Cultivars and oil extraction techniques affect Cd/Pb contents and health risks in oil of rapeseed grown on Cd/Pb-contaminated farmland

Substitute planting with rapeseed offers promise for safely using large areas of Cd/Pb-contaminated farmland.Cd/Pb distributions during rapeseed oil production were investigated and health risks posed by the oil were assessed.Tests were performed using three cultivars(Brassica rapa SYH and ZS100 and Brassica napus QY-1)and four oil extraction techniques(mechanical and low-temperature pressing and n-hexane and subcritical low-temperature butane extraction).The amounts of Cd and Pb in oil were 0.73%-8.44%and 3.14%-11.76%,respectively,of the amounts in rapeseed and were strongly affected by the cultivar and oil extraction technique.The heavy metal(HM)concentrations were lower in solvent-extracted oil(particularly subcritical low-temperature butane extracted oil,in which HMs were not detected)than mechanically pressed oil.The Cd and Pb transfer indices were lower(meaning larger proportions of HMs were retained by the rapeseed meal)for B.rapa than B.napus.This was attributed to a high HM binding protein content of B.rapa seed.Health risks to humans were assessed using a probabilistic risk assessment model.The carcinogenic risk was mainly(97.1%-99.9%)caused by Cd and poses more concern than non-carcinogenic risk.Stronger health risks are posed by mechanically pressed than solvent-extracted oil,and higher carcinogenic risks are posed to people living in rural areas than urban areas.Substitute planting with B.rapa and extracting oil with organic solvent(preferably subcritical low-temperature butane)are optimal for safely utilizing Cd/Pb-contaminated soil.Attention should be paid to the health risks posed by Cd in oil to rural populations.

Current status and developing trends of the contents of heavy metals in sewage sludges in China

It is essential to determine the heavy metal concentrations in sewage sludge to select appropriate disposal methods. We conducted a national survey of heavy metal concentrations of sewage sludge samples from 107 municipal sewage treatment plants located in 48 cities covering the 31 provinces and autonomous regions, as well as Hong Kong, Macao and Taiwan by Xinjiang Production and Construction Corps in 2006, and identified the temporal trends of heavy metal contents in sewage sludge by comparison with surveys conducted in 1994-2001. In 2006, the average concentrations of As, Cd, Cr, Cu, Hg, Ni, Pb, and Zn in sewage sludge were 20.2, 1.97, 93.1, 218.8, 2.13, 48.7, 72.3, and 1058mg.kg-1, respectively. Because of the decreased discharge of heavy metals into industrial wastewater in China and the increasingly stringent regulations governing the content of industrial wastes entering sewers, the average concentrations of Cd, Cr, Cu, Hg, Ni, Pb, and Zn have decreased by 32.3%, 49.7%, 54.9%, 25.0%, 37.2%, 44.8%, and 27.0%, respectively, during the past 12 years. The concentrations of Cd, Cr, Cu, Ni, and Zn in the samples exceeded the heavy metal limits of the Discharge Standard of Pollutants for Municipal Wastewater Treatment Plant in China （GB 18918-2002） by 6.5%, 3.7%, 6.5%, 6.5%, and 11.2%, respectively. From these results, 85 of the 107 municipal sludges analyzed would be considered suitable for land application.

Biodegradation of triclosan and triclocarban in sewage sludge during composting under three ventilation strategies

Triclosan (TCS) and triclocarban (TCC) are widely used in home and personal care products as antimicrobial agents. After these products are used, TCS and TCC enter the terrestrial environment and pose a great risk to humans and animals. In this research, the biodegradation of TCS and TCC was investigated during sewage sludge composting with ventilation rates of 10& 92, and 79 m^3/min. TCS and TCC were mainly biodegraded in the mesophilic and thermophilic phases, and the biodegradation rates improved with an increase in ventilation. After sewage sludge was composted for 16 days with forced ventilation (108 m^3/min), the concentration of TCS decreased from 497.4 to 214.5 μg/kg, and the concentration of TCC decreased from 823.2 to 172.7 μg/kg. The biodegradation rates of TCS and TCC were 65.2% and 83.1%, respectively. However, after the sewage sludge was stacked for 16 days, the biodegradation rates of TCS and TCC were only 17.0% and 18.2%, respectively. The environmental risks of TCS and TCC in the sewage sludge piles significantly decreased after composting. In the sludge pile with a ventilation rate of 108 m/min, the RQ values of TCS and TCC decreased from 8.29 and 20.58 to 3.58 and 4.32 after composting for 16 days, respectively. There is still a high risk if the sludge compost is directly used as a culture substrate. Nevertheless, the environmental risk could be decreased distinctly if a reasonable quantity of sludge compost is applied to land to ensure an RQ of< 1 for TCS and TCC.