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PubMed1996

Evaluation of the genotoxicity potential (by Mutatox test) of ten pesticides found as water pollutants in Cyprus.

Ten pesticides: aldicarb, aldicard sulfone, aldicarb oxide, carbofuran, propoxur, methomyl, diuron, linuron, alachlor and parathion-methyl, found as water pollutants in Cyprus, were evaluated for their genotoxicity potential with the Mutatox test, both directly and after exogenous activation with S9 hepatic enzymes. A dark variant (M 169) of the Photobacterium phosphoreum was used as the test organism. Trials were undertaken in triplicate using ground-water spiked with pesticides solutions at testing concentration theoretically corresponding to acute effects of 0.004%, up to a maximum of 2%. All tested pesticides were found to be 'suspect genotoxic' directly and after S-9 activation, except for Alachlor which after S-9 activation was found to be 'genotoxic' at 30 micrograms/l. Among the ten pesticides Linuron was found to be 'suspect genotoxic' after S-9 activation at the lowest concentration, i.e. 2 micrograms/l. Genotoxicity after activation with S-9 was demonstrated at a concentration 1-3 orders of magnitude lower than the respective concentration for direct genotoxic effects. Moreover, genotoxicity after S-9 was developed at levels where the acute toxic effects (Microtox) were 'non measurable' to 'negligible'. The investigation of possible genotoxic effects provides essential information on the impacts of pesticides on the Ecosystem and can contribute to the selection of pesticides with the least possible effects.

Animals↗
PubMed2000

Occurrence of cotton herbicides and insecticides in playa lakes of the High Plains of West Texas.

During the summer of 1997, water samples were collected and analyzed for pesticides from 32 playa lakes of the High Plains that receive drainage from both cotton and corn agriculture in West Texas. The major cotton herbicides detected in the water samples were diuron, fluometuron, metolachlor, norflurazon, and prometryn. Atrazine and propazine, corn and sorghum herbicides, were also routinely detected in samples from the playa lakes. Furthermore, the metabolites of all the herbicides studied were found in the playa lake samples. In some cases, the concentration of metabolites was equal to or exceeded the concentration of the parent compound. The types of metabolites detected suggested that the parent compounds had been transported to and had undergone degradation in the playa lakes. The types of metabolites and the ratio of metabolites to parent compounds may be useful in indicating the time that the herbicides were transported to the playa lakes. The median concentration of total herbicides was 7.2 microg/l, with the largest total concentrations exceeding 30 microg/l. Organophosphate insecticides were detected in only one water sample. Further work will improve the understanding of the fate of these compounds in the playa lake area.

Fresh Water↗
PubMed2003

Pigments as biomarkers of exposure to the vineyard herbicide flazasulfuron in freshwater algae.

Weed control in Champagne vineyards has long relied on the use of diuron and substituted triazines; these compounds are now being replaced by flazasulfuron, a sulfonylurea that is used at a much lower dosage. The vineyards of Champagne are planted on steep slopes and runoff is important, and even though low doses of these herbicides are used, they may present some potential risk for freshwater ecosystems. Therefore, the effects of the sulfonylurea herbicide, flazasulfuron (formulated as Katana) was investigated on the unicellular green alga Scenedesmus obliquus. The pigment content of the algal suspensions was followed as a biomarker of exposure to the herbicide. The results demonstrate that flazasulfuron induced a reduction in chlorophyll content at concentrations of 10 microg/L, while the increase of pigment content in the culture was reduced with the lowest concentration tested (0.1 microg/L). Among the three pigments tested, chlorophyll a appeared to be the most sensitive biomarker. In the algal medium, flazasulfuron was slowly degraded (DT(50) approximately 8 days) in a compound that was tentatively identified. The toxicity of this herbicide for the algae was comparable to that of older herbicides which are used at a much higher rate. Therefore, we may speculate that even if flazasulfuron comes into contact with freshwater ecosystems, its effects on algae will be less deleterious than that of traditional herbicides.

Agriculture↗
PubMed2004

Worldwide occurrence and effects of antifouling paint booster biocides in the aquatic environment: a review.

