Joe L. White

Factors influencing the adsorption, desorption and movement of pesticides in soil.

Seven factors are known to influence the fate and behavior of pesticides in soil systems: (1) chemical decomposition, (2) photochemical decomposition, (3) microbial decomposition, (4) volatilization, (5) movement, (6) plant or organism uptake, and (7) adsorption. The phenomenon of adsorption-desorption directly or indirectly influences the magnitude of the effect of the other six factors. Adsorption, therefore, appears to be one of the major factors affecting the interactions occurring between pesticides and soil colloids.

In vivo absorption of aluminium-containing vaccine adjuvants using 26Al

Aluminium hydroxide (AH) and aluminium phosphate (AP) adjuvants, labelled with 26Al, were injected intramuscularly (i.m.) in New Zealand White rabbits. Blood and urine samples were collected for 28 days and analysed for 26Al using accelerator mass spectrometry to determine the absorption and elimination of AH and AP adjuvants. 26Al was present in the first blood sample (1 h) for both adjuvants. The area under the blood level curve for 28 days indicates that three times more aluminium was absorbed from AP adjuvant than AH adjuvant. The distribution profile of aluminium to tissues was the same for both adjuvants (kidney > spleen > liver > heart > lymph node > brain). This study has demonstrated that in vivo mechanisms are available to eliminate aluminium-containing adjuvants after i.m. administration. In addition, the pharmacokinetic profiles of AH and AP adjuvants are different.

ALUMINUM COMPOUNDS USED AS ADJUVANTS IN VACCINES

The structure of nine commercially manufactured aluminum-containing adjuvants was investigated by X-ray diffraction, infrared spectroscopy, transmission electron micrography, and energy dispersive spectrometry. Seven samples which were labeled as aluminum hydroxide were identified as boehmite, a crystalline aluminum oxyhydroxide [AIO(OH)]. However, the degree of crystallinity varied between the samples. Two samples which were labeled as aluminum phosphate were found to be amorphous aluminum hydroxyphosphate. Buffer anions and sulfate anions substitute for hydroxyls in the amorphous aluminum hydroxide formed by the in situ alum precipitation method. Finally, the aluminum-containing adjuvant in diphtheria and tetanus toxoid, U.S.P., produced by three manufacturers was characterized.

Predicting the adsorption of proteins by aluminium-containing adjuvants.

The adsorption of two model proteins, albumin and lysozyme, by boehmite or amorphous aluminium hydroxyphosphate adjuvants was studied. Electrostatic, attraction has a major role in adsorption. At physiological pH, boehmite, which has a point of zero charge above 7.35, extensively adsorbed albumin, which has an isoelectric point of 4.8, but was not effective in adsorbing lysozyme (isoelectric point, 11.0). Conversely, amorphous aluminium hydroxyphosphate (point of zero charge, 4.0) was effective in adsorbing lysozyme but adsorbed relatively little albumin. The results suggest that the selection of either boehmite or amorphous aluminium hydroxyphosphate as an adjuvant should be based in part on the isoelectric point of the antigen.

Contribution of electrostatic and hydrophobic interactions to the adsorption of proteins by aluminium-containing adjuvants.

The effect of ionic strength and ethylene glycol on the adsorption of bovine serum albumin (BSA) or lysozyme by a commercial aluminium hydroxide or aluminium phosphate adjuvant was studied at pH 7.4 and 25 degrees C. The adsorption of BSA by aluminium hydroxide adjuvant and lysozyme by aluminium phosphate adjuvant was found to be inversely related to ionic strength. This indicates that electrostatic attractive forces contribute to adsorption. The adsorption of lysozyme by aluminium phosphate adjuvant was reduced by the addition of ethylene glycol. However, no change in the adsorption of BSA by aluminium hydroxide adjuvant was noted when up to 40% ethylene glycol was present. This behaviour indicates that hydrophobic forces contribute to the adsorption of lysozyme but not of BSA. However, virtually no adsorption was observed when the protein and the adjuvant had the same surface charge. Thus, attractive forces may not be sufficient to produce adsorption of an antigen by an aluminium-containing adjuvant if electrostatic repulsive forces are present.

