Arsenic speciation in more than 1600 freshwater fish samples from fifty-three waterbodies in Alberta, Canada

•1638 of 1643 freshwater fish samples (99.7%) had detectable concentrations (>0.25 µg/kg) of arsenobetaine.•1514 samples (92.1%) had detectable concentrations of dimethylarsinic acid.•Inorganic arsenate was detectable in 68.1% or 1119 fish samples, and its concentration was lower in northern pike than in lake whitefish and walleye.•Monomethylarsonic acid was detectable (> 0.25 µg/kg) in 25.4% or 418 fish samples.•Seven unknown arsenic species were detected, with 33.4% (549 of 1643) samples containing at least one unknown. We report here arsenic speciation in 1643 freshwater fish samples, representing 14 common fish species from 53 waterbodies in Alberta, Canada. Arsenic species were extracted from fish muscle tissue. Arsenic species in the extracts were separated using anion-exchange high-performance liquid chromatography (HPLC) and quantified using inductively coupled plasma mass spectrometry (ICPMS). The total arsenic concentrations in fish ranged from 2.8 to 1200 µg/kg (in wet weight of sample) (mean 71 ± 101 µg/kg), which are all below the 2000 µg/kg (wet weight) maximum allowable total arsenic in fish, recommended by the Ontario Ministry of the Environment. In 99.7%, or 1638 of all 1643 freshwater fish samples analyzed, arsenobetaine (AsB) was detectable, with concentrations higher than the method detection limit of 0.25 µg/kg (wet weight). Dimethylarsinic acid (DMA) was detectable (concentration >0.25 µg/kg) in 92.1%, or 1514 of the 1643 freshwater fish samples. Inorganic arsenate (iAsV) was detectable (>0.25 µg/kg) in 1119 fish (i.e., 68.1% of 1643 samples). Monomethylarsonic acid (MMA) was detectable (>0.25 µg/kg) in 418 fish (25.4% of 1643 samples). The concentrations of arsenic species in the 1643 fish samples varied by as much as three orders of magnitude, ranging from below the method detection limit of 0.25 µg/kg to the maximum concentrations of 380 µg/kg for AsB, 150 µg/kg for DMA, 70 µg/kg for iAsV, and 51 µg/kg for MMA. AsB made up 46.1% ± 26.2% of total arsenic species. Arsenic speciation patterns varied between lake whitefish, northern pike, and walleye, the three most common types of fish analyzed. The relative proportion of DMA in northern pike was larger than in lake whitefish and walleye, and conversely, the relative proportion of iAsV was lower in northern pike. Seven unknown arsenic species were detected, and their chromatographic retention time did not match with those of available arsenic standards. At least one unknown arsenic sp