## 1 Introduction  
More than 1 billion pounds of pesticides are used in the United States each year and nearly 6 billion pounds are used worldwide [1]. The use of pesticides is of major importance to agriculture, but their widespread occurrence and persistence in the environment can be hazardous to living organisms. It was reported that less than 1% of the total of applied pesticides reach the targets, so a high percentage of these chemicals may move off-target [2,3]. The residues of pesticides are frequently detected in various environmental matrixes, such as soil, water, air, and organism bodies [4]. Moreover, natural and man-made disasters (such as hurricanes and floods) can significantly mobilize these environmental contaminants, exposing humans and animals to contaminated soil and sediment and threatening the safety of municipal drinking water and food sources. Highly toxic and widely distributed pesticides that are on a watch list due to a potentially severe and/or cumulative risk to human health and/or the environment, or have been banned for use as suggested by the United Nations and the Food and Agriculture Organization [5; 6], were chosen for this study. These include: the organochlorines: pentachlorophenol (PCP), 2,4,6-trichlorophenol (2,4,6-TCP) and lindane; an organophosphate: diazinon; a urea-type pesticide: linuuron; a dinitroaniline: trifuralin; and a bipyridyl pesticide: paraquat [7]. PCP is widespread, persistent in the environment and highly toxic to humans and animals [8]. It has been classified as a possible carcinogen by the International Agency for Research on Cancer (IARC) [9]. PCP has been banned for purchase and use by the general public, but it is still used frequently for industrial applications. 2,4,6-TCP has been commonly used as a pesticide and wood preservative [10]. It has been reported that exposure to 2,4,6-TCP may increase the risk of behavioral impairment in children and carcinogenicity in humans. These chlorophenol compounds are persistent in the environment and can be commonly detected in rivers, ponds and soils [11]. Lindane is a hexachlorocyclohexane that is widely used to treat scabies and pediculosis. It is persistent and undegradable, and thus tends to bioaccumulate in the food chain [12]. Diazinon is an organophosphorus insecticide, which has been effectively used throughout the world with applications in agriculture and horticulture for controlling insects. Its toxicity is due to the inhibition of the enzyme acetylcholine esterase [13]. Linuuron is a phenylurea herbicide used widely to selectively control weeds and grasses by inhibiting photosynthesis. It has been shown to act as an androgen receptor ligand that can competitively inhibit the binding of androgens and produce reproductive malformations [14; 15]. Trifluralin is dinitroaniline herbicide which controls a wide variety of grasses and broadleaf weeds by interrupting mitosis, controlling weeds as they germinate. It is one of the most widely used herbicides [16]. Trifluralin has been banned in the European Union since 2008, primarily due to its high toxicity to aquatic life [17]. Paraquat is one of the most widely used herbicides due to its rapid, contact-dependent killing of weeds and plants [18]. It is the leading cause of death from pesticide self-poisoning and murder. Exposure to these pesticides can stimulate lipid peroxidation, paralyze the respiratory system, cause endocrine disruption and affect the nervous and reproductive system, etc. [19; 20; 21]. The molecular models of each pesticide, derived from a computational quantum mechanical AM1 method in HyperChem, are shown in Figure 1.  
Previously, our laboratory has conducted a series of intervention studies showing that montmorillonite clay is safe for short-term human and animal consumption [22].