Organic booster biocides were recently introduced as alternatives to organotin compounds in antifouling products, after restrictions imposed on the use of tributyltin (TBT) in 1987. Replacement products are generally based on copper metal oxides and organic biocides. This ban has led to an increase in alternative coating products containing the above biocides. The most commonly used biocides in antifouling paints are: Irgarol 1051, diuron, Sea-nine 211, dichlofluanid, chlorothalonil, zinc pyrithione, TCMS (2,3,3,6-tetrachloro-4-methylsulfonyl) pyridine, TCMTB [2-(thiocyanomethylthio) benzothiazole], and zineb. Since 1993, several studies have demonstrated the presence of these biocides in European coastal environment as a result of their increased use. More recently, the presence of these biocides was also revealed in waters from Japan, United States, Singapore, Australia and Bermuda. This paper reviews the currently available data on the occurrence of these biocides in the aquatic environment. Some data dealing with the environmental fate, partitioning, behaviour and risk assessment of antifouling paint booster biocides are also reported in order to discuss the detected levels of contamination.

Animals↗
PubMed2000

Activation of the hsp70 promoter by environmental inorganic and organic chemicals: relationships with cytotoxicity and lipophilicity.

Stress proteins (heat shock proteins, HSPs) have been proposed as general markers of cellular aggression and their use for environmental monitoring is often suggested. The aim of this work was to study the potency of various environmentally relevant organic and inorganic chemicals to induce the expression of the HSP70 marker. For this purpose, we used an established HeLa cell line containing the chloramphenicol acetyl transferase (CAT) gene under the control of the hsp70 promoter. The screening of three metallic and 15 organic chemicals revealed differences in their capacities to induce the hsp70 promoter. The three metals tested (cadmium, zinc and mercury) were able to induce a stress response. Some organochlorine compounds (chlorophenol derivatives, tetrachlorohydroquinone, 3, 4-dichloroaniline, ethyl parathion and 1-chloro-2,4-dinitrobenzene) induced a response, whereas other common halogenated pesticides or aromatic hydrocarbons (e.g. benzo(a)pyrene, 2, 4-dichlorophenoxyacetic acid, endosulfan, diuron, 4-nonylphenol) did not. The potency to induce hsp70 was significantly correlated to the octanol-water partition coefficient (log K(ow)) of the inducing chemicals, except for 1-chloro-2,4-dinitrobenzene and ethyl parathion. Cytotoxicity assays run in parallel to the induction measurements revealed that the three metals were effective at non cytotoxic doses whereas all organic compounds, except tetrachlorohydroquinone and 1-chloro-2,4-dinitrobenzene, induced the promoter at cytotoxic doses. These results suggest that hsp70 is induced by different mechanisms of toxicity. We propose that this model can be used in mechanistic studies for the detection of toxic effects of certain pollutants.

Cadmium↗
PubMed1999

Herbicide use on railway tracks for safety reasons in Germany?

A short overview on the occurrence of herbicides in groundwater and drinking water located in the vicinity of railway tracks in Germany is presented. The study has been conducted using the experience of various water supply companies and includes a literature research on the subject. It has been documented that in Germany only 1% of the total area treated with pesticides was under management of the former Deutsche Bundesbahn before 1990. The specific amount applied on the railway tracks was, however, a factor of 6 higher than that used in agriculture, although it must be borne in mind that the retaining capacity of railway tracks for pesticides is much lower. The herbicides applied ranged from 2,4-D and 2,4,5-T, triazine derivatives, e.g. atrazine and urea derivatives such as diuron. Traces of almost all of the herbicides applied could be detected in samples of groundwater and drinking water in the vicinity of railway tracks. Since 1997 only glyphosate has been used.

Germany↗
PubMed2000

Screening of selected pesticides for inhibition of CYP19 aromatase activity in vitro.

