Leaching of simazine in organic-amended soils

A laboratory study with a 1x3 factorial design has been conducted to assess the effect of the addition of 10% and 20% w/w of an organic amendment [26% organic carbon (C)] in sorption, degradation and leaching of simazine in a sandy soil (0.66% organic C, 75% sand, 16% clay). Sorption studies have be en performed following a batch equilibration procedure and sorption isother ms fitted to Freundlich equation. The Kf increased by a factor of 2.5 and 1 .8 with high and low amendment dose, respectively. Simazine treated soils w ere incubated at -33 KPa moisture content and 20 degrees C for 28 days (d). Soils were sampled periodically and simazine residues extracted with metha nol. No changes in simazine residues with incubation time were observed for the original unamended soil, whereas calculated half-lives obtained by fit ting simazine dissipation curves in the amended soils to first order kineti cs were 123 d for the lower dose and 69 d for the high dose. Mobility was s tudied in handpacked soil columns under fluctuating saturated/unsaturated f low conditions. Breakthrough curves were consistent with an inverse relatio nship between leaching and sorption, with greater mobility of simazine in t he untreated sandy soil than in the amended soils. Recoveries of initially applied simazine in leachates after the application of 750 mt of water were 93% for the original soil, 88% for soil amended with the low dose of humic amendment, and 53% for the high dose, which is also consistent with degrad ation studies. These results indicate that the humic amendment reduces herb icide leaching by promoting sorption and degradation processes.