Sorption, mineralization and mobility of N-(phosphonomethyl)glycine (glyphosate) in five different types of gravel.
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.
Strange-Hansen
Rikke
R
Geological Survey of Denmark and Greenland, Department of Geochemistry, Oster Voldgade 10, DK-1350 Copenhagen K, Denmark.
Holm
Peter E
PE
Jacobsen
Ole S
OS
Jacobsen
Carsten S
CS
D000327:Adsorption; D018533:Biomass; D002247:Carbon Isotopes; D003718:Denmark; D004784:Environmental Monitoring; D019015:Geologic Sediments / Q000737:chemistry*; D005998:Glycine / Q000031:analogs & derivatives* / Q000737:chemistry*; D006540:Herbicides / Q000737:chemistry*; D007700:Kinetics; D012989:Soil Pollutants / Q000032:analysis*; D013696:Temperature; D014874:Water Pollutants, Chemical / Q000032:analysis; D000097797:Glyphosate
D002247:Carbon Isotopes; D005998:Glycine; D006540:Herbicides; D012989:Soil Pollutants; D014874:Water Pollutants, Chemical; D000097797:Glyphosate