Tracing Pharmaceuticals in the Unsaturated Zone (10 pp)

Background, Aim and Scope   One of the first occurrences of pharmaceutically active compounds in groundwater was reported from the sewage irrigation farms south of Berlin. At these sewage irrigation farms treated sewage effluent passed the soil and unsaturated zone before reaching the aquifer. Clofibric acid was detected in pore water from soils of those sewage irrigation farms in concentrations between 65 ng/L and 1430 ng/L. The aim of this study was to investigate the transport behavior of regularly detected clofibric acid, diclofenac, ibuprofen, and propyphenazone under conditions comparable to those at the sewage irrigation farms in a multiple compound sand column laboratory experiment. Materials and Methods   Sediment column experiments were conducted to study the transport of pharmaceuticals in the unsaturated zone. The migration was measured in fine to medium grained sand and leaching solution containing 1 mg/L of pharmaceutically active compounds and 61 mg/L of the tracer lithium chloride (LiCl). For the analysis of the pharmaceutical compounds the water samples were adjusted to a pH value of 2 and then extracted by solid-phase extraction (SPE). Before extraction, the samples were spiked with a surrogate standard for analytical quality control. The sample extracts were analyzed by capillary gas chromatography-mass spectrometry (GC-MS) with selected ion monitoring (SIM). Depending on the sample volume (100 to 200 mL) and the matrix, the limits of detection were between 1 and 10 ng/L, and the limits of quantitation were between 5 and 25 ng/L. Analysis for calcium, magnesium and lithium were carried out using a 'Trace Scan' ICP-AES from Thermo Jarrel Ash. Sodium, potassium, iron and manganese were analyzed using a Philips PU 9400 flame AAS. Analysis of anions was performed on a Dionex ion chromatograph DX 120. Results   At the sewage irrigation farms the average concentrations of clofibric acid in the unsaturated zone declined from higher values near ground surface (480 ng/L) to lower values near the groundwater table (65 ng/L). From the pharmaceuticals analyzed only clofibric acid, primidone and propyphenazone could be analyzed in the first (upper) aquifer at the sewage irrigation farms. All other pharmaceuticals could neither be detected in the first aquifer nor in the deeper aquifers. Breakthrough curves from soil column experiments revealed no transformation and no retardation for clofibric acid, whereas transformation of diclofenac was so high (79%) that no retardation factor could be calculated. Ibuprofen was significantly transformed (37%), transformation of propyphenazone (17%) was quite low and retardation (Rf = 2.05) was in the range of previously conducted column experiments. Discussion   The results confirm previously conducted experiments with clofibric acid where this compound was identified as highly mobile and persistent. The results that diclofenac and ibuprofen are significantly transformed where unexpected as other studies exhibited much lower transformation under saturated conditions at least for diclofenac. However, lower pH values and higher oxygen contents in the unsaturated zone compared to the aquifer may explain this observed high transformation of these compounds at the column experiments. Conclusions   We conclude that irrigation with sewage effluent containing the compounds used in our experiments will lead to an input into groundwater of clofibric acid, whereas diclofenac and ibuprofen will most likely be transformed during the passage. Propyphenazone will be retarded but will most likely occur in groundwater. These results from the column experiments coincide very well with the occurrence of the pharmaceuticals clofibric acid, primidone, and propyphenazone in the first aquifer. Recommendations and Perspective  : The results underline the need to study the sorption of pharmaceuticals on various materials. e.g. organic matter, surfaces at pH values occurring in the unsaturated zone. Future field studies will also include the investigation of desorption behavior in the unsaturated zone.     

Partition Isotherms of Chlorobenzenes in a Sediment–Water System

Partition experiments for a series of chlorobenzenes, 1,4-dichlorobenzene (1,4-DCB), 1,3,5-trichlorobenzene (1,3,5-TCB), 1,2,4,5-tetrachlorobenzene (1,2,4,5-TeCB), pentachlorobenzene (QCB), and hexochlorobenzene (HCB), in a sediment–water system were carried out and the sediment–water partition isotherms for the chlorobenzenes were determined. The partition isotherms were well described by the linear and the Langmuir models. However, experimental data indicated that the partition isotherms exhibited nonlinear trends at high concentrations. The maximum concentrations that can be adsorbed from the Langmuir model decreased with K _OW values of the chlorobenzenes. QSAR analysis showed that strong relationships exist between the partition parameters (partition coefficients and maximum concentration that can be adsorbed) and physicochemical properties (molar volume, solubility in water, and K _OW values).     

