{{redirect|Tordon|the Swedish ships|HSwMS Tordön}} {{chembox | Verifiedfields = changed | Watchedfields = changed | verifiedrevid = 472033103 | ImageFile = Picloram.png | ImageSize = 160 | ImageAlt = Skeletal formula | ImageFile1 = Picloram-3D-spacefill.png | ImageSize1 = 160 | ImageAlt1 = Picloram molecule | PIN = 4-Amino-3,5,6-trichloropyridine-2-carboxylic acid | OtherNames = Picloram<br>Tordon<br>Grazon |Section1={{Chembox Identifiers | PubChem = 15965 | ChemSpiderID_Ref = {{chemspidercite|correct|chemspider}} | ChemSpiderID = 15170 | InChI = 1/C6H3Cl3N2O2/c7-1-3(10)2(8)5(9)11-4(1)6(12)13/h(H2,10,11)(H,12,13) | InChIKey = NQQVFXUMIDALNH-UHFFFAOYAR | StdInChI_Ref = {{stdinchicite|correct|chemspider}} | StdInChI = 1S/C6H3Cl3N2O2/c7-1-3(10)2(8)5(9)11-4(1)6(12)13/h(H2,10,11)(H,12,13) | StdInChIKey_Ref = {{stdinchicite|correct|chemspider}} | StdInChIKey = NQQVFXUMIDALNH-UHFFFAOYSA-N | Abbreviations = ATCP | CASNo_Ref = {{cascite|correct|CAS}} | CASNo = 1918-02-1 | UNII_Ref = {{fdacite|changed|FDA}} | UNII = O7437X49DW | EINECS = | ChEMBL_Ref = {{ebicite|correct|EBI}} | ChEMBL = 461349 | SMILES = Nc1c(Cl)c(Cl)nc(C(=O)O)c1Cl | RTECS = | MeSHName = | ChEBI_Ref = {{ebicite|correct|EBI}} | ChEBI = 34922 | KEGG_Ref = {{keggcite|correct|kegg}} | KEGG = C14310 }} |Section2={{Chembox Properties | C=6 | H=3 | Cl=3 | N=2 | O=2 | Appearance = colorless to white crystalline solid<ref name=PGCH/> | Odor = chlorine-like<ref name=PGCH/> | Density = | MeltingPtC = 218.5 | MeltingPt_notes = decomposes | BoilingPt = | BoilingPt_notes = | Solubility = 0.04% (20°C)<ref name=PGCH/> 430 mg/L at 25 deg C<ref>{{Cite web | url=https://pubchem.ncbi.nlm.nih.gov/compound/picloram#section=Solubility&fullscreen=true |title = Picloram}}</ref> | VaporPressure = 0.0000006 mmHg (35°C)<ref name=PGCH/> | SolubleOther = | Solvent = | pKa = | pKb = }} |Section7={{Chembox Hazards | MainHazards = | NFPA-H = | NFPA-F = | NFPA-R = | NFPA-S = | HPhrases = | PPhrases = | GHS_ref = | FlashPt = | AutoignitionPt = | ExploLimits = | PEL = TWA 15 mg/m<sup>3</sup> (total) TWA 5 mg/m<sup>3</sup> (resp)<ref name=PGCH>{{PGCH|0514}}</ref> | IDLH = N.D.<ref name=PGCH/> | REL = none established<ref name=PGCH/> }} }}
'''Picloram''' is a systemic herbicide used for general woody plant control. It also controls a wide range of broad-leaved weeds, but most grasses are resistant.<ref name="PMEP">[https://pmep.cce.cornell.edu/profiles/extoxnet/metiram-propoxur/picloram-ext.html Picloram Pesticide Information Profile], Pesticide Management Education Program, Cornell University.</ref> A chlorinated derivative of picolinic acid, picloram is in the pyridine family of herbicides.
Picloram can be sprayed on foliage, injected into plants, applied to cut surfaces, or placed at the base of the plant where it will leach to the roots. Once absorbed by the foliage, stem, or roots, picloram is transported throughout the plant.
