MICROHOMOGENIZATION OF INDIVIDUAL ZOOPLANKTON SPECIES IMPROVES MERCURY AND METHYLMERCURY DETERMINATIONS

A new method for processing zooplankton improves the accuracy and prec ision of mercury (Hg) and methylmercury (MeHg) determinations and perm its the analysis of Hg species and ancillary variables, such as dry we ight and C, N, and protein contents on subsamples of the same tissue h omogenate using clean technique. In this study, 10-50 individual zoopl ankton were sorted from live samples, homogenized in 500 mu L of low-H g water, subsampled, and then digested for analysis without contaminat ion. Detection limits ranged from 4 to 12 pg for Hg and from 0.8 to 4. 3 pg for MeHg. Procedural blanks averaged 18.7 pg Hg and 5.3 pg MeHg. Yield from certified reference materials was consistently high on smal l masses of tissue homogenate (96% for Hg and 89% for MeHg), and recov ery from spiked samples was good (99% for Hg and 92% for MeHg). We als o present results for Daphnia and Chaoborus from Mud Lake, Wisconsin, processed in this manner. The new method improves our ability to deter mine the distribution of Hg species at lower levels of aquatic food we bs and to investigate factors potentially regulating the bioaccumulati on of Hg and MeHg in specific taxa.