Microhomogenization of individual zooplankton species improves mercury and methylmercury determinations

A new method for processing zooplankton improves the accuracy and precision of mercury (Hg) and methylmercury (MeHg) determinations and permits the analysis of Hg species and ancillary variables, such as dry weight and C, N, and protein contents on subsamples of the same tissue homogenate basing clean technique. In this study, 10-50 individual zooplankton were sorted from live samples, homogenized in 500 pL of low-Hg water, subsampled, and then digested for analysis without contamination. Detection limits ranged from LC to 12 pg for Hg and from 0.8 to 4.3 pg for MeHg. Procedural blanks averaged 68.7 pg Hg and 5.3 pg MeHg. Yield from certified reference materials was consistently high on small masses of tissue homogenate (96% for Hg and 89% for MeHg), and recovery from spiked samples was good (99% for Hg and 92% for MeHg). We also present results for Daphnia and Chaoborcfs from Mud Lake, Wisconsin, processed in this manner. The new method improves our ability to determine the distribution of Hg species at lower levels of aquatic food webs and to investigate factors potentially regulating the bioaccumulation of Hg and MeHg in specific taxa. RCsumC : Une nouvelle mCthode de traitement du zooplancton arnCZiore l'exactitude et la prCcision des dosages du mercure (Hg) et du mCthylmercure (MeHg), et permet l'analyse des espkces de Hg et des variables secondaires, comrne le poids sec, le carbone, l'azote et les protCines dans des