A new hazard index of complex mixtures integrates bioconcentration and toxicity to refine the environmental risk assessment of effluents

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 (Kow) using reverse-phase high performance liquid chromatography (RP–HPLC) and 2) the toxicity identification evaluation (TIE). Forty seven compounds with known Kow and different molecular structures where used for the calibration of the log Kow 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 Kow and RP–HPLC retention time. This Kow estimation method was furthermore validated using seven additional compounds, showing acceptable estimations of the log Kow 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