Saddle towers with infinitely many ends

We prove the existence of nonperiodic, properly embedded minimal surfaces in $\mathbb{R}^2\times\mathbb{S}^1$ with genus zero, infinitely many ends and one limit end (in particular, they have infinite total curvature).Comment: 16 pages, 3 figure

Elimination de l'ion chrome hexavalent dans l'eau par les celluloses greffées

L'étude concerne le chrome (VI) et son élimination dans l'eau par les celluloses greffées (échangeuse d'anions) AE2 sous forme OH¯, Cl¯, S04=.La capacité d'échange correspond à 0,5-0,6 meq g-1 de cellulose. Les cinétiques d'échanges du Cr (VI) avec les ions CL¯ OH¯ et SO4 ont été déterminées en fonction du pH du milieu, de la température, de ta force ionique, de La quantité de détergents et des formes de celluloses AE2. Les résultats expérimentaux montrent que les formes de celluloses sont efficaces dans l'ordre OH¯ > Cl¯ > SO4= vis-à-vis du Cr (VI) et que l'échange décroît pour les ions étudiés dans l'ordre suivant : CrO4= > Cr207= > HCrO4¯.Ion exchange is used extensively for water and waste water treatment for the removal of a variety of ion species. It is known that at acidic pH nome anion-exchange resins can selectively remove and recover chromate from cooling water (SENGUPTA, 1986) where chromate is used as a corrosion inhibitor. This method is employed for plating waste treatment and to recover hexavalent chromium. The waste stream is first passed through a cation exchanger to remove metal ions such as iron, zinc, nickel and trivalent chromium. The hexavalent chromium passes through as CrO4=, and is subsequently removed in a anion exchanger.Hexavalent chromium may exist in the aqueous phase in different ionic forms with total chromate concentration and pH dictating which particular chromate species will predominate. The equilibrium reactions for different Cr (VI) species are :H2CrO4 ⇌ HCrO-4 + H+HCrO-4 ⇌ CrO-4- + H+Cr2O-7- + H2O ⇌ 2HCrO-4Cr2O-7- + H2O ⇌ 2CrO-4- + 2H+In the present study a description is given of the extraction of small quantities of Cr (VI) ion in water by modified cellulose (anionic form, (AE2) counterions OH¯, Cl¯, S04= ; 0,5-0,6 meq l-1 ion exchange capacity) which is represented by the following chemical formula : (CHATELIN, 1982 ; WATTIEZ, CHATELIN, 1981).Cell - O - CH2 - CH - O - CH2 - CH -                          |                         |                        CH2                    CH2                          |                         |                         N+    CL-             N+    CL-                       /  |  \                   /  |  \             CH3  CH3  CH3         CH3  CH3  CH3Kinetics of exchange and effects of pH, competiting ions, concentration, temperature, ionic strength, surfactants and types of cellulose (Cl¯, OH¯, SO4=) have been studied.Chromate only, chromate-pH, chromate-chloride, chromate-sulfate and chromate-surfactant kinetics (20 ± 1 °C) were determined for different anionic forms of modified cellulose. Kinetics data were generated by a batch equilibration technique where a weighed amount (5 g) of modified cellulose was shaken gently for 0.5-1 h with a fixed volume of solution (500 ml) containing Cr (VI) with successively H+, Cl¯, SO4=, a surfactant of known initial composition. A the end of the equilibration solution, the composition was determined again to calculate the Cr (VI) uptake. Equilibrium was achieved in 0.5 h, but 75 % of Cr (VI) was removed in 5 min.RESULTSSome specific aspects of the ion-exchange process for chromate recovery from industriel waste have been reported.It was observed that the more efficient types of cellulose for chromium removal where OH¯ > Cl¯ > SO4= respectively and that ion exchange decreased as followsCrO4= > Cr207= > HCrO4¯

Sentinel California sea lions provide insight into legacy organochlorine exposure trends and their association with cancer and infectious disease.

