Levels of polycyclic aromatic hydrocarbons in different types of hospital waste incinerator ashes.

Waste ashes from three types of hospital waste (HW) incinerators, built in SARS (Severe Acute Respiratory Syndrome) period and currently running in China, were collected and polycyclic aromatic hydrocarbons (PAH) properties in the ashes were investigated. The mean summation PAH levels in the waste ashes varied widely from 4.16 mg kg(-1) to 198.92 mg kg(-1), and the mean amounts of carcinogenic PAHs ranged from 0.74 to 96.77 mg kg(-1), exceeding the limits regulated by several countries. Among the three types of incinerators, two medium-scale incinerators generated relatively high levels of PAHs (mean summation PAH 22.50 and 198.92 mg kg(-1)) compared to small-scale and large-scale incinerators (mean summation PAH 4.16 and 16.43 mg kg(-1)). Bottom ashes were dominated by low molecular weight PAHs (LM-PAH; containing two- to three-ringed PAHs) and medium molecular weight PAHs (MM-PAH; containing four-ringed PAHs), while fly ashes were abundant in MM-PAH and high molecular weight PAHs (HM-PAH, containing five- to six-ringed PAHs). Statistical analysis indicated that there was a positive relationship (R2=0.88) between organic matter and total PAHs thus it has the potential to be used as an indicator for PAHs in HW ashes. Moreover, it was found that PAHs in the ashes correlated highly with some metallic elements either positively (e.g. Fe, Ti, Mg) or negatively (Ca), indicating that these elements might promote or prevent PAH formation during HW combustion. Although bottom ash resulted from HW incinerators has not been classified as hazardous material, the results of this study indicated that this type of waste ash contained high levels of PAHs thus need special treatment before landfill.