Measuring Total Mercury Through Freeze-Thaw Cycles

Total mercury (THg) analysis of fish tissue requires the samples to be frozen for long-term storage or analyzed immediately after the fish sample has been obtained. Such rigid field sampling protocols do not account for the logistical challenges that can occur if sampling is conducted in remote areas or collaboratively via community-based monitoring initiatives. Here we present a study that examines the loss of THg from Walleye tissue that has thawed for 3 and 5 days, mimicking potential thaw during transport from remote locations. THg concentrations were not significantly influenced (Kruskal-Wallace, p-value > 0.05) by the thaw and refreeze events. The mean THg concentration per day group was 0.67 ug/g, SD = 0.03, 0.65 ug/g, SD = 0.01, and 0.72 ug/g, SD = 0.01 for the control (no thaw), 3-day thaw and 5-day thaw, respectively. Results from this study suggest the analytical integrity of samples may be maintained if freeze-thaw situations arise when conducting community-based mercury monitoring programs.