| Polycyclic aromatic hydrocarbons (PAHs) are a group of ubiquitous persistent organic pollutants, which are highly lipophilic and hydrophobic. Because of their toxicity and persistence, and their carcinogenic, teratogenic and mutagenic properties, PAHs are a topic of growing concern. The Baotou section of the Yellow River is located at 109.2533°-111.4403° E and 40.2489°-42.7303° N, in which the icebound season is longer and pollution characteristics must be different from the ice-free period. In this study, ice and water samples were collected from eight sites along the Baotou section of the Yellow River.16 priority-controlled polycyclic aromatic hydrocarbons (PAHs) were selected as target contaminant. The main aims of this study were to obtain information on the PAH concentrations in the Baotou section of the Yellow River in freezing-thawing process; to determine how PAHs were distributed in water and in ice; to monitor the contaminant sources in the study area and develop an understanding of the fate and transport of PAHs in a multimedia environment; to discuss the photodegradation of fluoranthene, the dominant pollutant in the Baotou section of the Yellow River, in the water and ice phase; to investigate the influence of light-sensitive materials (H2O2, acetone and sediment) on the photodegradation of fluoranthene in the water and ice phase; and to analyze environmental risk of PAHs in this area. In this paper, the main results are as follows:(1) There were 11 kinds of PAHs detected in water samples of Baotou section of the Yellow River. The total PAH concentrations in water samples ranged from 6.58 ng·L-1 to 222.37 ng·L-1with the mean value was 61.48 ng·L-1, and PAH concentrations were dominated by fluoranthene. Some of them were higher than the standard of EPA882-Z-99-001, and benzo[a]pyrene exceeded the standard of GB3838-2002 《Surface Water Environment Quality Standard》. In ice samples, there were 8 kinds of PAHs detected, the total PAH concentrations ranged from 4.91 ng·L-1 to 59.39 ng·L-1 with the mean value was 27.17 ng ·L-1, and PAHs were dominated by fluoranthene The spatial distributions of PAHs in ice and in water were similar and were significantly correlated, and PAH concentrations were highest at Huajiangyingzi section and were also relatively high at Dachengxi section.(2) The temporal and spatial distribution of PAHs in the ice samples were derivatived based on the continuously monitoring on the Toudaoguai section. The results showed that the total PAH concentrations in ice samples ranged from 0.71 ng·L-1 to 11.04 ng·L-1 with the mean value was 3.88 ng·L-1. The concentrations of PAHs were low in the ice flood season, and then reached the maximum value after initial ice cover formed. The PAH concentrations were decrease with the increase of ice cover thickness, and it was higher in the low layer than up layer. At the end of the winter, PAHs released into the water with ice melting.(3) Principal Component Analysis (PCA) was carried out in SPSS version 19.0 to verify the reliability of the PAH ratios and determine the PAH sources. In water, three components were achieved, and which explained 80.00% of the variance. The components indicate that PAHs are from industrial wastewater and municipal sewage discharge, coal combustion sources, and transportation sources. In ice, two components were achieved, and which explained 83.68% of the variance. The components indicate that PAHs are from coal combustion sources, and transportation sources.The result was matched with the fact.(4) The fluoranthene light experiment was carried out under exposure to UV light with low fluoranthene concentrations, using a light conversion function in the water and ice phase. The results show that the fluoranthene degradation was consistent with a first-order kinetics reaction, and the degradation rates of were 0.031 μg L-1·h-1 and 0.0293 μg L-1·h-1, respectively. The fluoranthene concentration in the basic phase remained unchanged when exposed to the dark reaction.(5) In our study, the effects of different concentrations of light-sensitive materials (H2O2, acetone, and sediment) were investigated after photodegradation of fluoranthene. In water phase, high H2O2 concentrations promoted photoconversion, likewise, low concentrations of H2O2 inhibited fluoranthene photodegradation; in ice phase, low concentrations of H2O2 promoted photoconversion in the initial stages of the reaction, and that degradation rates decreased later in the reaction. The degradation rate of fluoranthene increased slightly when oxidant concentrations were high. The degradation rates of fluoranthene in water and ice phase were lower with acetone than without, and the fluoranthene degradation was consistent with a first-order kinetics reaction. In water phase, as the acetone concentration increased, the fluoranthene degradation rate decreased; in ice phase, the acetone promoted photoconversion in the initial stages of the reaction, and that inhibited fluoranthene photodegradation later in the reaction. The presence of sediment reduced the degradation rate of fluoranthene in water and ice phase.(6) Based on the concentrations of 6 PAHs in the Baotou section of the Yellow River in freezing-thawing process, a preliminary assessment of the health risk caused by ingestion from drinking water and dermal contact with shower water was performed by using a health risk method of US EPA. The results showed that the total risks’index sequence was icebound season> ice flood season> ice melting season, and the maximum value was Huajiangyingzi section. The risk index of benzo[a]pyrene was less than 1.0 ×10-04 from drinking water, and the results obtained showed that the distribution of potential risk of benzo[a]pyrene is in the acceptable, but the risk of cancer compared with other section of the Yellow River is still high. The non-carcinogenic risk indexes of 5 PAHs sequence was Fluoranthene>Pyrene>Fluorene>Phenanthrene> Anthracene, and the total risk was far lower than of the standard value US EPA, which didn’t show potential non-carcinogenic risk to human health. However, the non-carcinogenic risk index of fluoranthene was higher contrasting others, so the potential risk can not be ignored.(7) According to the ecological risk assessment of individual PAHs, the risks of anthracene were relative higher in water and ice phase, the risk probability of anthracene in the water and ice phase were 83.92% and 69.96%, when the percent of aquatic organisms affected more than 5.00%. Water and ice phase ∑ PAH joint toxicity were higher than that of the ecological risk of anthracene largest single role toxicity, even greater than the monomer ∑ PAH overlap area, the sum of joint toxicity showed a significant effect. According to the joint risk assessment of PAHs, the joint risks were much higher than that of individual PAHs in water and ice phase, and the joint toxicity showed significant effects. |
PDF Full Text Request