Many pesticides are able to block or activate the steroid hormone receptors and/or to affect the levels of sex hormones, thereby potentially affecting the development or expression of the male and female reproductive system or both. This emphasizes the relevance of screening pesticides for a wide range of hormone-mimicking effects. Twenty-two pesticides were tested for their ability to affect CYP19 aromatase activity in human placental microsomes using the classical [(3)H](2)O method. Prochloraz, imazalil, propioconazole, fenarimol, triadimenol, triadimefon (all fungicides), and dicofol (an acaricide) gave rise to a statistically significant inhibition of aromatase activity. The IC(50)s of prochloraz, imazalil, propioconazole fenarimol, triadimenol, and triadimefon were calculated from dose-response curves to be 0.04, 0.34, 6.5, 10, 21 and 32 microM, respectively. The IC(50) of dicofol was greater than 50 microM. The positive control 4-hydroxyandrostendione (1 microM) caused an inhibition of aromatase activity by 74%. The compounds, which did not affect the aromatase activity, were bromopropylate, chlorfenvinphos, chlorobenzilate, chlorpyrifos, diuron, heptachlor, iprodion, linuron, pentachlorphenol, procymidon, propyzamide, quintozen, tetrachlorvinphos and tetradifon. With the purpose of comparing the results for fenarimol obtained with the microsomal system with data from an intact cell system, an aromatase assay based on JEG-3 cells was established. 4-Hydroxyandrostendione (1 microM) inhibited the aromatase activity in JEG-3 cells by 94%. The IC(50) for fenarimol in this system was 2 microM, slightly lower than that observed in the microsomal system. For the first time, fenarimol has been demonstrated to inhibit aromatase activity in human tissues and, furthermore, propioconazole, triadimefon, and triadimenol were identified as weak aromatase inhibitors. In conclusion, seven out of 22 tested pesticides turned out to be weak to moderate aromatase inhibitors in vitro, indicating the relevance of elucidating the endocrine effects in vivo of these- compounds.

Aromatase Inhibitors↗
PubMed2003

Optical whole-cell biosensor using Chlorella vulgaris designed for monitoring herbicides.

An optical biosensor was designed for determination of herbicides as aquatic contaminants. Detection was obtained with immobilised Chlorella vulgaris microalgae entrapped on a quartz microfibre filter and placed in a five-membrane-home-made-flow cell. The algal chlorophyll fluorescence modified by the presence of herbicides was collected at the tip of an optical fibre bundle and sent to a fluorimeter. A continuous culture was set up to produce algal cells in reproducible conditions for measurement optimisation. Effects of flow rate, algal density, temperature, and pH on the biosensor response to atrazine were studied. Reversibility and detection limits were determined for DNOC and atrazine, simazine, isoproturon, diuron. Detection of photosystem II (PSII) herbicides was achieved at sub-ppb concentration level.

Atrazine↗
PubMed1993

Rapid biorecognition assay for herbicides in biological matrices.

A rapid assay capable of detecting several commonly used herbicides at nanogram per milliliter concentrations in biological fluids is described. The assay is based on inhibition of photosynthetic electron transport in spinach thylakoids by the target compounds with colorimetric detection using a redox dye. Using a microtiter plate format, high throughput assays of water, urine, and homogenized tissue were performed in minutes with minimal sample preparation. Detection limits of 3 ng/mL for atrazine, 3 ng/mL for diuron, and 1 ng/mL for terbutryn were observed.

Animals↗
PubMed1993

Characterization of mutations in the cytochrome b subunit of the bc1 complex of Rhodobacter sphaeroides that affect the quinone reductase site (Qc).

The cytochrome b subunit of the bc1 complex contains two heme components, cytochrome bL and cytochrome bH, and is the locus of both a quinol oxidizing site (Qo or Qz) and a quinone reducing site (Qi or Qc). The quinone reductase site has been previously characterized as the site of interaction for a set of inhibitors including antimycin A, diuron, funiculosin, and HQNO. In this paper, four highly conserved residues in the cytochrome b subunit of Rhodobacter sphaeroides (A52, H217, K251, and D252) were targeted for site-directed mutagenesis. These residues were chosen as being likely to be at or near the quinone reductase site, on the basis of known locations of missense mutations in the homologous yeast subunit that confer resistance to Qc-directed inhibitors. The site-directed mutants all exhibit a normal rate of reduction of cytochrome bH, suggesting a fully functional quinol oxidizing site. However, each of the mutants is impaired, to varying degrees, in the rate of reoxidation of cytochrome bH. Two mutants (H217A and D252A) are unable to grow photosynthetically, indicating a severe defect in the bc1 complex. In both cases, the cause of the defect is the lack of reoxidation of cytochrome bH by ubiquinone. This is the first report of mutations that selectively impair the rate of electron transfer from cytochrome bH to the Qc-site. This set of mutations will be useful not only for modeling the structure of the quinone reducing site but also in elucidating the catalytic mechanism of this portion of the Q-cycle.

Amino Acid Sequence↗
PubMed1994

The D-E region of the D1 protein is involved in multiple quinone and herbicide interactions in photosystem II.

