A new methodology to evaluate the overall environmental hazard of unknown mixtures, based on bioconcentration potential and toxicity, was developed using a combination of two methodologies: 1) the estimation of the octanol–water partition coefficient (K_ow) using reverse-phase high performance liquid chromatography (RP–HPLC) and 2) the toxicity identification evaluation (TIE).
Forty seven compounds with known K_ow and different molecular structures where used for the calibration of the log K_ow in relation to the retention time in reverse-phase high performance liquid chromatography (RP–HPLC). A linear regression with an R²=0.81 and an sd=0.69 was established between log K_ow and RP–HPLC retention time. This K_ow estimation method was furthermore validated using seven additional compounds, showing acceptable estimations of the log K_ow of unknown substances.
Two different mixtures were tested, one containing 3,4 Dichloroaniline, Diazinon and 4-Nonylphenol and another one containing a mixture of 16 pesticides. Both mixtures were first tested as a whole effluent and then fractionated and tested, using a miniaturized Daphnia magna test.
An equation is presented, that combines both methodologies and establishes a relative hazard index RHI, ranging from 1 to 10 for any particular mixture of chemicals.
The results show how the method presented can refine the security factors that could be included in the environmental risk assessment of effluents in the future.