Figure 2:

Calculated mass loads (mg/d) of each neonicotinoid in the effluent (gray circles) and at downstream 2 (DS2, green diamonds) for all sampling dates (8/24/2018–8/29/2019). Mass loads are determined from individual grab samples concentrations (representing an instantaneous measurement), the daily processed flow from the North Liberty WWTP and the flow rate at the DS2 gaging station (USGS) during time of sampling. The daily mass loads were calculated using flow rates and concentrations at each location for the day (assumed due to sampling under base flow conditions). A total of n=17 effluent and n=18 DS2 samples were used in statistical analysis. Of the mass loads used for statistics, thiamethoxam was not detected in n=4 effluent and n=1 DS2 samples, while imidacloprid urea was not detected in n=3 effluent samples. Where a neonicotinoid was not detected, the value of ½LLD was used in when calculating the mass load (omitted from figure). Data distribution (median and interquartile ranges) and p-values reflect all data. Note that imidacloprid urea is a transformation product of imidacloprid while clothianidin is sometimes a transformation product of thiamethoxam.