| As one class of major contaminants in aquatic environments, heavy metals are ready to be transported and accumulated through the food chains and enter human body through consumption of fish and other aquatic products, posing a serious threat to human health. Thus much attention has been paid to heavy metal contamination in aquatic environments. Serving as the main water source of the Yellow River basin and the citys in Henan province, Xiaolangdi reservoiris very important in terms of both social and economic values. Thus study of transport, transformation, and risk assessment of heavy metals in the reservoir would have important scientific and social implications. In the present study, water, surface sediment, pore water, and fish samples were collected in the dry(May) and wet season(October) of 2013. Heavy metals(Cr, Cd, As, Pb, Cu, Mn and Ni)in the samples were determined using inductively coupled plasma mass spectrometry method. Cold vapor atomic fluorescence spectrometry and aqueous phase ethylation derivatization-gas chromatography-atomic fluorescence spectrometry methods were used for analysis of total mercury(THg) and methylmercury(MeHg), respectively. Bioaccumulation of Heavy metals in fish of Xiaolangdi reservoir was then discussed and the ecological risk and health risk induced by heavy metals were assessed. The main conclusions obatined were listed as follows:(1) Concentrations of As, Pb, Cu, Cr, Mn and Ni in water were 2.49~3.04 μg/L, 0.20~0.65 μg/L, 5.37~6.47 μg/L, 1.45~4.13 μg/L, 1.23~3.14 μg/L and 8.53~19.50 μg/L, respectively. As, Cr, Pb and Cu in water could meet the requirement of Class I criterion of national surface water environmental quality standard(GB 3838-2002), while Mn and Ni could meet the specific standard set for surface water sources of drinking water. In general, water in the Xiaolangdi reservoir has not been significantly contaminated by heavy metals.(2) Average concentrations of Cr, Cd, As, Pb, Cu, Mn and Ni in sediments were 64.37±12.20 mg/kg, 0.22±0.03 mg/kg, 18.05±2.54 mg/kg, 33.17±15.24 mg/kg, 31.94±4.92 mg/kg, 697.34±67.25 mg/kg and 37.72±2.53 mg/kg, respectively. The average contents of Cr, Cu, Ni and Pb could meet the requirement of Class I criterion of national soil environmental quality standard(GB 15618-1995), while the average content of Cd and As could meet the requirement of Class Ⅱ criterion. In comparison with sediments of Xiangjiang Yueyang section, Dushan lake, Huangpu River, and Yellow River Inner Mongolia section, theavy metal cntents in sediments of Xiaolangdi reservoir were at the medium level. It might be related to the weak economic activity in this aera.(3) In the muscule tissues of six popular fish species(bighead carp, Barracuda, Crucian carp, Yellow catfish, Sharpbelly, and Arch fish), thecontents of Cr, Cd, As, Pb, Cu, Mn, and Ni were in the range of ND~4.30 mg/kg, 0.14~2.76 mg/kg, ND~1.67 mg/kg, 0.21~1.28 mg/kg, 0.12~3.99 mg/kg and 0.08~4.50 mg/kg, respectively. The contents of As in muscle tissues of all the six fish species, thecontent of Cr in Sharpbelly, and the content of Pb in Bighead carp were higher than the corresponding limit values of national standards(GB 2762-2012 and GB 18406.4-2001). Bioaccumulation factors of Pb in Barracuda, Sharpbelly, and Yellow catfish, as well as that of Mn in Arch fish were greater than 103, while the bioaccumulation factors in all the other cases were smaller than 103.(4) Concentrations of THg in water were 0.90~2.49 ng/L and 0.71~1.42 ng/L during dry and wet seasons, respectively, while MeHg in water was below the method detection limit. THg in water during both seasons could meet the requirement of Class I criterion of national surface water environmental quality standard(GB 3838-2002).(5) Concentrations of THg in sediments were 95.66~172.52 ng/g and 51.74~90.42 ng/g, while MeHg in the corresponding sediment samples were 0.18~0.39 ng/g and 0.09~0.26 ng/g for dry and wet seasons, respectively. The ratio of MeHg/THg in sediment were relatively small in comparison to other aqueous systems. This might be attributed to the high dissolved oxygen content of bottom water and low organic carbon content of the sediments. THg concentration in pore water of sediments were 5.46~41.04 ng/L and 4.27~9.49 ng/L, and MeHg concentrations were 0.07~1.01 ng/L and 0.09~0.99 ng/L, respectively. THg concentration was significantly higher than that of the overlying water, indicating the diffusion of Hg from the sediment to the water.(6) Concentrations of THg in fish muscle tissues varied from 43.47 to 304.98 ng/g, while MeHg varied from 10.77 to 265.23 ng/g. MeHg in fish muscle tissues could meet the requirement of national food safety standards(GB 2762-2012)(Non carnivorous fish 500 ng/g, Carnivorous fish 1000 ng/g). Bioaccumulation factors of THg were 1.3×105 for Bighead carp, 9.3×104 for Barracuda, 4.7×104 for Crucian carp, 5.0×104 for Sharpbelly, 1.7×105 for Yellow catfish, and 3.9×104 for Arch fish.(7) Referring to the highest background values of heavy metals in global sediment before modern industrialization, the geo accumulation index and the potential ecological risk index calculations reviewed that the pollution level and ecological risk induced by heavy metals in sediments of Xiaolangdi reservoir were low. However, if the geochemical data of sediment in the Yellow River were refered, pollution status of heavy metals I Xiaolangdi reservoir was assessed to be at slight to moderate level, and ecological risk would be medium to strong, with Hg and Cd being the most significant contributors.(8) The health risk caused by genotoxic substances(Cr and As) were 1.82×10-5 a-1 and 5.96×10-5 a-1, respectively. The annual risk values of As and Cr were higher than the levels recommended by the Royal Society, the Swedish Environmental Protection Bureau, and the Construction and Environment Department of Netherlands(1×10-6 a-1) by nearly 20 and 60 times. In addition, the annual risk value of Cr was slightly higher than that recommended by ICRP(5×10-5 a-1). Average annual individual health risk values induced by body toxic heavy metals were 10-10~10-12 a-1, lower than the negligible levels recommended by the Construction and Environemntal Protection Department of Netherlands and the Royal Society. Except for sampling section #2, where health risk induced by heavy metal in water followed an order of Cu>Ni>Mn>Pb>Hg, health risk induced by heavy metals in water of all the other sampling sections followed an order of Cu>Ni>Pb>Mn>Hg. The health risk induced by genotoxic substances was much higher than that induced by body toxic substances.(9) According to the reference dose for MeHg recommended by USEPA, the maximum amount of fish muscule consumed by people would be 50, 90, 150, 190, 190, and 40 g for bighead carp, Barracuda, Crucian carp, Sharpbelly, Arch fish and Yellow catfish, respectively. On the other hand, only 10-30 g of fish muscule could be comsumed by people according to the reference dose for As. Thus it is suggested that sensitive population such as pregnant and breastfeeding women and infants should limit the amount and frequency of fish consumption. Target hazard quotient calculations reviewed that health risk induced by As in fish(except Crucian carp) muscule was high, while that induced by other heavy metals were low. |
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