The Fate And Ecotoxicological Effects Of BFRs In Soil Environment

Brominated flame-retardants (BFRs) are a new, diverse group of global environmental pollutants. BFR production has increased dramatically over the past 20 years. Recently, concern for this emerging class of chemicals has risen duo to their occurrence in the environment, wildlife, and people. Whereas, knowledge about their fate in siol and ecotoxicological effects on organisms (aquatic and terrestrial) is very limited.The fate of tetrabromobisphenol A (TBBPA) and hexabromocyclododecane (HBCD) diastereomers (α-,β-, andγ-HBCD), the ecotoxicological effects of TBBPA on tubifex (Monopylephorus limosus) and wheat(Triticum aestivum), the ecotoxicological effects of HBCD on wheat were all investigated. The results indicated that:1. In a short-term (8 weeks) experiment, sorption to soil matrix resulted in 90% decline in recovery of TBBPA and HBCD in planted and unplanted soils. However, nearly 50% of initial HBCD recovered under the combined cabbage and radish treatment situation, which suggested that interactions between plant species might enhance the bioavailability of HBCDs. Although both plant species could uptake TBBPA and HBCDs, cabbage showed greater accumulating ability. Up to 3.5-10.0-fold higher HBCD concentrations were observed than TBBPA concentrations in all plant tissues, and the distribution of HBCDs in plant tissues for both species was diastereomer-specific. The predominance of a-HBCD in shoot tissues for both species might be attributed to diastereomer-specific translocation of HBCDs, shift in diastereomer pattern and/or selective metabolization of y-HBCD within plants.The result showed that strong sorption to soil particles reduced the bioavailability and potential of human exposure to BFRs in the soil, However, plants may increase the exposure risk by enhancing their bioavailability in the soil and by uptaking these compounds. The results also provide insight into transport mechanisms of TBBPA and HBCD diastereomers in soil-plant systems. 2. After a 8-day exposure, the SOD activity of tubifex was enhanced at first and then inhibited gradually, at last enhanced again. The highest activity of SOD (p<0.01) was examined under 0.05 mg L-1 concentration of TBBPA. And the activity of SOD was much higher than that of control(1.5 times～7.8 times more than that of control). While the CAT activity showed a tendency of induction firstly, then inhibition, then induction again and at last inhibition. The activity of CAT reached the highest value under 0.5 mg L-1 concentration of TBBPA. Furthermore, the CAT activity was higher than that of control (1.1 times～1.9 times more than that of control) except that under 0.005 mg L"1 and 0.25 mg L-1 concentration. Moreover, the highest activity of GST (p < 0.01) was observed under 0.25 mg L-1 concentration of TBBPA. The activity of GST was enhanced gradually at first and then inhibited. As the same as SOD, the activity of GST was induced significantly (p< 0.05). The changes in the SOD activity showed an "M" trend, while that in the CAT activity showed a "N" trend. And the activity of SOD is steadier than that of CAT. Thus, the changes in the activity of SOD and GST, especially SOD, can better reflect the toxic effects of pollutants on tubifex.3. No significant effect on the germination rate of wheat was observed with the increase of TBBPA concentration. The trend of changes in the specific growth rate (μ) value of shoot growth with exposure time was similar treated with different TBBPA concentrations. And the peak of theμvalue of shoot growth was detected after the 42-hour exposure. Whereas, there were no significant differences in theμvalue of root elongation with the increase of exposure time from 38 to 46 hours as TBBPA concentration increased. The shoot growth was stimulated with the increase of TBBPA concentration from 0.002 to 0.02 mg L-1. And theμvalue of shoot growth treated with 0.02 mg L-1 of TBBPA was the highest. While the root elongation was stimulated by 0.002-0.05 mg L"1 TBBPA treatments. The 0.05 mg·L-1 TBBPA treatment significantly increased theμvalue of root elongation.4. After both 7-and 10-day exposure, reduction of the CHL content in wheat leaves could be observed. However, the changes in the CHL content with the increasing TBBPA concentration from 50 to 5000 mg kg-1 were insignificant. Increased MDA levels detected in wheat leaves at the two time intervals reflected the presence of poisoning AOS and the oxidative stress induced by TBBPA. It can be concluded from the enhancing POD activity in wheat leaves after a 12-day exposure that wheat plants had the capability to protect themselves by increasing the activity of antioxidant enzyme POD with the exposure time. Our data also showed that the plant has the capacity to counteract the oxidative stress at the first stage of stress when the concentration of TBBPA was 0.5-50 mg kg-1, but the capacity would be lost with prolonged exposure. Moreover, the defensive effect of antioxidative enzymes would be lost with the increasing TBBPA concentration. The increasing CAT activity might be induced by H2O2 produced from sources of SOD after a 7-day exposure, but the increasing POD activity was induced not only by H2O2 produced from sources of SOD after a 12-day exposure. There were no dose-response effects in the changes between the activity of antioxidant enzymes (SOD, POD and CAT) and the concentration of TBBPA. It also could be concluded that the decrease in the activity of POD and CAT could be considered as good biomarkers of serious stress by TBBPA in soil.5.5-500 mg kg-1 HBCD treatments caused significant damage to CHL accumulation in wheat seedlings after 7-10 days of exposure. As a marker of oxidative damage, the LPO was increased in both wheat leaves and roots. SOD activity in wheat leaves was significantly (p< 0.01) increased with prolonged exposure. On the contrary, it decreased more or less in wheat roots. POD activity in both wheat leaves and roots was significantly (p< 0.01) increased by all HBCD concentrations during the 10-day experimental period.0.5-50 mg kg-1 HBCD treatments significantly (p< 0.01) increased CAT activity in wheat leaves after the 8-day exposure. However, CAT activity in wheat roots was not significantly (p> 0.05) affected by HBCD exposure. All these results demonstrated that HBCD could induce oxidative stress in terrestrial organisms and wheat plants had the capacity to tolerate oxidative stress. POD and CAT might be induced by H2O2 produced from different sources. Wheat roots were more Sensitive to HBCD than wheat leaves. Also, POD played the main role in AOS detoxification under the stress of HBCD in soil environment.