Sorption and transport of 17beta-estradiol and testosterone in undisturbed soil columns

Land-applied domestic animal wastes contain appreciable amounts of 17beta-estradiol (henceforth, estradiol) and testosterone. These sex hormones may be transported through soil to groundwater and streams, where they may adversely affect the environment. Previous column transport studies with these hormones used repacked soil and did not consider preferential flow. We, therefore, determined the sorption and transport characteristics of estradiol and testosterone in undisturbed soil columns (15-cm i.d. by 32-cm height). In the sorption experiment, isotherms for estradiol and testosterone were nonlinear with Freundlich exponents (n) less than one. Sorption of both hormones decreased with soil depth, and estradiol sorbed more strongly than testosterone. Average estradiol Freundlich sorption coefficients (K(f)) values were 36.9 microg(1 - n) mL(n) g(-1) for the 0- to 10-cm soil depth and 25.7 microg(1 - n) mL(n) g(-1) for the 20- to 30-cm soil depth. Average testosterone K(f) values were 26.7 microg(1 - n) mL(n) g(-1) for the 0- to 10-cm soil depth and 14.0 microg(1 - n) mL(n) g(-1) for the 20- to 30-cm soil depth. In the transport experiment, 27% of the estradiol and 42% of the testosterone leached through the soil columns. Approximately 50% of the remaining soil-bound hormones were sorbed in the top 10 cm of soil. In almost all instances, breakthrough concentrations of estradiol, testosterone, and a chloride tracer peaked simultaneously. Simultaneous breakthrough and HYDRUS-1D transport parameters indicated both chemical and physical nonequilibrium processes affected hormone transport. This suggests hormones placed on soil surfaces may contaminate groundwater under conditions of preferential flow.     

Aging effects on cadmium transport in undisturbed contaminated sandy soil columns

Limited information is available on the effects of contaminant aging (i.e., the contact time of Cd with the soil) on Cd transport in soils. We conducted displacement experiments in which indigenous Cd and freshly applied Cd were leached simultaneously from undisturbed samples of three Spodosol horizons. Sorption of Cd was described using Freundlich isotherms, whereas transport was described as a convection-dispersion process. Parameter optimization analysis using a mobile-immobile transport model applied to nonsorbing tracer displacement data showed that 16 to 22% of the water in the columns was immobile. The low dimensionless mass transfer coefficients in the mobile-immobile model were indicative of diffusion-limited transfer between mobile and immobile water, and hence physical nonequilibrium. A two-site kinetic sorption model could be fitted closely to breakthrough curves of the non-aged Cd for three soil horizons. No conclusive evidence was found that contaminant aging in soil affects cadmium transport. On the one hand, predictions of aged Cd leaching, using parameters estimated from displacement experiments with nonaged Cd, differed from those for the aged Cd in the E horizon. On the other hand, no meaningful differences in transport behavior between aged and non-aged Cd were found for the humus Bh and Bh/C horizons. The two-site kinetic rate coefficient alphac was found to depend on water flux, further indicating that mass transfer between sorption sites and the liquid is limited by diffusion rather than by kinetic sorption.     

Solute movement through an allophanic soil

Allophanic soils are widespread around the world, but little research has been done on their transport properties. This study reveals the effect of two soil water potential heads and two water-flow regimes of continuous and intermittent flow on solute transport through undisturbed soil columns of Horotiu silt loam (Typic Hapludand), an allophanic soil. Two different methods--breakthrough curves (BTCs) and time domain reflectometry (TDR)--were employed to determine the extent of preferential solute transport in the topsoil. The TDR data were also used to look at the depth dependence of the transport properties. The convection-dispersion equation (CDE) with the appropriate boundary conditions adequately described the movement of both Br and Cl under the various flow conditions. Although no preferential flow was found under the imposed unsaturated flow conditions, the flow of water and transport of solute became more uniform with depth. The results show that both Br and Cl are retarded in this allophanic soil. Retardation values range from 1.5 to 1.9, and, as the TDR data showed, increase from the depth of 5.0 to 10.0 cm. Intermittent leaching results showed that there was no effect on solute concentrations in the leachate following no-flow periods. This suggests that water and solute transport in this soil were either relatively uniform or that transverse mixing during flow was already fast enough to eliminate concentration gradients between regions of different "mobility."     