The region between helices D and E (D-E region) of the D1 protein of photosystem II (PSII) is exposed at the stromal side of the photosynthetic membrane, contains the secondary plastoquinone (QB) binding niche, and is involved in processes at the reducing side of PSII. The role of the D-E region was studied in 27 site-directed mutants generated in the psbAII gene of the cyanobacterium Synechocystis sp. PCC 6803. The photochemical performance of the modified PSII reaction centers was assessed with respect to photoautotrophic growth, oxygen evolution, fluorescence induction, and herbicide inhibition. A few mutations, located at positions presumably involved in essential interactions in the QB binding niche, greatly interfered with PSII performance. On the other hand, mutations in the presumptive loop region between helices D and de resulted in relatively minor effects, indicating a flexible region not critical for photochemical function. Indeed, although more than 80% of the D-E region is phylogenetically invariant, the bulk of the mutations affected the measured parameters only moderately. The significance of the conserved residues appears to be in subtle interactions that optimize the thermodynamic balance between some of the redox components of PSII, as indicated by mild changes in the steady state fluorescence. Many mutations modified tolerances to PSII herbicides. The dispersion of these mutations throughout the D-E region indicates the complex nature of the interactions, direct and indirect, affecting herbicide binding in the QB niche. Mutation of codons Ser221 and Ser222 to Leu221 and Ala222 revealed a new location coordinating the herbicide diuron in the D1 protein.(ABSTRACT TRUNCATED AT 250 WORDS)

Amino Acid Sequence↗
PubMed2004

Herbicide runoff along highways. 2. Sorption control.

Controversy remains about the importance of nonlinear sorption isotherms, desorption rate limitations, and aging effects, collectively referred to as nonideal sorption processes, in controlling the fate and transport of organic contaminants. Herbicide runoff from highway soils represents a good test case for assessing the relative importance of nonideal sorption because runoff flow rates are often high, soil-water contacttimes are short, and significant time is available for contaminant aging after application. This study examines the sorption and desorption of five herbicides with a wide range of properties (isoxaben, oryzalin, diuron, clopyralid, and glyphosate) on soil samples from two roadsides in northern California and uses the results to examine field runoff data from multiple rainy seasons. Nonideal sorption processes do not appear to be significant in determining herbicide runoff at the field sites because (i) sorption isotherms were linear or slightly nonlinear for all compounds but glyphosate, (ii) field runoff concentration ratios between isoxaben and oryzalin were consistent with linear partitioning predictions, (iii) runoff leaving the site appeared to be in equilibrium with local soil concentrations, and (iv) desorption distribution coefficients for aged herbicides on soil samples collected from the field site did not differ substantially from those obtained in short-term laboratory adsorption experiments. Collectively, these findings indicate that linear equilibrium models are adequate for predicting the concentration of herbicides in runoff in these field settings and that more complicated nonideal models do not need to be invoked. Vegetated slopes effectively reduced the herbicide loads, with average removals of 35-80% occurring as runoff traversed a 3-m segment 1 m from the edge of the spray zone.

Adsorption↗
PubMed2005

In vitro assessment of modes of toxic action of pharmaceuticals in aquatic life.

An ecotoxicological test battery based on a mode-of-action approach was designed and applied to the hazard identification and classification of modes of action of six pharmaceuticals (carbamazepine, diclofenac, ethinyl estradiol, ibuprofen, propranolol, and sulfamethoxazole). The rationale behind the design of the battery was to cover the relevant interactions that a compound may have with biological targets. It is thus not comprehensive but contains representative examples of each category of mode of toxic action including nonspecific, specific, and reactive toxicity. The test battery consists of one test system for nonspecific toxicity (baseline toxicity or narcosis), two test systems for specific effects, and two test systems for reactive toxicity. The baseline toxicity was quantified with the Kinspec test, which detects membrane leakage via measurements of membrane potential. This test system may also be used to detect the specific effects on energy transduction, although this was not relevant to any compound investigated in this study. As examples of specific receptor-mediated toxicity, we chose the yeast estrogen screen (YES) as a specific test for estrogenicity, and the inhibition of chlorophyll fluorescence in algae to assess specific effects on photosynthesis. Reactive modes of action were assessed indirectly by measuring the relevance of cellular defense systems. Differences in growth inhibition curves between a mutant of Escherichia coli that could not synthesize glutathione and its parent strain indicate the relevance of conjugation with glutathione as a defense mechanism, which is an indirect indicator of protein damage. DNA damage was assessed by comparing the growth inhibition in a strain that lacks various DNA repair systems with that in its competent parent strain. Most compounds acted merely as baseline toxicants in all test systems. As expected, ethinylestradiol was the only compound showing estrogenic activity. Propranolol was baseline-toxic in all test systems exceptforthe photosynthesis inhibition assay, where it surprisingly showed a 100-fold excess toxicity over the predicted baseline effect. The exact mode of toxic action could not be confirmed, but additional chlorophyll fluorescence induction experiments excluded the possibility of direct interference with photosynthesis through photosystem II inhibition. Mixture experiments were performed as a diagnostic tool to analyze the mode of toxic action. Compounds with the same mode of toxic action showed the expected concentration addition. In the photosynthesis inhibition assay, agreement between experimental results and prediction was best for two-stage predictions considering the assigned modes of action. In a two-stage prediction, concentration addition was used as a model to predict the mixture effect of the baseline toxicants followed by their independent action as a single component combined with the specifically acting compound propranolol and the reference compound diuron. A comparison with acute toxicity data for algae, daphnia, and fish showed generally good agreement for the nonspecifically acting compounds but also that the proposed test battery offered better diagnostic value in the case of the specifically acting compounds.

