Polyoxymethylene passive samplers to assess the effectiveness of biochar by reducing the content of freely dissolved fipronil and ethiprole.

An equilibrium passive sampler based on polyoxymethylene (POM) was used to determine the freely dissolved concentrations (Cfree ) of fipronil and ethiprole. The sorption equilibrium times of fipronil and ethiprole in POM were 14.2d and 24.0d, respectively. The POM-water partitioning coefficients (logKPOM-water ) were 2.6 for fipronil and 1.4 for ethiprole. The method was further used to evaluate the sorption behavior of biochars which produced by pyrolysis of Magnolia wood (Magnolia denudata) at 300°C, 500°C and 700°C. The amounts of target compounds adsorbed increased with increasing pyrolysis temperature of the biochars. Biochars characterized by a low polarity index had better sorption capacity for the target compounds. The additions of biochars to sediment were effective in reducing Cfree , and the enhancement was found to be more pronounced with high biochar content. Cfree in sediment with more organic matter was significantly higher after biochar addition. Increasing the sediment-biochar contact time from 7 to 30d resulted in an increase in sorption of the compounds. We conclude that Magnolia wood biochar effectively reduces the content of freely dissolved fipronil and ethiprole content in sediment.