Transport of sulfadiazine in undisturbed soil columns: effects of flow rate, input concentration and pulse duration

Antibiotics reach soils via spreading of manure or sewage sludge. Knowledge on the transport behavior of antibiotics in soils is needed to assess their environmental fate. The effect of flow rate and applied mass, i.e., input concentration and pulse duration, on the transport of 14C-sulfadiazine (SDZ; 4-aminoN-pyrimidin-2-yl-benzenesulfonamide) was investigated with soil column experiments and numerical studies. Sulfadiazine was applied in pulses (6.8, 68 or 306 h) under steady-state (0.051 and 0.21 cm h(-1)) and intermittent flow conditions and at two input concentrations (0.57 and 5.7 mg L(-1)). Breakthrough curves (BTCs) of 14C were measured and for one experiment concentrations of SDZ, and its transformation products 4-(2-iminopyrimidin-1(2H)-yl)aniline (An-SDZ) and N(1)-2-(4-hydroxypyrimidinyl)benzenesulfanilamide (4-OH-SDZ) were determined. After finalizing the leaching experiments, 14C was quantified in different slices of the columns. A lower flow rate led to remarkably lower eluted masses compared with the higher flow rates. All BTCs could be described well using a three-site attachment-detachment model for which a common set of parameters was determined. However, the BTC obtained with the high input concentration was slightly better described with a two-site isotherm-based model. The prediction of the concentration profiles was good with both model concepts. The fitted sorption capacities decreased in the order SDZ > 4-OH-SDZ > An-SDZ. Overall, the experiments reveal the presence of similar mechanisms characterizing SDZ transport. The dependence of model performance on concentration implies that although the three-site attachment-detachment model is appropriate to predict the transport of SDZ in soil columns, not all relevant processes are adequately captured.     

Effect of soil properties on saturated and unsaturated virus transport through columns

Viruses from contaminant sources can be transported through porous media to drinking water wells. The objective of this study was to investigate inactivation and sorption of viruses during saturated and unsaturated transport in different soils. Bacteriophages phiX174 and MS-2, and Br- tracer in a phosphate-buffered saline solution were introduced into saturated and unsaturated soil columns as a step function under constant flow rate and hydraulic conditions. Results showed that significantly greater virus removal occurred in the unsaturated columns than in the saturated columns in the two soils containing high metal oxides content. However, the increase in virus retention under unsaturated conditions was not significant in two other soils having high phosphorus and calcium contents and high pH, and in another soil with high organic matter content. The results imply that the extent of water content effect on inactivation and sorption of viruses can range from significant to minimal depending on the properties of the transport medium. We found that the presence of in situ metal oxides was a significant factor responsible for virus sorption and inactivation. Therefore, soils with high metal oxides content may have the potential to be used as hydrological barriers in preventing microbial contamination in the subsurface environments. We also found that the water content effect on virus removal and inactivation strongly depended on solid properties of the testing medium.     

Organic manure and urea effect on metolachlor transport through packed soil columns

Application of organic manure (OM) amendments and nitrogen fertilizers can affect the sorption and movement of pesticides in soil. This study summarizes the sorption and leaching of metolachlor [2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylphenyl) acetamide] in soils after cow (Bos taurus) manure (2.5 and 5.0%) and urea (60 and 120 kg N ha(-1)) amendments in batch and column experiments. Both cow manure and urea applications increased metolachlor sorption in soils. The values of the Freundlich adsorption parameter K(r)(1/n) for treatments T0, T1 (OM), and T2 (OM) were 2.31, 3.32, and 3.96 in Soil 1; 2.02, 2.77, and 3.32 in Soil 2; and 1.10, 1.46, and 2.02 in Soil 3, respectively. Similarly, K(f)(1/n) values for treatment T1 (urea) and T2 (urea) were 2.37 and 2.84 in Soil 1; 2.16 and 2.83 in Soil 2; and 1.50 and 1.70 in Soil 3, respectively. Column leaching studies using Soil 1 indicated that OM application drastically reduced the metolachlor leaching losses from 50% (natural soil) to < 1.0% (5.0% OM amendment). Likewise, urea application also decreased metolachlor mobility and leaching losses in columns treated with 60 and 120 kg N ha(-1) urea were 33 and 20%, respectively. The reduction in the metolachlor leaching losses was achieved through the increase in the sorption capability of the OM- and urea-amended soil. Therefore, coapplication of metolachlor with cow manure or urea fertilizers will not enhance metolachlor mobility and reduces metolachlor leaching losses in low-organic-matter soil.     

