Microcystin concentration equivalent by PPI assay rt-QPCR for mcyE Negative (<0.05 μg/L) 0.05 μg/L ≤ Microcystin < 1 μg/L Microcystin ≥ 1 μg/L Total Negative 1 4 0 5 Positive 2 9 4 15 Taotal 3 13 4 20

Table 2: rt-QPCR and PPI results of 20 reference samples.