Deer, Howard M.

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PesticidesFact SheetPESTICIDE ADSORPTIONAND HALF -LIFEHoward M. Deer, Extension Pesticide Specialist Utah State University, Logan UT 84322-4620February 1999 AG/Pesticides/15This chart lists the soil adsorption coefficient (K oc) and soil half-life (T1/2) for commonlyused pesticides. The soil adsorption coefficient can be considered an index for pesticide mobility,but one must also take into account the pesticide’s half-life. For instance, the top three pesticideshave relatively low soil adsorption coefficients, which implies that they have the potential to leach.However, they also have short half-lives so generally they do not last long enough in the soil toreach ground water. These numbers are useful for comparing relative differences betweenpesticides and should not be construed as absolute values.Common Name/Trade NameSoil Adsorption Coefficient (µg/g)*K ocHalf-life (Days)**T 1/2acephate/Orthenedicamba/Banvelmethamidophos/Monitorpicloram/Tordon2,4-D /Weedonedimethoate/Cygon, Dimatecarbofuran/Furadanoxamyl/Vydatealdicarb/Temikbromacil/Hyvar1,3-dichloropropene/Telonebentazon/Basagranmetalaxyl/Apronhexazinone/Velparterbacil/Sinbarethoprop/Mocapmethomyl/Lannatetebuthiuron/Spike2251620202225303232345054557072803146901075043060102070901202530360Common Name/Trade NameSoil Adsorption Coefficient (µg/g)*K ocHalf-life (Days)**T 1/2atrazine/Aatrexacifluorfen/Tacklesimazine/Princepprometon/Pramitolalachlor/Lassocyanazine/Bladexcaptan/Orthocideeptc/Eradicanemetolachlor/Dualcarbaryl/Sevinlinuron/Loroxdiuron/Karmexterbufos/Counternorflurazon/Solicamoryzalin/Surflanfonofos/Dyfonateazinphos-methyl/Guthiondiazinon/Knox-Out, D.Z.N.phorate/Thimetchlorothalonil/Bravo, Daconilmalathion/Cythion, Fyfanonbenomyl/Benlateethalfluralin/Sonalan, Curbitfenvalerate/Ectrinfluazifop-p-butyl/Fusiladechlorpyrifos/Lorsbantrifluralin/Treflan, Tri-4diclofop-methyl/Hoelonglyphosate/Roundupparaquat/Gramoxone1001131301501701902002002003004004805006006008701,0001,0001,0001,3801,8001,9004,0005,3005,7006,0708,00016,00024,0001,000,000601460500151436901060905902040104060301240603515306037471,000*The larger the K oc, the more strongly the pesticide is held to soil organic matter and theless likely it will leach. The K oc value represents the adsorption of the pesticide on the soilnormalized by the organic matter to provide a single representation of a particular pesticide for allsoils. For this reason, the uncertainty could be plus or minus twice the listed value.**Half-life is the period of time it takes for one-half of the amount of pesticide in the soilto degrade. Each half-life that passes reduces the amount of pesticide present in the soil by one-half, i.e. 1 to 1/2 to 1/4 to 1/8 to 1/16, etc. Half-life can vary due to soil microbial populations, soilmoisture, soil temperatures, and other factors. These numbers represent a typical value from thescientific literature. Nonpersistent pesticides have a half-life of 30 or less days, moderatelypersistent pesticides have a half-life of 30 to 99 days, persistent pesticides have a half-life greaterthan 100 days.Source: SCS/ARS/CES, Pesticide Properties Database for Environmental Decision-Making, August 10, 1994.Utah State University Extension and its employees are not responsible for the use, misuse ordamage caused by application or misapplication of the products or information in this publication, and makeno endorsement explicitly or implicitly of this publication or information listed herein.Utah State University Extension is an affirmative action/equal employment opportunity employer andeducational organization. We offer our programs to persons regardless of race, color, national origin, sex,religion, age or disability.Issued in furtherance of Cooperative Extension work, Acts of May 8 and June 30, 1914, incooperation with the U.S. Department of Agriculture, Robert L. Gilliland, Vice-President and Director,Cooperative Extension Service, Utah State University, Logan, Utah. (EP/DF/03/99)PRECAUTIONARY STATEMENTAll pesticides have both benefits and risks. Benefits can be maximized and risks minimizedby reading and following the labeling. Pay close attention to the directions for use and theprecautionary statements. The information on pesticide labels contains both instructions andlimitations. Pesticide labels are legal documents and it is a violation of both federal and state lawsto use a pesticide inconsistent with its labeling. The pesticide applicator is legally responsible forproper use. Always read and follow the label.

Pesticide Adsorption and Half-Life

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Pesticide Adsorption and Half-Life

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