Molecular Structure and Conformation of Biodegradable Water-Soluble Polymers Control Adsorption and Transport in Model Soil Mineral Systems.

Water-soluble polymers (WSPs) are used in diverse applications, including agricultural formulations, that can result in the release of WSPs to soils. WSP biodegradability in soils is desirable to prevent long-term accumulation and potential associated adverse effects. In this work, we assessed adsorption of five candidate biodegradable WSPs with varying chemistry, charge, and polarity characteristics (i.e., dextran, diethylaminoethyl dextran, carboxymethyl dextran, polyethylene glycol monomethyl ether, and poly-l-lysine) and of one nonbiodegradable WSP (poly(acrylic acid)) to sand and iron oxide-coated sand particles that represent important soil minerals. Combined adsorption studies using solution-depletion measurements, direct surface adsorption techniques, and column transport experiments over varying solution pH and ionic strengths revealed electrostatics dominating interactions of charged WSPs with the sorbents as well as WSP conformations and packing densities in the adsorbed states. Hydrogen bonding controls adsorption of noncharged WSPs. Under transport in columns, WSP adsorption exhibited fast and slow kinetic adsorption regimes with time scales of minutes to hours. Slow adsorption kinetics in soil may lead to enhanced transport but also shorter lifetimes of biodegradable WSPs, assuming more rapid biodegradation when dissolved than adsorbed. This work establishes a basis for understanding the coupled adsorption and biodegradation dynamics of biodegradable WSPs in agricultural soils.

Water-soluble and Water-dispersible Polymers Used in Commercial Agricultural Formulations: Inventory of Polymers and Perspective on their Environmental Fate.

Agricultural formulations contain water-soluble and water-dispersible polymers (WSPs and WDPs) to increase the application efficiency of the active ingredients (e.g. pesticides and fertilizers). Despite their direct release to soils and crops, there is currently no inventory of used polymers and their fate in soils is poorly studied and understood. Herein, we identify WSPs and WDPs used in agricultural formulations on the German and Swiss markets. By searching the scientific literature, patents, and manufacturer websites, we tentatively identified that 233 of the 1815 listed trade names of formulation additives contained polymers, the majority of which belonged to three main chemical classes: polyethylene glycol (PEG)-based (co)polymers, functionalized polysaccharides (PSacs), and vinylic (co)polymers (VCPs). We report information on their functionalization, molecular weights, and market significance. In 2015, their estimated combined annual application volume in Switzerland surpassed 100 tonnes. Low molecular weight PEGs and natural, unfunctionalized PSacs reportedly biodegrade, suggesting no accumulation in soils associated with their use as formulation additives. Conversely, high molecular weight functionalized PEGs, functionalized PSacs, and the majority of the VCPs have been reported to undergo only slow or no soil biodegradation. These polymers may thus persist and accumulate in agricultural soils, requiring more detailed investigations of their environmental fate and resulting exposure scenarios. There is a need for systematic studies on the effects of polymer structure, molecular weight, and functionalization on soil biodegradability.

Expansion of Zirconium Oxide Clusters by 3d/4f Ions.

Two series of charge-neutral coordination clusters featuring quasi-isostructural metal oxide cores, isolated as [Zr6Fe2Ln2O8(ib)14(bda)2(NO3)2]·xMeCN (Ln = La (1), Ce (2), Pr (3), and Nd (4); ib- = isobutyrate; H2bda = N-butyldiethanolamine) and [Zr6Fe2Ln2O8(ib)14(mda)2(NO3)2]·xMeCN (Ln = La (5), Ce (6), Pr (7), and Nd (8); H2mda = N-methyldiethanolamine), were obtained via one-pot reactions of [Fe3O(ib)6(H2O)3]NO3 as a critical precursor, Ln(NO3)3·6H2O (Ln = La, Ce, Pr, and Nd), the respective aminoalcohol, and [Zr6O4(OH)4(ib)12(H2O)]·3Hib in an acetonitrile solution. The coordination clusters in 1-8 feature {Zr6O8} cores that are structurally expanded by two 4f (Ln3+) and two 3d (Fe3+) metal ions, each individually coordinated to one of the eight oxide centers of {Zr6O8}, producing a metal skeleton where the 3d/4f positions cap four of the triangular faces of the central Zr6 octahedron. The coordination clusters differ in the chosen aminoalcohol coligands, N-butyldiethanolamine or N-methyldiethanolamine, which lead to a different isobutyrate coordination pattern in the two series, while the {Fe2Ln2Zr6O8} core structure remains virtually unaffected. All eight coordination clusters are obtained in moderate to good yields of 29-66% after only several days. Complexes 1-8 are stable against air and moisture; they are also surprisingly thermally stable up to 280 °C in air and in nitrogen atmosphere, and they represent the first reported examples of 3d/4f-functionalized zirconium oxide clusters.