## 3 Results
### Cr(VI) Weakly Affected Sociability and Social Novelty Preference in the 3-Chamber Assay
Data represent mean \(\pm\) SEM. For 11 weeks sociability by age, we observed a similar overall preference for interacting with cagemates, except for young or middle-aged rats exposed to 0.1 mg Cr(VI)/L, which exhibited no preference between the cagemate and empty cage (Figure 9D). In young rats, we still observed no effect in cagemate interactions, whereas empty cage interactions increased: 8.4, 9.0, and 12.0 empty cage interactions for control, 0.05, and 0.1 mg Cr(VI)/L groups, respectively (Figure 9D). In middle-aged rats exposed to 0.1 mg/L we observed a slight decrease in cagemate interactions. Geriatric rats exhibited slightly more interactions with both cagemate and empty cages after Cr(VI) exposure, with the increase in empty cage interactions more noticeable: 5.2, 6.6, 6.6 cagemate interactions and 1.9, 3.5, and 4.2 empty cage interactions for control, 0.05, and 0.1 mg Cr(VI)/L, respectively (Figure 9D). When we considered these data as a ratio by individual rats, we observed that the ratios for young and geriatric rats increased after 0.05 mg Cr(VI)/L (Supplementary Figure S2D). Altogether, these results suggest that Cr(VI) reduced sociability in middle-aged rats after 5 or 11 weeks and in young and geriatric rats after 11 weeks. To assess social novelty preference, we examined (1) the number of interactions between a test rat and its cagemate, (2) the number of interactions between a test rat and a stranger rat, and (3) the ratio of cagemate to stranger-rat interactions during the 3-chamber assay (Figure 10, Supplementary Figure S3). We first considered the effects of Cr(VI) on social preference, regardless of age (Figure 10A,B). Across all groups, we observed a strong preference for interacting with a stranger rat after 5 and 11 weeks, indicating a strong preference for social novelty. After 5 weeks, we observed no changes in interactions with  
Figure 10: **Cr(VI) Slightly Increased Social Novelty Preference in Young Female Rats. ** We quantified direct and indirect interactions with a cagemate or a stranger rat during the 3-chamber assay after 5 or 11 weeks of Cr(VI) exposure. Overall, female rats interacted with strangers more than with cagemates. (**A,B**) Data were compared across Cr(VI) groups ((**A**), \(n\) = 23, 27, and 24, respectively; (**B**), \(n\) = 25, 27, and 27, respectively). (**C,D**) Data were then compared across age groups ((**C**), young \(n\) = 6, 7, and 6, respectively; mid-aged \(n\) = 8, 8, and 8, respectively; geriatric \(n\) = 9, 12, and 10, respectively; (**D**), young \(n\) = 8, 8, and 8, respectively; mid-aged \(n\) = 8, 8, and 8, respectively; geriatric \(n\) = 9, 11, and 11, respectively). Data represent mean \(\pm\) SEM. a cagemate or stranger rat. After 11 weeks, we observed a slight increase in stranger interactions: 9.6, 10.3, and 11.3 straner interactions for control, 0.05, and 0.1 mg Cr(VI)/L, respectively. When considering these data as a ratio (cagemate/stranger), we observed no change after 5 weeks and a statistically significant decrease in the 0.05 mg Cr(VI)/L group after 11 weeks (Supplementary Figure S3A,B). We then considered Cr(VI) effects on social preference across age groups (Figure 10C,D; Supplementary Figure S3C,D). After 5 weeks, we observed that young rats exhibited a concentration-associated increase in stranger-rat interactions with no change in cagemate interactions: 11.8, 14.3, and 15.2 straner interactions for control, 0.05, and 0.1 mg Cr(VI)/L, respectively. We observed no change in cagemate interactions by middle-aged rats after 5 weeks but a slight decrease in stranger interactions in the 0.05 mg Cr(VI)/L group. We observed a slight concentration-associated decrease in cagemate interactions by geriatric rats and a slight decrease in stranger-rat interactions by geriatric rats exposed to 0.1 mg Cr(VI)/L (Figure 10C).