BackgroundOrganochlorine contaminants (OCs), like polychlorinated biphenyls (PCBs) and dichlorodiphenyltrichloroethanes (DDTs), are widespread marine pollutants resulting from massive historical use and environmental persistence. Exposure to and health effects of these OCs in the marine environment may be examined by studying California sea lions (Zalophus californianus), which are long lived, apex predators capable of accumulating OCs.MethodsWe evaluated PCB and DDT levels in 310 sea lions sampled between 1992 and 2007: 204 individuals stranded along the coast of central California, 60 healthy males from Washington State, and 46 healthy females from southern California. Lipid-normalized contaminant concentrations were analyzed using general linear models and logistic regression to ascertain temporal trends; differences between stranded and healthy sea lions; and association of organochlorines with sex, age, and presence of cancer or fatal infectious disease.ResultsConcentrations of the contaminants in stranded adults decreased over time in the study period (adjusted for sex, as adult males had higher mean blubber concentrations than adult females and juveniles). Cancer was almost eight and six times more likely in animals with higher summed PCBs and DDTs, compared to those with lower levels (95% CI 5.55-10.51 and 4.54-7.99, respectively). Fatal infectious diseases were similarly seven and five times more likely in animals with higher contaminant burdens (95% CI 4.20-10.89 and 3.27-7.86, respectively). Mean contaminant loads were significantly higher in stranded sea lions than in healthy live captured animals (p < 0.001).ConclusionOrganochlorine contamination has significant associations with health outcomes in California sea lions, raising concerns for humans and other animals eating tainted seafood. While environmental exposure to these organochlorines appears to be decreasing over time based on levels in sea lion tissues, their persistence in the environment and food web for all predators, including humans, and the associated serious health risks, warrant monitoring, possibly through sentinel species like marine mammals

Magnetic structures of Mn3-xFexSn2: an experimental and theoretical study

We investigate the magnetic structure of Mn3-xFexSn2 using neutron powder diffraction experiments and electronic structure calculations. These alloys crystallize in the orthorhombic Ni3Sn2 type of structure (Pnma) and comprise two inequivalent sites for the transition metal atoms (4c and 8d) and two Sn sites (4c and 4c). The neutron data show that the substituting Fe atoms predominantly occupy the 4c transition metal site and carry a lower magnetic moment than Mn atoms. Four kinds of magnetic structures are encountered as a function of temperature and composition: two simple ferromagnetic structures (with the magnetic moments pointing along the b or c axis) and two canted ferromagnetic arrangements (with the ferromagnetic component pointing along the b or c axis). Electronic structure calculations results agree well with the low-temperature experimental magnetic moments and canting angles throughout the series. Comparisons between collinear and non-collinear computations show that the canted state is stabilized by a band mechanism through the opening of a hybridization gap. Synchrotron powder diffraction experiments on Mn3Sn2 reveal a weak monoclinic distortion at low temperature (90.08 deg at 175 K). This lowering of symmetry could explain the stabilization of the c-axis canted ferromagnetic structure, which mixes two orthorhombic magnetic space groups, a circumstance that would otherwise require unusually large high-order terms in the spin Hamiltonian.Comment: 11 pages, 13 figure

Influence de l'origine et de la nature des substances humiques sur l'adsorption de l'atrazine sur charbon actif en poudre

