Pickhardt Paul C, Folt Carol L, Chen Celia Y, Klaue Bjoern, Blum Joel D
Department of Biological Sciences, Dartmouth College, Hanover, NH 03755, USA.
Sci Total Environ. 2005 Mar 1;339(1-3):89-101. doi: 10.1016/j.scitotenv.2004.07.025.
There is a well documented accumulation of mercury in fish to concentrations of concern for human consumption. Variation in fish Hg burden between lakes is often high and may result from differences in Hg transfer through lower levels of the food web where mercury is bioconcentrated to phytoplankton and transferred to herbivorous zooplankton. Prior research derived patterns of mercury accumulation in freshwater invertebrates from field collected animals. This study provides results from controlled mesocosm experiments comparing the effects of zooplankton composition, algal abundance, and the chemical speciation of mercury on the ability of zooplankton to accumulate mercury from phytoplankton and transfer that mercury to planktivores. Experiments were conducted in 550-L mesocosms across a gradient of algal densities manipulated by inorganic nutrient additions. Enriched, stable isotopes of organic (CH3(200HgCl)) and inorganic (201HgCl2) mercury were added to mesocosms and their concentrations measured in water, seston, and three common zooplankton species. After 2 weeks, monomethylmercury (MMHg) concentrations were two to three times lower in the two copepod species, Leptodiaptomus minutus and Mesocyclops edax than in the cladoceran, Daphnia mendotae. All three zooplankton species had higher MMHg concentrations in mesocosms with low versus high initial algal abundance. However, despite higher concentrations of inorganic mercury (HgI) in seston from low nutrient mesocosms, there were no significant differences in the HgI accumulated by zooplankton across nutrient treatments. Bioaccumulation factors for MMHg in the plankton were similar to those calculated for plankton in natural lakes and a four-compartment (aqueous, seston, macrozooplankton, and periphyton/sediments) mass balance model after 21 days accounted for approximately 18% of the CH3(200Hg) and approximately 33% of the 201Hg added. Results from our experiments corroborate results from field studies and suggest the importance of particular zooplankton herbivores (e.g., Daphnia) in the transfer of Hg to higher trophic levels in aquatic food webs.
鱼类体内汞的积累情况已有充分记录，其浓度已达到令人担忧的程度，会对人类食用造成影响。不同湖泊中鱼类汞负荷的差异通常很大，这可能是由于汞在食物网较低层级的转移存在差异，汞在这些层级被生物浓缩到浮游植物中，然后转移到食草性浮游动物体内。先前的研究从野外采集的动物中得出了淡水无脊椎动物体内汞积累的模式。本研究提供了来自受控中宇宙实验的结果，该实验比较了浮游动物组成、藻类丰度以及汞的化学形态对浮游动物从浮游植物中积累汞并将汞转移到食浮游动物体内能力的影响。实验在550升的中宇宙中进行，通过添加无机养分来控制藻类密度梯度。向中宇宙中添加了富集的、稳定同位素标记的有机汞（CH3(200HgCl)）和无机汞（201HgCl2），并测量了它们在水、悬浮颗粒以及三种常见浮游动物物种中的浓度。两周后，两种桡足类动物，即微小细镖水蚤和近亲中剑水蚤体内的一甲基汞（MMHg）浓度比枝角类动物门多塔水蚤低两到三倍。在初始藻类丰度低的中宇宙中，所有三种浮游动物物种的MMHg浓度都高于初始藻类丰度高时的情况。然而，尽管来自低养分中宇宙的悬浮颗粒中无机汞（HgI）浓度较高，但不同养分处理下浮游动物积累的HgI没有显著差异。浮游生物中MMHg的生物积累因子与天然湖泊中浮游生物的计算值相似，一个四室（水相、悬浮颗粒、大型浮游动物和周丛生物/沉积物）质量平衡模型在21天后解释了添加的CH3(200Hg)的约18%和201Hg的约33%。我们实验的结果证实了野外研究的结果，并表明特定的浮游动物食草动物（如多塔水蚤）在水生食物网中汞向更高营养级转移方面的重要性。
