Study On Mechanisms Of Atrazine Adsorption Onto Surficial Sediments And Their Main Components With Cu²⁺ Present

Atrazine (2-chloro-4-ethylamino-6-isopropylamine-s-triazine, AT) is one of the most widely used herbicides which is used as a selective herbicide for the control of grassy and broadleaf weeds in maize, sorghum, rangeland, sugarcane, and other crops. The intensive production and use of atrazine have led to ecological problem all the world. It is considered to be persistent and recalcitrance toward degradation in the environment, it creates a risk for public health because atrazine is considered as possible human carcinogens and endocrine disrupting substances. Studying its adsorption behavior in surficial sediments of natural water body can further understand the rule of migration and transformation for organic pollutants in the sediments-water environment and the final end-result, biological and ecology effect in the environment.Nowdays, more and more research have been focused on the co-contamination. Study on co-contamination is very important to administer the environment and agricultural production synthetically because the presence of co-contamination will influence the biologic activity and toxicity of one pollutant or different pollutants. Presence of the metal ions is an important influencing factor of the adsorption to organic pollutants in aquatic environments. Metal ions could affect the adsorption of organic pollutants by combinable function, competitive function, ionization of organic pollutants, and so on. In recent years, more and more researchers concerned on this topic and had achieved plenty of academic and practical achievements, mostly studied the interaction of single pollutants, such as metals and organo-pesticides, but less investigations were reported on the interaction and mechanism of heavy metals and organic pollutants while there have obvious differences between characters of them. Further more, the processes of co-contamination are quite complicated, most researches are focused on relation of different correlative factors, the mechanisms of reaction were less to be repoted. Research on co-contamination of organic pollutants and heavy metal have important signification to evaluate migration and transformation of different pollutants and help persons find reasonable measures to deal with. In conclusion, it is necessary to study on mechanisms of atrazine adsorption onto surficial sediments (surface coatings) and their main components with heavy metal ions present.Sequential chemical extraction technology was employed to separate different components (Fe oxides, Mn oxides and organic materials) of surficial sediments sampled directly in the Songhua River, Jilin Province. With atrazine as the targeted pollutants, the objectives of this paper were to find the best method for batch determination, to study the adsorption behavior of atrazine in the surficial sediments and their main components to explore the roles of the main chemical components during the adsorption and the effect of co-existing inorganic pollutants Cu²⁺ on the adsorption of atrazine, finally mechanisms of atrazine and Cu²⁺ adsorption onto surficial sediments were discussed.In this paper, the following results were obtained:(1) Sequential chemical extraction technology was employed to separate different active components of surficial sediments (surface coatings) sampled directly in the Songhua River. Extraction efficiencies of Fe oxides, Mn oxides and organic materials could be achieved 76.44% (78.89%), 83.14% (82.00%) and 84.54% (88.42%), respectively. Organic materials content in surficial sediments (surface coatings) was significantly greater than those of Fe oxides and Mn oxides; the contents of active components (Fe oxides, Mn oxides and organic materials) in surface coatings were higher than those in surficial sediments.(2) The adsorption isotherms of atrazine and Cu²⁺ onto surficial sediments (surface coatings) could be both adequately described by the Langmuir equation and parameters, the maximum adsorption of atrazine and Cu²⁺ would be higher with the concentration of atrazine and Cu²⁺ increasing, respectively; compared with surficial sediments, surface coatings had stronger ability to adsorb atrazine and Cu²⁺; total extractable components had stronger ability to adsorb atrazine and Cu²⁺ than pseudo-total components; there are differences between the main adsorption sites of atrazine and Cu²⁺ on surficial sediments (surface coatings), Fe oxides and organic materials are the main adsorption sites for AT adsorption on surficial sediments (surface coatings) while Fe oxides, Mn oxides and organic materials are the main adsorption sites of Cu²⁺, however, Mn oxides in surficial sediments (surface coatings) prohibited atrazine adsorption. Accordingly, the most probably places where competitive adsorption occurred are on the organic materials and Fe oxides of surficial sediments (surface coatings).(3) The maximum adsorption of atrazine onto surficial sediments (surface coatings) and their main components decreased while the concentration of Cu²⁺ increasing, the competitive function of Cu²⁺ is obvious. the addition of Cu²⁺ in different concentrations influence the adsorption of atrazine on samples removal of Mn oxides and Fe/Mn oxides most evidently, while the influence of adsorption of atrazine on samples removal of organic materaials could be negligible, it indicated that Cu²⁺ could affect the adsorption of atrazine on surficial sediments (surface coatings) by combining with organic materials; the addition of Cu²⁺ affect the adsorption of atrazine on surface coatings much observably than that on surficial sediments. We could conclude by the experimental results that the main sites on surficial sediments (surface coatings) where competitive adsorption occurred between atrazine and Cu²⁺ are organic materials and Fe oxides.(4) When atrazine and Cu²⁺ were added simultaneously or Cu²⁺ was added after atrazine adsorbed, addition of Cu²⁺ in treatment solution restrained adsorption of atrazine, and the restraining ability became more and more obvious with Cu²⁺ concentration increasing; if atrazine were added after Cu²⁺ had been adsorbed, addition of Cu²⁺ in treatment solution facilitated adsorption of atrazine, and the maximum adsorption of atrazine were higher with the concentration of Cu²⁺ decreasing. It might because competitive adsorption activities occurred when Cu²⁺ were added in the system, and the competitive function was negligible when the Cu²⁺ was lower, but while the concentration of Cu²⁺ increased, the superfluous Cu²⁺ might inhabit much more adsorption sites and inhibited the adsorption of atrazine. Cu²⁺ has ability to form monomer and dimer complexes with groups of organic molecules of atrazine, if Cu²⁺ was added first, it could form complexes with atrazine and might hold much more adsorption sites to inhibit the adsorption of atrazine, but if atrazine was added first, Cu²⁺ might not form new metal ion-atrazine complexes with atrazine which had been adsorbed by sorbents.(5) Samples of surficial sediments (surface coatings) which before and after the adsorption of atrazine and Cu²⁺ were analyzed with infrared spectroscopy, it could be found that adsorption of atrazine and Cu²⁺ on surficial sediments (surface coatings) didn't influence the structure of sorbents because the optical absorption peaks didn't change before and after adsorption. But phenomenon of wavelength shifts indicated that some groups of surficial sediments (surface coatings) reacted with atrazine or Cu²⁺. The functional groups participated in the adsorption were identified, and which were -OH and -NH of surficial sediments and -OH, -NH, -C=O of surface coatings.