Methylmercury, total mercury and total selenium in four common freshwater fish species from Ya-Er Lake, China

Snakehead fish (Ophiocephalus argus cantor), silver carp (Hypophthalmichthys molitrtix), crucian carp (Carassius carassius), and common carp (Cyprinus carpio) are four common freshwater fish species in China. In this study, the level of methylmercury (MeHg), total mercury (T-Hg), and total selenium (T-Se) in muscle samples of these four fish species from Ya-Er Lake, China, were analyzed using atomic fluorescence spectrometry coupled with high-performance liquid chromatography, and inductively coupled plasma mass spectrometry. The concentrations of MeHg in all the fish species were significantly correlated with those of T-Hg. Higher T-Hg and MeHg concentrations had accumulated in the snakehead fish, which is a strongly predatory fish, than in the other three species. The concentration ratios of MeHg and T-Hg in the muscles of these four fish species were almost equal. Conversely, there was negative correlation between the concentrations of T-Hg and T-Se, which implies that there is a competition between these two elements with respect to bioaccumulation. It is noteworthy that of all the muscle samples tested, the level of T-Hg exceeded the maximum allowable limit in fish [0.4 mg kg(-1) (w/w) recommended by the World Health Organization] in 38.46% of those of the silver carp, 18.18% of those of the crucian carp, and 100% of those of snakehead fish. These results show that the consumption of contaminated fish is a potential threat to human health and that necessary preventive measures to safeguard public health should be emphasized.

Determination of Hg(II) in waters by on-line preconcentration using Cyanex 923 as a sorbent - Cold vapor atomic absorption spectrometry

Using a solid phase extraction mini-column home-made from a neutral extractant Cyanex 923, inorganic Hg could be on-line preconcentrated and simultaneously separated from methyl mercury. The preconcentrated Hg (11) was then eluted with 10% HNO3 and subsequently reduced by NaBH4 to form Hg vapor before determination by cold vapor atomic absorption spectrometry (CVAAS). Optimal conditions for and interferences on the Hg preconcentration and measurement were at 1% HCl, for a 25 mL sample uptake volume and a 10 mL min(-1) sample loading rate. The detection limit was 0.2 ng L-1 and much lower than that of conventional method (around 15.8 ng L-1). The relative standard deviation (RSD) is 1.8% for measurements of 40 ng L-1 of Hg and the linear working curve is from 20 to 2000 ng L-1 (with a correlation coefficient of 0.9996). The method was applied in determination of inorganic Hg in city lake and deep well water (from Changchun, Jilin, China), and recovery test results for both samples were satisfactory.

气候变化对高纬度流域中汞和甲基汞迁移转化的影响——以降水量增加为例

全球变化的研究发现：19世纪以来全球平均气温大约上升了0.6℃，并预计在21世纪会升高更多。温室效应的直接结果是导致全球地面增温，温度的升高会增加下垫面的蒸发量。根据全球水平衡原理，蒸发量应该与降水量相等，因而降水量也会相应增加。气候变化的情景模式研究表明，世界各地雨量变异大，在高纬度地区，包括北欧地区，降水会增加。 流域是水生系统的一个重要的汞和甲基汞的输入源。欧洲淡水系统中，鱼体汞含量过高的湖泊主要局限于北方的高纬度森林地区。在斯堪的纳维亚半岛，就有上万湖泊中的鱼体汞含量超过了健康食用标准0.5 mg/kg。水生系统甲基汞输入源包括：水体或沉积物通过甲基化形成甲基汞，通过大气干、湿沉降输入的甲基汞和陆地生态系统的地表径流输入的甲基汞。 本研究的主要目标是搞清楚未来气候变化引起的大气降水量的增加对北方高纬度森林流域土壤中汞的迁移和形态转化有何影响。未来大气降水量的增加可能会增强森林地区流域土壤中汞的迁移，进而对水生系统的汞循环产生影响。一方面，如果地下水水位上涨，当水流过富含有机质结合含汞土壤层时，将会增加土壤中汞和甲基汞的迁移性，由此而导致流域向河流、湖泊等水生系统中汞输出通量的增加。另一方面，氧化还原电位改变、DOC和营养物质的释放会加剧汞在土壤中的释放过程，并且可能会促进汞的形态转化，可能增加毒性较强的甲基汞的产量，最终导致甲基汞从土壤向水生系统的输出通量的增加。 本研究选择瑞典西海岸花园湖（Gårdsjön）的G1流域作为研究对象，在流域内进行人工模拟增加降雨试验，模拟未来气候变化降水量增加的情景，观测流域地表径流中汞和甲基汞的变化。并在流域内选择四个点（1×1m²），进行汞同位素加入示踪试验。测定土壤剖面甲基汞和总汞及其同位素组成，来分析汞的迁移和形态转化。主要研究结果如下： 1. 通过对G1流域土壤中甲基汞分布的调查，发现甲基汞含量范围为0.020-3.1ng/g，甲基汞含量与TOC含量具有正相关的关系，表明土壤甲基汞的迁移受TOC迁移的影响。估算G1流域的甲基汞储库通量为123g/km2，G1流域甲基汞储库容为0.65g。 2. 通过甲基汞含量和甲基汞储库在土壤剖面的分布，可以看出表层腐殖质层甲基汞浓度最高，甲基汞最富集，而在较深的土壤层位甲基汞储库容量最大，表明甲基汞具有向下迁移的趋势。 3. 根据总汞同位素组成结果，汞同位素（198Hg(NO3)2）加入土壤中后，202Hg/198Hg比值迅速下降，然后随时间推移而上升，表明加入土壤中的汞与土壤中原始汞形态不同，具有不同的迁移方式，且加入土壤中二价汞的迁移性比土壤中的原始汞更强。计算表明，外界加入的汞，将有50-60%长期滞留在土壤中。 4. 根据甲基汞的同位素组成结果，Wet点的新加入的198Hg甲基汞分数要大于其它三点，表明湿润土壤中汞甲基化速率要快于较干燥的土壤中。另外，Wet点的甲基汞分数比以前无人工模拟增加降雨的同位素示踪结果高很多，表明降水量增加会导致汞的甲基化作用在土壤中的形态转化过程中占主导地位，最终导致甲基汞产率的提高。 5. 人工模拟增加降雨试验进行后，地表径流中总汞的浓度没有发生变化，而甲基汞的浓度增大了很多，从0.03ng/L增大到了1ng/L以上，表明降水的增加可以促进土壤中汞的甲基化作用。 6. 地表径流向流域外总汞和甲基汞的输出量的计算显示，受人工模拟增加降雨的影响，流域地表径流量也会增加，最终年地表径流中总汞和甲基汞的输出通量都变大。