Desorption behaviour of polycyclic aromatic hydrocarbons after long-term storage of two harbour sludges from the port of Rotterdam, The Netherlands

Purpose

The desorption behaviour of 16 polycyclic aromatic hydrocarbons (PAHs) in sludges from two sites of the port of Rotterdam, The Netherlands, which are designated to be stored in a subaqueous sludge depository, was investigated after a storage time of 14 years at 4 °C under anaerobic conditions in the dark, mimicking depository conditions. Such long-term storage is believed to effect the desorption of the PAHs.

Materials and methods

Batch desorption experiments over a time period of 130 days were performed with the brackish Beerkanaal (BK) sludge and the freshwater Beneden Merwede River (BMR) sludge. The organic carbon–water partitioning coefficient (K _OC) values were calculated and compared to values of a previous study on the same sludges after a storage time of 3 years and to values obtained from calculations based on octanol–water partitioning coefficient (K _OW) values. Additionally, the organic matter of the sludges was characterised by C and N elemental analysis and solid-state ¹³C nuclear magnetic resonance spectroscopy.

Results and discussion

Only desorption of low molecular weight PAHs up to pyrene was detected. Several K _OC values were higher compared to the values from the previous study, and all were increased compared to values based on K _OW values. It is assumed that the increase in K _OC was an effect of the prolonged contact time, causing slow intradomain diffusion of PAHs into the condensed carbon domains. Desorption was higher in BK than in BMR, which is explained by differences in organic matter composition because BMR (containing predominantly aromatic carbon) and BK (which was dominated by lipids) contained the same amount of organic carbon. It is inferred that lipids compete with PAHs for sorption sites on the aromatic carbon, so that lipids block these sorption sites, and the PAHs are adsorbed to the lipids.

Conclusions

Since the amounts of PAHs desorbed from both sludges in this study were so low, it is supposed that long-term storage of these sludges in subaqueous depositories will likely result in increased sorption and thus a reduced release of these contaminants into the environment over time.     

Ibuprofen Sorption to Coastal Plain Soils

Ibuprofen is commonly detected in onsite wastewater systems. Such onsite systems are abundant in coastal plain areas, globally. Coastal plain soils have unique mineralogy. Rapid subsurface transport may occur in coastal plain soils due to their characteristic permeable soils and seasonally high water tables. Laboratory batch sorption studies were conducted on Norfolk, Goldsboro, and Lynchburg, three archetypical coastal plain soils, with varying physicochemical properties, to evaluate ibuprofen sorption. Sorption distribution coefficients (K_D values) across all three soils ranged from 0.63 to 1.26 L kg^?1. Sorption of ibuprofen to Norfolk and Goldsboro soils was able to be modeled using a Freundlich isotherm; however, the Lynchburg soil, was not, likely due to soil heterogeneity. In general, sorption of ibuprofen was influenced by soil organic carbon content.     

