珠江三角洲4种代表性土壤/沉积物中自由态与结合态有机氯农药的含量与分布特征

Characterization of Free and Bound Organochlorine Pesticides in Four Soil/Sediments of the Pearl River Delta,China

有机氯农药在土壤/沉积物中主要以自由态和结合态存在.本研究选取珠江三角洲地区4种代表不同沉积环境的典型土壤/沉积物样品,先采用碱萃取、盐酸/氢氟酸去矿物等方法对样品进行了组分分离,再采用有机溶剂萃取法对不同组分中自由态和结合态有机氯农药进行了系统分析.结果显示,4种土壤/沉积物总有机氯农药含量为20.96--134.22μg.kg^-1,其中HCHs总含量为5.66--22.87μg.kg^-1,DDTs总含量为1.51--11.70μg.kg^-1,-βHCH、七氯、艾氏剂、异狄氏剂、硫丹硫酸盐和甲氧滴滴涕等6种农药为主要成分,占总有机氯农药的53.56%--77.26%.自由态有机氯农药含量为8.46--88.45μg.kg^-1,占总有机氯农药的40.37%--65.90%.结合态有机氯农药含量为11.46--45.77μg.kg^-1,占总有机氯农药的34.10%--59.63%,主要存在于土壤/沉积物的腐殖酸和胡敏素组分,反映了环境中结合态有机氯农药的大量存在.自由态DDT和HCH类有机氯农药的分布情况表明,4种样品均没有新鲜HCH类农药输入而部分样品仍有新鲜DDT类农药输入.结合态有机氯农药在腐殖酸和胡敏素间的分布与有机质碳含量相关,占总有机碳57.71%--80.55%的胡敏素结合了94.78%--97.48%的结合态有机氯农药.风险评价结果表明,部分游离态有机氯农药如-γHCH、艾氏剂、异狄氏剂、DDT类农药可能存在一定的生态风险.由于单个化合物的总量要比自由态高出约1--30倍,同时结合态农药在一定条件下有释放到环境的可能,因此有机氯农药的环境风险评价和环境标准建立均需考虑结合态有机氯农药.

Free and bound residues are the main form of organochlorine pesticides （OCPs） in soils/sediments. Four surface soil/sediments from the Pearl River Delta, China, were selected to characterize free and bound OCPs in different fractions of organic matters in the samples through alka-extraction, HCI/HF demineralization and organic solvent extraction. Total OCPs concentrations of samples were 20.96-134.22μg.kg^-1 , total HCHs concentrations were 5.66-22.87 μg.kg^-1 , and total DDTs concentrations were 1.51-11.70 μg.kg^-1 . β-HCH, heptachlor, aldrin, endrin, endosulfan sulfate and methoxychlor were the dominate compounds which took 53.56%-77.26% of total OCPs. Concentrations of free OCPs were 8.46-88.45 μg.kg^-1 and took 40.37%-65.90% of total OCPs while concentrations of bound OCPs were 11.46-45.77 μg.kg^-1 and took 34.10%-59.63 % of total OCPs. Most of bound OCPs were in the humic acid and humin fractions of the samples which shows the significantly occurrence of bound OCPs in environment. Distributions of free DDTs and HCHs showed that there were no fresh HCHs poured into these samples but there were fresh DDTs poured into some of the samples. The distribution of OCPs in these two fractions were associated with the organic C content of the fractions, and 94.78%-97.48% of bound OCPs were in humin fraction which took 57.71%-80.55% of total organic C in the samples. Environmental risk estimate showed that some free OCPs such as γ-HCH, aldrin, endrin and DDTs may have risk to environment and total of free and bound concentration of each compound were 1 - 30 times higher than free concentration of each compound. Therefore bound OCPs should be considered while making the environmental risk estimate and establishing environmental criteria.