Molecular weight of dissolved organic matter-napropamide complex transported through soil columns

Soil-derived dissolved organic matter (DOM) has been shown to form stable complexes with the herbicide napropamide [2-(alpha-naphthoxy-N,N-diethylpropionamide] capable of enhancing the transport of napropamide through soil columns. Two soils, one containing sewage sludge-derived organic matter (SS) and the other having only natural organic matter (NoSS) were treated with napropamide and allowed to dry to promote complex formation. Soil columns were prepared by packing a 10-cm layer of untreated, dry, sieved soil followed by an overlying 5-cm layer of napropamide-treated soil. Columns were irrigated and the effluent collected and placed in dialysis chambers. After equilibration napropamide concentrations were determined on both sides of the membrane and complex and quantified based on the amount of napropamide unable to cross the membrane. it was found that for the SS soil 7% and for the NoSS 2.4% of the applied napropamide underwent facilitated transport. In addition, most of the complex transported through the columns had a molecular weight between 500 and 1000 Daltons (Da). The solutions from the SS soil were also found to have formed at least two distinct complexes that were resolved after passing through the untreated soil layer. The results obtained were in agreement with other published results and the techniques used offer a way to separate and concentrate DOM complexes from column effluents for further characterization.     

Transport of di(2-ethylhexyl)phthalate (DEHP) applied with sewage sludge to undisturbed and repacked soil columns

Municipal sewage sludge is often used on arable soils as a source of nitrogen and phosphorus, but it also contains organic contaminants that may be leached to the ground water. Di(2-ethylhexyl)phthalate (DEHP) is a priority pollutant that is present in sewage sludge in ubiquitous amounts. Column experiments were performed on undisturbed soil cores (20-cm depth x 20-cm diameter) with three different soil types: a sand, a loamy sand, and a sandy loam soil. Dewatered sewage sludge was spiked with 14C-labeled DEHP (60 mg kg(-1)) and bromide (5 g kg(-1)). Sludge was applied to the soil columns either as five aggregates, or homogeneously mixed with the surface layer. Also, two leaching experiments were performed with repacked soil columns (loamy sand and sandy loam soil). The DEHP concentrations in the effluent did not exceed 1.0 microg L(-1), and after 200 mm of outflow less than 0.5% of the applied amount was recovered in the leachate in all soils but the sandy loam soil with homogeneous sludge application (up to 3.4% of the applied amount recovered). In the absence of macropore flow, DEHP in the leachate was primarily sorbed to mobilized dissolved organic macromolecules (DOM, 30.3 to 81.3%), while 2.4 to 23.6% was sorbed to mobilized mineral particles. When macropore flow occurred, this changed to 16.5 to 37.4% (DOM) and 36.9 to 40.6% (mineral particles), respectively. The critical combination for leaching of considerable amounts of DEHP was homogeneous sludge application and a continuous macropore structure.     

Coupled effects of treated effluent irrigation and wetting-drying cycles on transport of triazines through unsaturated soil columns

The physical and chemical parameters controlling the movement of atrazine (6-chloro-N2-ethyl-N4-isopropyl-l,3,5-triazine-2,4-diamine; 98.8%) and prometryn [N,N'-bis(1-methylethyl)-6-(methylthio)-l,3,5triazine-2,4-diamine; 99.5%] were investigated in columns infiltrated with treated effluent under unsaturated transient conditions and subjected to drying events at 22 or 60 degrees C followed by rewetting. Three soils varying in soil pH and texture and three solutions were used. The infiltrating solutions consisted of either a CaCl2 matrix (CC), a swine waste-derived lagoon effluent (SW), or a simulated buffer solution (SB) representative of the element composition and pH of the SW but with no dissolved organic matter. Several parameters were monitored including leachate triazine concentrations, pH, dissolved organic carbon (DOC), inorganic carbon, and flow rates. Compared with CC, application of SW and SB increased column leachate pH, enhanced dissolution of organic carbon and particle dispersion, and decreased average flow rates, which allowed for increased desorption time. The coupled effect of these processes enhanced movement of triazines in some cases, with SW generally having the greatest effect. The individual effect of increased pH was more pronounced for prometryn (pKa=4.05) versus atrazine (pKa=1.66), and most dramatic for the soil with the lowest initial pH. High-temperature drying, which simulated intensive evaporation, further enhanced the dissolution of soil organic matter and the reduction in leachate flow rates with SW and SB applications; however, the net effect under the experimental conditions employed varied with soil type. Relative to low-temperature drying, high-temperature drying in the silty clay loam-packed columns reduced pesticide migration.     