Les essais d'adsorption sur charbon actif en poudre, de sept acides humiques (H) ou fulviques (F) et pour trois pH (5,6 ; 7,0 ; 8,8) marquent que ces acides ont un comportement différent suivant leur origine.Lorsque le pH de la suspension de charbon est basique, l'adsorption des différentes fractions humiques diminue, ce qui est en relation avec l'augmentation de leur solubilité. Pour un même pH de la suspension, les acides humiques et fulviques d'origine aqueuse s'adsorbent mieux que ceux d'origine commerciale ou que ceux extraits de sol.La capacité maximale d'adsorption de l'atrazine sur charbon actif en poudre : 260 mg.g-1 (Langmuir), est plus fortement diminuée en présence d'acides fulviques que d'acides humiques d'une part, et plus inhibée (jusqu'à 40 %) par les acides fulviques extraits d'eau (F1, F2) que par ceux extraits de sol (F3) d'autre part.Par contre, les acides humiques provenant de substances commerciales (H4, H5) influencent moins l'adsorption de l'atrazine.L'ensemble des essais montre que l'origine et la nature des substances humiques joue un rôle prépondérant sur l'adsorption de l'atrazine sur charbon actif, le pH ayant une influence limitée.Enfin l'étude de l'influence de l'atrazine sur l'adsorption des substances humiques sur charbon actif en poudre indique également une différence de comportement entre les acides fulviques, pour lesquels on note peu de variation, et les acides humiques, pour lesquels on note à la fois une promotion de l'adsorption et une meilleure affinité d'adsorption sur le charbon actif en poudre en présence d'atrazine.Ce travail met en évidence l'importance du choix des substances humiques pour des essais d'évaluation des interactions substances humiques - pesticides lors de l'adsorption sur charbon actif en poudre.Though the subject was copiously and oldly studied, this work is bringing a new contribution to the study of the influence of the origin and the nature upon their properties and in particular with atrazine, the more used herbicide these fast years.In order to study this influence of the origin and nature of various humic substances upon the removal of atrazine by adsorption onto powdered activated carbon (PAC), humic substances were obtained from different sources :- Natural aquatic fulvic (F1) and humic (H1) acids isolated from Beaune Lake (Limoges, France).- Natural aquatic fulvic (F2) and humic (H2) acids extracted from hydroxyde sludges of the water treatment plant of La Bastide (Limoges, France).- Soil fulvic acids (F3) extracted from a canadian top soil horizon.- Commercial humic acids (Aldrich. H4 and Jansen H5) obtained from commercial sodium humates.The results of adsorption test of humic acids, fulvic acids and atrazine (alone or together) onto powdered activated carbon (PAC) at three different pH (5,6 ; 7,0 ; 8,8) were expressed by Freundlich's and Langmuir’s models and permitted us to note that :- According to the increasing of water solubility of humic substances with basic pH, their adsorption was better in acidic medium.- Natural aquatic humic substances (H1, H2, F1, F2) were more adsorbed onto PAC than humic substances tram soil (H3) or commercial origines (H4, H5).- Atrazine adsorption capacity was 260 mg.g-1 according to Langmuir's model.- Atrazine adsorption decreased with F1 for all pH ; the same result was also observed with the other natural aquatic humic substances.- Commercial humic acids didn’t importantly affect atrazine adsorption. These differences appeared to be derived from the nature and the origin of fulvic and humic acids. The rose of atrazine on the humic substances adsorption showed a difference between humic and fulvic acids whose adsorption was not influenced by atrazine even humic acids only presented an increasing of adsorption.All these results showed the importance of the selection of humic substances to evaluate the interaction SH-Pesticides during adsorption onto PAC and let us think to a competitive adsorption between fulvic acids and atrazine onto PAC

Influence du dodécylsulfate de sodium sur l'adsorption des acides humiques sur charbon actif en poudre

L'objectif de ce travail est d'étudier l'influence d'un tensioactif anionique, le dodécylsulfate de sodium (DSS) sur l'adsorption d'acides humiques (AH), sur le charbon actif en poudre (CAP).L'adsorption sur CAP, en fonction du temps, des AH seuls, puis du DSS seul, a été effectuée en réacteur discontinu, à différents pH (7,0 et 10,5). Les mêmes expériences ont été réalisées avec le mélange des deux composés et l'on a pu constater une inhibition réciproque de leur adsorption, moins importante à pH basique (10,5).L'influence de l'ordre d'introduction des coadsorbats, sur l'adsorption de chacun d'eux, a permis de montrer que l'inhibition de l'adsorption des AH sur CAP par le DSS est encore plus importante lorsque les AH sont ajoutés sur une suspension DSS-CAP déjà en équilibre. Aucune désorption du DSS n'a pu être mise en évidence après 24 heures. Ces résultats pourraient permettre de conclure à une adsorption « compétitive » des AH et du DSS sur les mêmes sites superficiels du charbon actif.Ce travail permet de préciser les phénomènes d'adsorption pouvant intervenir entre divers micropolluants susceptibles de s'adsorber simultanément soit sur des sédiments naturels, soit sur charbon actif lors du traitement des eaux naturelles.The removal of humic acids (HA) from natural waters is a very old yet modern problem : humic substances are at the origin of the coloration of water but also, they give off nocive trihalomethanes during chlorination.Humic acids are also known to be a metal micropollutant vector and their behavior is not well defined when there is coadsorption.The purpose of this work was to study the effect of an anionic surfactant, sodium dodecyl sulphate (SDS), on the adsorption on powdered activated carbon (PAC) of humic substances from a commercial source, as a function of the pH (7.0 or 10.5), as well as the effect of the order of introduction of the coadsorbate.Results (fig. 1 to 3 and fig. 6) showed an inhibition of the adsorption for both HA and SDS in the presence of the coadsorbate. The inhibition was more significant for a pH = 7.0.Results of the influence of the order of introduction of the coadsorbate on the adsorption (fig. 4 and 5) showed a more significant inhibition of HA adsorption when HA were introduced into the equilibrium suspension SDS-PAC (the contact lime was 24 hours).Table 1 gives parameter values of the Langmuir equation for the adsorption on PAC of HA atone or with SDS.All these results suggest that a competition on the same sites occurs during the adsorption on PAC of HA and SDS

