Behavioral Disruption in Brachionus plicatilis Exposed to Bisphenol A: A Locomotion-Based Assessment

This study investigates the effects of Bisphenol A (BPA)-a ubiquitous endocrine disruptor-on the swimming behavior of the rotifer <i>Brachionus plicatilis</i>. Across a 0-40 ppm gradient, a biphasic response was observed, with swimming speed peaking at 20 ppm (100.42 ± 12.17 µm/s) and then significantly declining by 43% to 57.58 ± 30.59 µm/s at 40 ppm (Tukey, <i>p</i> < 0.05). Speed-frequency plots revealed co-existing hyper- and hypoactive sub-populations at 10-30 ppm, whereas severe inhibition dominated at 40 ppm. Additionally, temporal analysis confirmed that BPA effects were both concentration- and time-dependent, with the mean speed at 10 ppm declining only slightly over time (slope ≈ -0.8), whereas at 40 ppm, the decrease was an order of magnitude steeper (slope ≈ -16.9). Additionally, BPA exposure also triggered a sharp rise in abrupt turns (582.53 ± 477.55 events) and greater path sinuosity, consistent with neuromuscular disturbance. These findings demonstrate that rotifer locomotion provides an early and sensitive indicator of environmental BPA exposure.