Comparison of Two Total Mercury Screening and Assessment Methods in Fishes: Biopsy Punch and Dried Muscle Samples

Rapid and effective quantification of total mercury concentrations ([THg]) in fish muscle is an important part of ongoing monitoring to provide reliable and near real-time public health guidance. Methods for quantifying THg in fish muscle frequently require the use of large sample mass and numerous preparation steps. Wet (aka fresh weight) biopsy punch samples of fish muscle have been used to quantify THg directly, without drying and homogenization. Both methods have advantages and disadvantages. We compare the use of fresh weight biopsy punches for quantifying THg to using larger, dried homogenized samples. The [THg] determination for the two sampling methods was EPA method 7473. Three separate biopsy punch samples and a large muscle sample were taken from each fish and analyzed on a Direct Mercury Analyzer. There were no statistical differences between mean log transformed wet weight [THg] from biopsy punches and homogenized muscle across all samples or within individual species. Similarly, across the range of [THg] (7.5-612.7 ng/g ww), linear regression of [THg] from biopsy punch and homogenized muscle samples was not different from a 1:1 linear relationship. Linear regression statistics of [THg] with fish fork length produced similar results for both biopsy punch and homogenized muscle samples. However, the coefficient of variation among biopsy punch replicates for individual fish was frequently above the acceptable threshold of 15%. We recommend biopsy punches be used as an effective tool for broad-scale rapid monitoring of fish resources for Hg, while homogenized muscle samples be used for fine-scale ecological and health questions.