Untargeted Screening and Distribution of Organo-Iodine Compounds in Sediments from Lake Michigan and the Arctic Ocean

The majority of halogenated organic
compounds present in the environment
remain unidentified. To address this data gap, we recently developed
an untargeted method (data-independent precursor isolation and characteristic
fragment; DIPIC-Frag) for identification of unknown organo-bromine
compounds. In this study, the method was adapted to enable untargeted
screening of natural and synthetic organo-iodine compounds (NSOICs)
in sediments. A total of 4,238 NSOIC peaks were detected in sediments
from Lake Michigan. Precursor ions and formulas were determined for
2,991 (71%) of the NSOIC peaks. These compounds exhibited variations
in abundances (<103 to ∼107), m/z values (206.9304–996.9474),
retention times (1.0–29.7 min), and number of iodine atoms
(1–4). Hierarchical cluster analysis showed that sediments
in closer proximity exhibited similar profiles of NSOICs. NSOICs were
screened in 10 samples of sediment from the Arctic Ocean to compare
the profiles of NSOICs between freshwater and marine sediments. A
total of 3,168 NSOIC peaks were detected, and profiles of NSOICs in
marine sediments were clearly distinct from Lake Michigan. The coexistence
of brominated and iodinated analogues indicated that some NSOICs are
of natural origin. Different ratios of abundances of iodinated compounds
to brominated analogues were observed and proposed as a marker to
distinguish sources of NSOICs.