Sorption, mineralization and mobility of N‐(phosphonomethyl)glycine (glyphosate) in five different types of gravel

Abstract

Sorption, mineralization and mobility of glyphosate were studied in six substrates: the five types of gravel most frequently used as surfacing in Denmark and a sandy agricultural soil from Simmelkaer that served as a reference soil. Cumulative mineralization of [methyl-14C]glyphosate in batch studies was highest in coarse gravel, amounting to 14% after 4 days at 30 degrees C and 32% after 31 days. Mineralization was slowest in the sandy reference soil, amounting to only 2% after 31 days. The adsorption coefficient (Kd) of glyphosate in gravel ranged from 62 to 164 litre kg(-1), while that in the sandy reference soil was 410 litre kg(-1). The results indicate that the relatively low Kd in gravel allows a relatively high rate of glyphosate mineralization by the biomass. When Kd is high, in contrast, mineralization is slow. Lowering the temperature to 10 degrees C decreased mineralization by 50% in one of two gravels. The leaching of glyphosate was screened in simple columns of gravel or soil in which precipitation events (20 mm over a 2-h period) were simulated on three occasions, starting either immediately after or 2 days after application of glyphosate. [14C]Glyphosate was applied as a tracer mixed with the commercial product Roundup Garden at the recommended rate of 2.4 kg glyphosate ha(-1), equivalent to 1 microg g(-1) soil. The highest concentration of [14C] compounds (expressed in terms of glyphosate concentration) in leachate from the columns exceeded 1300 microg litre(-1), and was detected in rounded gravel after the first rain event. No glyphosate was detected in leachate from the sandy reference soil.

Glyphosate bioavailability in soil

“…In case of GP, it adsorbs on soil particles mainly through interactions with soil minerals, aluminum hydroxides, ferric oxides, organic matter (Morillo et al 2000;Gimsing et al 2004;Piccolo et al 1996). The GP distribution coefficient K d, that characterizes its sorption capacity (concentration in liquid and solid phases ratio), depends on a soil type and can vary from 8 to 410 l/kg (Gimsing and Borggaard 2002;Strange-Hansen et al 2004). Such a wide dispersion is determined mostly by differences in the cation-exchange capacity of soil types (Glass 1987).…”

Effect of soil metal contamination on glyphosate mineralization: Role of zinc in the mineralization rates of two copper‐spiked mineral soils

“…Although evidence exists that glyphosate degradation can occur abiotically by manganese oxide [6], soil microbial activity is considered to be primarily responsible for the degradation reactions [7][8][9]. Several soil microorganisms are capable of degrading glyphosate [10], with Pseudomonas spp.…”

Metabolic and cometabolic degradation of herbicides in the fine material of railway ballast

“…While leaching can be substantial from coarse-textured environments such as railways, research indicates that the microbial degradation might be accelerated in these kinds of soils because of the high availability of herbicides to microorganisms (Hassink et al, 1994;Klein, 2002;Strange-Hansen et al, 2004). However, microbial degradation of herbicides is also related to the amount and activity of microorganisms (Anderson, 1984;Torstensson and Stenström, 1986;Voos and Groffman, 1997;Jones and Ananyeva, 2001), and these are both known to be of very limited magnitude on railways (Smith et al, 1981;Cederlund and Stenström, 2004).…”