Residual soil nitrate after potato harvest

Nitrogen loss by leaching is a major problem, particularly with crops requiring large amounts of N fertilizer. We evaluated the effect of N fertilization and irrigation on residual soil nitrate following potato (Solanum tuberosum L.) harvests in the upper St-John River valley of New Brunswick, Canada. Soil nitrate contents were measured to a 0.90-m depth in three treatments of N fertilization (0, 100, and 250 kg N ha(-1)) at two on-farm sites in 1995, and in four treatments of N fertilization (0, 50, 100, and 250 kg N ha(-1)) at four sites for each of two years (1996 and 1997) with and without supplemental irrigation. Residual soil NO3-N content increased from 33 kg NO3-N ha(-1) in the unfertilized check plots to 160 kg NO3-N ha(-1) when 250 kg N ha(-1) was applied. Across N treatments, residual soil NO3-N contents ranged from 30 to 105 kg NO3-N ha(-1) with irrigation and from 30 to 202 kg NO3-N ha(-1) without irrigation. Residual soil NO3-N content within the surface 0.30 m was related (R2 = 0.94) to the NO3-N content to a 0.90-m depth. Estimates of residual soil NO3-N content at the economically optimum nitrogen fertilizer application (Nop) ranged from 46 to 99 kg NO3-N ha(-1) under irrigated conditions and from 62 to 260 kg NO3-N ha(-1) under nonirrigated conditions, and were lower than the soil NO3-N content measured with 250 kg N ha(-1). We conclude that residual soil NO3-N after harvest can be maintained at a reasonable level (<70 kg NO3-N ha(-1)) when N fertilization is based on the economically optimum N application.     

Depth distribution of sulfonamide antibiotics in pore water of an undisturbed loamy grassland soil

Despite the concern raised by the detections of veterinary antibiotics like sulfonamides (SA) in the environment, their fate in soils is still not sufficiently understood. In a previous article, we demonstrated that manure may substantially influence losses of SA via runoff from soils. Here, we report on the effect of manure on SA availability in soil pore water. Three sulfonamides (sulfadimidine, sulfadiazine, sulfathiazole) and two tracers (bromide and Brilliant Blue) were either applied in manure or as aqueous solution on grassland plots. After 1 and 3 d contact time, the plots were irrigated with deionized water. One day after irrigation, soil cores were taken and profiles of pore water concentrations were determined. The median SA concentrations of the top layer on manured plots varied between 40 and 60 microg L(-1) and between 10 and 30 microg L(-1) on the controls. For the conservative tracer Br the mass recovery was about 60 to 75% and much lower for the SA (2 to 14%). Apparent distribution coefficients K(d,app) of the SA in the topsoil ranged between 3 and 15 L kg(-1) on the manured plots and between 30 to 35 kg L(-1) on the controls. Below the top layer, the concentration distribution showed a pattern typical for preferential flow. Locally, SA concentrations down to 30- to 50-cm depth were as high as in the top 5 cm with little effect of the two application matrices. In the topmost layer, the data indicate that 10 to 25% of sulfadimidine were transformed to its acetyl-metabolite.     

