# Effect of Montmorillonite on 4-Nonylphenol Enrichment in Zebrafish
## 4 Discussion  
With a concentration of 4-NP in a real environment of 3.2133 \(\mathrm{\SIUnitSymbolMicro g}\)/L, which is three-times that of LOQ, this concentration of 4-NP was set as the minimum concentration of the exposure concentration, and the 4-NP concentrations of 32.133 \(\mathrm{\SIUnitSymbolMicro g}\)/L and 321.33 \(\mathrm{\SIUnitSymbolMicro g}\)/L were set as the medium concentration and the maximum concentration. The results suggested that in all experimental groups, the concentration of 4-NP in liver, muscle and gills showed increasing trends at first, and then decreased; the concentration of 4-NP drop in the later stage may be attributed to the zebrafish that had resistance and enhanced the decomposition ability. The concentration of 4-NP in the gills at the same time was not significantly different among groups (\(p>0.05\)), suggesting that while 4-NP in aquaculture water was directly in contact with the gills, the concentration of 4-NP in gills was not related to MMT. Generally speaking, MMT in aquaculture water could affect 4-NP enriched in the fish in two ways, and MMT can reduce the concentration of 4-NP in aquaculture water by its adsorption effect. Moreover, MMT in the fish could slow the metabolism of 4-NP and reduce the rate of excretion; and may, in this way, serve the in vivo enrichment of 4-NP. We used the enzyme activity as the indicator to investigate the toxicity effect of 4-NP on zebrafish, and the result showed a complexity of environmental hormones, that is the low dose of 4-NP had a stronger bioactivity than the high dose of 4-NP. In addition, the enzyme activity of SOD was 175.82% of the control, while the enzyme activity of GST was lower (139.65%), suggesting that SOD is more sensitive to 4-NP, and it is also more suitable for the detection index of 4-NP. The test 4-NP concentration employed in our study was set to 3.2133 \(\mathrm{\SIUnitSymbolMicro g}\)/L, which was consistent with the environmental 4-NP concentration, and this concentration of 4-NP, as well as the 4-NP concentrations of 32.133 \(\mathrm{\SIUnitSymbolMicro g}\)/L and 321.33 \(\mathrm{\SIUnitSymbolMicro g}\)/L were used in the respective experiments. The results showed that the concentrations of 4-NP in the liver, muscle and gills of zebrafish in all the experimental groups reached a peak at Day 7, then decreased at Day 15 and Day 30 (\(p<0.01\)). There were no differences in the concentrations of 4-NP in muscle and gills between Day 15 and Day 30 for each group; data from the liver were relatively complicated, i.e., the differences of N2, N3, N1M1, N2M1, N2M3 (\(p<0.01\)) and N1M3 (\(p<0.05\)) versus the control were significant, while those of the other groups were not. Overall, 4-NP concentrations in the liver, muscle and gill of all the experimental groups were high at first and later decreased, and the declined concentration in the late period could be explained by enhanced resistance or decomposition by the zebrafish. In the absence of MMT, enrichment of 4-NP in the liver at Day 7 was more significant at a lower dose of 4-NP, namely N1 \(>\) N2 \(>\) N3 (\(p<0.01\)), while at Day 15 and Day 30, a higher enrichment effect was observed at a higher dose; accumulation of 4-NP in the muscle at Day 7 and Day 15 was higher in N1 and N2 than in N3 (\(p<0.01\)); while enrichment of 4-NP in gills was not highly correlated to its concentration. In the presence of MMT, enrichment of 4-NP in the liver was significantly decreased at 7 d in all N1 groups (\(p<0.01\)), but such decreased accumulation in N1 was only observed in N1M1 at 15 d. Accumulation of 4-NP was enhanced in all N2 and N3 groups except for the N2M1 group (\(p<0.01\)), but such enhanced accumulation was observed only in the N2M2 group until Day 30. In the muscle, enrichment of 4-NP at Day 7 was reduced by MMT in N1, but increased by MMT in N2 and N3, and the altered enrichment was maintained until Day 30 only in the N1M3 group.