Carbon and nitrogen stable isotope ratios can estimate anionic polyacrylamide degradation in soil

Abstract

Water-soluble anionic polyacrylamide (PAM) is applied to millions of hectares worldwide as a highly effective erosion-preventing and infiltration-enhancing polymer, when applied at rates of 1 to 2 kg ha − 1 (i.e., 1 to 10 g m − 3 ) in furrow water. PAM degradation has not directly been measured in soil. We tested the ability of stable isotopes of C and N at natural abundance to estimate PAM degradation rates. Values of δ 13 C were related to anionic PAM concentration in a positive curvilinear relationship in a low-C, low-N, Durinodic Xeric Haplocalcid (Portneuf series) soil. The other soils with higher organic C or N concentrations did not show significant relationships between PAM concentrations and δ 13 C values. The δ 15 N values were not related to anionic PAM concentration in any of the soils tested. When 2691 active ingredient (ai) kg PAM ha − 1 was applied to the Durinodic Xeric Haplocalcid soil, 49% and 74% of the PAM was degraded after 6 and 12 yr respectively. When 5382 kg ai PAM ha − 1 was applied to the Durinodic Xeric Haplocalcid soil, 13% was degraded after 6 yr, and 73% of the PAM was degraded after 12 yr. We calculated PAM degradation rate based on δ 13 Cfor the Durinodic Xeric Haplocalcid soil to be 9.8% yr − 1 . Further testing using labeled PAM is necessary to estimate degradation rates in higher C soils, and to determine what portion of the C is released from decomposing PAM is emitted to the atmosphere, incorporated into soil organic matter and living microbial biomass.

Effects of anionic polyacrylamide on maize growth: a short term 14C labeling study

“…Higher rates of PAM might have had stronger effects as frequently showed in other studies, because higher application rate provides more ion charges that contribute to the flocculation processes, thus improve the soil structure and WHC (Levy et al 1995;Abu-Zreig et al 2007). However, in common agricultural practices, PAMs are applied at rates of 1 to 100 g m −3 in furrow irrigation water, corresponding to 1-100 kg dry PAM per hectare (Sojka et al 2007;Entry et al 2008). Ten kilograms per hectare has been recommended as standard rate for widespread application that could provide balanced effects in terms of economic, environmental and food-safety considerations, and higher rates (>100 kg ha −1 ) are not recommended (Natural Resources Conservation Service 2001;Sojka et al 2007;Lentz and Sojka 2009).…”

“…As a result, and due to their age and soil-moisture specific characteristics, the PAM effects might be subjected to more trivial factors that influence the rhizodeposition processes, such as the degradation of labile PAM into ineffective monomers (Entry et al 2008), the priming effects inspired by the input of 14 C label , the enhanced aggregation process due to the extrusion of inorganic elements and SOMs (Abiven et al 2009), the disturbance processes between aggregation and seal formation (Shainberg and Levy 1994), as well as the accelerated SWC oscillation driven by the increasing demand for water for plant growth, etc. Because of this fact, and in order to better understand the processes that the PAM is involved in and to evaluate its effects, more intensive spatiotemporal sampling or modeling are required in later studies.…”

Behavior of Nitrogen in Frac Sand Waste Fines

“…Malik and Letey (1991) found polyacrylamide strongly adsorbs to soil, especially those that are finely textured. Although it has been found to degrade in soil at 9.8% per year (Entry et al, 2008), the fate of the nitrogen contained in polyacrylamide is poorly understood. Nitrogen is a critical nutrient in plants but is also a potential groundwater contaminant.…”

Turbidimetric Determination of Anionic Polyacrylamide in Low Carbon Soil Extracts

“…They emphasized that any method for quantifying PAM in soil waters should be sensitive at low concentrations (<1 mg L -1 ) and insensitive to interferences such as dissolved salts and organic matter (OM). The analytical methods for aqueous PAM are generally based on (i) the chemical properties of amide groups in PAM assessed by N-bromination of the amides (Scoggins and Miller, 1979;Lu and Wu, 2001); (ii) the physical properties of the PAM solution determined by viscosity measurement ( Jungreis, 1981), flocculation-based methods (Lentz et al, 1996), or size exclusion chromatography (Hunt et al, 1988); (iii) the combined physical and chemical properties determined by turbidimetric methods (Allison et al, 1987) or polarography (Smith-Palmer et al, 1988); and (iv) methods based on total organic carbon (TOC) concentration and radioactive labeling (Ben-Hur et al, 1992;Entry et al, 2008). Most of these methods are complicated procedures that may require expensive laboratory equipment.…”