Contribution à l'étude de la validité de différents modèles, utilisés lors de l'adsorption de solutés sur charbon actif

Les résultats de l'adsorption sur charbon actif en poudre de solutions aqueuses de différents composés organiques: phénol, aniline, nitrobenzène, acide salicylique, nitro-4 phénol, méthyl-2 dinitro-4,6 phénol, phénylalanine et tyrosine ont été traités à l'aide des équations de Langmuir, Elovich, Freundlich, Temkin, Fowler-Guggenheim, Hill et De Boer, Kiselev afin de déterminer divers paramètres d'équilibre: la capacité maximum d'adsorption, l'énergie d'adsorption, l'énergie d'interaction, les constantes d'équilibre adsorbat-adsorbant et les interactions (éventuelles) entre les molécules adsorbées.La relation de Temkin (3=RTt~Q In KoC permet de déterminer la variation de l'énergie d'adsorption ~Q et la constante Ko de l'équilibre (~3 est le degré de re- couvrement du charbon par le soluté, et C la concentration à l'équilibre). L'équa- tion de Fowler-Guggenheim KC=~3/(1~3) Exp (2 ~ W/RT) conduit à la déter- mination de l'énergie d'interaction W entre molécules adsorbées et à une constante d'équilibre K. Par contre, dans l'équation de Hill et de De Boer KlC=~/(1~)) Exp [~/(1~) - K2~/RTI, K2 représente une constante d'énergie d'interaction entre molécules adsorbées et, dans celle de Kiselev KIC=~3/[(1+ ~) (1 + Kn~3)]~ Kn est une constante de formation de complexe éventuel entre molécules adsorbées. On vérifie que l'application de la relation de Temkin est satisfaisante pour tous les composés étudiés et permet de les classer selon leur affinité sur le charbon mais les résultats obtenus en utilisant les équations suivantes (Fowler ...) montrent qu'il n'y aurait pas de formation de complexe ou d'interaction entre molécules adsorbées.Analysis of the results of adsorption from aqueous liquid media onto activated carbon can be carried out by different models based on thermodynamic principles. Classically the Langmuir (eq. 1), Freundlich or Elovich (eq. 4) isotherms are used, which lead to the determination of an experimental maximum capacity, qm, and a constant K, characteristic of the adsorbate-adsorbent interactions. The following equations (Table I) have been transposed from the vapour phase to the liquid phase. With the Temkin relation: [Theta]=RT/[Delta]QlnK[inf]0C (eq. 6), it is possible to determine the variation of adsorption energy, [Delta]Q, between the adsorbed molecules and the solid phase, and the equilibrium constant K[inf]0 ([Theta] is the degree of surface covering of the solid phase [Theta]=q/qm, q is the adsorption capacity). The Fowler-Guggenheim equation: KC=[[Theta]/(1-[Theta])] Exp (2[Theta]W/RT) (eq. 7) gives the interaction energy, W, between the adsorbed molecules and an equilibrium constant, K. The Hill and De Boer relation: K[inf]1C=[Theta]/(1-[Theta])] Exp [[Theta]/(1-[Theta]) -K[inf]2[Theta]/RT] (eq. 8) yields an energetic interaction constant K[inf]2 (J.mol-¹) characteristic of the interactions between the adsorbate molecules and an equilibrium constant, K[inf]1. In the Kiselev relation: K[inf]1C=([Theta]/[(1-[Theta]) (1 + K[inf]n[Theta]] (eq. 9), K[inf]n is a complex formation constant between adsorbed molecules and K[inf]1 is a constant relative to the adsorbate-adsorbent interaction. Linearization of the equations of Langmuir, and Elovich leads to qm and K values. For the Freundlich relation, if the experiments are made at constant Co and variable concentrations of adsorbent, the Freundlich relation can be transformed as relation (5): q=qm (C/Co)[sup]1/n). The value of qm and K are reported in the Table II. When the values obtained by the Elovich equation are very different from the Langmuir relation, they are not in concordance with the experimental adsorption isotherm as shown on the Figures 4, 5 and 6.A value of qm is necessary to calculate the ([Theta](=q/qm) of the Temkin, Hill-De Boer, Fowler- Guggenheim and Kiselev equations; [Theta] is calculated with the Langmuir value of qm: the linearized relations were tested for the following compounds: phenol, aniline, nitrobenzene, salicylic acid, 4-nitro phenol, 2-methyl-4,6 dinitro phenol, phenylalanine and tyrosine, studied at micromolar concentration. The results are shown in Table II. The Temkin linearization is of good quality for all the compounds; an example is given on the Figure 1. For the others (Figs. 2, 3), the linearization is not always verified (Hill-De Boer for phenylalanine: Fig. 3a) and the results are framed two times in the Table II.With the obtention of the two parameters [Delta][Theta], K K, W; K[inf]1, K[inf]2 and K[inf]1, K[inf]n, the isotherm can be recalculated. The results for some solutes are on Figures 4, 5, 6, 7, 8. Relatively poor results are obtained for Fowler-Guggenheim, Kiselev or Hill-De Boer models, where no association is present between the adsorbed molecules.The evolution of the variation of the adsorption energy ([Delta][Theta]) is reported on the Figure 9 for the different compounds. The greatest values are obtained for nitrobenzene and 4-nitro-phenol (+ 80, + 40 kJ.mol-¹ probably due to the presence of the nitro group). All the values are positive (exothermic reaction ( [Delta][Theta]=-[Delta]H)) showing the affinity of molecules for the activated carbon

