Michael Durand

Thiosulfate in human urine following minor exposure to hydrogen sulfide: implications for forensic analysis of poisoning

Thiosulfate is a sulfide metabolite and a biological marker, especially in urine, of exposure to hydrogen sulfide gas (H2S). In many suspected poisoning cases, victims are known to be exposed to low concentrations of H2S, but it is difficult to establish the degree of exposure to H2S responsible for the poisoning. In such cases it is necessary to account for a possible chronic exposure signal by subtracting any background thiosulfate from the measured total. However, no data exist on the background levels of thiosulfate in individuals exposed to relatively low levels of H2S. We obtained preexposure and postexposure urine thiosulfate data from eight individuals exposed to H2S in the ppb to low ppm range. Mean thiosulfate concentrations in urine increased from 4.6 to 11.5 μmol/l following exposure (P ≤ 0.05). When normalized against creatinine, mean thiosulfate increased from 7.2 to 9.8 μmol/mol (P ≤ 0.05). However, positive changes were not consistent between individuals. Whilst these findings support the idea that relatively minor exposures to H2S can be confirmed by thiosulfate in urine, it also suggests that the response of this biomarker to minor H2S exposure may vary significantly between individuals.