摘要
最近我们对美国东南部地区许多水域系统肉食性鱼类身上可能造成健康危险的超标汞(Hg)含量进行了测量。根据从出版的有关汞的水地球化学的实验数据得出的假设,我们调查了某些自然和人为的条件对莫尔比-亚拉巴马河系(MARS)中现场甲基汞(MeHg)含量的影响。从不同类型的环境采集了水样,假设这些水样具有不同的水甲基汞含量,并分析了总汞(THg)和甲基汞浓度以及一些主要的地球化学参数。结果如下:①总的来说,莫比尔-亚拉巴马河系水域中的总汞浓度分布相当均匀,从0.2ng/L到6ng/L不等,表明除了地质来源外,大气沉降肯定是所研究的水系中汞输入的主要来源。②在具有可比较的总汞含量的地点,以甲基汞形式存在的汞部分在从莫比尔-亚拉巴马河系的沿岸平原部分采集的样品中的含量始终比从其他地质区域采集的样品中的高。③我们的现场观测证实了从实验室试验获得的结论,即:甲基汞在水域系统中的丰度与硫酸盐(但只是在较窄的浓度范围内)有关,以及与pH的减少相关,而与硝酸盐或磷酸盐均无直接的关系。④对单一场所生物区中汞的累积的调查表明,在总汞浓度较低但甲基汞/总汞之比较高的水域系统中,生物的汞含量可能超出安全界限。因此,即使水相没有显示出有汞严重富集的迹象,也可能存在对食鱼人群的潜在健康威胁。
Mercury (Hg) concentrations above levels that could pose health risks have been measured recently in predatory fish from many aquatic systems in the southeastern region of the United States.Based on hypotheses derived from published experimental data on the aqueous geochemistry of Hg,we investigated the effect of certain natural and human-imposed conditions on in situ levels of methylmercury (MeHg) in the Mobile-Alabama River System (MARS).Water samples were collected from different types of environments,hypothesized to have contrasting levels of MeHg in the aqueous phase,and were analyzed for total-Hg (THg) and MeHg concentrations,as well as some key geochemical parameters.The results showed the following,i) Overall,total Hg concentrations in waters of the MARS are quite uniformly distributed and vary from 0.2 to 6 ng L^(-1),suggesting that besides geological sources,atmospheric deposition is certainly the main source of Hg inputs in the studied system,ii) In locations with comparable THg levels,the Hg fraction present as MeHg was consistently higher in samples collected from the Coastal Plain portion of the MARS as compared to those from other geological provinces,iii) Our in situ observations confirmed conclusions derived from laboratory experiments,in that,MeHg abundance in aquatic systems correlates with sulfate (but only within a narrow range of concentrations);decreasing pH;and has no direct relationships with either nitrate or phosphate,iv) The investigation of Hg accumulation in biota at a single site showed that an aquatic system with low THg concentrations but a high MeHg:THg ratios, could have organisms with Hg content above safe levels.Therefore,potential health risks to fish eating populations can exist even when the aqueous phase does not show signs of significant Hg enrichment.
