六叉河农业小流域多水塘沉积物中HCHs的历史分布和残留

On the historical distribution and the residues of HCH in the multi-pond sediments of Liucha River near Chao Lake

采集六叉河流域多水塘沉积物,利用沉积物年代学方法,建立未受扰动水塘沉积物年代序列,分析有机氯农药HCHs在江淮地区典型农业流域多水塘沉积物中的残留特征和降解过程,评估农药残留的生态风险。结果表明,过去几十年的农业集约化中农药的投入,是导致农药残留主要因素。HCH的历史投入量约为18 400 kg,多水塘沉积物中残留的HCH为0.177 kg,HCH残留量已经不再显著。对于HCHs 4种异构体,α- HCH在所有样品中均未检出;β-HCH与γ-HCH的检出率为6.98%,β-HCH最高残留质量比为7.88 ng/g,γ-HCH为9.51 ng/g;δ-HCH检出率为3.49%,最高残留质量比为5.07ng/g。表明流域水塘沉积物中累积的HCHs在过去几十年基本已经被降解,流域存在较低的HCHs残留风险。在空间分布上看,不同类型的水塘由于其下垫面土地利用类型差别,其沉积物中HCH残留存在明显差异,γ-HCH(林丹)仅在河塘中被检出(检出率为20.7%),表层沉积物质量比9.51 ng/g。研究表明,六叉河流域的HCH已经基本全部降解,不存在HCH农药残留风险,但流域尺度上可能存在新的HCH输入来源。

The paper is engaged in a study of the historically accu- mulated deposits and the residues of HCH in the multi-pond sediments of Liucha River near Chao Lake by using 137Cs dated sediment cores taken from the multi-pond system of Liucha River＇ s watershed, a typical farming watershed with high-yield grain production character- ized by multi-pond systems along the Yangtze-Huai Rivers＇ reaches. Our research purpose was to disclose the effect of intensified farming on the residuals of hexachlorocyclohexanes （HCHs） and its environ- mental damage in the past decades. The results show that it has been the key factor to frequently use pesticides to lead to the damage to the watershed eco-environment. Statistically speaking, about 18 400 kg of HCH were used to the paddy fields in Liucha watershed to prevent and control the rice stem borers from their attacking the growth of the young seedlings. However, what is left over just 0. 177 kg in sedi- ments of the mulipond system, which clearly revealed that almost all the HCH had been degraded already and thus had little environmental risk in terms of I/CH residue. In addition, the number of samples in which ^- HCH and y- HCH were detected accounts only for 6.98% of the total number of samples, with a high concentration of 7.88 ng/g and 9.51 ng/g, respectively. For the four isomers of HCHs in the sediment cores taken from the multi-pond of Liucha River water- shed, the. detection rate for ~ - HCH was only 3.49%, with their highest content rate being 5.07 ng/g, but with no a- HCH detected, which indicates most of HCH were degraded in the past several decades. Thus, there was no distinctive trend found in the temporal scale because of the historical degradation. However, in the spatial scale, a distinctive variety was found among the different types of ponds. The rate of presence of 13 - HCH in the sediment of paddy rice field pond was found as high as 28.6% , whereas only 8.7 was de- tected in the farmland pond. Moreover, no trace was detected either in the village pond or in the stream pond. 7 HCH （lindane） was only found in the sediment （detection rate 20.7%） of the stream ponds with a moderately high concentration of 9.51 ng/g in the sedi- ment surface, which implies that there were new sources of HCHs in- put besides the historical residuals. Over 80% of the residues found ＂were 13- HCH from the total amount of 140 g residues. Therefore, our research suggested that almost all the HCH being dosed to the rice field during 1967 to 1983 had already been decomposed in the natural environment, with hardly no risk of HCH residues, though there may still exist some new and unknown HCH input in the water-shed scale.