho) and 367 mg/liter (rainbow) when Krenite exposures were 4 days, and 250 mg/liter (coho) when fish were held in Krenite for 12 days. Longer Krenite exposures did not lower the lethal threshold further. A comparison of available information concerning the toxicity found for Krenite relatve to other brush control herbicides (2.4-D; 2,4,5-T; silvex; picloram; amitrole; and Roundup) indicated that Krenite was from 100 to 10,000 times less toxic to salmonid fish than these alternative chemicals.
While the toxic effects of Krenite are very modest In comparison with other brush control agents, it should be noted that increases in temperature, pH, hardness and alkalinity were found in some cases to enhance the toxicity of Krenite considerably. A theoretical estimate of the maximum strength of Krenite that would be found in shallow surface waters, due to direct overhead spray application. indicated that Krenite strengths 75 times this maximum theoretical strength would be required to cause detrimental effects. This estimate was based on the threshold-effect concentrations of this herbicide found for salmonid fish in partial lifecycle studies, assuming moderate (12°C) test temperatures and diluent waters with low pH, alkalinity and hardness characteristics.
For further information request; Toxicity Studies witl) the Brush-Control Herbicide Krenite and Salmonid Fish, Final Report, September, 1980. from the address below.
B.C. Ministry of Forests
Information Services Branch
1450 Government Street,
[Abstract contains full text of memo.]
BC Forest Service - Research Division. 1980. Toxicity studies with the brush-control herbicide Krenite and salmonid fish. British Columbia Ministry of Forests, Lands, Natural Resource Operations and Rural Development. Research Memo (FLNRORD). RM43
Topic: FLNRORD Research Program
Keywords: FLNRORD, Research Memo, British Columbia
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