| Atrazine ( 2-chloro-4-ethylamino-6-isopropylamine-s-triazine, C8H14ClN5) is one of the most widely used herbicides, which is employed as a selective herbicide for the control of grassy and broadleaf weeds in maize, sorghum, rangeland, sugarcane, and other crops. Atrazine is considered to be persistent due to its water solubility (33 mg/L). Although atrazine is stable in slight acid and alkali solution, it could be hydrolyzed as hydroxyl derivates, losing its weeding activity under alkali or salty condition at high temperature. Nowadays, Atrazine has been listed as global environmental precedence control pollutant. In recent years, more and more researches on impact of atrazine for human health have been conducted because atrazine is considered as a possible human carcinogens and endocrine disrupting substance. Because of its long residue period, about 4-57 weeks, it needs long time to be mineralized by microbe. Herbicides spray on surface soil to pose a potential risk of leaching to under aquierfers, causing contamination of water resources. Moreover, due to its long residue period in soil and accumulation ability in organism, potential threaten on food security may occur.Transference of hydrophobic organic compound (HOC) in water is influenced by many chemical processes, in which adsorption-desorption is one of major processes. It is important to predict environmental carrying capacity for releasing HOC precisely, and effectively rehabilitate natural environment as well. Adsorption on sediments is very an important process for transferring atrazine between sediments and water. The initial mechanism of decreasing atrazine concentration and its metabolite in water is adsorption. Wetland, surficial sediments, turf and soil have similar ingredients, for example, high concentration of organic carbon, which is considered as good adsorbent for pesticides. Many scholars began to study adsorption mechanism under coexisting system of organic pollutants. On the other hand, there are very few studies on competitive adsorption among atrazine, other organic pesticides and heavy metals. It is also found that the research on mechanism of atrazine adsorption is very rare.This paper studies atrazine adsorption characteristics on the surficial sediments (surface coatings), based upon deeply analysis on chemical composition of surficial sediments and surface coatings taken from natural Songhua River. The adsorption characteristic of atrazine on the surficial sediments (surface coatings) and theirs components is investigated. The relative contribution of its major components, such as manganese oxides, iron oxides and organic materials on the surficial sediments and surface coatings are studied as well. The difference of adsorption capacity and characteristic between surficial sediments and surface coatings is compared.Moreover, the influence on atrazine adsorption under atrazine-cadmium, atrazine-copper and atrazine-malathion coexisting systems is studied respectively in this paper, and influence when joined together as well. The interactional mechanism of above three coexisting systems is also analyzed, so as to forecast transfer rule of atrazine in natural water.The high performance liquid chromatography (HPLC) method is employed for determining atrazine in water. Without extraction, atrazine is directly detected by HPLC after infiltrated through membrane in water samples. The detection limit is 0.0002 mg/L. This process can be suitable for the simulate study of atrazine adsorption in lab. Herbicides, such as imazethapy, fluazifop-butyl, and dliclofop methyl do not disturb determination of atrazine.Selective extraction techniques followed by batch adsorption experiments and statistical analyses were employed to investigate the adsorption behavior of atrazine onto the surficial sediments and surface coatings and to estimate the relative contribution of components to the atrazine adsorption. Result shows that surficial sediments and surface coatings have similar main components, such as manganese oxides, iron oxides and organic materials, among which organic materials has highest concentration, followed by iron oxides and manganese oxides. Under selected condition, the process of atrazine adsorption on surficial sediments and surface coatings is conformed to the first order kinetics. The adsorption rate of surface coatings is much higher than surficial sediments, reaches maximum adsorption amount after 48 hours. It is clear that nonlinear Langmuir model can describe the adsorption behavior of atrazine onto surficial sediments and surface coatings before and after extraction treatments with correlation coefficient above 0.97. But the adsorption capacity of atrazine onto surface coatings is higher than surficial sediments before and after extraction. It is evident that surface coatings have higher impact on transfer of atrazine than surficial sediments. Adsorption contribution of the main components in surficial sediments (surface coatings) is different. It is also found that Fe oxides and OMs facilitate the adsorption of atrazine, but Mn oxides directly or indirectly restrain the interaction of atrazine with surficial sediment (surface coatings) particles. The contribution of Fe oxides to atrazine adsorption is more than that of OMs: the greatest contribution to adsorption on a molar basis is from the Fe oxides.The characteristic of atrazine adsorption is also investigated under atrazine-cadmium, atrazine-copper and atrazine-malathion coexisting systems respectively. In atrazine-cadmium coexisting system, Cd of lower concentration (<4.0 mg/L) has a significant synergetic effect on the adsorption of atrazine. However, intensity of synergism is closely related to sequence of which will be adsorbed first. The highest intensity of synergism occurs