Rothenberg Sarah E, Ambrose Richard F, Jay Jennifer A
Environmental Science and Engineering Program, Department of Environmental Health Sciences, University of California, Los Angeles, California 90095, USA.
Environ Sci Technol. 2008 Aug 1;42(15):5400-6. doi: 10.1021/es702819f.
Of the approximately 780 U.S. EPA approved mercury total maximum daily loads (TMDLs), most specify a reduction in total mercury (Hg(T)) loads to reduce methylmercury levels in fish tissue, assuming a 1:1 correspondence. However, mercury methylation is more complex, and therefore, proposed load reductions may not be adequate. Using multiple regression with microlevel and macrolevel variables, the potential efficacy of mercury TMDLs on decreasing aqueous methylmercury levels was investigated in four coastal watersheds: Mugu Lagoon (CA), San Francisco Bay Estuary, Long Island Sound, and south Florida. Hg(T) and methylmercury levels were positively correlated in all watersheds except in Long Island Sound, where spatial differences explained over 40% of the variability in methylmercury levels. A mercury TMDL would be least effective in Long Island Sound due to spatial heterogeneity but most effective in south Florida, where the ratio between aqueous Hg(T) and methylmercury levels was close to 1 and the 95% confidence interval was narrow, indicating a probable reduction in aqueous methylmercury levels if Hg(T) loads were reduced.
在美国环境保护局（EPA）批准的约780个汞的总最大日负荷量（TMDL）中，大多数规定了降低总汞（Hg(T)）负荷量，以降低鱼类组织中的甲基汞水平，前提是假设二者存在1:1的对应关系。然而，汞的甲基化更为复杂，因此，提议的负荷量减少可能并不足够。通过使用包含微观和宏观变量的多元回归分析，在四个沿海流域研究了汞TMDL对降低水体中甲基汞水平的潜在效果：穆古泻湖（加利福尼亚州）、旧金山湾河口、长岛海峡和南佛罗里达。除了长岛海峡外，所有流域中的Hg(T)和甲基汞水平均呈正相关，在长岛海峡，空间差异解释了甲基汞水平超过40%的变异性。由于空间异质性，汞TMDL在长岛海峡的效果最差，但在南佛罗里达效果最佳，在那里水体中Hg(T)与甲基汞水平的比值接近1，且95%置信区间很窄，这表明如果降低Hg(T)负荷量，水体中甲基汞水平可能会降低。
