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Certain organic carbon moieties in drinking source waters of the Sacramento-San Joaquin Delta can react with chlorine during disinfection to form potentially carcinogenic and mutagenic trihalomethanes. The properties of reactive organic carbon in Delta waters, particularly those of soil origin, have been poorly understood. This study attempts to characterize trihalomethane reactivity of soil organic carbon from three representative Delta peat soils. Soil organic carbon was extracted from all three soils with either deionized H2O or 0.1 M NaOH and sequentially separated into humic acids, fulvic acids, and nonhumic substances for quantitation of trihalomethane formation potential. Water-extractable organic carbon represented only 0.4 to 0.7% of total soil organic carbon, whereas NaOH extracted 38 to 51% of total soil organic carbon. The sizes and specific trihalomethane formation potential (STHMFP) of individual organic carbon fractions differed with extractants. Fulvic acids were the largest fraction in H2O-extractable organic carbon, whereas humic acids were the largest fraction in NaOH-extractable organic carbon. Among the fractions derived from H2O-extractable carbon, fulvic acids had the greatest specific ultraviolet absorbance and STHMFP and had the majority of reactive organic carbon. Among the fractions from NaOH-extractable organic carbon, humic acids and fulvic acids had similar STHMFP and, thus, were equally reactive. Humic acids were associated with the majority of trihalomethane reactivity of NaOH-extractable organic carbon. The nonhumic substances were less reactive than either humic acids or fulvic acids regardless of extractants. Specific ultraviolet absorbance was not a good predictor of trihalomethane reactivity of organic carbon fractions separated from the soils.

Measurement of the available soil P pool is required for making P fertilization recommendations. Extractants capable of estimating this P pool are needed. The objective of this study was to explore the utility of the acid ammonium oxalate method for estimating available soil P pools in diverse soils. Oxalate extraction in the dark dissolves mainly active noncrystalline Fe and Al in the soil. Oxalate extractable P (P ox ) has rarely been investigated for predicting the available P pool in highly weathered soils, where Fe and Al oxides are usually abundant. We estimated P ox in five highly weathered soils and three slightly weathered soils amended with varying amounts of P. The size of the available P pool in each soil was also estimated by a modified Hedley sequential extraction and verified in a 14-crop exhaustive greenhouse experiment. Results indicated that P ox in all soils appeared to be largely plant-available. P ox was found unsuitable for quantifying the available P pool in the calcareous, slightly weathered soils. Carbonates raised the pH of the oxalate solution and reduced the concentration of the oxalate anion to differing degrees, thus making this method unreliable for quantifying available P pools in calcareous soils. In highly weathered soils, the relationship between the quantity of available P and P ox was described by a linear equation, Y = 294.7 + 1.05 X (r 2 = 0.81), where Y is estimated available P in mg P kg ', and X is P ox in mg P kg 1 . The P ox was a good predictor of the available P pool in the highly weathered soils that were measured by the Hedley procedure and a multicrop exhaustion experiment.

Supercritical carbon dioxide (SC-CO(2)) is effective in extracting nonpolar and slightly polar chemicals from soils. However, pure SC-CO(2) is unsatisfactory for recovering polar chemicals in soils. A simple supercritical fluid extraction (SFE) procedure was developed to quantitatively recover polar and nonpolar chemicals from soils. The polar chemicals tested were aromatic acids and phenols. The nonpolar and slightly polar chemicals used as model compounds were common pesticides and environmental pollutants such as polycyclic aromatic hydrocarbons. The procedure required pretreatment of the samples with 15% water (g/g), 5% (ethylenedinitrilo)tetraacetic acid tetrasodium salt (Na(4)EDTA) (g/g), and 50% methanol (mL/g) prior to extractions using SC-CO(2) at 60 °C and 34.5 MPa. Recoveries ranged from 90 to 106% for the aromatic acids using the Na(4)EDTA-assisted SFE compared with only 7-63% recoveries of the corresponding chemicals when no Na(4)EDTA was used. The method quantitatively extracted 2,4-D and its close analogues aged in the soil for 2-30 days. The Na(4)EDTA-assisted SFE was also adequate for extracting phenolic analytes including picric acid and pentachlorophenol with recoveries from 85 to 104%. Na(4)EDTA is a good enhancer for extraction of the 29 analytes representing a wide range of polarity from the soil using SC-CO(2). The method is valuable for the analysis of parent pollutants and transformed products, particularly oxygen-borne metabolites in the environment.