Fate and plant uptake of persistent organic pollutants in soil

Many persistent organic pollutants (POPs), notably hexachlorocyclohexanes (HCHs), chlorinated cyclodienes, and dichlorodiphenyltrichloroethanes (DDTs), remain in Japanese farming soils, more than 40 years after their use as insecticides was prohibited. In recent years, residues of chlorinated cyclodienes in cucurbit fruits have become a problem. But, though HCHs and DDTs have been staying in the soil, residues of these chemicals in crops have not been a problem. So we compared the fates of HCHs (α-, β-, γ-HCHs), chlorinated cyclodienes (dieldrin, endrin, heptachlor exo-epoxide), and DDTs (DDE, dichlorodiphenyldichloroethylene; DDD, dichlorodiphenyldichloroethane) in soil and investigated their uptake by several non-cucurbits and cucurbits. As for the fate of POPs in soil, not only the total concentrations but also the concentrations in soil solution as bioavailable POPs were determined. The half-lives of total β-HCH and DDTs in soil were the longest, and α- and γ-HCHs the shortest. On the other hand, the half-lives of bioavailable POPs ranged from 1/3 to 1/20 of those of total POPs. The ratio of the half-lives of bioavailable POPs to those of total POPs decreased in the order of HCHs > chlorinated cyclodienes > DDTs. Because hydrophobic chemicals were adsorbed strongly to the soil, the bioavailable POPs in soil are controlled by their hydrophobicity, indicated by the values of log K _OW (K _OW: n-octanol-water partition coefficient). The shoot concentrations of chlorinated cyclodienes and DDTs were higher in cucurbits than in non-cucurbits. However, among POP insecticides, HCHs did not show clear differences. As for the root concentrations, all tested POPs were higher in cucurbits than in non-cucurbits. Through the determination of POPs in soil solution, we could compare the abilities of plants to take up the chemicals using soil solution bioconcentration factors (BCF_SS). The values of BCF_SS increased with the magnitude of log K _OW, in the order of HCHs < chlorinated cyclodienes < DDTs. In addition, BCF_SS did not show marked differences among isomers or chemicals with similar structure. Therefore, plant uptake ability was influenced mainly by log K _OW. After being applied to agricultural land, α- and γ-HCHs seemed to disappear quickly, β-HCH persisted longer but the uptake in roots was low because of the low log K _OW, and DDTs also persisted longer but the bioavailability decreased rapidly in the soil because of their high log K _OW. Chlorinated cyclodienes have remained in the soil and have remained available, because they are less likely than HCHs (except β-HCH) to disappear and less likely than DDTs to become adsorbed to the soil. In addition, their higher log K _OW than that of HCHs makes them more easily taken up by roots. However, shoot concentrations were high only in cucurbits, for which they remain a problem in Japan.     

BTEX Sorption by Montmorillonite Organo-Clays: TMPA,Adam, HDTMA

Organo-clay can be utilized for the containment of environmentalpollutants originating from waste sites or accidental spills. Abatch study was conducted using organo-clays produced from aWyoming montmorillonite (SWy) and three organic cations(trimethylphenylammonium (TMPA), trimethylammonium adamantane(Adam), and hexadecyltrimethylammonium (HDTMA)) to characterizeBTEX (benzene, toluene, ethylbenzene, o-, m-, p-xylene) sorption. Sorption data were fitted to two models,with Freundlich resulting in greater correlations of the datathan the Langmuir model (R ² at P ≤0.001-0.05). The Freundlich conditional index (n _f),which describes the experimental sorption characteristics,decreased curvilinearly with organic-cation molecular weights,thus suggesting organo-clays with smaller cations had greaterhydrocarbon retention. Sorption of BTEX followed the order ofTMPA > Adam > HDTMA organo-clays. A similar sequence in themagnitudes of log K _d and log K _omsupportedthis finding. Positive log K _om/K _ow valuesfor TMPA and Adam derivatives indicated there was a greaterretention of BTEX by these organo-clays than octanol. The orderof log K _om for SWy-HDTMA, although concentration-dependent, was analogous to the log K _ow order,indicating partitioning was the dominant sorption mechanism forthe HDTMA-clay. Isotherms for SWy-TMPA and SWy-Adam followed aconvex up pattern. In contract, a concave up curvature, notedfor SWy-HDTMA isotherms, was probably caused by a cosorptiveenhancement process resulting from an effective increase in organic matter content of the organo-clay due to furtherhydrocarbon sorption,in concurrence with a decrease inadsorbate activity coefficients. Values of binding affinityconstant, K _f, for SWy-TMPA were consistently higherthan SWy-Adam. The K _f values determined for totalBTEX sorption by TMPA and Adam derivatives were higher thanthose for the individual hydrocarbons. With SWy-HDTMA, the same order was observed for benzene and toluene; however, ethylbenzene and xylenes had greater K _f values thanthat for the BTEX mixture, possibly due to higher partitioningaffinity of the larger alkylbenzenes. With SWy-HDTM, thesequence of K _f values was: ethylbenzene > m-xylene > p-xylene > o-xylene > toluene >benzene. Trends for SWy-TMPA and SWy-Adam were in contrast tothat of the partitioning order, suggesting that adsorption, ratherthan partitioning, was the primary sorption mechanism for thesetwo organo-clays. With respect to the equilibriumconcentrations, the sorbed amounts for total BTEX mixture weregenerally higher than those for the individual compounds. Ascompared to benzene and toluene, the large-size alkylbenzenesshowed greater partitioning affinity due to their high hydrophobicity.     