when adsorbing atrazine and cadmium simultaneously, followed by adsorbing cadmium in ahead. The lowest intensity occurs when adsorbing atrazine first. However, cadmium concentrations (>8.0 mg/L) have an antagonistic effect on the adsorption of atrazine, inhibiting atrazine adsorption. In preloading atrazine system, cadmium inhibits atrazine adsorption when cadmium concentration reaches 4.0mg/L. On the other hand, atrazine can also disturb cadmium adsorption. It is found that atrazine has antagonistic effect on the Cd adsorption in preloading atrazine condition, but atrazine has synergetic effect on Cd adsorption on other two conditions-Cd adsorbed first or adsorbed cadmium and atrazine simultaneously, the synergetic effect of atrazine is less than that of cadmium.It is evident that residue of cadmium highly disturbs transference of atrazine in water, and competitive adsorption of cadmium and atrazine may occur in water. Due to higher concentration of Fe oxides and other active components on surface coatings, adsorption capacity of atrazine and cadmium onto surface coatings is higher than surficial sediments. After selective extraction of samples, atrazine adsorption characteristics are similar to original samples without extraction, while adsorbing cadmium and atrazine simultaneously. This indicates that adsorption of cadmium and atrazine is closely related to their active components, such as manganese oxides, iron oxides and organic materials. On the other hand, copper has different chemical characteristic compared with cadmium. The organic materials exert the greatest influence on Cu binding. It is proven that Cu is more prone to chelate with organic materials than other heavy metals, such as cadmium. Cu can form inner-sphere chelate with organic materials. The behavior of copper and cadmium on interfering atrazine adsorption is quite different. Under atrazine-copper coexisting systems, Cu has antagonism effect during atrazine adsorption onto surficial sediments (surface coatings). The more Cu concentration is, the more antagonism of atrazine adsorption is while adsorbing copper and atrazine simultaneously and preloading atrazine. Result shows that, when Cu concentration increases, maximum adsorption amount onto surface coatings decreases faster than onto surficial sediments with Cu concentration increasing. If adsorbing Cu first, Cu will have synergetic effect on atrazine adsorption: the less the concentration of copper is, the more synergetic effect is. On the other hand, atrazine also have antagonism effect on Cu adsorption under above three adsorption conditions, although the maximum adsorption capacity is slightly different. Result indicates that atrazine has more influence on copper adsorption than vice versa. The maximum Cu adsorption amount, with atrazine coexisting, decreases 75% compared with non atrazine coexisted. The antagonistic effect of atrazine on Cu adsorption is slightly different between surficial sediments and surface coatings: the changing adsorption of Cu onto the surficial sediments is small with the different adding sequence of copper and atrazine. For the surface coatings, the sequence for adsorption of atrazine and Cu will strongly interfere the adsorption of copper. The strongest antagonistic effect occurs when adsorbing atrazine first, followed by adsorbing these two materials simultaneously. While adsorbing Cu first, antagonistic effect is the lowest. Result also shows that competitive adsorption of Cu and atrazine may occur on surficial sediments (surface coatings), just as phenomenon in cadmium and atrazine system. It is concluded that heavy metal plays very important role on atrazine transference process in heavy metal-atrazine coexisting system.In malathion-atrazine coexisting system, malathion can facilitate atrazine adsorption on both surficial sediments and surface coatings, no matter atrazine is prior adsorbed before malathion, or they are adsorbed simultaneously. It is clear that the higher concentration of malathion is, the more synergism effect is. However, under the above system, the maximum adsorption amount of atrazine onto surface coatings is higher than onto surficial sediments. While adsorbing malathion before adsorbing atrazine, malathion inhibit atrazine adsorption which means that the more malathion, the less inhibition. Moreover, the interference of malathion on atrazine adsorption onto surficial sediments is less than surface coatings. In atrazine-heavy metal (copper or cadmium)-malathion coexisting system, atrazine adsorption capacity is slightly different. In atrazine-copper-cadmium coexisting system, the adsorption of atrazine is inhibited; while in atrazine-cadmium-malathion coexisting system, the adsorption of atrazine is facilitated; in atrazine-copper-malathion coexisting system, strong inhibition on atrazine adsorption occurs. Result indicates that atrazine could not be adsorbed on surficial sediments and the maximum adsorption amount of atrazine on surface coatings decreases 77.3% compared with atrazine adsorption only. Results also show that copper can have strongest interference on atrazine adsorption than cadmium and malathion.By means of Infrared spectrum, the adsorption mechanism of atrazine on surficial sediments (surface coatings) is studied before and after selective extraction. The adsorption mechanism of atrazine in atrazine-heavy metal (copper or cadmium)-malathion coexisting system is also investigated as well. Result shows that displacement of O-H and C=O characteristic absorption peak occur during above processes. It is evident that carboxyl plays very important role in atrazine adsorption process, and has close relationship with atrazine adsorption on active components in coexisting system.
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