作物根系对土壤中老化HCH-DDT的富集作用

Accumulation of Aged HCH-DDT by Corn(Zea mays L.)and Wheat(Triticum aestivum L.)Roots from Soils

在室温条件下，采用盆栽试验方法研究了小麦和玉米作物根系对自然污染土壤中不同水平老化HCH、DDT的富集作用及其影响机制。通过连续提取，将根系富集的有机氯农药分为弱吸着、强吸着和吸收3种不同形态。结果表明，作物对老化HCH、DDT的富集存在选择性。在60d的试验周期内，玉米根系富集的HCH、DDT中55．4％～62．2％为根表强吸着，23．3％～36．9％为根内吸收；而小麦根系中HCH,DDT的73．8％-76．9％被根表强吸着，仅15．4％-20．5％可以进入根系组织内部。不同形态组分中异构体及代谢物的组成比例差异化明显，其中吸收态以β-HCH为主，强吸着态以P，p＇-DDT、p，p＇-DDE和P，p＇-DDD为主。随着土壤污染水平的增加，小麦和玉米根系对HCH、DDT的富集总浓度增加，而生物蓄积系数逆浓度梯度增加，小麦根系的富集能力强于玉米。在控制污染水平的条件下，作物根系对土壤老化HCH、DDT的富集量与其根系比表面积大小和总脂含量极显著正相关，而向根系深层组织运移的过程主要受总脂含量控制。

Organochlorine pesticides （OCPs） in soils may still impact plants though their uses were stopped 30 years ago. In this study, the accumulation of aged HCH-DDT by com（Zea mays L. ） and wheat（ Triticum aestivum L. ） roots from naturally contaminated soil was stud- ied in a pot experiment to access the phyto-bioavailability of aged OCPs.HCH and DDT were extracted sequentially to measure weakly ad- sorbed, strongly adsorbed, and absorbed fractions in root tissues. The results showed that corn and wheat accumulated aged HCH and DDT selectively. After 60 days of exposure, corn roots strongly adsorbed about 55.4%-62.2% of the total HCH and DDT detected on the root sur- faces, but absorbed approximate 23.3%-36.9% into the roots. Wheat roots adsorbed 73.8%-76.9%, but absorbed only 15.4%-20.5% of the HCH and DDT detected. Differences in the ratios of isomers and metabolites were found in different fractions. The absorbed fraction was mainly β-HCH, whereas strong adsorbed fraction was p,p＇-DDT, p,p＇-DDE and p,p＇-DDD. The accumulation of HCH and DDT in crop roots increased, but bioaeeumulation factor （BAF） decreased with their concentrations in soils. Wheat roots accumulated HCH and DDT greater than corn roots did. The concentrations of HCH and DDT in crop roots were significantly positively correlated with root specific sur- face area and total lipid contents. The absorbed fractions of HCH and DDT in root tissues were controlled mainly by total lipid contents.