Phosphorus leaching from cow manure patches on soil columns

The loss of P in overland flow or leachate from manure patches can impair surface water quality. We studied leaching of P from 10-cm-high lysimeters filled with intact grassland soil or with acid-washed sand. A manure patch was created on two grassland and two sand-filled lysimeters, and an additional two grass lysimeters served as blanks. Lysimeters were leached in the laboratory during 234 d with a diluted salt solution, and column effluent was passed through a 0.45-microm filter, analyzed for pH, dissolved reactive P (DRP), and total dissolved P (TDP). At the end of the experiment lysimeter soil was sampled and analyzed for pH, available P, and oxalate-extractable P, Fe, and Al. The concentration of TDP in the effluent from the sand column increased to 25 mg L-1 during the first weeks and remained above 10 mg L-1 during the rest of the percolation. In effluent from grass + patch lysimeters TDP gradually increased to 4 mg L-1. Both in the manure and in the effluent of the sand lysimeter P was found mainly in the form of DRP, but in the effluent from the grass lysimeters was found mainly as dissolved unreactive P (DUP=TDP-DRP). Earthworm activity was responsible for decomposition of the manure patch on the grass lysimeters. Manure patches and their remains were found to be a long-term source of high concentrations of P in leachates. Spreading of patches after a grazing period could reduce their possible negative impacts on the environment.     

Economically optimal nitrogen rate reduces soil residual nitrate

Post-harvest residual soil NO(3)-N (RSN) is susceptible to transfer to water resources. Practices that minimize RSN levels can reduce N loss to the environment. Our objectives were (i) to determine if the RSN after corn (Zea mays L.) harvest can be reduced if N fertilizer is applied at the economically optimal N rate (EONR) as compared to current producer practices in the midwestern USA and (ii) to compare RSN levels for N fertilizer rates below, at, and above the EONR. Six experiments were conducted in producer fields in three major soil areas (Mississippi Delta alluvial, deep loess, claypan) in Missouri over 2 yr. Predominant soil great groups were Albaqualfs, Argiudolls, Haplaquolls, and Fluvaquents. At four transects in each field, six treatment N rates from 0 to 280 kg N ha(-1) were applied, the EONR was determined, and the RSN was measured to a 0.9-m depth from five treatment plots. The EONR at sampling sites varied from 49 to 228 kg N ha(-1) depending on site and year. Estimated average RSN at the EONR was 33 kg N ha(-1) in the 0.9-m profile. This was at least 12 kg N ha(-1) lower than RSN at the producers' N rates. The RSN increased with increasing Delta EONR (total N applied - EONR). This relationship was best modeled by a plateau-linear function, with a low RSN plateau at N rates well below the EONR. A linear increase in RSN began anywhere from 65 kg N ha(-1) below the EONR to 20 kg N ha(-1) above the EONR at the three sites with good data resolution near the EONR. Applying N rates in excess of the EONR produced elevated RSN values in all six experiments. Our results suggest that applying the EONR will produce environmental benefits in an economically sound manner, and that continued attempts to develop methods for accurately predicting EONR are justified.     

Fertilizer use efficiency and nitrate leaching in a tropical sandy soil

Maize (Zea mays L.) production in the smallholder farming areas of Zimbabwe is based on both organic and mineral nutrient sources. A study was conducted to determine the effect of composted cattle manure, mineral N fertilizer, and their combinations on NO3 concentrations in leachate leaving the root zone and to establish N fertilization rates that minimize leaching. Maize was grown for three seasons (1996-1997, 1997-1998, and 1998-1999) in field lysimeters repacked with a coarse-grained sandy soil (Typic Kandiustalf). Leachate volumes ranged from 480 to 509 mm yr(-1) (1395 mm rainfall) in 1996-1997, 296 to 335 mm yr(-1) (840 mm rainfall) in 1997-1998, and 606 to 635 mm yr(-1) (1387 mm rainfall) in 1998-1999. Mineral N fertilizer, especially the high rate (120 kg N ha(-1)), and manure plus mineral N fertilizer combinations resulted in high NO3 leachate concentrations (up to 34 mg N L(-1)) and NO3 losses (up to 56 kg N ha(-1) yr(-1)) in 1996-1997, which represent both environmental and economic concerns. Although the leaching losses were relatively small in the other seasons, they are still of great significance in African smallholder farming where fertilizer is unaffordable for most farmers. Nitrate leaching from sole manure treatments was relatively low (average of less than 20 kg N ha(-1) yr(-1)), whereas the crop uptake efficiency of mineral N fertilizer was enhanced by up to 26% when manure and mineral N fertilizer were applied in combination. The low manure (12.5 Mg ha(-1)) plus 60 kg N ha(-1) fertilizer treatment was best in terms of maintaining dry matter yield and minimizing N leaching losses.     

