Methylmercury is the Predominant Form of Mercury in Bird Eggs: A Synthesis

• Published in: Environmental science & technology 2013-02, Vol.47 (4), p.2052-2060
• Main Authors: Ackerman, Joshua T, Herzog, Mark P, Schwarzbach, Steven E
• Format: Article
• Language: English
• Subjects: Animal, plant and microbial ecology; Animals; Applied ecology; Aves; Biological and medical sciences; Birds; Charadriiformes; Contamination; Ecotoxicology, biological effects of pollution; Eggs; Environmental Monitoring; Environmental Pollutants - analysis; Fundamental and applied biological sciences. Psychology; General aspects; Mercury; Mercury - analysis; Methylmercury Compounds - analysis; Ovum - chemistry; Risk assessment; Toxicity; Vertebrates: general zoology, morphology, phylogeny, systematics, cytogenetics, geographical distribution
• ISSN: 0013-936X; 1520-5851
• DOI: 10.1021/es304385y

Bird eggs are commonly used in mercury monitoring programs to assess methylmercury contamination and toxicity to birds. However, only 6% of >200 studies investigating mercury in bird eggs have actually measured methylmercury concentrations in eggs. Instead, studies typically measure total mercury in eggs (both organic and inorganic forms of mercury), with the explicit assumption that total mercury concentrations in eggs are a reliable proxy for methylmercury concentrations in eggs. This assumption is rarely tested, but has important implications for assessing risk of mercury to birds. We conducted a detailed assessment of this assumption by (1) collecting original data to examine the relationship between total and methylmercury in eggs of two species, and (2) reviewing the published literature on mercury concentrations in bird eggs to examine whether the percentage of total mercury in the methylmercury form differed among species. Within American avocets (Recurvirostra americana) and Forster’s terns (Sterna forsteri), methylmercury concentrations were highly correlated (R 2 = 0.99) with total mercury concentrations in individual eggs (range: 0.03–7.33 μg/g fww), and the regression slope (log scale) was not different from one (m = 0.992). The mean percentage of total mercury in the methylmercury form in eggs was 97% for American avocets (n = 30 eggs), 96% for Forster’s terns (n = 30 eggs), and 96% among all 22 species of birds (n = 30 estimates of species means). The percentage of total mercury in the methylmercury form ranged from 63% to 116% among individual eggs and 82% to 111% among species means, but this variation was not related to total mercury concentrations in eggs, foraging guild, nor to a species life history strategy as characterized along the precocial to altricial spectrum. Our results support the use of total mercury concentrations to estimate methylmercury concentrations in bird eggs.