Animals↗
PubMed2006

Including mixtures in the determination of water quality criteria for herbicides in surface water.

Monitoring programs throughout America and Europe have demonstrated the common occurrence of herbicides in surface water. Nevertheless, mixtures are rarely taken into account in water quality regulation. Taking mixtures into account is only feasible if the water quality criteria (WQC) of the single compounds are derived by a common and consistent methodology, which overcomes differences in data quality without settling on the lowest common denominator but making best use of all available data. In this paper, we present a method of defining a risk quotient for mixtures of herbicides with a similar mode of action (RQm). Consistent and comparable WQC are defined for single herbicides as a basis for the calculation of the RQm. Derived from the concentration addition model, the RQm can be expressed as the sum of the ratios of the measured environmental concentration and the WQC for each herbicide. The RQm should be less than one to ensure an acceptable risk to aquatic life. This approach has the advantage of being easy to calculate and communicate, and is proposed as a replacement for the current limit of 0.1 microg/L for herbicides in Switzerland. We illustrate the proposed approach on the example of five commonly applied herbicides (atrazine, simazine, terbuthylazine, isoproturon, and diuron). Their risk profile, i.e., the RQm as a function of time for one exemplary river, clearly shows that the single compounds rarely exceeded their individual WQC. However, the contribution of peaks of different seasonally applied herbicides, whose application periods partially overlap, together with the continuously emitted herbicides from nonagricultural use, results in the exceedance of the RQm threshold value of one upon several occasions.

Herbicides↗
PubMed2005

Aquatic passive sampling of herbicides on naked particle loaded membranes: accelerated measurement and empirical estimation of kinetic parameters.

Water-sampler equilibrium partitioning coefficients and aqueous boundary layer mass transfer coefficients for atrazine, diuron, hexazionone and fluometuron onto C18 and SDB-RPS Empore disk-based aquatic passive samplers have been determined experimentally under a laminar flow regime (Re = 5400). The method involved accelerating the time to equilibrium of the samplers by exposing them to three water concentrations, decreasing stepwise to 50% and then 25% of the original concentration. Assuming first-order Fickian kinetics across a rate-limiting aqueous boundary layer, both parameters are determined computationally by unconstrained nonlinear optimization. In addition, a method of estimation of mass transfer coefficients--therefore sampling rates--using the dimension-less Sherwood correlation developed for laminar flow over a flat plate is applied. For each of the herbicides, this correlation is validated to within 40% of the experimental data. The study demonstrates that for trace concentrations (sub 0.1 microg/L) and these flow conditions, a naked Empore disk performs well as an integrative sampler over short deployments (up to 7 days) for the range of polar herbicides investigated. The SDB-RPS disk allows a longer integrative period than the C18 disk due to its higher sorbent mass and/or its more polar sorbent chemistry. This work also suggests that for certain passive sampler designs, empirical estimation of sampling rates may be possible using correlations that have been available in the chemical engineering literature for some time.

Environmental Monitoring↗
PubMed2006

Relative rate constants of contaminant candidate list pesticides with hydroxyl radicals.