Water Remediation by Columns Filled with Micelle–Vermiculite Systems

Photodegradation of four pharmaceuticals (i.e. carbamazepine, ibuprofen, ketoprofen and 17α-ethinylestradiol) in aqueous media was studied using a solar light simulator (Xe lamp irradiation) and sunlight experiments. These experiments were carried out in river and seawater and compared to distilled water. The latter was used to evaluate the direct photodegradation pathways. Irradiation time was up to 400 min and 24 days for the solar light simulator and sunlight assays, respectively. Pharmaceutical photodegradation followed a first-order kinetics and their half-lives calculated in every aqueous matrix. Moreover, the sensitizing effect of DOC was evaluated by comparison with the kinetics obtained in distilled waters. Ketoprofen was rapidly transformed via direct photolysis in all the waters under both sunlight (t _1/2?=?2.4 min) and simulated solar light simulator test (t _1/2?=?0.54 min). Under xenon lamp radiation, ibuprofen and 17α-ethinylestradiol were photodegraded at moderate rate with half-lives from 1 to 5 h. Finally, carbamazepine had the lowest photodegradation rate (t _1/2?=?8–39 h) attributable to indirect photodegradation. Indeed, its elimination was strongly dependent on the DOC concentration present in solution. Finally, several ketoprofen photoproducts were identified and plotted against solar light simulator irradiation time. Accordingly, the photodegradation pathway of ketoprofen was postulated.     

Molecular properties as descriptors of octanol-water partition coefficients of herbicides

Molecular modeling techniques were used to establish relationships between the octanol/water partition coefficient (K _ow) and molecular properties of 90 herbicides with several types of chemistry. The K_ow values were obtained from the literature. Various molecular properties were calculated by quantum mechanical methods using molecular modeling software. The quantitative structure activity relationship (QSAR) analysis of all herbicides showed that K _ow was dependent on bulk (van der Waals volume, VDW_v) and electronic (dipole moment, µ; superdelocalizability of highest occupied molecular orbital, SHOMO; nucleophilic superdelocalizability, SN) properties, and the model explained 68% of the variation in K _ow. Herbicides were broadly divided into six families (ureas, acid amides, triazines, carbamates, diphenyl ethers, and dinitroanilines) based on structural similarities, and separate equations were established for each group. The QSAR models accounted for 74 to 98% of the variation in K _ow within these six groups. Applicability of these models was tested for some herbicides. The QSAR models produced estimates that correlate well with experimental values and appear to be specific to structurally similar compounds.     

Zur statistischen Abhängigkeit der Adsorption verschiedener Herbizidwirkstoffe vom Anteil der organischen Substanz in Böden

On the relation of herbicide adsorption and soil organic fraction Freundlich adsorption isotherms were measured for four herbicides (atrazine, terbuthylazine, chlorotoluron, isoproturon) and 24 soil horizons, which are typical of Schleswig-Holstein, northern Germany. The relationship between the adsorption constant (K_Fr) of a chemical and the fraction of organic carbon (f_OC) of the soil horizons was evaluated. Chemical specific K'_OC-values, that are independent of soil organic carbon fraction varied considerably for each herbicide (CV about 50%); therefore these values as well as K_OC-values, that are determined by linear regression of K_Fr and f_OC should be evaluated critically before application. K'_OC- and K_OC-values derived from experiments showed decreasing affinity of the herbicides to soil horizons in the order terbuthylazine > chlorotoluron > atrazine ? isoproturon. Calculation of K_OC from K_OW or water solubility of each herbicide, however, led to changes in the above mentioned ranking. Hence, especially K_OW or water solubility based K_OC-values may lead to false conclusions concerning chemical mobility. For atrazine, terbuthylazine and isoproturon Freundlich adsorption constants increased overproportionally with increasing organic carbon content of soils. The relationships between K_Fr and f_OC therefore were described better by a non-linear equation (second order polynom) than by a linear approach. Contrary, for chlorotoluron a linear relation between K_Fr and f_OC holds at least for the range of f_OC investigated in this study.     

Sorption of 2,4-D and other phenoxy herbicides to soil, organic matter, and minerals

Purpose

We review 2,4-dichlorophenoxyacetic acid (2,4-D) and other phenoxy herbicide sorption experiments.

