Bone developmental toxicity of organophosphorus flame retardants TDCIPP and TPhP in marine medaka Oryzias melastigma.

The global phase-out has decreased the use of polybrominated diphenyl ethers (PBDEs), thereby, rapidly increasing the production and use of their important surrogates, organophosphorus flame retardants (OPFRs). Currently, OPFRs are often found at higher levels in the environments compared to PBDEs. Although the two typical OPFRs, tris (1,3-dichloroisopropyl) phosphate (TDCIPP) and triphenyl phosphate (TPhP), have been frequently detected in marine environments with significant concentrations, their toxicity to marine organisms remains unknown. We used Oryzias melastigma to investigate and compare their developmental toxicity in marine organisms through two-generational chronic exposure. The results showed that TDCIPP and TPhP exposure shortened the body length and length of the pectoral fin of O. melastigma. Both TDCIPP and TPhP deformed the pectoral fins in the 1st fry and caused spinal curvature in adult fish. Therefore, these two chemicals may pose potential risks to marine fish and marine ecosystems. Further studies suggested that although these two chemicals caused similar developmental bone toxicity, they had different modes of modulating the expression of bone developmental genes such as, bmp4, bmp2 and runx2.

Toxicity and bioaccumulation of three hexabromocyclododecane diastereoisomers in the marine copepod Tigriopus japonicas.

The three major hexabromocyclododecane (HBCD) diastereoisomers, i.e. α-, ß- and γ-HBCD, have distinct physical and chemical properties that may potentially result in different levels of bioaccumulation and toxicity in aquatic organisms. To assess the impact of diastereomeric variation in HBCDs, the marine copepod Tigriopus japonicus was exposed to α-, ß- and γ-HBCD in isolation. Results showed that all the three diastereoisomers had a similar potency to cause growth delay in T. japonicas. Variation was observed in the overall survival rate with exposure to α- and ß-HBCD, and this resulted in significantly higher lethal toxicity in T. japonicas than that with exposure to γ-HBCD. Exposure to α-, ß- and γ-HBCD led to the generation of ROS in T. japonicas, a possibly toxic mechanism. Both α- and ß-HBCD showed a higher potential to induce oxidative stress, which may be a factor in the higher lethal toxicity observed with α- and ß-HBCD exposure. It is of note that T. japonicus was found to be more sensitive to all three diastereoisomers in the F1 generation than in the F0 generation. The bioconcentration potential of HBCD diastereoisomers can be ranked in the order α-HBCD>γ-HBCD>ß-HBCD and was found to be higher in T. japonicus than has been reported for fish species.

Developmental toxicity of three hexabromocyclododecane diastereoisomers in embryos of the marine medaka Oryzias melastigma.

The composition of major hexabromocyclododecane (HBCD) diastereoisomers, i.e. α-, ß-, and γ-HBCDs, in marine biota is different from that of the commercially available form (technical HBCD), which is used extensively for toxicological studies. To properly evaluate the impact of HBCDs, the embryos of Oryzias melastigma were used to examine the developmental toxicity of the individual diastereoisomers. Results showed that HBCD diastereoisomers at the environmentally realistic concentrations in the embryos induced malformation rate and heartbeat, and caused the appearance of apoptotic heart. In addition, α-, ß-, and γ-HBCDs had similar potency to stimulate the generation of reactive oxygen species, consequently leading to apoptosis in O. melastigma embryos. The order of the developmental toxicity of α-, ß-, and γ-HBCDs in O. melastigma embryos was different from that in zebrafish embryos studied previously, which highlighted the importance of using species from both fresh and salt water for toxicity assessment.