Developmental toxicity assessment of 4-MBC in Danio rerio embryo-larval stages

Enormous production of cosmetic products and its indiscriminate use tends to discharge into the aquatic environment and might threaten non-target organisms inhabiting aquatic ecosystems. In the present study, developmental toxicity of 4-methylbenzylidene camphor (4-MBC), a widely used organic UV filter in personal care products has been evaluated using zebrafish embryo-larval stages. Waterborne exposure induced developmental toxicity and deduced 2.71 mg/L as 96 h LC₅₀ whereas embryos exposed to sub-lethal concentrations (50 and 500 μg/L) caused a significant delay in hatching rate, heart rate, reduced larval length, and restricted hatchlings motility besides the axial curvature. Chronic exposure to 10 dpf resulted in significant decrease in SOD activity at 500 μg/L with no changes in CAT level besides a significant increase in GST enzyme at 5 μg/L concentration in 5 dpf sampled larvae. However, all the three enzymes were significantly elevated in 10 dpf larvae indicating differential oxidative stress during the stages of development. Similar trend is noticed for acetylcholine esterase enzyme activity. A concentration dependent increase in malondialdehyde content was noted in larvae sampled at 5 and 10 dpf. In addition, multixenobiotic resistance (MXR) activity inhibition, and elevated oxidative tissue damage were noticed at 5 dpf with no significant changes in 10 dpf larvae. Furthermore, immunoblot analysis confirms 4-MBC induced apoptosis in zebrafish larvae with promoted cleaved Caspase-3, Bax and inhibited Bcl-2 proteins expression. Subsequently, docking studies revealed the binding potential of 4-MBC to zebrafish Abcb4 and CYP450 8A1 proteins with the binding energy of -8.1 and -8.5 kcal/mol representing target proteins interaction and toxicity potentiation. Our results showed that 4-MBC exposure triggers oxidative stress at sub-lethal concentrations leading to apoptosis, deformities and locomotion perturbations in developing zebrafish.This is first of its kind in systematically demonstrating developmental toxicity of 4-MBC and the information shall be used for aquatic toxicity risk assessment.