# Effect of Montmorillonite on 4-Nonylphenol Enrichment in Zebrafish
## 1 Introduction  
Environmental endocrine-disrupting compounds (EDCs) interfere with the synthesis, release, transport, metabolism, binding, action or elimination of endogenous hormones and then impact the normal endocrine system of organisms, leading to reproduction and immune dysfunctions [1]. In addition to the reversible or irreversible biological effects on the organisms, the offspring or the population, EDCs also compromise the disease resistance of the body [2, 3] and even cause diseases and cancer [4, 5, 6, 7]. For instance, nonylphenol (NP), a common industrial raw material, is a typical phenolic environmental hormone and mainly accumulates in water bodies with a solubility of 5.43 mg/L [8]. NP is a general term for the isomers, and its formula is C\({}_{6}\)H\({}_{4}\)(OH)C\({}_{9}\)H\({}_{19}\). 4-NP is one of the major components of NP, almost 90% of the total. This chemical presents genotoxicity, developmental toxicity, immunotoxicity and neurotoxicity [9, 10, 11, 12, 13]. Additionally, it may deposit in living organisms and exhibit biological effects via the water body, as well as through the food chain, and the effect of environmental EDCs might be more harmful after enrichment by the food chain [14, 15].  
The dose of environmental EDCs is generally low in nature, and the correlation between their effect and dose is complex. For example, the toxicity of bisphenol A is stronger at low doses than at high doses [16; 17]. The application of biomarkers is a common method to evaluate and analyze the toxic effects of toxicants. The antioxidant enzymes of zebrafish are commonly-used biomarkers [18; 19; 20]. However, the dose used in the current study of the dose-effect relationship is basically the dose of toxicants' exposure in the environment, and the study of the concentration-effect relationship between toxicant concentrations and markers in tissues or organs of zebrafish has rarely been reported. The situation is more complicated in an actual natural environment, where a variety of substances, especially some nanoparticles in the water, modify the biological effects of environmental EDCs and impact the adsorption, transport, enrichment and even the toxicity of EDCs [21; 22; 23]. Montmorillonite (MMT) is a typical layered aluminosilicate mineral that is adsorptive, hydrophilic, electrically charged, dispersedly suspended and swells in water [24; 25; 26]; therefore, it is widely used in medicine, aquaculture and sewage treatment [27; 28; 29; 30; 31; 32]. MMT, as a common nanoparticle in water bodies, has the potential to enhance the toxicity of harmful substances and meanwhile reduces the accumulation of harmful substances and exhibits a detoxification function in aquatic animals [33; 34; 35; 36]. Few studies have reported the role of MMT in a specific water environment, and in theory, MMT could affect aquatic animals, resulting in them absorbing NP due to the adsorptivity of MMT; while the NP enters the body, MMT could also affect the transport and metabolism of NP. These effects can be found through the distribution patterns of in vivo NP affected by MMT; however, there is still no research on these effects that has been reported. In the present study, the effect of MMT on NP accumulation in zebrafish was investigated in a water environment using NP as a specific toxic substance. In addition, the relationship between the concentration of NP in liver and the enzyme activity of SOD and GST was also analyzed.