Total Microcystin Concentration Variability in Water Samples and Recommended Minimum Volume (20 mL) for Freeze Thaw Cycles

Cyanobacterial harmful algal blooms (cyanoHABs) continue to be a monitoring and research focus, particularly on the occurrence of toxins like total microcystins. The objectives of this study were to evaluate sampling and analytical variability in measured total microcystin concentrations and then to evaluate the volume of raw water needed in the freeze thaw cycle to reduce sampling variability. Water samples were collected from a recreational lake with annual cyanoHABs, and then 2 mL was used in freeze thaw cycles before total microcystin analysis. Then, sample volumes used in the freeze thaw cycles varied from 2 to 300 mL for total microcystin analysis. With three separate experiments, we observed a great deal of sampling variability (when using 2 mL in the freeze thaw cycles) while analytical variability was much less. In fact, sampling variability could potentially account for temporal variability observed in the routine monitoring. However, when sample volume used in the freeze thaw cycles increased, total microcystin variability decreased. We recommend at least 20 mL to be used in the freeze thaw cycles when analyzing total microcystins in environmental samples.