Methods

A database with 469 soil–water distribution coefficients K _d (in liters per kilogram) was compiled: 271 coefficients are for the phenoxy herbicide 2,4-D, 9 for 4-(2,4-dichlorophenoxy)butyric acid, 18 for 2-(2,4-dichlorophenoxy)propanoic acid, 109 for 2-methyl-4-chlorophenoxyacetic acid, 5 for 4-(4-chloro-2-methylphenoxy)butanoic acid, and 57 for 2-(4-chloro-2-methylphenoxy)propanoic acid. The following parameters characterizing the soils, solutions, or experimental procedures used in the studies were also compiled if available: solution CaCl₂ concentration, pH, pre-equilibration time, temperature, soil organic carbon content (f _oc), percent sand, silt and clay, oxalate extractable aluminum, oxalate extractable iron (Oxalate Fe), dithionite–citrate–bicarbonate extractable aluminum, dithionite–citrate–bicarbonate extractable iron (DCB Fe), point of zero negative charge, anion exchange capacity, cation exchange capacity, soil type, soil horizon or depth of sampling, and geographic location. K _d data were also compiled characterizing phenoxy herbicide sorption to the following well-defined sorbent materials: quartz, calcite, α-alumina, kaolinite, ferrihydrite, goethite, lepidocrocite, soil humic acid, Fluka humic acid, and Pahokee peat.

Results

The data review suggests that sorption of 2,4-D can be rationalized based on the soil parameters pH, f _oc, Oxalate Fe, and DCB Fe in combination with sorption coefficients measured independently for humic acids and ferrihydrite, and goethite.

Conclusions

Soil organic matter and iron oxides appear to be the most relevant sorbents for phenoxy herbicides. Unfortunately, few authors report Oxalate Fe and DCB Fe data.     

Chlorophenol binding to dissolved and particulate soil organic matter determined in controlled equilibrium systems

We determined the sorption of 2,4‐dichlorophenol (DCP), 2,4,5‐trichlorophenol (TCP) and pentachlorophenol (PCP) to dissolved (DOM) and particulate soil organic matter (POM) from the same soil in controlled equilibrium systems, using ¹⁴C‐labelled chlorophenols in combination with reversed‐phase high‐performance liquid chromatography (RP‐HPLC) and liquid scintillation. Associations of DCP, TCP and PCP to DOM and POM were satisfactorily described by linear adsorption isotherms. Together with the absence of substantial competition between DCP and TCP for binding sites, this indicates a hydrophobic partitioning mechanism. The organic carbon normalized partitioning coefficient (K_OC) for the binding of DCP was similar in magnitude for POM (K_POC) and for DOM (K_DOC), whereas K_POC for the more hydrophobic compounds TCP and PCP were approximately one order of magnitude greater than K_DOC. On the basis of the relationships between log K_OC and the organic carbon normalized partitioning coefficient (log K_OW), the extent of association to POM increases more with the hydrophobicity of the chlorophenol than the extent of association to DOM. This holds for our data obtained for DOM and POM of similar origin, as well as for various sources of POM and DOM reported in the literature. Differences in the magnitude of K_POC and K_DOC in our study could not be accounted for by differences in gross carbon chemistry of POM and DOM, as determined by nuclear magnetic resonance (¹³C‐NMR) and X‐ray photoelectron spectroscopy (XPS). Thus, other factors such as the average size and capacity of hydrophobic moieties could explain differences in chlorophenol association between POM and DOM. We conclude that K_POC and K_DOC need to be determined explicitly, when the transport and retention of chlorophenols is modelled, and not calculated from relationships between log K_OC and log K_OW.     

Pharmaceuticals in Rivers of Two Regions with Contrasted Socio-Economic Conditions: Occurrence, Accumulation, and Comparison for Ukraine and France

The goal of our study was to identify pharmaceuticals, their potential sources and consumption level in two different socioeconomic and geographical regions??Bordeaux, France and Kharkiv, Ukraine. These substances were monitored in rivers water during contrasted seasonal conditions with application of passive samplers. The 21 pharmaceuticals (psychiatric drugs: alprazolam, amitriptyline, diazepam, fluoxetine, nordiazepam, carbamazepine, bromazepam; analgesics: aspirin, paracetamol; broncholidator: clenbuterol, salbutamol, terbutaline; non-steroidal anti-inflammatory drug: diclofenac, ibuprofen, ketoprofen, naproxen; lipid regulator: gemfibrozil; stimulants: caffeine, theophylline) were identified in sites upstream and downstream of urban areas and discharge of wastewaters. Caffeine, carbamazepine, and diclofenac were relatively abundant into the surface water and could be considered as potential anthropogenic markers of wastewater discharges into rivers. A mass balance modeling has been applied to calculate approximate consumption rates for carbamazepine, diclofenac, and caffeine in both regions to assess socio-economic factors linked with pharmaceuticals behavior.     

