Download as file - Meetings, agendas, and minutes

ANNEX 1
Key points raised by the Health Protection Agency on Hydrogen
sulphide and the odour threshold and health effects relating to
Finmere Quarry Landfill, Finmere, Oxfordshire
1.
Background
Following odour arising from the Finmere Quarry Landfill, the Environment Agency
approached the Health Protection Agency for information on hydrogen sulphide and
the possible health effects when exposed to elevated concentrations.
Currently there is a temporary cap over the waste with some landfill gas control by
venting and some by flaring. There have been odour complaints from the site up to 2
km from the site boundary.
2.
Odour Threshold and Health Effects
2.1.
Odour threshold values
Several authors have reported odour detection thresholds ranging from 0.0005 to
0.13 ppm. The duration of exposure in these studies ranged from a few seconds to
less than a minute.
The odour threshold is the lowest concentration of a vapour in air which can be
detected by smell but this threshold will vary considerably depending on individual
sensitivity. The characteristic “rotten egg” odour of hydrogen sulphide (0.2 to 0.3
ppm) is an important aspect of the toxicology of the gas as it can be a very good
indicator of its presence in low concentrations. However at higher concentrations
(150 ppm) the gas exerts a paralyzing effect on the olfactory system (sense of smell)
and thus the value of odour as a warning signal is lost.
2.2.
International Recommendations
Hydrogen sulphide in ambient air concentrations at the odour thresholds 0.0005 to
0.13 ppm has not been shown to have any systematic biological activity in man or
animals. In terms of odour nuisance the World Health Organisation has reported that
an odour threshold of 0.005 ppm averaged over 30 minutes should not produce
odour nuisance in most situations. It is possible to adopt longer averaging times with
appropriately adjusted concentration limits.
2.3.
AEGL Programme
Acute Exposure Guideline Levels, or AEGLs, are intended to describe the risk to
humans resulting from once-in-a-lifetime, or rare, exposure to airborne chemicals
over short periods of time. The National Advisory Committee for AEGLs is
developing these guidelines to help both national and local authorities, as well as
private companies, deal with emergencies involving spills, or other catastrophic
exposures. Within this system level 1 (AEGL 1) indicates the threshold above which
exposure may lead to discomfort, level 2 the threshold for serious effects and level 3
the level above which exposure may be life threatening.
565337124
PN8 - page 2
AEGL 1
AEGL 2
AEGL 3
3.





(Interim)
4 hr
0.36
20
37
8 hr
0.33
17
31
Hydrogen Sulphide Toxicology
3.1.


Hydrogen sulphide 7783-06-4
Ppm
10 min
30 min
60 min
0.75
0.60
0.51
41
32
27
76
59
50
Summary of Human Toxicity
Hydrogen sulphide has a characteristic pungent ‘rotten egg’ odour
Hydrogen sulphide is rapidly absorbed almost exclusively by inhalation and it is a
respiratory toxin
It is irritant to the respiratory tract, eyes and skin
It reacts with surface moisture of mucous membranes to form sodium sulphide
which produces the irritant effect
Metabolism of hydrogen sulphide involves three different pathways; oxidation to
sulphate (thought to be the major metabolic pathway) and methylation both of
which represent detoxification with the major conversion site being the liver and
reaction with proteins which accounts for the toxic action of hydrogen sulphide
Hydrogen sulphide toxicity is considered to be due primarily to the reversible
inhibition of cytochrome oxidase which impairs cell respiration
At high concentrations (0.1 to 0.2% in the atmosphere) it causes rapid collapse,
respiratory paralysis, imminent coma followed by death within minutes
Table 1: Toxicity of Hydrogen Sulphide
Concentration
(ppm)
0.0005 to 0.13
0.3
3-5
10
20-30
50
50-100
100
250
1000
565337124
Health Effect
Odour threshold
Distinct odour
Offensive, moderately intense odour
Obvious unpleasant odour; sore eyes
Strong, intense odour, but not intolerable
Eye irritation, watery eyes first noticeable
Mild irritation of respiratory tract and eyes after 1 hour
Loss of smell in 3-15 minutes, may sting eyes and throat
Prolonged exposure may cause pulmonary oedema
Rapid collapse, respirator paralysis, imminent coma, followed by
death within minutes
PN8 - page 3
3.2.









Acute Clinical Effects
3.2.1. Inhalation Effects
Respiratory symptoms develop on prolonged exposure. Rhinitis, pharyngitis,
pneumonia, bronchitis and pulmonary oedema may develop.
Systemic effects may include vomiting, diarrhoea, headache, lethargy, horizontal
or vertical nystagmus, vertigo, olfactory paralysis, drowsiness, tremors,
numbness and weakness of the extremities, dyspnoea, tachypnoea, tachycardia
and hypotension.
Albuminuria, casts, haematuria and acidosis have been reported.
At high doses the central nervous system is the target organ with rapid collapse,
respiratory paralysis resulting in asphyxia, convulsions, imminent coma and
cardiac arrhythmias followed by death within minutes.
3.2.2. Dermal Effects
Discolouration of the skin has been reported.
3.2.3. Eye Effects
Symptoms of eye irritation develop on prolonged exposure with gradual onset of
irritation and inflammation, with lacrimation, burning, conjunctival hyperaemia,
redness and swelling of the lids.
Symptoms progress to greater burning discomfort and photophobia, painful
conjunctivitis, injection of the conjunctivae, ocular pain, blepharospasm and
seeing coloured haloes around lights and clouding of vision.
In severe cases the corneal surface may become lusterless and eroded from loss
of epithelial cells.
Recovery is usually spontaneous and complete but there may also be permanent
damage or loss of vision.
3.3.
Chronic Clinical Effects
Chronic central nervous system effects may be cumulative. Prolonged exposures
may lead to chronic headache, fatigue, dizziness, irritability, conjunctivitis, digestive
disturbances and weight loss.
4.
Concentrations at Finmere Quarry Landfill
Monitoring data from the perimeter of the site resulted in concentrations of 0.040.1ppm. These concentrations are lower than all of the AEGL concentrations and,
although they are slightly over the odour threshold, are not expected to lead to any
adverse health effects.
However, concentrations of 2500 -2600ppm have been monitored in the landfill gas
wells on the landfill site (currently capped). Release of such high concentrations of
hydrogen sulphide may potentially be detrimental to both the health of those on site
and those off site.
Henrietta Harrison
Senior Environmental Scientist, CHaPD, April 2008
565337124