Preliminary ecotoxicity hazard evaluation of DOPO-HQ as a potential alternative to halogenated flame retardants

Recent regulatory and environmental pressures have led to increasing demands for environmentally friendly flame retardants as alternatives to halogenated flame retardants (HFRs). A new flame retardant alternative, 10-(2, 5-dihydroxyl phenyl)-9, 10-dihydro-9-oxa-10- phosphaphenanthrene-10-oxide (DOPO-HQ), was applied due to its high thermal stability and glass transition temperature. However, there is little information available for its ecotoxicology. For this purpose, the preliminary ecotoxicity of DOPO-HQ was investigated and evaluated, using aquatic, terrestrial and microorganism toxicity according to Organization for Economic Co-operation and Development (OECD) guidelines under the framework of the Registration, Evaluation, Authorisation and Restriction of Chemicals (REACH) regulation. No effect was observed on Pseudokirchneriella subcapitata, Daphnia magna and Gobiocypris rarus at the saturation water solubility. For active sludge, Eisenia foetida and seedling emergence, no effect was observed at the limited highest concentration of 1000 mg/L or 1000 mg kg^-1 dw. However, moderate effect on the shoot weight is observed with the maximum inhibition rate of 46.3% when exposed to 1000 mg kg^-1 dw. Comparing the ecotoxicity of DOPO-HQ with that of HFRs and their typical alternatives, the toxicity of DOPO-HQ is markedly lower than those of triphenyl phosphate (TPP) and HFRs such as tris(2-chloro-1-methylethyl) phosphate (TCPP), tris(1,3-dichloro-2-propyl) phosphate (TDCCP), tris(2-chloroethyl) phosphate (TCEP) and tetrabromobisphenol A (TBBPA). Similar low effect levels were observed for resorcinol bis (biphenyl) phosphate (RDP), bisphenol A bis (biphenyl) phosphate (BDP) and its parent chemical 9, 10-dihydro-9-oxa-10-phosphaphenanthrene -10-oxide (DOPO). DOPO-HQ could be a potential alternative to HFRs from an environmental perspective.