Influence de l'ordre d'introduction des solutés (Naphtol-2 et Calcium) sur l'adsorption des tensioactifs sur charbon actif F400

L'effet de l'ordre d'introduction des solutés Naphtol-2 et Calcium (N-2 et Ca) sur l'adsorption de tensioactifs par le charbon actif en poudre (CAP) F400 brut a été étudié en discontinu. Les mélanges étudiés sont: le tensioactif anionique dodécyl-sulfate de sodium (DSS) et le N-2; le DSS, le N-2 et le Ca; le tensioactif cationique bromure de benzyldodécyldiméthylammonium (BBDDA) et le N-2 et enfin le BBDDA et Ca. Les résultats expérimentaux montrent tout d'abord que quel que soit l'ordre d'introduction des solutés N-2 et Ca, les concentrations en DSS à l'équilibre sont sensiblement identiques. Par ailleurs, la cinétique d'adsorption du DSS et du BBDDA croît en présence des ions Ca.Cependant, la cinétique d'adsorption du N-2 en présence du DSS diminue ce qui se traduit par une inhibition de l'adsorption du N-2 par le DSS. Quant à l'adsorption du BBDDA en présence du N-2 pour différents ordres d'introduction, le tracé des isothermes de LANGMUIR montre que la capacité maximale d'adsorption Г∞ du BBDDA ne change pas tandis que la constante de LANGMUIR (K) diminue. Par contre la capacité maximale d'adsorption du N-2 ** varie légèrement et passe de 1,67 à 1,5 mmol/g pour différent ordre d'introduction du BBDDA. On note également que Г∞ du N-2 en présence de concentrations croissantes en BBDDA diminue fortement et passe de 1,67 à 0,8 mmol/g.L'ajout de N-2 après 3 heures de contact du BBDDA /CAP ne provoque pas la désorption de ce dernier. Le même comportement a été observé avec le N-2, alors que l'ajout du DSS au mélange N-2/CAP provoque la désorption de celui ci.The effect of the introduction order of naphtol-2 and calcium (N-2 and ca) on the adsorption of surfactants by raw powdered activated carbon (PAC) F 400 has been studied in a static system, studied mixtures included the anionic surfactant: sodium dodecyl-sulfate (SDS) with N-2 or with N-2 + Ca, and the cationic surfactant beniyldodecyldimethylarnmoniurn bromide (BDDAB) with N-2, or with Ca. The experimental results demonstrate that whatever the order of solute introduction, the SDS concentrations at equilibrium are almost identical. Moreover, the adsorption kinetics of SDS and BDDAB increase in the presence of calcium ions. The adsorption kinetics of N-2 decrease in the presence of SDS, suggesting inhibition of N-2 adsorption by SDS. Concerning the adsorption of BDDAB the presence of N-2, for different introduction orders, plotting of the LANGMIIIR isotherms shows that the maximal BDDAB adsorption capacity Г∞, does not change but the LANGMUIR constant (K) decreases. For naphtol-2, however the maximal adsorption capacity Г∞, does vary slightly, going from l,67 to l.5 mmol/g for different BDDAB introduction orders. In the presence of increasing BDDAB concentrations, the maximum adsorption capacity of N-2 decreases from 1.67 to 0.8 mmol/g.The addition of N-2 after 3 hours of BDDAB/PAC contact does not lead to BDDAB desorption. similar behavior is observed on addition of N-2 after 3 hours of SDS/PAC contact, even though the addition of SDS to a N-2/PAC mixture leads to N-2 desorption

