Environmental contextBrominated organic compounds of both natural and anthropogenic origin are commonly found in the environment. Bromine has two stable isotopes and the isotopic composition of brominated compounds may vary depending on production pathways and degradation processes. These variations are a result of isotope fractionation effects, when heavy isotopes react slower than lighter isotopes. We apply compound-specific bromine isotope analysis to industrial brominated organic compounds, and one naturally produced analogue, to test the feasibility of the technique to investigate the source and environmental fate of these compounds. AbstractThe stable bromine isotopic composition (?81Br) was determined for six industrially synthesised brominated organic compounds (BOCs) and one natural BOC by gas-chromatography multi-collector inductively coupled plasma mass spectrometry (GC-mcICP-MS). The ?81Br compositions of brominated benzenes, phenols (both natural and industrial), anisoles, and naphthalenes were constrained with the standard differential measurement approach using as reference a monobromobenzene sample with an independently determined ?81Br value (–0.39‰ v. Standard Mean Ocean Bromide, SMOB). The ?81Br values for the industrial BOCs ranged from –4.3 to –0.4‰. The average ?81Br value for the natural compound (2,4-dibromophenol) was 0.2?±?1.6‰ (1 s.d.), and for the identical industrial compound (2,4-dibromophenol) –1.1?±?0.9‰ (1 s.d.), with a statistically significant difference of ~1.4 (P?<?0.05). The ?81Br of four out of six industrial compounds was found to be significantly different from that of the natural sample. These novel results establish the bromine isotopic variability among the industrially produced BOCs in relation to a natural sample.