三峡库区消落带沉积物对鱼体富集汞的影响

水体环境中的汞（Hg）容易被鱼体富集.为了研究三峡库区消落带沉积物对鱼体Hg含量的影响，采用不同Hg含量的消落带沉积物进行了为期90 d的模拟淹水实验.结果表明沉积物淹水后，水体总汞（THg）和甲基汞（MeHg）含量显著增加，鱼体肌肉中THg和MeHg含量不断增加，而内脏和头部中THg和MeHg含量前期不断增加，后期则有轻微减小的趋势.肌肉对Hg的富集量大于内脏和头部，后两者的富集量没有显著性差异.与对照组（无沉积物）相比沉积物的存在明显增加了鱼体富集Hg的量，而且当沉积物中Hg含量较高时，鱼体对Hg的富集量也显著增加.鱼体各部位THg和MeHg含量变化曲线高度相似，各部位对MeHg的富集系数（bioaccumulation factors，BCF）在1.93×10⁵~8.89×10⁵之间，对无机Hg的BCF在1.3×10³~12.8×10³之间，表明鱼体所富集的Hg形态上主要为MeHg.鱼体各部位MeHg和THg含量均为极显著相关，线性回归方程表明，在富集Hg的量中，MeHg占THg比例分别为：肌肉80.1%、内脏79.3%、头部66.7%.消落带沉积物再淹水后会发生一定程度的净甲基化现象产生MeHg，由于扩散作用使水体MeHg浓度在一段时间内升高，这导致了鱼体对Hg的富集量增加.因此对三峡库区大面积消落带可能存在的Hg污染风险不可忽视.

Effect of Sediments on Bioaccumulation of Mercury in Fish Body in the Water-Level-Fluctuating Zone of the Three Gorges Reservoir Area

Mercury (Hg) in the aquatic environment is easy to accumulate in fish. In order to study the effect of the sediments on Hg accumulation in fish in the water-level-fluctuation zone of the Three Gorges Reservoir, we conducted a 90-days simulated flooding experiment by using the sediments with different concentrations of Hg. Our study showed that the concentrations of the total mercury (THg) and methyl mercury (MeHg) in the overlying water increased after flooding, and the concentrations in the muscle of fish kept increasing in the period of experiment, the concentrations in the viscera and head increased in the earlier period but seemingly decreased in the later period. The bioaccumulated Hg content in the fresh was higher than that in the viscera and head, between which there was no significant difference. Compared with the control group (no sediment), the presence of sediments obviously increased the content of Hg bioaccumulated in fish, and the bioaccumulated Hg level increased with the Hg concentrations in sediment. The THg and MeHg in different fish parts presented a similar variation trend with the BCF ranging 1.93×10⁵-8.89×10⁵ for MeHg and 1.3×10³-12.8×10³ for inorganic mercury, indicating that MeHg was more prone to accumulate in fish. The MeHg in fish was significantly related with THg, and accumulated MeHg occupied about 80.1% (muscle), 79.3% (visceral) and 66.7% (head) of increased THg. After the reflooding of the sediment in the water-level-fluctuating zone, net methylation could occur with MeHg as the product, and then MeHg would diffuse to overlay water, further increasing the Hg bioaccumulation in fish. Therefore, the potential pollution risk of Hg in the water-level-fluctuationg zone with large area of the Three Gorges Reservoir cannot be ignored.