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

Additions of montmorillonite clay and soil of high organic matter content to growth media consisting of sand and nutrient solution significantly decreased the phytotoxicity of 2-methylthio-4,6-bis(isopropylamino)-s-triazine (prometryne) to wheat [Triticum aestivum L. em. Thell. (aestivum group) “Wakeland”]. Phytotoxicity was decreased to a greater extent at pH 4.5 than at pH 6.5. The reduction in phytotoxicity was attributed to adsorption of the herbicide by the additives. A larger proportion of the prometryne was present in the protonated form at the lower pH and the increased adsorption probably resulted from the coulombic bonding of these cations to the soil additives. Adsorption mechanisms are postulated and discussed.

Eight technically pure herbicides were evaluated for their relative phytotoxicity to hydroponically grown seedlings of red maple (Acer rubrum L.) and white ash (Fraxinus americana L.). Six of the herbicides (acids) were prepared as the triethylamine salts to provide formulation uniformity. With four compounds, equi-mole dosages per plant produced different toxic responses depending upon whether the herbicide was applied to the shoot or root. The 2,4,5-trichlorinated phenoxyaliphatic acids 2,4,5-trichlorophenoxyacetic acid (2,4,5-T), 2(2,4,5-trichlorophenoxy) propionic acid (2,4,5-TP), and 4(2,4,5-trichlorophenoxy) butyric acid (2,4,5-TB) were consistently more toxic on a mole basis when applied to the roots of both species than when applied to the shoots. The opposite effect was observed with ammonium sulfamate (AMS) where shoot treatments were always more toxic. Shoot and root treatments were equally effective for the compounds 2,4-dichlorophenoxyacetic acid (2,4-D), 2-methoxy-3,6-dichlorobenzoic acid (dicamba), 4-amino-3,5,6-trichloropicolinic acid (picloram), and 3-amino-l,2,4-triazole (amitrole). Differential species susceptibilities to certain compounds were observed.