Toxicity of 4-chloroaniline in early life stages of zebrafish (Danio rerio): II. Cytopathology and regeneration of liver and gills after prolonged exposure to waterborne 4-chloroaniline

Ultrastructural alterations in liver and gills of embryonic and larval zebr afish (Danio rerio) following prolonged exposure to waterborne 0.05, 0.5, a nd 5 mg/L 4-chloroaniline for up to 31 days as well as after a 14-day regen eration period were investigated by means of light and electron microscopy. Acute toxicity was also tested at 25 and 50 mg/L. Survival of zebrafish em bryos and larvae was only impaired from 25 mg/L 4-chloroaniline, but-after a transient stimulation following exposure to 0.5 mg/L-4-chloroaniline hatc hing was retarded after exposure to greater than or equal to 5 mg/L, and fi sh displayed increasing rates of abnormal development and pigmentation. In contrast, hepatocytes displayed a time- and dose-dependent response from 0. 05 mg/L 4-chloroaniline, including changes in nuclei, mitochondria, peroxis omes, endoplasmic reticulum, Golgi fields, lysosomes, and hepatic glycogen and lipid stores, as well as invasion of macrophages. In gills, dose-depend ent effects were evident from 0.5 mg/L 4-chloroaniline and included deforma tion of secondary lamellae due to vacuolization and desquamation of respira tory epithelial cells in conjunction with dilation of intercellular spaces. Respiratory epithelial cells displayed progressive mitochondrial changes, induction of cytoplasmic myelinated structures, augmentation of lysosomes, and modifications of Golgi fields. Erythrocytes were severely deformed. A 1 4-day regeneration period was sufficient for almost complete recovery of pa thological symptoms in both liver and gills. Only minor volumetric changes in hepatocellular organelles and a limited number of myelinated bodies, lys osomes, and cytoplasmic vacuoles were reminiscent of prior 4-chloroaniline exposure. In both qualitative and quantitative terms, most effects in hepat ocytes after exposure of embryonic and larval zebrafish to waterborne I -ch loroaniline are comparable to the reaction of hepatocytes in adult zebrafis h liver after prolonged sublethal exposure as well as in larval zebrafish a fter microinjection. Morphological changes in erythrocytes indicate disturb ance of respiration as an additional mode of action of 4-chloroaniline.