The effects of temperature and exposure time on the adsorption of four organic compounds by montmorillonite, kaolinite, charcoal, and an anion-exchange resin in a phosphate buffer of pH 6.0 were investigated. Organic cations (diquat and paraquat) were preferentially adsorbed by the clays up to the cationexchange capacity. Adsorption appeared to be one of ion exchange. X-ray analysis indicated the cations were held in the lattice of the montmorillonite with die plane of the ring parallel to the silicate sheets. An organic anion (2,4-D) was negatively adsorbed by the clays; and a i-triazine compound (prometone) in molecular form, was adsorbed by montmorillonite but not kaolinite. X-ray analysis indicated diat prometone was located within the clay lattice but the orientation was uncertain. The adsorption mechanism was physical in nature being temperature dependent.The 2,4-D was adsorbed by the anion-exchange resin through ion exchange forces and the equilibrium was influenced by temperature and exposure time. Prometone was adsorbed by the anion-exchange resin to a much lesser degree, was also temperature and time dependent, and appeared to be physically bound.All of the organic compounds were adsorbed by charcoal and each was influenced differently by temperature and exposure

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The influence of soil pH (4.3 to 7.5) on the phytotoxicity of herbicides incorporated into high organic soils was studied. Phytotoxicity increased as the soil pH increased and reached a maximum at pH 6.5 for the weak aromatic acids 3,6-dichloro-o-anisic acid (dicamba) and (2,4-dichlorophenoxy)-acetic acid (2,4-D) and the weak bases 2,4-bis(isopropylamino)-6-methoxy-s-triazine (prometone) and 3-amino-s-triazole (amitrole). Conversely, phytotoxicity increased as soil pH decreased and reached a maximum at pH 4.3 for the weak aliphatic acid 2,2-dichloropropionic acid (dalapon), the cationic herbicides 6,7-dihydrodipyrido[1,2-a:2′,1′-c]pyrazinediium ion (diquat) and 1,1′-dimethyl-4,4′-bipyridinium ion (paraquat), and a nonionic herbicideS-propyl dipropylthiocarbamate (vernolate). Soil pH levels between 4.3 and 7.5 had no effect on the phytotoxicity of (a) the weak aromatic acids 3-amino-2,5-dichlorobenzoic acid (chloramben) and 4-amino-3,5,6-trichloropicolinic acid (picloram); and (b) the nonionic herbicides 2,6-dichlorobenzonitrile (dichlobenil), 5-bromo-3-isopropyl-6-methyluracil (isocil), 3-(3,4-dichlorophenyl)-1,1-dimethylurea (diuron), and 4-(methylsulfonyl)-2,6-dinitro-N,N-dipropylaniline (nitralin). A change of one pH unit decreased the phytotoxicity of 2,4-D, dicamba, dalapon, prometone, amitrole, paraquat, and vernolate by a factor of two to four depending on the particular herbicide and the pH values considered.

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