Di-butyl phthalate disrupts muscle, motor and sensory neuron development in embryonic zebrafish

Phthalates are added to plastics to enhance its flexibility, durability and transparency. Phthalates are not covalently bound to plastics and leach into the environment. Phthalates are now pervasive and ubiquitously present in the atmosphere, soil and sediment, surface and wastewater. Phthalates are known endocrine disruptors and their effects on male and female reproduction are well noted. However, studies on the developmental effects of di-butyl phthalate (DBP) are limited. Here we investigated the developmental toxicity of DBP on motor and sensory neuron populations and the muscle structures motor neurons innervate using the zebrafish vertebrate model system. We investigated these effects during the time window of development spanning the period where embryonic patterning determines adult structures. We found that treatment with 2.5 μM DBP from 6 h post-fertilization (hpf) until 72hpf induces loss and disorganization of primary motor neuron innervation of the somatic tissue with concomitant disruptions to muscle fiber organization. Furthermore, we found disruptions to sensory motor neuron development including defects in dorsal root ganglion and their peripherally extending axons. Rohon-Beard sensory neurons were also disrupted showing loss of the bilateral soma positioning along the length of the spinal cord and their afferent axonal projections to the epithelium. Thus, we concluded that DBP is toxic to developing motor and sensory neurons during embryonic development.