RESUMO
A Quick, Easy, Cheap, Effective, Rugged, and Safe (QuEChERS) pretreatment technique combined with HPLC-MS/MS was established to detect 26 pesticides in traditional Chinese medicinal leeches. The sample was extracted by acetonitrile solution with sodium acetate-0.1% (v/v) acetic acid as a buffer system, then cleaned up by a mixture of 750 mg of MgSO4, 150 mg of C18, and 150 mg of PSA, separated by an ACQUITY BEH C18 column, and determined in the dynamic multiple reaction mode. Under the optimized conditions, the peak areas of the 26 pesticides in leeches showed good linearity (r > 0.99) between their mass concentrations from 1 to 100 µg/L. At the spike levels of 10, 20, and 100 µg/kg, the recoveries of 26 pesticides in leeches were 72.9-101.6% with an RSD of 1.1-12.8%, an LOQ of 10 µg/kg, and an LOD of 0.1-5.4 µg/kg. This method is easy, rapid, sensitive, and practical and meets the requirements of pesticide residue detection standards.
RESUMO
Being subject to climate change and human intervention, the land-use pattern in the agro-pastoral ecotone of Northern China has undergone complex changes over the past few decades, which may jeopardize the provision of ecosystem services. Thus, for sustainable land management, ecosystem services should be evaluated and monitored. In this study, based on Landsat TM/ETM data, we quantitatively evaluated the losses of ecosystem service values (ESV) in three sections of the agro-pastoral ecotone from 1980-2015. The results were as follows: (1) the main characteristic of the land conversions was that a large area of grassland was converted into cultivated land in the agro-pastoral ecotone; (2) on the spatial scale, the ESV losses of the agro-pastoral ecotone can be called an "inclined surface" in the direction of the northeast to southwest, and the northeastern section of the agro-pastoral ecotone lost more ESV than the middle and northwest sections (p < 0.05), on the temporal scale, the order of losses was 1990-2000 > 1980-1990 > 2000-2015; (3) the agro-pastoral ecotone lost more ESV, which was mainly due to four kinds of land conversion, which were grassland that was transformed into cultivated land, grassland transformed into unused land, grassland transformed into built-up areas, and cultivated land transformed into built-up areas; (4) although these land conversions were curbed after the implementation of protection policies at the end of the 1990s, due to reduced precipitation and increasing temperatures, the agro-pastoral ecotone will face a more severe situation in the future; and, (5) during the period of 1990-2015, the overall dynamic processes of increasing population gradually expanded to the sparsely populated pastoral area. Therefore, we believe that human interventions are the main cause of ecological deterioration in the agro-pastoral ecotone. This study provides references for fully understanding the regional differences in the ecological and environmental effects of land use change and it helps to objectively evaluate ecological civilization construction in the agro-pastoral ecotone of Northern China.
