Toxic responses of medaka, d-rR strain, to polychlorinated naphthalene mixtures after embryonic exposure by in ovo nanoinjection: A partial life-cycle assessment

Polychlorinated naphthalenes (PCNs) are organic compounds with some chemica l properties and uses similar to polychlorinated biphenyls. Polychlorinated naphthalenes have been detected in biota from certain aquatic environments . The toxicities of several PCN technical mixtures (Halowax) to medaka (Ory zias latipes) were determined by use of an embryo nanoinjection method. Med aka eggs (early gastrula) were injected with 0.5 nl of triolein (vehicle co ntrol) or 0.5 nl of four to five graded doses (0.3-30 ng/egg) of Halowax 10 14, Halowax 1013, or Halowax 1051 in triolein. Following exposure, embryos developed, and fry were reared to sexual maturity (4 months), at which time they were euthanized. Responses were evaluated as early life stage (ELS) a nd early adult life stage (EALS) assessments. For ELS, lethality and sublet hal alterations in embryos and larvae (<16 d old), such as craniofacial, ca rdiovascular, and myoskeletal deformities and abnormal or delayed hatch, we re monitored for the first 9 d, and a dose severity index was computed. The EALS assessment examined the survival of 16-d-old larvae until early adult hood (123 +/- 3 d old), including gonadosomatic index (GSI) and morphometry . Halowax 1014 was found to be the most toxic mixture (LD50 4.2 ng/egg), wh ereas Halowax 1013 and 1051 were significantly less toxic (LD50s could not be determined). The gonadosomatic index of females was significantly less i n fish dosed with Halowax 1014 or 1051. The LD50 for medaka embryos nanoinj ected with 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) is about 0.75 pg/egg. Thus, Halowax 1014 was 5,585-fold less patent than TCDD. For Halowax 1014, ELS assessments accurately predicted the results of EALS assessments.