CONCENTRATION, SOURCES AND RISK ASSESSMENT OF POLYCYCLIC AROMATIC HYDROCARBONS (PAHS) IN SEWAGE SLUDGE FROM XUCHANG CITY, CHINA

Polycyclic aromatic hydrocarbons (PAHs) are persistent organic pollutants in the urban environment, because of their hydrophobic and lipophilic character, PAHs is an easily enriched in sludge, which is by-product of sewage treatment and widely used in cultivated land. Xuchang city is an important grain production area in China, the amount of sludge for agricultural utilization in Xuchang city is gradually increasing during recent years. To investigate the concentrations, potential sources and ecological risk of PAHs in sludge of Xuchang City, dewatered sludge samples from 10 large-scale sewage treatment plants were collected and analyzed. The results showed that the total concentration of PAHs varied from 1835 to 7188 mu g/kg, with a mean value of 4362 mu g/kg. The average value of PAHs concentration met the limit of China's agricultural sludge control standard, while the total concentrations of PAHs from HY, YC and RH exceeded the control standard and cannot be directly used for agricultural utilization. PAHs mainly contain 4 similar to 6 rings species, while 2 similar to 3 rings species occur rarely. The source tracing results showed that vehicle exhaust, industrial sources, coal and wood combustion are the main sources of PAHs in sludge. The ecological risk assessment showed that the toxic equivalent concentration TEQ(BaP16) range from 75.5 to 760.2 mu g/kg and TEQ(BaPcancer) range from 74.6 to 758.5 mu g/kg. TEQ(BaPcancer) accounts for up to 98% of TEQ(BaP16), suggesting that carcinogenic PAHs species are the main contributors to the risk of PAHs. TEQ(BaP10) in this study was almost 8 times higher than that specified value in the agricultural soil standard. The result of risk assessment suggests that PAHs in sludge of Xuchang City pose serious ecological and carcinogenic risk. Therefore, sludge must be conducted harmless treatment before agricultural utilization.