Clays and Clay Minerals

, Volume 53, Issue 3, pp 268–277 | Cite as

Castor Toxin Adsorption to Clay Minerals

  • William F. JaynesEmail author
  • Richard E. Zartman
  • Cary J. Green
  • Michael J. San Francisco
  • John C. Zak


The extremely toxic protein, ricin, is derived from castor beans and is a potential terrorist weapon. Adsorption to clays might minimize the environmental persistence and toxic effects of this toxin. Ricin adsorption to clay minerals was measured using batch adsorption isotherms. Enzyme-linked immunoassay methods were used to quantify aqueous ricin concentrations. Montmorillonite, sepiolite and palygorskite effectively adsorbed ricin from aqueous solutions and yielded mostly Langmuir-type isotherms. The monolayer adsorption capacity from a Langmuir equation fit at pH 7 was 444 g ricin/kg for montmorillonite (SWy-2), but was only 5.6 g ricin/kg for kaolinite (KGa-1b). Monolayer capacities for sepiolite (SepSp-1) and palygorskite (PFl-1) at pH 7 were 59.2 and 58.1 g ricin/kg. The high-charge montmorillonite (SAz-1) effectively adsorbed ricin at pH 7, but yielded a linear isotherm with K = 5530 L/kg. At pH 5, both montmorillonites (SWy-2 and SAz-1) yielded Langmuir-type isotherms with monolayer capacities of 694 and 641 g ricin/kg. Clay samples with higher cation exchange capacities generally adsorbed more ricin, but adsorption also followed specific surface area. X-ray diffraction of <2 μm SWy-2 treated with 470 g ricin/kg indicated expansion up to 34.6 Å at buffered pHs of 4 and 7, but not at pH 10. Furthermore, ricin adsorption was greatest at pH 4 and 7, but minimal at pH 10. Treatment with 1.41 kg of purified ricin/kg clay at pH 5 yielded a 35.3 Å peak and adsorption of ~1.2 kg ricin/kg. Similar treatment with lower-purity ricin yielded less expansion and lower adsorption. The 35.3 Å peak interpreted either as a d002 or d001 reflection indicates a 70.6 Å or a 35.3 Å ricin/SWy-2 complex. This implies that adsorption and air drying have compressed interlayer ricin molecules by 18 to 65%. Effective ricin adsorption by montmorillonite suggests that it could be used to minimize the toxic effects of dispersed ricin.

Key Words

Adsorption Cation Exchange Capacity Kaolinite Lectin Montmorillonite Palygorskite pH Protein Ricin Sepiolite Specific Surface Area 


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Copyright information

© The Clay Minerals Society 2005

Authors and Affiliations

  • William F. Jaynes
    • 1
    Email author
  • Richard E. Zartman
    • 1
  • Cary J. Green
    • 1
  • Michael J. San Francisco
    • 2
  • John C. Zak
    • 2
  1. 1.Plant and Soil Science DepartmentTexas Tech UniversityLubbockUSA
  2. 2.Biological Sciences DepartmentTexas Tech UniversityLubbockUSA

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