## 3 Results
### Cr(VI) Behavior Effects Are Distinct across Sexes  
We previously reported results from male rats in this study [44]. Here, we report behaviors where we observed notable sex differences after Cr(VI) exposure (Figure 11). After 2 weeks, we observed that middle-aged female rats exposed to 0.05 mg Cr(VI)/L exhibited increased center exploration, whereas males exposed to the same concentration exhibited significantly decreased center exploration (Figure 11A). After 2 weeks, young female rats exhibited little to no Cr(VI) impact on distance traveled, whereas male rats exhibited significantly decreased distance traveled in the 0.05 mg Cr(VI)/L group (Figure 11B). After 7 weeks, we observed a concentration-associated decrease in female grip strength with statistical significance in the 0.1 mg Cr(VI)/L group, whereas males exhibited significantly increased grip strength in the 0.05 mg Cr(VI)/L group (Figure 11C). After 8 weeks, we observed a statistically significant decrease in female rearing but no effect in males (Figure 11D). After 9 weeks, we observed a slight decrease in female open-arm exploration following 0.05 mg Cr(VI)/L during the elevated plus maze, whereas males exhibited a statistically significant decrease in the 0.1 mg Cr(VI)/L group (Figure 11E). After 10 weeks, we observed a concentration-associated decrease in female alternations in the Y-maze, whereas males exhibited a concentration-associated increase; both groups were statistically significant in the 0.1 mg Cr(VI)/L groups (Figure 11F). After 10 weeks, we also observed activity in the Y-maze was unaffected in middle-aged females, whereas males exhibited significantly decreased activity with Cr(VI) exposure (Figure 11G). After 11 weeks, middle-aged females exhibited fewer cagemate interactions in the 0.1 mg Cr(VI)/L group with no impact on empty cage interactions, whereas males exhibited significantly decreased interactions with both in the 0.05 mg Cr(VI)/L group and slightly decreased interactions with both in the 0.1 mg Cr(VI)/L group (Figure 11H). Also, after 11 weeks, we observed a stronger preference for social novelty in female rats, regardless of age, than in male rats(Figure 11). After Cr(VI) exposure, females exhibited a slight concentration-associated increase in stranger-rat interactions and no impact on cagemate interactions, whereas males exposed to 0.05 mg Cr(VI)/L exhibited the same number of interactions with both cagemates and strangers. We further observed a sex difference in this assay for the young rats (Figure 11). Young female rats exhibited a slight concentration-associated increase in stranger-rat interactions and no impact on cagemate interactions, whereas young male rats exhibited more interactions with cagemates after exposure to 0.05 mg Cr(VI)/L with no impact on stranger interactions and increased stranger interactions in the 0.1 mg Cr(VI)/L group with no impact on cagemate interactions. Figure 11: Sex Differences in Cr(VI) Behavior Effects Were Predominantly in Middle-Aged Rats. We considered sex differences in Cr(VI) effects on behaviors assessed in our study. We limited data presentation to those with significant or notable differences after Cr(VI) exposure; sex differences in controls are not reported. (**A**) After 2 weeks, we observed opposite effects in center exploration during the open-field assay between middle-aged male and female rats. (**B**) After 2 weeks, males exhibited a more severe decrease in distance traveled than females. (**C**) After 7 weeks, we observed a decrease in grip strength for middle-aged females, whereas males exhibited an increase after exposure to 0.05 mg/L and a slight decrease after 0.1 mg/L. (**D**) After 8 weeks, we observed no effect in middle-aged  
male rearing but a significant decrease in middle-aged females. (**E**) After 9 weeks, we observed no effect in open arm exploration in middle-aged females, while middle-aged males exhibited a significant decrease.