STP891

    An Aquatic Hazard Assessment: Picloram

    Published: Jan 1985


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    Abstract

    Picloram (4-amino-3,5,6-trichloropicolinic acid) exhibits herbicidal activities on broadleaf weeds and woody plants and is registered under the trademarks of TORDON®, GRAZON®, and AMDON® herbicides. It is an organic acid (pKa = 3.2); thus at environmental pH ranges it is usually found in the ionized anionic form. Other physicochemical characteristics of picloram are water solubility 430 mg/L and vapor pressure 6.16 × 10−7 mm mercury at 35°C. The rate of dissipation of picloram in soil is dependent on the application rate, soil type, and climate. Picloram is classified as having moderate mobility in soil; however, the runoff potential of picloram is normally limited to less than 5% of the applied chemical removed from the site in runoff waters.

    Picloram is relatively nontoxic to freshwater fishes, with acute LC50 values for technical acid ranging from 4.3 mg/L for lake trout [Salvelinus namaycush (Walbaum)] to 55.3 mg/L for fathead minnows (Pimephales promelas Rafinesque). Freshwater invertebrates show similar susceptibility to technical picloram with acute LC50 values ranging from 27 mg/L for Gammarus lacustris Sars to 68.3 mg/L for Daphnia magna Straus. The most sensitive marine invertebrate tested is the eastern oyster [Crassostrea virginica (Gmelin)] with 18 < EC50 < 32 mg/L when exposed to a potassium salt formulation of picloram. Because of its relatively low toxicity to aquatic organisms and low potential for substantial quantities to enter the aquatic environment, picloram is not expected to present a hazard to the aquatic environment.

    Keywords:

    aquatic biology, weeds, herbicides, environmental chemistry, aquatic toxicity, picloram, hazard assessment


    Author Information:

    Mayes, MA
    Aquatic toxicologist, Health and Environmental Sciences Department, and soil physicist, Agricultural Products Department, The Dow Chemical Co., Midland, MI

    Oliver, GR
    Aquatic toxicologist, Health and Environmental Sciences Department, and soil physicist, Agricultural Products Department, The Dow Chemical Co., Midland, MI


    Paper ID: STP33577S

    Committee/Subcommittee: E47.01

    DOI: 10.1520/STP33577S


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