result in runoff of residues so improved incorporation of pre-emergence herbicides into the soil is recomPre-emergence herbicide residues were detected in domestic wells mended to reduce concentrations in runoff water. sampled near Tracy, CA. This study sought to determine the source Thesetwoscenarios arenotinclusiveof allgeographiof contamination by comparing soil distribution of diuron [N-(3,4cal settings where residues have been detected in Calidichlorophenyl)-N,N-dimethylurea] and hexazinone [3-cyclohexyl6-(dimethylamino)-1-methyl-1,3,5-triazine-2,4(1H,3H)-dione] in an fornia’s ground water (Troiano et al., 2000). Pre-emeragricultural field where the soil was a cracking clay to infiltration of gence herbicide residues were detected in seven wells residues in water captured by an adjacent holding pond. Diuron and sampled within a 1554-ha area located near the town hexazinone were applied in December to a 3-yr-old alfalfa (Medicago of Tracy, CA: atrazine was detected in five wells at 0.16 sativa L.) crop. Water content of soil taken after major rainfall but to 2.8 gL 1 , diuron in one well at 0.06 gL 1 , hexazibefore irrigation at 106 d after application was elevated at the lowest none in three wells at 0.051 to 0.11 gL 1 , and simazine depth sampled centered at 953 mm, indicating water was available (6-chloro-N,N-diethyl-1,3,5-triazine-2,4-diamine) in one for percolation. Herbicide residues (reporting limit 8 gk g 1 ) were well at 0.098 gL 1 . Tracy is centrally located on the confined above the 152 mm soil depth, even after subsequent applicawestern side of the Central Valley of California (Fig. 1). tion of two border-check surface irrigations. The pattern of distribuThe predominant cropping pattern was a rotation of tion and concentration of residues in the soil were similar to results obtained from the LEACHM model, suggesting that macropore flow alfalfa with corn (Zea mays L.) and bean (Phaseolus was limited to a shallow depth of soil. Herbicide residues were mea- vulgaris L.). The residues were related to agricultural sured in runoff water at the first irrigation at 20 gL 1 for diuron applications, especially since the only reported pestiand 1 gL 1 for hexazinone. Runoff water captured in the pond cidal use of hexazinone was on alfalfa. The affected area rapidly infiltrated into the subsurface soil, causing a concomitant rise was surveyed for any obvious potential pathways to in ground water elevation near the pond. Herbicide residues were ground water. The predominant soil was a clay soil that also detected in the sampled ground water. We concluded that the developed surface cracks on drying. Rapid movement pond was the predominant source for movement to ground water. through soil, termed macropore flow, has been identiSince addition of a surfactant to the spray mixture did not reduce fied as a potential pathway for contamination (Bouma concentrations in runoff water, mitigation methods will focus on min

Certain organic C moieties of soil origin in drinking source waters of Sacramento-San Joaquin Delta (Delta) can react with chlorine to form trihalomethanes (THMs) during the disinfection process. Isolation and characterization of them and quantitation of their THM formation potential (THMFP) is necessary for developing effective strategies to reduce their influxes in Delta waters and for removing them during drinking water treatment. In this study, organic C from two Delta soils was extracted using deionized H(2)O and four Na- or Ca-based electrolytes of varying electrical conductivity values. Extracts were filtered into particulate, colloidal, fine colloidal, and soluble organic C for quantitation and THMFP determination. Results suggested that1.5% of soil organic C was electrolyte-extractable. The soluble organic C fraction from both soils dominated in quantity and THMFP. Electrolyte effects were cation dependent. Sodium-based electrolytes at either conductivity level did not significantly decrease extractable organic C (EOC) or THMFP compared with deionized H(2)O. In contrast, Ca-based electrolytes reduced EOC and THMFP by50% even at 1 dS m(-1). Further increase in Ca concentration did not significantly decrease EOC or THMFP. Most reduction in EOC and THMFP by Ca-based electrolytes occurred with the fractions other than the soluble organic C. Results suggested that under natural soil leaching and runoff conditions, the majority of THMFP is associated with organic C of0.025 mum in diameter. Further molecular characterization of the fractions with high THMFP may help understand the nature of chlorine-reactive organic C from Delta soils.

Filters with a pore size of 0.45 microm have been arbitrarily used for isolating dissolved organic carbon (DOC) in natural waters. This operationally defined DOC fraction often contains heterogeneous organic carbon compounds that may lead to inconsistent results when evaluating trihalomethane formation potential (THMFP). A finer pore size filter provides more homogeneous DOC properties and enables a better characterization of organic matter. In this study, we examined the effects of filter pore size (1.2, 0.45, 0.1 and 0.025 microm) on characterizing total organic carbon, ultra-violet absorbance at 254 nm (UV(254)) and THMFP of water extracts from a mineral and organic soil in the Sacramento-San Joaquin Delta, California. Results showed that the majority of water extractable organic carbon (WEOC) from these soils was smaller than 0.025 microm, 85% and 57% in organic and mineral soils, respectively. A high proportion of colloidal organic carbon (COC) in mineral soil extracts caused water turbidity and resulted in an abnormally high UV(254) in 1.2 and 0.45 microm filtrates. The reactivity of organic carbon fractions in forming THM was similar for the two soils, except that COC from the mineral soil was about half that of others. To obtain a more homogeneous solution for characterizing THM precursors, we recommend a 0.1 microm or smaller pore-size filter, especially for samples with high colloid concentrations.

Pressurized fluid extraction (PFE) is a new sample extraction method operated at elevated temperatures and pressures with liquid solvents. The use of PFE was investigated for the extraction of four Hawaiian clayey soils fortified with the selected chloroacetanilide and nitrogen heterocyclic herbicides Alachlor, Bromacil, Hexazinone, Metribuzin, and Tebuthiuron. The effects of operation temperature, pressure, flush volume, and static cycles on PFE performance were studied. Water was the most effective modifier of PFE for quantitative recoveries of the five herbicides in soils. The simple extraction method required pretreatment of the soil with 37.6% water and subsequent two-static-cycle extraction with a total of 32 mL of acetone at 1500 psi and 100 degrees C. Average recoveries of Alachlor, Bromacil, Hexazinone, Metribuzin, and Tebuthiuron ranged from 93 to 103% by the water-assisted PFE, compared with only 68-83% recoveries of the corresponding chemicals when no water was used. The extraction time and total organic solvent consumption were reduced from 18 h and 300 mL by Soxhlet to 22 min or less and 80 mL or less of organic solvent by PFE.