Étude de l'adsorption de l'atrazine sur le charbon actif en poudre en présence de tensioactifs

Les tensioactifs, adjuvants participant à la formulation des pesticides peuvent se trouver en compétition avec ces derniers lors de l'adsorption sur charbon actif en poudre (CAP) utilisé au cours du traitement de potabilisation des eaux. L'adsorption de l'atrazine, qui reste l'un des produits phytosanitaires le plus souvent détecté dans les eaux de surface malgré les réglementations sur son utilisation, a été étudiée en présence de trois tensioactifs afin de déterminer l'influence de ces derniers; il a été choisi un tensioactif anionique (DSS), cationique (BHTA), et un non ionique (DE6). Les résultats ont montré que quelle que soit la nature du tensioactif, celui-ci diminue toujours l'adsorption de l'atrazine pour des pH variant de 3,5 à 10 ce qui a pour conséquence une diminution à la fois de la constante de vitesse (Adams et Bohart) et de la capacité d'adsorption (Langmuir). L'étude de l'influence de l'ordre d'introduction des différents éléments participant à l'adsorption (CAP, atrazine, tensioactif) a montré que la fixation préalable de DSS anionique, favorisée en milieu acide, inhibe davantage l'élimination de l'atrazine. L'application des modèles d'adsorption compétitive et non compétitive de Langmuir n'a pas permis de définir avec certitude la nature des interactions entre l'herbicide et les différents tensioactifs.Atrazine, in spite of the restrictions concerning its use, remains one of the most prevalent pesticides in natural surface waters. If a sudden pollution incident occurs, powdered activated carbon (PAC) is used during the flocculation step of water treatment; under such circumstances, atrazine might be in adsorption competition with surfactants included in commercial formulations. The aim of this study was thus to determine the influence of three surfactants [anionic (sodium dodecylsulphate, SDS), cationic (hexadecyl-trimethylammonium bromide, HTAB) and nonionic (2-dodecyloxy-pentaethanoxy)-ethanol, DE6)] on atrazine adsorption onto PAC. At pH 5.5, adsorption onto PAC of atrazine alone was estimated to be 230 mg. g-¹; it was inhibited whatever the nature of the surfactant (cationic anionic or nonionic: figs. 2, 3 and 4). The adsorption capacities (Langmuir) and the kinetic constants (Adams & Bohart) decreased in the presence of the surfactants (table 4) and this diminution was most important for HTAB (fig. 5), perhaps the consequence of a steric effect.The adsorption onto PAC of the molecular form of atrazine (pK=1.68) was not affected by the pH variations. However, when the pH was increased (3.5 to 10) in the presence of SDS, adsorption onto PAC of the anionic surfactant decreased and atrazine adsorption increased (fig. 9). In contrast, for the same experimental conditions but with the cationic surfactant HTAB, adsorption of the surfactant increased over the pH range 3.5 to 10 and the relative adsorption of atrazine diminished (fig. 9). The nonionic surfactant DE6 had no influence.A study of the introduction order of the different components (atrazine, SDS surfactant and PAC) showed the same final equilibrium distribution of atrazine was obtained (fig. 10), regardless of the order of introduction. A similar result was obtained for the adsorption of SDS (fig. 11).For all these cases, the Langmuir equation yielded the adsorption capacity for atrazine and the equilibrium constant. However, competitive and noncompetitive adsorption models (table 1) were unsuccessful in predicting the nature of the interactions between atrazine and the surfactants (table 5)