So, all in all, an interesting article. Also of interest is that the Regional Council will not release their monitoring data, but it would appear, were prepared to attribute the ‘odour’ / toxic gas to different sources … organic orchards and lime sulfur use?
The placement of the monitor is such that it will only measure H2S from the northeast form the sewage works, so it is well placed in regards to apportioning source in respect to this gas … wind direction, rain or fine, and presumably will also have recorded sulfur dioxide, nitrous oxide and PM2.5 particulate matter.

That it was stated that the H2S measured (presumably from July to the time of this report) ranged from 4 to 7 parts per million (ppm) strongly indicates that the ambient H2S levels were at minimum greater than 4ppm – not ppb (billion) as one would expect from background levels in an area without geothermal activity. This is of real concern and is something that urgently needs addressing.
That the Regional Council forced the closure of the plant suggests that it was not only in breach of odour standards, but also health standards.

Will Arnott’s missive on lids and a resource consent for discharging an odour resolve this issue? Or is this equivalently naive? It is, not just a bad smell, it is a toxic gas.

To emphasise this point, and that the requisite information has been available for a long time:

The Illinois Institute For Environmental Quality reported its findings on Hydrogen Sulfide Health Effects and Recommended Air Quality Standards in 1974. The Illinois Institute summarized the literature on human health effects and their observations on the health effects in Illinois ambient air concentrations. In general the following was reported:

Concentration of H2S Symptoms:
O.12 mg/m3 (0.08 ppm) – Increased mental depression, dizziness and blurred vision.

0.45 mg/m3 (0.32 ppm) – Increased incidence of nausea, loss of sleep, shortness of breath, and headaches

1.0-10 mg/m3 (0.7-6.7 ppm) – Increased incidence of decreased corneal reflex (convergence and divergence)

10-70 mg/m3 (6.7-47 ppm) – Irritation of conjunctiva, fatigue, loss of appetite, insomnia.

The Illinois Institute recommended a standard for gaseous hydrogen sulfide of 0.015 mg/m3 (0.01 ppm) to minimize adverse health effects from chronic exposure in urban air.

Kilburn KH and Warshaw RH. Hydrogen sulfide and reduced-sulfur gases adversely affect neurophysiological functions. Toxicology and Industrial Health, Vol 11, pp. 185-19, 1995.

Kilburn KH, MD. (2004) Endangered Brains. Princeton Scientific Pulications Co. Inc., Birmingham, Alabama. ISBN : 0-9745460-0-3. pp. 77-85.
Ex-workers and neighboring residents (total of 35 individuals) were compared to 33 unexposed controls. The ex-workers and residents were exposed to hydrogen sulfide and other reduced-sulfur compounds emitted from a refinery. The concentrations of hydrogen sulfide and other reduced-sulfur compounds were monitored at ground level. Depending upon the day and year hydrogen sulfide concentrations ranged from a low of 10 ppb to 8.8 ppm. Reduced sulfur compounds (dimethylsulfide, mercarptans, carbon oxide sulfide) ranged from 2 ppb to 71 ppm.

Symptoms involving the respiratory tract (chest tightness, palpitations, chest pain, dry cough, cough with blood, dryness (mouth, nose, throat,), throat irritation, eye irritation, reduced sense of smell were greater in the exposed than the controls.

Neurological symptoms were also elevated over the controls. These included: dizziness, lightheadedness, loss of balance, lack of concentration, recent and long-term memory loss, mood unstableness, irritability, exhilartion.

Sleep disturbances were also noted in the exposed, which were: cannot fall asleep, wake frequently, sleep few hours, somnolence.

Skin symptoms were itching, dryness and redness.

General Symptoms were: headache, nausea, libido decrease, excess fatigue, indigestion, loss of appetite, lack of tolerance to alcohol.

Neurophysiological deficits were found in the exposed group: simple reaction time was increased; sway speed was faster, color discrimination was reduced and psychomotor speed was time was increased.

The neurological injury is accumulative. That is each exposure results in increased brain damage. The damage individual does not recover, and brain dysfunction continues for years. These observations are supported by research on animals, where it has been shown that accumulative exposures adversely affect cytochrome oxidase enzyme activity and changes in the hippocamal EEG

Profile Mood States (POMS) also showed abnormalities when compared to controls. There were increased scores for anger, depression, tension, confusion, fatigue and vigor.

The automatic (subconscious) parts of the neuro-axis were impaired. Impaired performance was accompanied by reduced perceptual motor speed.

The exposure to reduced-sulfur gases, predominantly hydrogen sulfide, was considered the most plausible explanation of the neurotoxic effects in this study.

Gaitonde UB, Sellar RH and O’Hare AE. Long-term exposure to hydrogen sulphide producing subacute encephalopathy in a child. British Medical Journal. Vol 294, pp. 614, 1989.

This is a report on a 20-month old infant exposed for a year to 0.6 ppm hydrogen sulfide downwind from a burning tip gas ignition point for a colliery. The child had subacute necrotizing encephalopathy in the basal ganglia and white matter.

Chronic Reference Dose (RfD) Based upon animal studies and the child reported by Gaitonde et al, the U.S.E.P.A. has recommended a RfD of 0.8 micrograms per cubic meter of air for both subchronic and chronic human inhalation exposure. The RfD is that concentration at which no adverse health effects should occur. Concentrations above the RfD may result in adverse health effects, including neurotoxicity.

Conclusion: Chronic and subchronic exposure to low concentrations of hydrogen sulfide and other organosulfur compounds (reduced sulfur compounds) do cause long-term health problems in humans. These problems appear as various symptoms of the upper and lower respiratory tract, central nervous system, skin and eyes. The central nervous system symptoms are associated with permanent neurophysiologcal deficits. Injury to the central nervous system includes damage to the basal ganglia and white matter

0.02 ppm – No odor

0.13 ppm – Minimal perceptible odor

0.77 ppm – Faint, but readily detectable odor

4.6 ppm – Easily detectable odor, moderate odor

27.0 ppm – Strong, unpleasant odor, but not intolerable

The Hawkes Bay has the worst health statistics of any region in New Zealand … is it any wonder why?
Are our Regional Council doing enough in regards to our air quality? The sewage works issue is simply another example of what activities are being permitted without sufficient safe guards, with an almost cavalier disregard for public health.
Where are our Medical Officers of Health in respect to this and allied issues … we know they all use the toilet, but are they really all orchardists?
Hydrogen sulfide, sewer gas, H2S is a toxic gas with an odour of rotten eggs … it is not just a ‘bad smell.’ The two primary sources in the Hawkes Bay are the sewage works and the use of lime sulfur by organic orchardists.