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Biochar application to soil contaminated with potentially toxic elements has been paid particular attention as an effective amendment. This study was carried out to investigate the effect of wheat straw biochar on adsorption and accumulation of Cd2+ in paddy soil and rice. Biochar was applied once in four treatments of 10, 20, 30, and 40 t ha−1 and a control check (CK) was set up in Changsha County, China. The results showed that under biochar addition the Cd2+ adsorption process was dominated by inhomogeneous multi-surface adsorption. Biochar significantly increased adsorption capacity for Cd2+ and the maximum of sorption at A40 was 2713 mg kg−1. The available Cd concentration was also decreased by transforming S1 (decreased by 25%, acid soluble Cd) to S2 (increased by 40%, oxidizable Cd) and S3 (increased by 24%, reducible Cd). Also, biochar application resulted in significant reduction in Cd concentration in rice by inhibiting migration from soil to rice. The study demonstrated that the biochar of 40 t ha−1 reduced rice grain Cd concentration to 0.18 mg kg−1, which was within the Chinese safety limit. Therefore, the dose of 40 t ha−1 would be proper for reducing risk due to Cd contamination in agricultural production. [ABSTRACT FROM AUTHOR]

Atmospheric ambient gaseous ammonia (NH 3), the most abundant alkaline gas, affects public health and climate change through its key role in the formation of secondary aerosols via reactions with acidic gases. Estimation of the contributions of ammonia sources is very challenging in the urban atmosphere. Stable nitrogen isotope ratio (δ15N) measurements have shown that urban aerosol NH 4 + and gaseous NH 3 are derived from fossil fuel combustion-related (FF) sources, such as coal combustion, NH 3 slip, and vehicle exhaust, and volatilization-related sources, such as agriculture and urban water volatilization. Biomass burning (BB) sources, especially residential biofuel, can produce vast quantities of NH 3 and other pollutants and may greatly influence air quality and contribute to increased urban NH 3 emissions. In the present study, we continually collected PM 2.5 samples at three urban sites in Central China during autumn and analyzed the major water-soluble ions and δ15N values of aerosol NH 4 +. The concentrations of NH 4 + increased as the temperature decreased close to winter, whereas the δ15N values did not show this pattern. According to the Bayesian model after isotope fractionation correction, FF sources contributed to 56.4 ± 17.1%, 46.4 ± 18.2%, and 51.8 ± 14.9% of aerosol NH 4 + in Nanchang, Wuhan, and Changsha, respectively, throughout autumn. The contributions from BB sources were 34.5 ± 20.4%, 46.4 ± 21.4%, and 40.4 ± 17.4% for Nanchang, Wuhan, and Changsha, respectively. We also found the fraction of aerosol NH 4 + from BB increased in all three cities from September to November 2017, which was likely caused by increased heating demands with the decrease in temperature during the season. Furthermore, BB was responsible for a severe haze event (maximum PM 2.5 of 205.69 μg/m3) in Nanchang. These findings suggest government controls to improve air quality should include BB sources in addition to FF sources. Image 1 • Aerosol NH 4 + was mainly derived from fossil fuel combustion-related sources. • Biomass burning's contribution to aerosol NH 4 + increased as the temperature decreased. • Biomass burning greatly contributed to a severe haze event in Nanchang. [ABSTRACT FROM AUTHOR]