Accumulation of high-molecular-weight polycyclic aromatic hydrocarbon impacted the performance and microbial ecology of bioretention systems.

Bioretention has been considered as an effective management practice for urban stormwater in the removal of pollutants including polycyclic aromatic hydrocarbons (PAHs). However, the accumulation of high-molecular-weight (HMW) PAHs in bioretention systems and their potential impact on the pollutants removal performance and microbial ecology are still not fully understood. In this study, comparisons of treatment effectiveness, enzyme activity and microbial community in bioretention systems with different types of media amendments were carried out at different spiking levels of pyrene (PYR). The results showed that the removal efficiencies of chemical oxygen demand (COD) and total nitrogen in the bioretention systems were negatively impacted by the PYR levels. The relative activities of soil dehydrogenase and urease were increasingly inhibited by the elevated PYR level, indicating the declining microbial activity regarding organic matter decomposition. The spiking of PYR negatively affected microbial diversity, and distinct time- and influent-dependent changes in microbial communities were observed. The relative abundance of PAH-degrading microorganisms increased in PYR-spiked systems, while the abundance of nitrifiers decreased. The addition of media amendments was beneficial for the enrichment of microorganisms that are more resistant to PYR-related stress, therefore elevating the COD concentration removal rate by ∼50%. This study gives new insight into the multifaceted impacts of HMW PAH accumulation on microbial fingerprinting and enzyme activities, which may provide guidance on better stormwater management practices via bioretention in terms of improved system longevity and performance.

Source, temporal variation and health risk of volatile organic compounds (VOCs) from urban traffic in harbin, China.

The main of this work investigated the levels, emission sources, and associated health risks of ambient volatile organic compounds (VOCs) closed urban traffic trunk from June 2017 to November 2018. The seasonal variation trend for total VOCs (TVOCs) concentrations was autumn > winter > summer > spring. During the daily fluctuations in summer, the TVOC concentrations appeared to be the highest at midnight and the lowest at 14:00. In spring, autumn, and winter, the concentrations of TVOCs reached the highest levels at 06:00 and dropped to the lowest levels at 14:00 to 15:00; then, the levels increased after 20:00. Aromatics were the most important types of ambient VOCs for the formation of secondary organic aerosols (SOAs). The Positive Matrix Factorization (PMF) source analysis indicated that the traffic emission accounted for 28.9% of TVOCs, followed by combustion (24.7%), industrial (21.3%), gasoline volatilization (12.4%), and solvent (11.7%) sources. Carcinogenic and non-carcinogenic risks via inhalation exposure to the selected 10 toxic VOCs may be of more concern for residents nearby traffic trunk in Harbin in autumn.