Five samples of soil collected from a lead and zinc mine were used to assess the effect of combined contamination of heavy metals on soil bacterial communities using a polyphasic approach including characterization of isolates by culture method, community level catabolic profiling in BIOLOG GN microplates, and genetic commuruty fingerprinting by denaturing gradient gel electrophoresis of 16s rDNA fragments amplified by PCR from community DNA ( P C R -W E ) . The structure of the bacterial community was affected to a certain extent by heavy metals. The PCR-DGGE analysis of 16s rRNA genes showed that there were significant differences in the structure of the mcrobial community among the soil samples, which were related to the contamination levels. The number of bactena and the number of denaturing gradient gel electrophoresis ( W E ) bands in the soils increased with increasing distance from the lead and zinc mine tailing, whereas the concentration of lead (Pb) and cadmium (Cd) was decreased. Heavily polluted soils could be characterized by a community that differs from those of lightly polluted soils in richness and structure of dominating bacterial populations. The clustering analysis of the DGGE profiles showed that the bacteria in all the five samples of soil belonged to three clusters. The data from the BIOLOG analysis also showed the same result. This study showed that heavy metal contamination decreased both the biomass and diversity of the bacterial community in soil.
Previous studies have evaluated the impact of lockdown measures on air quality during the COVID-19 pandemic in China, but few have focused on the temporal characteristics and spatial heterogeneity of the impact across all 337 prefecture cities. In this study, we estimated the impact of the lockdown measures on air quality in each of 337 cities using the Regression Discontinuity in Time method. There was a short-term influence from January 24 th to March 31 th in 2020. The 337 cities could be divided into six categories showing different response and resilience patterns to the epidemic. Fine particulate matter (PM 2.5 ) in 89.5% of the cities was sensitive to the lockdown measures. The change of air pollutants showed high spatial heterogeneity. The provinces with a greater than 20% reduction in PM 2.5 and PM 10 and greater than 40% reduction in NO 2 during the impact period were mainly concentrated southeast of the “Hu Line”. Compared to the no-pandemic scenario, the national annual average concentration of PM 2.5 , NO 2 , PM 10 , SO 2 , and CO in 2020 were decreased by 6.3%, 10.6%, 7.4%, 9.0%, and 12.5%, respectively, while that of O 3 increased by 1.1%.This result indicates that 2020 can still be used as a baseline for setting and allocating air improvement targets for the next five years.
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