Studies On Desorption Kinetics Of Dechlorane Plus And Related Compounds From Sediments

Dechlorane plus (DP) is recommended as one of the possible substitutes of brominated Flame Retardants. Because of its high hydrophobicity, more attention has been paid to the bioavailability of sediment-bound DP. In the present thesis, biomimetic method based on Tenax-TA adsorbent was used to study the desorption process and its possible mechanism of DP from the sediment. Factors including organic matter content, aging time and experimental temperature were discussed. The sediment desorption capability of DP related compounds such as Dec602, Dec603, Dec604, αCl10-DP, αCl11-DP, Mirex and DPMA were also studied. The main results of the present thesis were as follow:(1) The desorption capabilities of DP from three sediments chosen were in the order of S1>S2>S3. After 1080h, the desorption proportions of DP were 58.3%,29.5%, and 6.6% of the original concentrations for S1, S2, and S3, respectively. The desorption capabilities of DP were negatively relative with TOC contents of the sediments. According to the computational formula used, Krap and Kslow of DP calculated were in the same order of magnitude with those of other hydrophobic substances.(2) The equilibrium desorption proportions of DP were 40.1%,58.3% and 68.1%, respectively when the experimental temperatures were set at 15℃, 30℃, and 45 ℃. Moreover, the values of Krap and Kslow both increased with the increase of temperature, suggesting that high temperature is in favor of the desorption process of DP from the sediment.(3) The equilibrium desorption proportions of DP decreased from 58.3% to 45.90% with the aging time increased from 14 day to 60 day. Both Krap and Kslow did not significantly changed, but Frap decreased when the aging time was added (from 53.66% to 37.75%), implying that the bioavailability will decrease if the aging time is increased.(4) The desporption capabilities of most of DP and its related chemicals were similar except Dec604, which was significantly higher, and Dec602, which is significantly lower. According to the thermodynamic parameters, bioavailabilities of sediment-bound chemicals tested in the present study were similar to that of BDE-209.(5) The thermodynamic parameters measured were similar to those calculated based on the kinetic models. With the first order kinetic formula, 1.6 years should be taken for Dec604 to completely desorbing from the sediment, while the corresponding value is 38.3 years for Dec602, and more than 3 years for others.