A novel controlled release formulation (CRF) of the herbicide imazapyr (IMP) was designed to reduce its leaching,which causes soil and water contamination. The anionic herbicide IMP was bound to polydiallyldimethylammonium-chloride (PDADMAC)-montmorillonite composites. PDADMAC adsorption reached a high loading of polymer, which resulted in charge reversal of the clay and promoted IMP binding. The composites were characterized by Fourier transform infrared, zeta potential, and X-ray diffraction measurements, indicating electrostatic interactions of the polycation with the surface, polycation intercalation in the clay and suggesting a configuration as loops and tails on the surface at high loadings. IMP binding to the composites is affected by polycation loading and flocculation. Upon adding high concentrations of IMP to a composite of 0.16 g/g, we obtained high herbicide loadings (66% active ingredient). IMP release from the CRFs applied on a thin layer of soil was substantially slower than its release from the commercial formulation (Arsenal). Accordingly, soil column bioassays indicated reduced herbicide leaching (nearly 2-fold) upon applying the CRFs while maintaining good herbicidal activity. The new PDADMAC-clay formulations are promising from the environmental and weed control management points of view.

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Pyrene removal by polycation-montmorillonite (MMT) composites and granulated activated carbon (GAC) in the presence of humic acid (HA) was examined. Pyrene, HA, and sorbent interactions were characterized by FTIR, fluorescence and zeta measurements, adsorption, and column filtration experiments. Pyrene binding coefficients to the macromolecules were in the order of PVPcoS (poly-4-vinylpiridine-co-styrene) > HA > PDADMAC (poly diallyl-dimethyl-ammonium-chloride), correlating to pyrene-macromolecules compatibility. Electrostatic interactions explained the high adsorption of HA to both composites (∼100%), whereas HA adsorption by GAC was low. Pyrene removal by the composites, unlike GAC, was enhanced in the presence of HA; removal by PDADMAC-MMT increased from ∼50 (k d = 2.2 × 10 3 kg/L) to ∼70% (k d = 2.4 × 10 3 kg/L) in the presence of HA. This improvement was attributed to the adsorption of pyrene-HA complexes. PVPcoS-MMT was most efficient in removing pyrene (k d = 1.1 × 10 4 kg/L, >95% removal) which was explained in terms of specific π donor−π acceptor interactions. Pyrene uptake by column filters of GAC reached ∼50% and decreased to ∼30% in the presence of HA. Pyrene removal by the PVPcoS-MMT filter was significantly higher (100−85% removal), exhibiting only a small decrease in the presence of HA. The utilization of HA as an enhancing agent in pollutant removal is novel and of major importance in water treatment. ■ INTRODUCTIONPolycyclic aromatic hydrocarbons (PAHs) are a group of persistent hydrophobic contaminants that have been detected in aquatic systems all over the world and are included in the US EPA and the EU priority list of pollutants (e.g., benzo(a)pyrene limit in water is 0.0002 mg/L). 1,2 Fate and transport of hydrophobic organic pollutants (including PAHs) in the environment is strongly affected by interactions with dissolved organic matter (DOM). 3−5 These interactions depend on both the chemical and structural characteristics of the pollutant and of the DOM and on the characteristics of the environmental system. 6 Studies have shown that in environmental systems the fate of organic contaminants can vary greatly in terms of adsorption or mobility. Several studies have demonstrated higher solubility and mobility of the pollutants in the presence of DOM. 7−9 For example, a study on enhanced organic pollutant solubility by DOM demonstrated increased partitioning coefficients into DOM with a decrease in pollutant water solubility and DOM polarity. 7 On the other hand, other studies have shown that the presence of DOM increased sorption and immobilization of organic pollutants to soil sediments and solid surfaces. 9−11 RavAcha and Rebhun 1992 suggested that DOM tended to solubilize organic pollutants when the adsorption coefficients (of the DOM) to the clay were relatively low, while adsorption of the pollutants to the clay increased as the DOM adsorption coefficients to the clay increased. 9 A later study also emphasized this complex behavior; the adsorption of an insecticide to soils d...