## 3 Results and Discussion
### Exposure Dependency Behavior of Microorganisms  
After initially assessing the swimming ability of microorganisms at 1.5 h. The comprehensive evaluation of the swimming ability under prolonged exposure conditions, specifically at 24 and 48 h intervals, was also performed. The exposure of Euglena and Paramecia to varying concentrations of Fe and Zn for 24 and 48 h revealed intriguing dynamics in their behavior. For 1.5 h, a clear concentration-dependent response was observed of exposure, exhibiting distinct behavioral changes in response to Fe and Zn metal concentrations. However, as the exposure duration increased, a remarkable shift occurred in the microorganisms' swimming ability. Surprisingly, the concentration dependency was observed initially after just 1.5 h of exposure vanished after longer exposure periods of 24 and 48 h.  
Figure 8a,b illustrate the Paramecia and Euglena behavior at varying Fe concentrations for different exposures, 24 and 48 h, along with 1.5 h. A two-way ANOVA was performed to analyze the effect of the concentration and time of exposure dependence on the correlation time. A statistically significant interaction was observed between them under varying Fe conditions (1.5 h of exposure was observed to be statistically significant, as compared to 24 and 48 h, for Euglena and Paramecia, respectively; however, no significance was observed between 24 h and 48 h of exposure in either microorganism). Similarly, under varying Zn conditions, a statistically significant interaction was observed (1.5 h of exposure was observed to be statistically significant, as compared to 24 and 48 h, for Euglena and Paramecia, respectively; however, no significance was observed between 24 h and 48 h of exposure in either microorganism). This disappearance of concentration dependency suggests a dynamic adaptation of microorganisms to their environment over time. A common pattern was observed in the case of both microorganisms under Zn and Fe exposure. There was an immediate and meaningful reduction in their swimming speed after 1.5 h. In addition to that, Paramecia and Euglena achieved a constant swimming state in the first 24 h of exposure to both heavy metal pollutants. This behavior may be due to the adjustment/adaption of the microorganism to the surroundings. It indicates that microorganisms may undergo physiological or behavioral changes in response to prolonged exposure to metals, leading to diminished sensitivity to metal concentrations. The precise mechanisms underlying this phenomenon require further investigation but may involve processes such as metal detoxification, metabolic adjustments, or changes in gene expression. The observed behavior of Euglena and Paramecia raised two possible scenarios for using swimming ability for water quality. First, the dependency of the organisms on the pollutants is rather complicated, especially at a low concentration range. Therefore, it is important to select the microorganism carefully. The disappearance in the concentration dependency or the adaptation behavior of microorganisms suggests the importance of considering the short exposure duration in water toxicity assessments for bioassays.