Determination of Threshold Levels of Sour Gas and H 2 S on the Mammalian Brain Funding Agreement Number BC Oil and Gas Commission Sheldon H. Roth Faculty of Medicine University of Calgary

Objectives of Study to determine threshold levels of hydrogen sulphide (H 2 S), sour gas and H 2 S/organic compound mixtures i.e. the Lowest Observable Adverse Effect Levels (LOAELs) and the No Observable Adverse Effect Levels (NOAELs) to evaluate the differences of effects between H 2 S alone and as a component of sour gas on in vivo and in vitro mammalian central nervous systems (CNS)

Hydrogen Sulphide (H 2 S) extremely toxic gas environmental & industrial pollutant produced by variety of human and natural processes produced endogenously in mammals

Hydrogen Sulphide colourless heavier than air flammable characteristic “rotten egg” odour odor threshold 0.5 ppb olfactory fatigue > 100 ppm ATSDR 1999 H 2 S Health Research & Risk Assessment Symposium 2000

H 2 S exposure “one of the leading causes of sudden accidental death in the workplace” affects many organ systems (broad spectrum toxicant) effects dependent on concentration, duration and rate of exposure organs with high O 2 demand - most susceptible

Broad spectrum effects of H 2 S nervous system (brain) lung heart reproductive & developing systems eye metabolic systems smell (olfactory)

Roth Env Epidemiol Toxicol 1999 Dose Response of H 2 S

Effects of H 2 S (low level exposure) eye, nose & throat irritation headache, sinus, etc nausea hoarseness, cough nasal congestion shortness of breath stress drowsiness Schiffman H 2 S Health Research & Risk Assessment Symposium 2000

Effects of H 2 S exposure on the nervous system (brain) mental depression irritability loss of memory lethargy dizziness loss of appetite fatigue headache memory Fundamentals of Neuroscience 1999

Amaral & Witter, 1989 functions of the hippocampus memory storage cognitive function sensory processing voluntary movements hippocampus

PS = amplitude of population spike placement of stimulating & recording electrodes Recording from hippocampus

Methods prepare rat hippocampal slices place slices in recording chamber activate excitatory synaptic inputs to CA1 pyramidal neurons record field potentials (PS) of CA1 neurons apply H 2 S gas (in nitrogen) analyze data using custom software

Interscan Corporation 4000 Series Compact Portable Analyzer ppb 1 ppb resolution electrochemical voltammetry sensor Monitor

control experiments nitrogen

Exposure to 50 ppm H 2 S

25 ppm H 2 S Exposure to 25 ppm H 2 S

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1 ppm H 2 S Exposure to 1 ppm H 2 S

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500 ppb H 2 S

Dose response curve - H 2 S

Nicholson et al J Toxicol Environ Health A 1998 cytochrome c oxidase whole brain IC 50 = 0.13 µM Inhibition of Respiratory Mechanisms

J Toxicol Environ Health A 1998

Conclusions long-lasting synaptic enhancement occurs following exposure to low levels of H 2 S effects appear to be concentration- dependent inhibition of respiratory enzymes (cytochrome oxidase, carbonic anhydase) confirmed effects may account for symptoms such as anxiety and cognitive impairment

Acknowledgements Investigators Ron Bennington James Brooks Russell Nicholson (SFU) Lisa Partlo R.S. Sainsbury Barbara Skrajny Lisa Strosher Steven Ip Ricardo Bonafine Peter O’Brien (U of T) D.P. Archer Funding BC Oil & Gas Commission Medical Research Council of Canada Alberta Heritage for Medical Research University of Calgary

Future Experiments H 2 S experiments in ppb range S. Ip Sour gas experiments S. Ip whole animal (in vivo) studies Dr. R. Bonafine further studies on respiratory enzymes Dr. P. O’Brien University of Toronto

Sour Gas

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