Relative mobilities of atrazine, five atrazine degradates, metolachlor, and simazine in soils of Iowa

The relative mobilities of atrazine (2-chloro-4-ethylamino-6- isopropylamino-s-triazine), five atrazine degradates, metolachlor (2-chloro-N-[2-ethyl-5-methylphenyl]-N-[2-methoxy-1 methylethyl]-acetamide), and simazine (2-chloro-4,6-bis-[ethylamino]-s-triazine) were determined in both surface and subsurface soils from five locations in Iowa by soil thin-layer chromatography (STLC). Based on mobility of the compounds, four groups were identified from this study. Deethylatrazine (2-chloro-4-amino-6-isopropylamino-s-triazine) was the most mobile compound. The intermediate mobility group included atrazine, deisopropylatrazine (2-chloro-4-ethyl-amino-6-amino-s-triazine), and didealkylatrazine (2-chloro-4,6-diamino-s-triazine). The less mobile group included metolachlor and simazine, and the nearly immobile group consisted of ammeline (4,6-diamine-s-triazine-2-ol) and hydroxyatrazine (2-hydroxy-4-ethylamino-6-isopropylamino s-triazine). A clear division between the intermediate and less mobile group was not seen in all soils. Mobilities of all eight compounds in this study were negatively correlated with soil organic matter content (p less than or equal to 0.05) and positively correlated (except for didealkylatrazine) with sand content (p less than or equal to 0.05). The greatest degree of mobility for the compounds studied was seen in Fruitland (sandy) and Nashua (sandy clay loam) subsurface soils, which also had the least organic matter contents. The mobility relationship of atrazine, deethylatrazine, and deisopropylatrazine in this study (deethylatrazine greater than or equal to atrazine-deisopropylatrazine) is consistent with groundwater monitoring reports. Similar mobilities of atrazine, deisopropylatrazine, and didealkylatrazine in some soils of this study suggest that didealkylatrazine is mobile enough to reach groundwater and therefore should be looked for in routine monitoring.