Identifying riparian sinks for watershed nitrate using soil surveys

The capacity of riparian zones to serve as critical control locations for watershed nitrogen flux varies with site characteristics. Without a means to stratify riparian zones into different levels of ground water nitrate removal capacity, this variability will confound spatially explicit source-sink models of watershed nitrate flux and limit efforts to target riparian restoration and management. We examined the capability of SSURGO (1:15 840 Soil Survey Geographic database) map classifications (slope class, geomorphology, and/or hydric soil designation) to identify riparian sites with high capacity for ground water nitrate removal. The study focused on 100 randomly selected riparian locations in a variety of forested and glaciated settings within Rhode Island. Geomorphic settings included till, outwash, and organic/alluvial deposits. We defined riparian zones with "high ground water nitrate removal capacity" as field sites possessing both >10 m of hydric soil width and an absence of ground water surface seeps. SSURGO classification based on a combination of geomorphology and hydric soil status created two functionally distinct sets of riparian sites. More than 75% of riparian sites classified by SSURGO as organic/alluviumhydric or as outwash-hydric had field attributes that suggest a high capacity for ground water nitrate removal. In contrast, >85% of all till sites and nonhydric outwash sites had field characteristics that minimize the capacity for ground water nitrate removal. Comparing the STATSGO and SSURGO databases for a 64000-ha watershed, STATSGO grossly under-represented critical riparian features. We conclude that the SSURGO database can provide modelers and managers with important insights into riparian zone nitrogen removal potential.     

Modeling effluent distribution and nitrate transport through an on-site wastewater system

Properly functioning on-site wastewater systems (OWS) are an integral component of the wastewater system infrastructure necessary to renovate wastewater before it reaches surface or ground waters. There are a large number of factors, including soil hydraulic properties, effluent quality and dispersal, and system design, that affect OWS function. The ability to evaluate these factors using a simulation model would improve the capability to determine the impact of wastewater application on the subsurface soil environment. An existing subsurface drip irrigation system (SDIS) dosed with sequential batch reactor effluent (SBRE) was used in this study. This system has the potential to solve soil and site problems that limit OWS and to reduce the potential for environmental degradation. Soil water potentials (Psi(s)) and nitrate (NO(3)) migration were simulated at 55- and 120-cm depths within and downslope of the SDIS using a two-dimensional code in HYDRUS-3D. Results show that the average measured Psi(s) were -121 and -319 cm, whereas simulated values were -121 and -322 cm at 55- and 120-cm depths, respectively, indicating unsaturated conditions. Average measured NO(3) concentrations were 0.248 and 0.176 mmol N L(-1), whereas simulated values were 0.237 and 0.152 mmol N L(-1) at 55- and 120-cm depths, respectively. Observed unsaturated conditions decreased the potential for NO(3) to migrate in more concentrated plumes away from the SDIS. The agreement (high R(2) values approximately 0.97) between the measured and simulated Psi(s) and NO(3) concentrations indicate that HYDRUS-3D adequately simulated SBRE flow and NO(3) transport through the soil domain under a range of environmental and effluent application conditions.     

Relative movement and soil fixation of soluble organic and inorganic phosphorus

There is considerable concern about pollution of surface waters with P. Although most of the research has focused on inorganic P in surface runoff, it has recently become possible to easily follow the fate of soluble organic P forms in soils and waters. Two experiments were performed to compare the relative mobility and soil fixation affinity of orthophosphate monoesters, orthophosphate diesters, and soluble inorganic P. We used three P substrates, 4-methylumbelliferyl phosphate (MUP), deoxyribonucleic acid (DNA), and KH(2)PO(4) in (i) a soil column experiment and (ii) a soil P adsorption test tube experiment. Shortly after columns were prepared, approximately two pore volumes of 0.005 M CaCl(2) were passed through 25 cm length columns containing 10 cm of loamy sand amended with approximately 10 mg P as MUP, DNA, or KH(2)PO(4) above 15 cm of nonamended loamy sand. The total net quantity of 757.8 microg P 2L(-1) of orthophosphate diesters in the leachate from the DNA columns exceeded the net quantity of orthophosphate monoesters in leachate from the MUP columns (4.6 microg P 2L(-1)) and soluble inorganic P from the KH(2)PO(4) columns (34.0 microg P 2L(-1)). Adsorption of soluble organic and inorganic P in the test tube experiment yielded similar results: DNA, containing orthophosphate diesters, had a relatively low affinity for soils. In both experiments, high concentrations of other P compounds were identified in samples treated with organic P substrates, suggesting enzymatic hydrolysis by native soil phosphatase enzymes. These findings indicate that repeated application of organic forms of P could lead to significant leaching of P to ground water.     

