Akademik Veri Yönetim Sistemi
59th Congress of the European Societies of Toxicology, Athens, Yunanistan, 14 - 17 Eylül 2025, cilt.411, sa.15, ss.118-119, (Özet Bildiri)
Due to their life cycle, amphibians are directly dependent on shallow
aquatic ecosystems during the early stages of their development and are
therefore at greater risk of being affected by contaminants in the environment.
It has been reported in the literature that several species of trout and
salmon, particularly coho salmon, are highly sensitive to
N-(1,3-dimethylbutyl)-N′-phenyl-p-phenylenediamine (6-PPD) and its related
degradation by-products. However, there is no information on its toxicity to
amphibians. On the other hand, comparative assessment of the response of
amphibians to other non-salmonid species that are reported to be less sensitive
to 6-PPD toxicity may be important for risk assessment of different classes of
aquatic vertebrates that may be relatively more tolerant. Therefore, the aim of
this study was to evaluate the comparative toxicity of 6-PPD in zebrafish (Danio rerio) and Xenopus laevis embryos at early developmental stages using
morphometric biomarkers. Wild-type zebrafish of the AB strain and wild-type X. laevis embryos obtained from a colony
maintained in our laboratory for many years were used in the study. The
toxicity of 6-PPD was evaluated for 96 hours starting at hpf 5-6 for D. rerio embryos and hpf 6-8 for X. laevis embryos, which are equivalent
in terms of embryonic developmental stage. The stock solution of 6-PPD was
prepared in ethyl alcohol (99%) and embryos were exposed to a range of 6-PPD
concentrations in the treatment groups with a maximum of 0.01% alcohol in the
medium. Experiments were performed in a 14:10 h light:dark environment, at a
temperature of 28 oC for D. rerio and
22 oC for X. laevis. E2 medium and FETAX solution were used for fish and frog
embryos, respectively. Lethality, malformations, dechorionation (for D. rerio),
motility, and heart rate were used as markers to assess toxicity. The 96-hour
LC50 for D. rerio and X. laevis
embryos was determined to be 0.63 mg/L and 2.50 mg/L, respectively, in our
study. Concentrations of 0.35 mg/L and above resulted in growth retardation
while concentrations of 0.53 and above caused a decrease in the number of
heartbeats in X. laevis embryos after
96 hours of exposure. According
to the teratogenic index value obtained (0.9), 6-PPD was not teratogenic for X. laevis embryos; however it caused intestinal
anomalies and edema. Contraversely, concentrations of 0.53 mg/L and above
resulted in growth retardation in D.
rerio embryos after 96 hours of exposure, and concentrations of 1.19 and
above caused a decrease in heartbeats after 48 hours of exposure. The
dechorionation of zebrafish embryos was also found to be prolonged in a
concentration-related manner. The most prevalent malformation observed in D. rerio embryos was depigmentation,
while yolk sac edema (SSE) and spinal curvature were other common
malformations. The findings of this study suggest that D. rerio embryos exibit a higher degree of susceptiblity to 6-PPD
toxicity than X. laevis embryos, as evidenced by the calculated LC50s. Nevertheless,
6-PPD was regarded as hazardous in the contexts of both fish and amphibian
embryonic development. This is due to its propensity to induce growth
retardation, physiological responses, including decreased heart rate, and
malformations in both test organisms. However, due to the relatively low
teratogenicity index observed in frog embryonic development, the risk for X. laevis is thought to be lower.