Study On The Preparation Of Environmental Persistent Free Radicals (EPFRs) Containing Biochar And Its Toxicity On Scenedesmus Obliquus

The effects of pyrolysis temperature and time on the formation of environmental persistence free radicals(EPFRs)in biochars were studied by using pine needles as raw material in the present study.The qualitative analysis(g-factor),quantitative analysis(concentration),and stability analysis(decay)of EPFRs in biochars prepared under different conditions were carried out.The effects of different pH and volume fraction ethanol treatments on the formed EPFRs were compared,and the effects of transition metal copper ion concentration on EPFRs formation were investigated.The effects of biochars at different pyrolyzed temperatures(i.e.,300,400,and 500 ?)on the cell growth,chlorophyll a synthesis,cell membrane integrity,reactive oxygen species(ROS),and superoxide dismutase(SOD)activity were measured by using Scenedesmus obliquus as tested organism,respectively.The main contents and conclusions are as follows:Firstly,the qualitative analysis of EPFRs in biochar showed that the prepared EPFRs were carbon-centered with an adjacent oxygen atom free radicals under the experimental conditions,of which the g-factors were in the range of 2.0030~2.0040.Quantitative analysis of EPFRs showed that the highest concentration of EPFRs was observed when biochar was pyrolyzed at 500 ? for 3 h,which was 8.12×1019 spins/g.The stability analysis of EPFRs showed that the EPFRs is stable when biochars were pyrolyzed at 300,400 and 500 ?,and the concentrations of EPFRs only decreased by 10.08%,25.05%,and 34.25% after they were stored at room temperature under dry conditions for 120 days,respectively.The treatments of biochar with different pH and ethanol treatment showed that the decrease of p H and ethanol solution could reduce the concentration of EPFRs in biochar,and the lower the pH,the higher the volume fraction of ethanol,resulting in EPFRs concentration decreased obviously.Secondly,the effects of 300,400 and 500 ? pyrolyzed biochar on Scenedesmus obliquus,of cell growth,chlorophyll-a synthesis,cell membrane integrity,ROS content,and SOD activity were investigated.The results showed that the 72 h-EC50 of biochars on cell growth were 129 mg/L,74 mg/L,and 66 mg/L,respectively.The biochars inhibited the synthesis of chlorophyll-a and destroyed the cell membrane integrity,leading to increased ROS levels and SOD activity of Scenedesmus obliquus.Thirdly,the possible toxic mechanism of different biochars was analyzed from the perspectives of particulate matter and free radicals.As a particulate matter,the toxicity mechanism of biochar may be related to the nature of the material,such as particle size,surface potential,functional groups,and so on.Meanwhile,the hydroxyl capture experiments of biochar suspension demonstrated that the EPFRs-containing biochar once released into the aqueous phase could induce the generation of hydroxyl radicals,which may also be the reason for oxidative damage caused by biochars.In summary,significant acute and chronic toxicity were observed after Scenedesmus obscurus exposed to biochars,showing a significant biological toxicity.In view of the wide application of biochar,its ecological effect on aquatic organisms and its toxic mechanism are also urgent to carry out in-depth study.Meanwhile,the correlation between potential risk of biochar application and new type environmental pollutants of EPFRs need more extensive research.