Contamination of water sources due to the use of agricultural chemicals can be minimized through understanding the transport relationships for organic chemicals in soil environments. In this study we evaluated seven non-hazardous dyes that have properties which were consistent with application as surrogates to organic agro-chemicals to assess mobility through soils with respect to adsorption and desorption mechanisms. This study presents the batch adsorption method to obtain soil/water partition coefficients (Kd) for both adsorption and desorption experiments and octanol/water partition coefficients (K-0W). Six hydrophobic disperse dyes were examined and one hydrophilic Food, Dye & Colorant Blue No. 1. Parameter testing of pH stability and adsorption ratios eliminated five dyes; Disperse Violet No. 1 and FD&C Blue No. I remained to be examined in detail. Two soil minerals were employed to demonstrate sorption properties of the dyes; a. soil sample from the B horizon of a Woodburn silt loam and a 30/40 grade clean silica sand. Significant hysteresis was observed between adsorption and desorption processes for the two dyes in the Woodburn soil, suggesting that these dyes do not have fully reversible desorption characteristics when organic matter and the Cation Exchange Capacity (CEC) play a role in organic chemical mobility. Our soil/water batch experiments show that FD&C Blue Dye No. 1 is suitable for use as a tracer for hydrophilic agro-chemicals that have potential to leach through the soil. Disperse Violet No. 1 was found to be an acceptable tracer for laboratory studies to examine the mobility of hydrophobic agro-chemicals that are similarly adsorbed. Experimental K0W values corresponded directly to the prediction of dye partitioning; 7.0 X 10-03 for FD&C Blue No. 1 suggested no partitioning into organic matter, where 6.3 X 10+05 for Disperse Violet No.l suggested strong partitioning into organic matter