Development of QSAR's in soil ecotoxicology: Earthworm toxicity and soil sorption of chlorophenols,chlorobenzenes and chloroanilines

Soil adsorption and the toxicity of four chloroanilines for earthworms were investigated in two soil types. The toxicity tests were carried out with two earthworm species, Eisenia andrei and Lumbricus rubellus. LC₅₀ values in mg kg^?1 dry soil were recalculated towards molar concentrations in pore water using data from soil adsorption experiments. An attempt has been made to develop Quantitative Structure Activity Relationships (QSAR's) using these results and data on five chlorophenols and dichloroaniline in four soils and five chlorobenzenes in two soils published previously (Van Gestel and Ma, 1988, 1990; Van Gestel et al., 1991). Significant QSAR relationships were obtained between 1) adsorption coefficients (log K _om ) and the octanol/water partition coefficient (log k _ow ), and 2) LC₅₀ values (in itμmol L^?1 soil pore water) and log K _ow . It can be concluded that both earthworm species tested are equally sensitive to chlorobenzenes and chloroanilines, E. andrei is more sensitive than L. rubellus to chlorophenols.     

Study of the Water Solubility and Sorption on Particulate Matters of Phthalate in the Presence of Humic Acid Using 14C Labelled Di-(2-Ethylhexyl)Phthalate

Phthalate esters have become widespread contaminants in the aquatic environment, because of their extensive use as non-reactive plasticizers. There is, however, little accurate data on their solubility, transportation, and distribution in the aquatic environment. In this work, we have investigated the influence of humic acid on the water solubility of di-(2-ethylhexyl)phthalate (DEHP), one of the most frequently used phthalate esters in the laboratory studies for DEHP. We have also studied the solid–water distribution of DEHP in the presence of humic acid and particulate matter (activated carbon, ferrihydrite, and kaolinite) to simulate their distribution in a natural aquifer (ternary system). The results show that the water solubility of DEHP can be significantly increased by humic acid. The shape K _eq value, the binding constant of DEHP between water and humic acid at equilibrium, was obtained by fitting experimental data for each humic acid. The shape K _eq values in the ternary system apparently decreased in the order of ferrihydrite ≤ kaolinite ≈ octanol/water partition activated carbon systems. This result shows that the increase in the hydrophobicity of HA remaining in the solution will lead to the apparent increase of shape K _eq in the system since more hydrophilic solid sorbs relatively more hydrophilic HA molecule. The solid–water partition coefficient (shape K _W-P ) for DEHP in the environment estimated from this study is consistent with those reported based on the experiments for natural samples. Quantitative values obtained in this study, such as K'_ow, shape K _eq, and shape K _W-P , can be useful for estimating the behavior of DEHP.     

Kinetics of microbial growth and degradation of organic substrates in subsoil as affected by an inhibitor, benzotriazole: Model based analyses of experimental results

