A FIELD-BASED STUDY ON THE EFFECT OF DISSOLVED ORGANIC-MATTER ON THE TRANSPORT OF TERBUTHYLAZINE

Between 145 and 169 samples were taken from the surface of each of 3 d ifferent agricultural soils. With batch studies, the relationship betw een the distribution coefficient (K(d)) for terbuthylazine -chloro-4-t ert-butylamino-6-ethylamino-s-triazine) and the water extractable orga nic material (WEOM) was investigated. In 2 of the soils no relationshi p could be determined. In the third soil, a highly significant statist ical relationship was present. However, the coefficient of determinati on was less than 20%, and sensitivity analysis with an advection-dispe rsion transport model indicated that other factors such as the Ap hori zon thickness and persistence half-life were theoretically quantitativ ely more important in the prediction of groundwater contamination risk . Therefore, it was concluded that WEOM is usually not a critical fact or in our ability to predict groundwater contamination by non-ionic pe sticides with water solubilities on the order of 10 mg/L. An intriguin g question remains unanswered. Why was the affinity of terbuthylazine for the soil's organic matter so variable?