Effect of Dissolved Organic Matter in Treated Effluents on Sorption of Atrazine and Prometryn by Soils

hanced transport has been clearly documented in batch and column studies (Chiou et al., 1986; Dunnivant et The apparent enhanced transport of soil-applied atrazine following al., 1992; Enfield et al., 1989; Hassett and Anderson, irrigation of treated effluents has been hypothesized to be from com1982; Hutchins et al., 1985; Kan and Tomson, 1990; plexation of atrazine with effluent-borne dissolved organic matter (DOM). Under long-term effluent irrigation, even small DOM-inMcCarthy and Jimenez, 1985; Vinten and Nye, 1983; duced decreases in pesticide sorption can result in significant enhanced Chin et al., 1991). Based on studies with primarily pesticide movement due to cumulative effects. The effect of atrazine aquatic humic substances, Chin et al. (1991) concluded and prometryn association with DOM extracted from municipal that the influence of organic colloids on sorption of wastewater (MW), swine-derived lagoon wastewater (SW), and disorganic compounds where hydrophobic interactions solved Aldrich humic acid (HA) on sorption by two soils was measured dominated would be small for compounds with octanolin batch equilibration studies. Individual association of pesticides to water partition coefficients (Kow) ,105, especially given DOM, sorption of DOM to soil, and pesticide sorption by soil were the low DOM concentrations typically in aquatic and also quantified. Pesticide association to DOM normalized to organic subsurface water systems. However, in aqueous solucarbon (OC) ranged from 30 to 1000 L/kg OC. DOM sorption by soil tions containing dissolved organic matter from various ranged from 1.5 to 10 L/kg with a silt loam having a higher affinity sources including sludge, crop residues, and secondary for the DOM than the sandy loam. DOM up to 150 mg OC/L did not significantly suppress sorption by soils of either atrazine or promewastewater, decreases in sorption or enhanced transport tryne in agreement with predictions using the independently measured have also been observed for weakly basic or nonionic, binary distribution coefficients in a model that assumed linear equilibmoderately soluble pesticides (Kow ,103) (Lee and rium behavior among pesticide, soil, and DOM. A sensitivity analysis Farmer, 1989; Barriuso et al., 1992; Graber et al., 1995; was performed using the same model to identify what combination Celis et al., 1998; Nelson et al., 1998). of soil, pesticide, and DOC variables may suppress sorption, resulting In addition to intrinsic solute properties, the concentrain facilitated transport. Results from the sensitivity analysis are pretion, source, size, polarity, and molecular configuration sented and the potential for effluent properties other than DOM to of organic colloids will effect their impact on solubility, facilitate pesticide transport is discussed. thus sorption of organic chemicals. In solubility enhancement studies of hydrophobic organic compounds (HOCs) with humic and fulvic acids, Chiou et al. (1986) found E to abate pollution and supplement available the affinity of hydrophobic chemicals to associate with water resources in many parts of the world have dissolved organic substances as follows: soil-derived huresulted in the increased use of effluents for irrigation. mics . soil-derived fulvics . aquatic humics . aquatic In semiarid areas, where fresh water is limited, the use fulvics. Complexation of s-triazines to DOM using wellof effluents for agricultural purpose has been common characterized humic acids suggest that complexation ocpractice over the last few decades (Rebhun et al., 1987; curs through either proton or electron transfer deRonen and Magaritz, 1985). In the USA, treated efflupending on the acidity of the humic acid and the basicity ent is one of the fastest growing sources of water for of the traizine rather than simple hydrophobic interacirrigating both agricultural and recreational facilities tions (Senesi et al., 1987; Sposito et al., 1996). In addition such as golf course, parks, school grounds and street to association of chemicals to DOM, DOM applied to medians (Miller, 1990). One potential side effect of this soils can sorb to soil surfaces, resulting in an overall practice is the long-term deterioration of groundwater enhancement in sorption and retardation, as demonquality. Organic chemicals originally present in the strated by Totsche et al. (1997) for HOCs with forest wastewater and soil-borne organic pollutants have been floor-derived DOM. Therefore, the impact of DOM on identified in ground water at effluent-irrigated sites sorption and subsequent transport will be dependent (Hutchins et al., 1985), or at greater depths in the soil on the intrinsic nature of the solute, soil, and DOM, profile than observed at sites irrigated with only high and the competition among solute–soil, solute–DOM, quality water (Muskat et al., 1993; Graber et al., 1995). and DOM–soil interactions. Effluent characteristics that may impact mobility of soilIn this study, the impact of effluent DOM extracted borne chemicals include DOM, ionic strength, ionic from swine waste lagoon effluent and municpal waste composition, and pH. water effluent, as well as a well-characterized humic Complexation or association of strongly hydrophobic acid on triazine sorption, was measured. The association substances (e.g., polychlorinated biphenyls, polyaromatic of atrazine and prometryne to DOM, sorption of DOM hydrocarbons, and organochlorine pesticides) with dissolved or colloidal organic matter resulting in the enAbbreviations: BF, Bloomfield; CEC, cation-exchange capacity; hanced aqueous solubility, decreased sorption, and enCOD, chemical oxygen demand; DOC, dissolved organic carbon; DOM, dissolved organic matter; DR, Drummer; HOCs, hydrophobic Dep. of Agronomy, Purdue Univ., West Lafayette, IN 47907-1150. organic compounds; HA, humic acid; HPLC, High Performance Liq*Corresponding author ([email protected]). uid wastewater; SOC, soil organic carbon; SOM, soil organic matter; SW, swine effluent. Published in Soil Sci. Soc. Am. J. 64:1976–1983 (2000).