Influence of organic waste type and soil structure on the bacterial filtration rates in unsaturated intact soil columns

Organic wastes are considered to be a source for the potentially pathogenic microorganisms found in surface and sub-surface water resources. Following their release from the organic waste matrix, bacteria often infiltrate into soil and may be transported to significant depths contaminating aquifers. We investigated the influence of soil texture and structure and most importantly the organic waste properties on the transport and filtration coefficients of Escherichia coli and total bacteria in undisturbed soil columns. Intact soil columns (diameter 16 cm and height 25 cm) were collected from two soils: sandy clay loam (SCL) and loamy sand (LS) in Hamadan, western Iran. The cores were amended with cow manure, poultry manure and sewage sludge at a rate of 10 Mg ha(-1) (dry basis). The amended soil cores were leached at a steady-state flux of 4.8 cm h(-1) (i.e. 0.12 of saturated hydraulic conductivity of the SCL) to a total volume of up to 4 times the pore volume of the columns. The influent (C(0)) and effluent (C) were sampled at similar time intervals during the experiments and bacterial concentrations were measured by the plate count method. Cumulative numbers of the leached bacteria, filtration coefficient (lambda(f)), and relative adsorption index (S(R)) were calculated. The preferential pathways and stable structure of the SCL facilitated the rapid transport and early appearance of the bacteria in the effluent. The LS filtered more bacteria when compared with the SCL. The effluent contamination of poultry manure-treated columns was greater than the cow manure- and sewage sludge-treated ones. The difference between cow manure and sewage sludge was negligible. The lambda(f) and S(R) values for E. coli and total bacteria were greater in the LS than in the SCL. This indicates a predominant role for the physical pore-obstruction filtration mechanisms as present in the poorly structured LS vs. the retention at adsorptive sites (chemical filtration) more likely in the better structured SCL. While the results confirmed the significant role of soil structure and preferential (macroporous) pathways, manure type was proven to have a major role in determining the maximum penetration risk of bacteria by governing filtration of bacteria. Thus while the numbers of bacteria in waste may be of significance for shallow aquifers, the type of waste may determine the risk for microbial contamination of deep aquifers.     

Colloid mobilization and arsenite transport in soil columns: effect of ionic strength

Colloid generation and transport in soils is of significance because of suspected colloid-facilitated transport of contaminants to the groundwater. In this study, colloid mobilization and its effect on the transport of arsenite [As(III)] were investigated in Olivier (fine-silty, mixed, active, thermic Aquic Fraglossudalfs) and Windsor (mixed, mesic typic Udipsamments) soil columns. Input solution of 10 mg L(-1) As(III) in 0.01 M NaCl was applied to water-saturated columns, and followed by leaching with deionized water (DIW). Flow interruptions were performed during the As(III) input and DIW leaching phases. Turbidity, electrical conductivity (EC), and pH of column effluents were monitored with time. Total and dissolved concentrations of As, Fe, and Al were analyzed. Effluent results demonstrated that colloid-facilitated transport contributed little to arsenic movement when the solution ionic strength was maintained constant. Mobilization of colloidal amorphous material and enhanced transport of As(III) were observed as a result of changes in ionic strength of the input solution. The peak of colloid generation coincided with peak concentrations of Fe, suggesting mobilization of Fe oxides and facilitated transport of As(III) adsorbed on oxide surfaces. Colloid mobilization was enhanced due to flow interruption in the Olivier column, which suggests slow dissociation of aggregated colloidal particles. Moreover, effluent results indicate significant effect of organic matter in stabilizing aggregates of colloidal particles.