The accumulation of metals, PAHs and alkyl PAHs in the roots of <i>Echinacea purpurea</i>

We examined the accumulation of polycyclic aromatic hydrocarbons (PAHs), alkyl PAHs, and toxic metals in soils by the roots of Echinacea purpurea (L.) Moench, in a 20-week greenhouse study and a 2-year field study. In the greenhouse study, inoculation by arbuscular mycorrhizal fungus (AMF), Rhizoglomus intraradices (N.C. Schenck & G.S. Sm.). increased the first order accumulation rates (k1) for PAHs by 10-fold, though had no effect on the bioaccumulation rates of toxic metals. In the greenhouse study, PAHs concentrations in soil increased over time with AMF inoculation, suggesting AMF promote ‘solvent depletion’ in soils by enhancing absorption of minerals and carbon by roots, concentrating the more hydrophobic PAHs in the residual soil. Under field conditions, contaminant concentrations in soils remained unchanged over the 2-year duration of the study. Despite this, all contaminants in E. purpurea roots increased significantly, as a result of a long term extraction of contaminants by plants from soil and a reduction in soil volume as a result of plant growth. First order accumulation rates by roots were inversely correlated to log Kow for the PAHs and alkyl PAHs, indicating that accumulation is inversely related to the compound’s hydrophobicity. This study is the first to our knowledge to assess the accumulation of alkyl PAHs by roots, with implications for soil bioremediation by plants because alkyl PAHs are a major source of petrogenic contamination in soils.本研究通过20周温室试验与2年田间试验，探究了紫锥菊（Echinacea purpurea (L.) Moench）根系对土壤中多环芳烃（polycyclic aromatic hydrocarbons, PAHs）、烷基取代多环芳烃及有毒金属的积累特征。在温室试验中，接种丛枝菌根真菌（arbuscular mycorrhizal fungus, AMF）根内根孢囊霉（Rhizoglomus intraradices (N.C. Schenck & G.S. Sm.)）可使多环芳烃的一级积累速率（k1）提升10倍，但对有毒金属的生物富集速率无显著影响。该试验中，接种AMF的土壤内多环芳烃浓度随时间推移逐渐升高，表明AMF可通过促进根系对矿物质与碳的吸收，强化土壤中的“溶剂耗竭”效应，使疏水性更强的多环芳烃在残留土壤中富集。在田间试验条件下，研究周期2年内土壤中的污染物浓度未发生明显变化，但紫锥菊根系内的各类污染物含量均显著提升，这源于植物长期从土壤中提取污染物，以及植物生长导致的土壤体积缩减。根系的一级积累速率与多环芳烃及烷基取代多环芳烃的辛醇-水分配系数对数（log Kow）呈负相关关系，说明污染物的根系积累程度与化合物的疏水性呈反比。据我们所知，本研究首次针对根系对烷基取代多环芳烃的积累情况开展系统评估，烷基取代多环芳烃是土壤中石油类污染的主要来源，因此本研究结果对植物介导的土壤生物修复具有重要参考意义。