Effects of waterborne exposure to 4-nonylphenol and nonylphenol ethoxylateon secondary sex characteristics and gonads of fathead minnows (Pimephalespromelas)

Fathead minnows were exposed to 4-nonylphenol (NP) or nonylphenol ethoxylat e (NPEO) to determine the effects of these weak estrogen agonists on second ary sex characteristics and gonads of sexually mature males and females dur ing 42-day continuous-flow exposures. Neither NP nor NPEO caused statistica lly significant effects on tubercles or fat-pad size at the concentrations tested. Exposure to 1.1 or 3.4 mu g NP/L caused changes in the number and s ize of Sertoli cells and germ cell syncytia. Necrotic aggregates of various stages of germ cells in the spermatogenic sequence were observed in the te stes of males exposed to NP. Electron microscopy of the testes of NP-expose d males revealed the presence of phagocytic cells in the lumina of seminife rous tubules. The cytoplasm of some Sertoli cells was distended with myelin figures and necrotic spermatozoa. No significant effects on the stages of follicular development were observed in females exposed to NP. There were n o differences in the gonads or secondary sex characteristics of males or fe males exposed to 5.5 mu g NPEO/L, the greatest concentration studied. The h istologic responses ob served are sensitive indicators of waterborne exposu re to NP at environmentally relevant concentrations, but not as sensitive a s induction of plasma vitellogenin. The secondary sex characteristics were not affected by concentrations of NP or NPEO as great as 3.4 or 5.5 mu g/L, respectively. Histologic responses occurred at concentrations that were le ss than the final chronic value based on survival and approximately the sam e as those required to cause effects on egg production. The histologic effe cts caused by NP were similar to, but not exactly the same as those caused by exposure of fathead minnows to 17 beta-estradiol. (C) 1999 Academic Pres s.