Odour Threshold Investigation 2012 - Bay of Plenty Regional Council

In relation to the second question of this investigation the groups were spatially different, with
one consisting of panellists from Whakatāne and Tauranga (non-geothermal areas) and one
group from Rotorua, where the panellists are frequently exposed to concentrations well
above the international literature odour thresholds. Other basic characteristics of the groups
showed that they were generally similar in profiles when it came to the age and sex of the
panellists. The residence time for the Rotorua panellists was also recorded. This was
compared with threshold values for this group. The results showed no relationship with
residence time and average measured threshold.
Several types of analysis of the grouped data showed that there was a statistically significant
difference between the geometric mean odour threshold results for the two groups (1.1 µg/m 3
for Rotorua and 0.5 µg/m 3 for Whakatāne). The difference was small, but in the direction we
would expect (Rotorua higher than non-geothermal locale). The results also showed that the
human response to odour is highly variable.
The difference between the two groups is interesting in a purely theoretical sense. However,
when taking into account – (i) the wide range of thresholds that have been published to date,
(ii) inaccuracies in the methodologies used in these investigations, and (iii) the end use
application of thresholds as a comparison point for modelled outputs, the difference shown
between the two groups would be regarded as insignificant and largely treated as being the
same for both. The analysis showed that the vast majority of the panellists were able to
detect H 2 S at the 7 µg/m 3 level.
In setting a guideline value it would be dependent on the receiving environments location, as
both groups appear “equal” when it comes to detecting. Variations in odour response would
be dependent on what is commonplace in their local environment. Communities that live in
close proximity to existing or proposed developments or natural settings where H 2 S
emissions are present are equally adept at detecting the odour at low concentrations, when
compared with the Whakatāne group, but more often than not would be accepting of the
odour profile because of location.
In regard to Council air quality policy, the findings of this investigation will be used in the
upcoming Bay of Plenty Regional Air Plan review process.
ii Environmental Publication 2012/06–A review of odour properties of H 2 S Odour Threshold Investigation 2012