Deep transport of degradable compounds through soils may occur if the metabolic activity in the soil profile is low; either by natural causes (low temperature during ice melt) or by toxic pollutants. De-icing chemicals (for roads and airports) represents a severe challenge to the soil's purifying capacity; rapid infiltration of contaminated water occurs in near-frozen soil, the contamination includes toxic compounds. Degradation experiments were conducted with toluene, and three compounds frequently used for de-icing; acetate, formate and glycol. The substrates were added to a subsoil (0.93 μmol substrate-carbon (C) g⁻¹ soil, with ample amounts of nitrogen (N) and phosphorous (P)); and their mineralization was monitored in the presence of a toxic compound, benzotriazol (BTA) at various concentrations. BTA is commonly used as an additive in commercial de-icing fluids. A second and third dose of substrate was added after complete degradation of the previous one. The mineralization curves of the three consecutive doses were used to estimate kinetic parameters by fitting to a Monod-model. The model parameters estimated for each substance were the initial biomass C of the organisms growing on each substrate, C_b0, their maximum substrate uptake rates, V_max, their apparent substrate affinity, K_S, and growth yield, Y. The C_b0 values for pristine soil were 4.9, 20.5 and 10 nmol C g⁻¹ soil for formate, glycol and acetate, respectively, and 1-2 orders of magnitude lower for toluene. The K_S values were 1.1, 0.6, 2.5 and 0.13 mM for formate, glycol, acetate, and toluene, respectively. The high K_S values probably reflect diffusion limitations. The estimated yields (Y) in the absence of BTA were 0.032, 0.53 and 0.42 g biomass-C g⁻¹ substrate-C for growth on formate, glycol and acetate, respectively. BTA invariably reduced the growth yield for organisms growing on the different substrates, and the yield reduction increased with increasing BTA concentrations (more than 50% reduction at 400 mg BTA l⁻¹). The degradation of the four substrates showed major differences in BTA-sensitivity, and there were strikingly weak signs (if any) of increasing BTA tolerance during growth in the presence of BTA (analyses of second and third dose experiments). The modelling of the consecutive substrate doses corroborated previous investigations of BTA effects on mineralization and community PLFA [Jia et al., 2006. Organic compounds that reach subsoil may threaten groundwater quality; effect of benzotriazole on degradation kinetics and microbial community composition. Soil Biology & Biochemistry 38, 2543-2556]. The results and the estimated Monod parameters are useful for predictive modelling of transport and degradation of pollutants as well as natural substances in sub-soils.     

Partition of Nonylphenol and Related Compounds Among Different Aquatic Compartments in Tiber River (Central Italy)

Nonylphenol (NP), nonylphenol mono- and di-ethoxylate (NP1EO, NP2EO) and bisphenol A (BPA) were determined in water, suspended particulate matter (s.p.m.) and bed sediment collected from the most polluted stretch of Tiber river (Italy) in the neighbourhood of Rome. Analytes were recovered from water samples by solid-phase extraction (SPE) on Si–C₁₈ cartridges and analysed by HPLC with fluorescence detection. Solid samples were extracted by using an aqueous solution of the non-ionic surfactant Tween 80. Results indicated that 2–42% of NP, 9–45% of NP1EO, 11–18% of NP2EO and 4–62% of BPA respectively occurred in the suspended phase. In general, for all compounds a higher affinity for s.p.m. than for bed sediments was observed, reflecting differences in the nature of particles and in their sorption capacity for organic micro-pollutants. The partition of target compounds in river compartments was affected by differences in hydrological conditions between the two sampling campaigns. Run-off from the basin or resuspension/redissolution from sediments was an important source of nonylphenol and bisphenol A during high discharge regimes. Partition coefficients of compounds (log K _oc ) between water and s.p.m. were calculated under stable flow condition. K _oc values, experimentally measured in the river, were higher than those predicted by K _ow , implying that specific chemical interaction could occur in the sorption mechanisms for these group of compounds.     

Cadmium soil sorption at low concentrations: VIII. correlation with soil parameters

Cadmium distribution coefficients, K _d were determined at low Cd concentrations (solute: 0.2 to 3.0 μg Cd dm^?3, soil: 0.044 to 1.1 mg Cd kg^?1) for 63 Danish agricultural soils. The K _d values ranged from 15 to 2450 L kg^?1. About 40% of the soils had K _d values below 200 L kg^?1. The observed K _d values correlated very well with soil pH (r ² = 0.72). Introducing soil organic matter content as a second parameter improved the correlation some (r ² = 0.79). No further improvements were obtained by introducing traditional soil parameters as clay, silt, fine sand, coarse sand and CEC or ‘reactive’ parameters as oxyhydroxides of Mn, Fe and Al. The identified regression equation for predicting K _d values indicates that K _d approximately doubles for each 0.5 unit increase in pH or 2% increase (weight basis) in organic matter content.     

Relationship between Freundlich isotherm Coefficients,log K F and 1 / n for atrazine desorption from soils in Japan

Desorption experiments were conducted on 21 soils at 3 atrazine concentrations. The Freundlich isotherm was used to estimate atrazine desorption. For the relationship between Freundlich isotherm coefficients, log K _F and 1 / n, 1 / n was also represented by a linear regression of log K _F as in the case of atrazine adsorption. All the linear regression lines of desorption exhibited larger slopes and intercepts than those of adsorption. When the atrazine concentration was high, the slope and intercept values were smaller than those for the desorption regression lines. The results showed that the larger the capacity of a soil to adsorb atrazine, the lesser the amount of atrazine desorbed. For the cultivated soils except for Andisols, the percentages of atrazine taken from solutions using the sequential exchange method after the first adsorption experiments, were the same as those desorbed from soils in relation to the initial amount adsorbed. Thus, reversible adsorption occurred in the soils due to weak physical adsorption.     