Structure and Properties of Aluminum-Containing Adjuvants

This chapter is concerned with the identification, characterization, and behavior of aluminum-containing adjuvants with proteins and anions similar to those occurring in vaccines and interstitial fluid. Aluminum-containing adjuvants referred to commercially as aluminum hydroxide have been identified as poorly crystalline aluminum oxyhydroxide with the structure of the mineral boehmite. Relevant properties of this material include its high surface area and its high pI, which provide the adjuvant with a high adsorptive capacity for positively charged proteins. Aluminum phosphate and alum-precipitated adjuvants may be classified as amorphous aluminum hydroxyphosphate with little or no specifically adsorbed sulfate. Variations in the molar PO4/A1 ratio of amorphous aluminum hydroxyphosphates result in PI values that range from 5 up to 7; the materials are negatively charged at a physiological pH of 7.4. The amorphous nature of these compounds gives them high surface area and high protein adsorptive capacity for positively charged proteins. Observations on the interactions of anions and charged proteins with charged adjuvant surfaces have provided a framework for predicting behavior of complex systems of vaccines and for designing specific combinations of adjuvants and antigens to optimize the stability and efficacy of vaccines.

Mode of Chemical-Degradation of s-Triazines by Montmorillonite

Chemical hydrolysis of the s-triazines after interaction with less than 2-micron (equivalent spherical diameter) montmorillonite clay occurs as a result of protonation at the colloidal surface; protonation occurs even when the exchange sites are occupied by metallic cations. The adsorbed hydrolytic degradation product is not the hydroxy analog, but it is predominantly the keto form of the protonated hydroxy species. This cationic form is held tightly by the clay which may restrict vertical movement and entrance into groundwater. Protonation of the hydroxy analog occurs on the heterocyclic ring nitrogen.

Infrared Study of the OH Groups in Expanded Kaolinite

Expansion of kaolinite with potassium acetate and with hydrazine followed by deuteration, shifts the absorption frequency at 3695 cm-1 to lower values, but does not aflect the intensity of the 3620-cm-1 absorption band. The band at 3695 cm-1 is correlated predominantly to inner-surface hydroxyls with the dipole at right angles to the basal plane and the band at 3620 cm-1 is related to inner hydroxyls with the dipole inclined toward empty octahedral sites.

Infrared Study of Selective Deuteration of Kaolinite and Halloysite at Room Temperature

Deuteration of expanded hydrazine-kaolinite complex at room temperature shifts the infrared stretching frequencies of the inner-surface hydroxyls from 3695, 3670, and 3650 cm-1 to 2725, 2710, and 2698 cm-1, respectively, and the inner hydroxyls absorbing at 3620 cm-1 to 2675 cm-1. The OH-OD exchange for the inner-surface hydroxyls varies from 60 to 67 percent, whereas it is only 22 percent for the inner hydroxyls.

Degree of antigen adsorption in the vaccine or interstitial fluid and its effect on the antibody response in rabbits

The effect of the degree of adsorption of lysozyme by aluminium hydroxide adjuvant on the immune response in rabbits was studied. The surface charge of the adjuvant was modified by pretreatment with phosphate anion to produce five vaccines having degrees of adsorption ranging from 3 to 90%. The degree of adsorption of vaccines exhibiting 3, 35 or 85% adsorption changed to 40% within 1 h after each vaccine was mixed with sheep interstitial fluid to simulate subcutaneous administration. The mean anti-lysozyme antibody titers produced by the vaccines were the same and were four times greater than that produced by a lysozyme solution. Thus, the degree of adsorption of lysozyme in sheep interstitial fluid rather than the degree of adsorption in the vaccine correlated with the immune response.