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底栖生物扰动对河口沉积物中甲基汞分布及生物可利用性的影响
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Abstract:
汞是全球广泛分布的有毒重金属。沉积物是汞在水生生态系统中的重要“源”和“汇”，但生物扰动等因素可能通过改变沉积物的理化性质，影响汞的分布和生物可利用性。本研究选取了底栖生物沙蚕作为研究对象，探究了生物扰动对于甲基汞在沉积物中的分布和生物可利用性的影响，并探讨了该影响的机理。研究发现，1) 沙蚕对甲基汞有较强的吸收能力；2) 暴露过程中生物周边沉积物汞含量逐渐升高，并最终高于非周边沉积物，但沙蚕对汞的吸收速率放缓；3) 生物周边沉积物中，有机质含量显著提高，这可能与沙蚕分泌物、掘穴与摄食等活动有关；4) 利用牛血清蛋白对沉积物中汞的生物可利用性评估发现，沉积物生物可利用性随暴露时间降低，这与沙蚕对汞吸收速率的放缓一致。我们推测沙蚕扰动提高了沉积物中有机质含量，增加了周边沉积物与甲基汞结合的能力，从而使得汞的生物可利用性有所下降。
Mercury (Hg) is a toxic heavy metal which widely distributed globally. In aquatic ecosystems, sediment acts as important sink and source for Hg, and its distribution and bioavailability can be affected by many factors, including bioturbation by benthic organisms which can modify the phys-icochemical properties of sediment. In the present study, we chose nereid (Neanthes japonica) as the experimental animal to investigate the effects of bioturbation on methylmercury distribution and bioavailability in estuary sediment, and explored the underlying mechanism. We found that 1) Methylmercury was significantly bioaccumulated by Nereid during exposure. 2) Methylmercury in bioturbated sediment increased gradually during exposure and finally exceeded the methylmercury concentration in non-bioturbated sediment, however, the uptake rate decreased with exposure time. 3) Bioturbated sediment had higher level of organic matter, which might be related with the living activities of benthic organisms, including mucus secretion, burrowing and feeding activities. 4) The bioavailability assessment using Bovine Serum Albumin (BSA) extraction method revealed that the bioavailability of methylmercury in sediment decreased with exposure time, which was consistent with the decreased uptake rate by Nereid. We suggest that bioturbation by Nereid increased the organic content in sediment, which enhanced the binding capacity with methylmercury in the surrounding sediment, thus reducing the bioavailability of methylmercury.
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