Soil macroporosity,hydraulic conductivity and air permeability of silty soils under long-term conservation tillage in Indiana

With the increasing use of conservation tillage, many questions about the long-term effects of tillage system on soil physical properties have been raised. Studies were conducted to evaluate saturated hydraulic conductivity (K_SAT), macropore characteristics and air permeability of two silty soils as affected by long-term conservation tillage systems in the state of Indiana. Measurements were taken during the tenth year of a tillage study on a Chalmers silty clay loam (Typic Haplaquoll) and the fifth year of a study on a Clermont silt loam (Typic Ochraqualf). Tillage systems were moldboard plow, chisel, ridge till-plant, and no-till in a rotation of corn (Zea mays L.) and soya beans (Glycine max L.). Saturated hydraulic conductivity was measured on large soil columns (25 × 25 × 40 cm) before spring tillage, and macropore size and continuity were assessed with staining techniques. Intact soil cores (8 cm diam × 10 cm) were collected in early July in the row and non-trafficked interrow at three depths (10–20, 20–30, and 30–40 cm) and were analyzed for air permeability (K_air), air-filled porosity and bulk density. Saturated hydraulic conductivity values were in the order plow > chisel > ridge till > no-till for the Chalmers soil and were significantly greater in the plow treatment than in the other 3 tillage systems on the Clermont soil. Differences in K_SAT between the 2 soils were generally greater than differences among tillage systems, and coefficients of variation were lower for treatments that did not include may fall tillage operations. At the 10-cm depth on the Chalmers soil, the chisel treatment had the greatest number of stained cylindrical channels, whereas for the Clermont soil the ridge till had the greatest number at this depth. Although the no-till treatment had similar or fewer total channels, it had the most continuous channels from the 10-cm depth to the 20- and 30-cm depths on both soils. Tillage system, row position and depth all affected K_air. On the Chalmers soil, plow, chisel and ridge systems had lower K_air between rows than in the row at the 10–20-cm depth, whereas no-till had constant K_air in the row and between the row. On the Clermont soil, ridge till had the highest K_air of all treatments at the 10–20-cm depth, and no-till had the highest K_air of all treatments at the 20–30-cm depth.     

Comparison of unconfined and confined unsaturated hydraulic conductivity

The field tension infiltrometer (TI) and the laboratory unit hydraulic gradient (UHG) methods are widely applied to determine the near-saturated soil hydraulic conductivity, K. Comparison between the two methods is relevant given that they differ in the explored soil volume (undetached or detached) and in the flow process (unconfined or confined). The objective of this investigation was to compare unconfined and confined measurements of unsaturated hydraulic conductivity. Twenty TI experiments were conducted in a relatively coarse-textured soil having an appreciable hysteretic behavior by using two different dry-to-wet-to-dry (DTWTD) sequences of pressure head, h₀, values that differed by the highest h₀ value imposed within the sequence (i.e. h₀ = − 150, − 75, − 30, + 5, − 30, − 75, − 150 in site A or h₀ = − 150, − 75, − 30, − 10, − 30, − 75, − 150 in site B). The same pressure head sequences were applied on twenty undisturbed soil cores, collected at the exact location of the TI measurements, to perform the laboratory UHG measurements. Regardless of the type of experiment (i.e. unconfined or confined) and the applied pressure head sequence (i.e. site A or B), higher K₀ values were obtained with a drying sequence of h₀ values (K_0,d) than with a wetting one (K_0,w)and the discrepancies between K_0,w and K_0,d decreased as the imposed h₀ value increased, as it was expected due to hysteresis. A tendency of the UHG method to overestimate the K₀ values was detected (ratios of mean K_0,1D to mean K_0,3D values ranging from 0.93 to 4.35), but the statistical significance of the observed differences varied with the considered sequence of pressure head values. It was concluded that both the TI and the UHG methods were effective in detecting hysteresis effects on K₀, but the laboratory method resulted in K₀ values that were higher and more variable probably as a consequence of a more substantial effect of macropore flow on the measured flow rates.