Herbicides containing picloram are sold under a variety of brand names. Dow Chemicals and now Dow AgroSciences sell herbicides containing it under the brand name Tordon.<ref name="Greene2005">{{cite book|author=Stanley A. Greene|title=Sittig's Handbook of Pesticides and Agricultural Chemicals|url=https://books.google.com/books?id=hAoKEHpyu6wC&pg=PA717|year=2005|publisher=William Andrew|isbn=978-0-8155-1903-4|page=717}}</ref>
During the Vietnam War, picloram and other herbicides were combined to make Agent White (commercially available as Tordon 101) and enhanced Agent Orange, which was previously used by the British military during the Malayan Emergency. Large quantities of these herbicides were sprayed by U.S. forces in areas where they considered its long-term persistence desirable, such as inland forests.<ref name="HerbicidesMedicine1994">{{cite book|author1=Committee to Review the Health Effects in Vietnam Veterans of Exposure to Herbicides|author2=Institute of Medicine|title=Veterans and Agent Orange: Health Effects of Herbicides Used in Vietnam|url=https://books.google.com/books?id=RjCHcoUE3B8C&pg=PA89|year=1994|publisher=National Academies Press|isbn=978-0-309-55619-4|pages=89–90}}</ref> In 1974, {{convert|413000|lbs|t}} of picloram were used in the U.S., mainly by government and industry.<ref>{{cite web |title=Pesticide Usage Survey of Agricultural, Governmental, and Industrial Sectors in the United States, 1974 |url=https://nepis.epa.gov/Exe/ZyPURL.cgi?Dockey=91012P4O.txt |website=epa.gov |publisher=EPA |date=1977}}</ref>
==Safety== Picloram is of moderate toxicity to the eyes and only mildly toxic on the skin.<ref name="PMEP"/> No history of human intoxication by picloram has been documented, so symptoms of acute exposure are difficult to characterize.
Picloram is the most persistent of its family of herbicides.<ref>[https://web.archive.org/web/20030402062329/http://www.epa.gov/safewater/contaminants/dw_contamfs/picloram.html Consumer Factsheet on: PICLORAM], U.S. Environmental Protection Agency</ref> It does not adhere to soil, so it may leach into groundwater, and has in fact been detected there. It is degraded in soil and water mainly by microbes. Picloram has very little tendency to accumulate in aquatic life.
Gardeners who use dung as fertilizer should check to make certain that the animal source has not grazed on picloram-treated hay, as the dung still has broadleaf-killing potency.<ref>[http://www.extension.umn.edu/distribution/livestocksystems/M1197.html#3 Use Caution When Harvesting and Feeding Ditch Hay] {{webarchive|url=https://web.archive.org/web/20100614011214/http://www.extension.umn.edu/distribution/livestocksystems/M1197.html |date=2010-06-14 }}, U. Minnesota Extension</ref>
In regards to occupational exposures, the U.S. Occupational Safety and Health Administration has established a permissible exposure limit of 15 mg/m<sup>3</sup> total exposure and 5 mg/m<sup>3</sup> for respiratory exposure, over an eight-hour workshift.<ref>[https://www.cdc.gov/niosh/npg/npgd0514.html NIOSH Pocket Guide to Chemical Hazards], Centers for Disease Control and Prevention</ref>
===Carcinogenicity=== A 2026 study in ''Nature Medicine'' reported an association between picloram exposure signatures and the alarming rise in early-onset colorectal cancer. The researchers used DNA methylation scores as indirect markers of previous exposure to lifestyle and environmental factors, including pesticides. A higher picloram-related methylation score was associated with colorectal cancer diagnosed before age 50, compared with colorectal cancer diagnosed at age 70 or older. This association was replicated in a meta-analysis of nine colorectal cancer cohorts.<ref name="Maas2026">{{cite journal |last1=Maas |first1=Silvana C. E. |last2=Baraibar |first2=Iosune |last3=Lemler |first3=Lea |last4=Butjosa-Espín |first4=Maria |last5=Blanco Irazuegui |first5=Odei |last6=Tabernero |first6=Josep |last7=Elez |first7=Elena |last8=Seoane |first8=Jose A. |title=Epigenetic fingerprints link early-onset colon and rectal cancer to pesticide exposure |journal=Nature Medicine |year=2026 |doi=10.1038/s41591-026-04342-5}}</ref>
The same study also compared estimated pesticide use with cancer incidence in 94 United States counties over 21 years. Picloram use remained associated with early-onset colorectal cancer incidence after adjustment for socioeconomic factors and other pesticide use. The authors noted that picloram was first registered as a herbicide in the United States in 1964, so people who could have been exposed to it from childhood would often still be younger than 70 in 2026. They suggested that this could partly explain why the association was mainly seen for early-onset disease. The study found an association, but did not perform research to (dis)prove that picloram causes colorectal cancer. Therefore, the authors stated that further longitudinal and experimental research is needed to test causality, dose dependence and latency.<ref name="Maas2026" />
==References== <references/>
==External links == * {{PPDB|525}}
{{Herbicides}}
Category:Auxinic herbicides Category:Chloropyridines Category:4-Aminopyridines Category:Aromatic acids Category:Herbicides Category:Beta-Amino acids Category:Group 4 herbicides