Dynamics of polycyclic aromatic hydrocarbon (PAH) accumulation in rice roots
水稻根系中多环芳烃的动态变化

The concentration of polycyclic aromatic hydrocarbons accumulated in rice roots shows an increasing trend with growth. The total amount of 15 measured PAHcompounds present in rice roots during various growth stages were 464, 969, 592, 1075 and 1059 ng·g-1 respectively, corresponding to heading, milk, dough, mature and wilting stages, in turn. The PAHs spectrum consisted of mainly 3-ring and lower molecular weight compounds. Three factors-root lipid content, specific surface area and root biomass-are discussed in this study. When normalizing the root dry weight PAHconcentration to root lipid concentration and root specific surface area, the differences among the growth stages were diminished by a factor of 4 to 5. However, the same normalization to the root biomass did not affect the differences significantly, indicating that rice root PAHuptake is affected by the root lipid content and surface area much more than by the root biomass. The PAHs in paddy field soil are significantly different from those in rice roots, both in the trend during growth stages and in the distribution patterns. Asignificant negative relationship was observed between the PAHs concentrations in rice roots and paddy soil. Soil PAHs decreased with rice growth and consisted predominantly (>50%) of 5 and 6 ring compounds. The combined effects of microbial activity, root exudates, hydrolysis and photolysis may explain the above observations.