Complex effects of two presumably antagonistic endocrine disrupting compounds on the goldfish Carassius aumtus: A comprehensive study with multiple toxicological endpoints

• We have first studied the combined effects of nonylphenol and letrozole on teleost.
• Letrozole inhibited aromatase activities, and did not induce plasma 17β-estradiol.
• Nonylphenol still induced estrogenic effects through binding to estrogen receptors.
• Letrozole could increase CYP17 and counteract the estrogenic effects of nonylphenol.
• Multiple biological endpoints should be considered in environmental risk assessment.

We studied the effects of endocrine disrupting compounds nonylphenol (NP) and letrozole (LE) on the male goldfish Carassius aumtus. Exposure to NP (20 μg l−1) alone caused a significant up-regulation in the expression of aromatase, estrogen receptors and vitellogenin (VTG) genes, an increase in hepatic and plasma VTG concentration, but no obvious testicular impairment. Exposure to LE (1 mg kg−1) alone resulted in a significant decline in aromatase activity, reduced levels of plasma 17β-estradiol (E2), and enhanced sperm maturation. Co-exposure with LE (1 mg kg−1) could only partially affect some of the estrogenic effects caused by NP (20 μg l−1) (i.e. expression of hepatic and brain estrogen receptor genes, hepatic VTG concentration), but inhibit other estrogenic effects (i.e. brain and testicular aromatase activity, plasma E2). In addition, co-exposure resulted in impairment of liver mitochondria (i.e. detachment of ridges from the membrane, and uneven distribution of the cytoplasm with clusters of glycogen granules), but did not cause significant damage to the testes (i.e. the morphology, the spermatogonia and spermatozoa densities). Our results clearly showed that nonylphenol and letrozole co-exposure could induce profound effects on fish, and highlighted the importance of adopting multiple toxicological endpoints when evaluating the combined effects of endocrine disrupting compounds.