, 2005). Hydrogen sulphide is acutely toxic with fatalities associated with concentrations in excess of 500 ppm. It has a very low odour threshold (0.008 ppm) but odour perception is lost at concentrations of 150–250 ppm (WHO, 2000), adding to the danger of high level exposures as they may not be recognised, by smell, by the individual. In Europe, there is a workplace exposure limit (8 h TWA) of 5 ppm (HSE, 2011 and SCOEL, 2007) with a

short-term (15-min) exposure limit of 10 ppm. Hydrogen sulphide has previously been reported as a causal agent of unconsciousness and death in a number of occupational exposure incidents (Kage et al., 2002 and Kage et al., 2004). In the UK it has been reported (Costigan, 2003) that around 125,000 workers in the UK are potentially exposed to hydrogen sulphide in work related to the treatment of sewage, effluent waste and farm slurry. check details In the offshore oil and gas industries about 3000 workers are potentially exposed. The UK Health and ATM/ATR activation Safety Executive has investigated several incidents of workplace accidents involving hydrogen sulphide exposure from slurry pits, animal rendering plants and biodigester facilities

in recent years. The increased prevalence of biodigesters and slurry storage may indicate an increased likelihood of further incidents in the future. Here we report three case studies using biological monitoring to determine hydrogen sulphide exposure. Blood or urine thiosulphate determination was carried out according to the method of Kage et al. (1991). Briefly, samples (200 μl) were buffered with ascorbic acid (200 mM, 50 μl) and 5% sodium chloride (50 μl) then derivatised using pentafluorobenzyl bromide (20 mM in acetone, 500 μl) and extracted into iodine ethyl acetate solution (25 mM, 2 ml) to form bis(pentafluorobenzyl)

disulphide. Tribromobenzene was used as an internal standard. Analysis was by gas chromatography–mass spectrometry (positive electron ionisation) using selected ion monitoring (m/z 426 for the thiosulphate derivative). Aliquots (1 μl) were injected (220 °C, splitless) onto a BP-5 equivalent column (30 m × 0.32 mm i.d., 1 μm film) with a helium flow of 1 ml/min. The oven temperature many was held at 100 °C for 2 min then ramped at 10 °C/min up to 220 °C, where it was held for 5 min. Calibration standards were prepared in blood or urine, as appropriate, and extracted as per the samples. The calibration curves were linear from 0 to 600 μmol/l (least squares regression > 0.99) and quality control samples were within the expected range showing a coefficient of variation of 12%. The detection limit was 1 μmol/l. Urine samples were also analysed for creatinine content using the alkaline picrate reaction ( Cocker et al.