Glyphosate skin binding, absorption, residual tissue distribution, and skin decontamination.
Glyphosate is a broad-spectrum postemergence translocated herbicide. Its interactions with skin and potential systemic availability through percutaneous absorption was studied by skin binding, skin absorption, residual tissue distribution, and skin decontamination. Glyphosate in a final formulation (Roundup) undiluted and diluted with water 1:20 and 1:32, would not partition into powdered human stratum corneum (less than 1%). In vitro percutaneous absorption through human skin into human plasma as receptor fluid was no more than 2% over a concentration range of 0.5-154 micrograms/cm2 and a topical volume range of 0.014-0.14 ml/cm2. Disposition of glyphosate following iv administration of 93 and 9 micrograms doses to rhesus monkeys was mainly through urine excretion, 95 +/- 8 and 99 +/- 4% in 7 days, respectively. Percutaneous absorption in vivo in rhesus monkey was 0.8 +/- 0.6% for the low dose (25 micrograms/cm2) and 2.2 +/- 0.8% for the high dose (270 micrograms/cm2). No residual 14C was found in organs of the monkeys euthanized 7 days after the topical application. Washing the skin application site with soap and water removed 90 +/- 4% of applied dose, and washing with water only removed 84 +/- 3% of applied dose. Both soap and water and water only were equal in ability to remove glyphosate from skin over a 24 hr skin application period. About 50% of the initially applied dose could be recovered after 24 hr. Glyphosate is very soluble in water and insoluble in most organics (octanol/water log P = -1.70) and therefore not compatible with the lipid-laden stratum corneum.(ABSTRACT TRUNCATED AT 250 WORDS)
Wester
R C
RC
Department of Dermatology, University of California, San Francisco 94143-0989.
Melendres
J
J
Sarason
R
R
McMaster
J
J
Maibach
H I
HI
D000287:Administration, Topical; D000818:Animals; D046508:Culture Techniques; D005260:Female; D005998:Glycine / Q000031:analogs & derivatives* / Q000737:chemistry / Q000378:metabolism / Q000493:pharmacokinetics; D006801:Humans; D007275:Injections, Intravenous; D008253:Macaca mulatta; D012867:Skin / Q000378:metabolism*; D012869:Skin Absorption; D014018:Tissue Distribution; D000097797:Glyphosate
D005998:Glycine; D000097797:Glyphosate