3.3. Case 3
One urine sample and one blood sample were received from a fatality (male, age unknown) involving a biodigester, where hydrogen sulphide was a suspected toxic agent. The urine sample was below the detection limit for thiosulphate. The blood sample had a detectable thiosulphate level of 22 μmol/l.
The blood level reported is at the lower end of the scale of previously reported fatalities (25–230 μmol/l) but definitely indicates significant hydrogen sulphide exposure – sufficient to cause unconsciousness, and possibly fatal poisoning. No thiosulphate was detected in urine, which is consistent with literature reports of sudden death caused by hydrogen sulphide (Kage et al., 2002) whereas survivors of hydrogen sulphide poisoning incidents tend to have raised urinary thiosulphate levels in the hours following the incident as thiosulphate is excreted.
It can therefore be concluded that the results of the thiosulphate analysis from blood and urine samples are consistent with acute hydrogen sulphide poisoning causing death rapidly. However, it should be noted that these analyses were conducted some nine months after the incident occurred. The samples were previously stored by a third party and thought to have been refrigerated. There have been reports that sulphide can be generated post-mortem in blood and other tissues (Nagata et al., 1990) and this can then be converted to thiosulphate within the sample (Tsuge et al., 2000). However, it has also been reported that refrigerated storage suppresses such post-mortem sulphide production (Nagata et al., 1990) which would therefore support the conclusion of acute hydrogen sulphide poisoning in this case.