Time-dependent hormesis of D. melanogaster behaviour under chronic toluene exposure via automatic biomonitoring

Toluene is widely present in industrial products and daily necessities, and its health impacts have drawn considerable attention. However, significant discrepancies have been identified among toluene limits prescribed by various agencies based on substantial studies, indicating deficiencies in the examination of long-term and low-concentration toluene exposure scenarios. Given ethical and resource considerations, D. melanogaster was selected as a model to investigate the effects of toluene exposure concentration and duration on locomotor ability. To this end, a multi-individual D. melanogaster trajectory tracking method was developed to efficiently quantify behavioural responses, and statistical and regression analyses were employed to examine the effects of exposure concentration, duration and sex. Stop frequency and turning angle number were identified as key parameters for describing toluene-induced locomotor toxicity. Furthermore, the relationships between these parameters and concentration exhibited time-dependent biphasic patterns, which indicated a concentration of approximately 2.00 mg/m 3 resulted in severe damage to locomotor ability at the early stage of exposure. Concentrations exceeding 6.66 mg/m 3 impaired D. melanogaster locomotor ability regardless of exposure duration. This study highlights the importance of exposure time in assessing the exposure risk of toluene, and addresses the data gap in long-term and low-concentration exposure scenarios.