The objective of this study was to establish the relative rate constants for the reactions of selected pesticides (linuron, diuron, prometon, terbacil, diazinon, dyfonate, terbufos, and disulfoton) listed on the U.S. EPA Contaminant Candidate Listwith UV and hydroxyl radicals (*OH). Batch experiments were conducted in phosphate buffered solution at pH 7. All pesticides were found to be very reactive toward *OH as indicated by rate constant values above 10(9) M(-1) s(-1). Using molinate as a reference compound, kOH ranged from 2.7 x 10(9) to 12.0 x 10(9) M(-1) s(-1) for the contaminants while slightly higher values from 2.9 x 10(9) to 14.3 x 10(9) M(-1) s(-1) were obtained using nitrobenzene as a reference compound. A method was established that accounts for direct photolysis when calculating kOH using UV/H2O2 process for compounds which degrade significantly by a direct photolysis mechanism.

Chromatography, High Pressure Liquid↗
PubMed2000

Multiresidue HPLC methods for phenyl urea herbicides in water.

High-performance liquid chromatography (HPLC) methods for the determination of phenyl urea herbicides in water are described. The target compounds include chlortoluron, diuron, fluometuron, isoproturon, linuron, metobromuron, metoxuron, monuron, neburon, and siduron. Water was subjected to solid phase extraction (SPE) using either automated SPE with 47 mm C(18) Empore disks or on-line precolumn concentration. Herbicides were separated on a C(18) reversed phase column with an acetonitile-water gradient and were detected with either a diode array detector (DAD) or a postcolumn photolysis and derivatization (PPD) detector system. Photolysis converted the phenyl ureas to monoalkylamines that were derivatized to fluorescent isoindoles by reaction with o-phthalaldehyde and 2-mercaptoethanol. The DAD monitoring at 245 nm was linear over three decades with instrument detection limits of approximately 0.01 mg/L. SPE efficiency was between 48 and 70% in laboratory reagent water, but use of the internal standard quantitation method improved accuracy. High total dissolved solids and total organic carbon values in surface water improved recoveries relative to laboratory reagent water for all of the phenyl ureas. In Colorado River water spiked at 1 or 50 microg/L, mean recoveries ranged from 74 to 104%. Method detection limits (MDLs) ranged from 4 to 40 ng/L (parts per trillion) with the DAD instrument. PPD detection was highly specific but resulted in a slight loss in chromatographic efficiency and average MDLs approximately 5 times higher using a single set of detection conditions. The study indicates that methods based on SPE followed by HPLC with diode array or PPD detection have practical utility for trace analysis of phenyl ureas in drinking water or surface waters.

Chromatography, High Pressure Liquid↗
PubMed2001

Potential contributions of smectite clays and organic matter to pesticide retention in soils.

Soil organic matter (SOM) is often considered the dominant sorptive phase for organic contaminants and pesticides in soil-water systems. This is evidenced by the widespread use of organic-matter-normalized sorption coefficients (K(OM)) to predict soil-water distribution of pesticides, an approach that ignores the potential contribution of soil minerals to sorption. To gain additional perspective on the potential contributions of clays and SOM to pesticide retention in soils, we measured sorption of seven pesticides by a K-saturated reference smectite clay (SWy-2) and SOM (represented by a muck soil). In addition, we measured the adsorption of atrazine by five different K-saturated smectites and Ca-saturated SWy-2. On a unit mass basis, the K-SWy-2 clay was a more effective sorbent than SOM for 4,6-dinitro-o-cresol (DNOC), dichlobenil, and carbaryl of the seven pesticides evaluated, of which, DNOC was sorbed to the greatest extent. Atrazine was sorbed to a similar extent by K-SWy-2 and SOM. Parathion, diuron, and biphenyl were sorbed to a greater extent by SOM than by K-SWy-2. Atrazine was adsorbed by Ca-SWy-2 to a much lesser extent than by K-SWy-2. This appears to be related to the larger hydration sphere of Ca(2+) (compared to that of K(+)) which shrinks the effective size of the adsorption domains between exchangeable cations, and which expands the clay layers beyond the apparently optimal spacing of approximately 12.2 A for sorption of aromatic pesticide structures. Although a simple relation between atrazine adsorption by different K-smectites and charge properties of clay was not observed, the highest charge clay was the least effective sorbent; a higher charge density would result in a loss of adsorption domains. These results indicate that for certain pesticides, expandable soil clays have the potential to be an equal or dominant sorptive phase when compared to SOM for pesticide retention in soil.

Absorption↗