Concentrations of benzene in New Zealand have been measured in Auckland, Christchurch, Hamilton and Dunedin as part of a Ministry of Health study. In addition, separate studies of benzene concentrations have been carried out in Auckland, Christchurch and Nelson. Results of this monitoring are presented relative to the current annual average guideline value for New Zealand of 10 µgm-3 and the 2010 annual average guideline value of 3.6 µgm-3.
The required monitoring method for benzene in New Zealand is the USEPA method TO1. Most benzene monitoring in New Zealand, however, has been carried out using passive sampling methods that do not comply with this technique.
6.1 Auckland, Hamilton, Christchurch and Dunedin - the MoH study
The Ministry of Health measured concentrations of benzene at different types of monitoring sites within the main urban centres of New Zealand from 1996 to 1999. Results of the study are documented in Benzene and Other Toxic Organics (Stevenson, 1999). Figure 6.1 shows that the current guideline value for benzene was exceeded only at sites located in central Auckland or Christchurch, near to major roads. The 2010 guideline value was also exceeded in Christchurch at a number of residential sites such as St Albans and Fendalton.
Concentrations of benzene have been measured at a number of sites in Auckland since June 2000. Figure 6.2 compares annual average benzene concentrations to the current and 2010 guideline values and shows seasonal variations in benzene concentrations at the different monitoring sites. Annual average concentrations measured during 2002 are within both guideline values at the Henderson, Mt Eden and Penrose sites. The annual average concentration of 11.7 µgm-3 at Khyber Pass Road exceeds both guideline values.
In addition to the monitoring carried out by the Ministry of Health in 1997 and 1998, Environment Canterbury conducted benzene monitoring at a number of sites in Christchurch during 2001. The monitoring programme sampled benzene, toluene, ethylbenzene and xylene at a range of ambient (residential neighbourhood), street level (traffic peak) and indoor sites (Gunatilaka, 2003). The sites used in the study and their classifications were:
- Burnside outer suburb - reserve - ambient
- Coles Place inner city suburb - ambient
- Haast Street inner city suburb - ambient
- Hoon Hay outer suburb - ambient
- Manchester Street inner city - roadside
- Packe Street inner city suburb - ambient
- Riccarton Road florist - inside major arterial road - indoor
- Riccarton Road florist - outside major arterial road - roadside
- Riccarton Road - inside major arterial road - indoor
- Riccarton Road - outside major arterial road - roadside
- Woolston outer suburb - ambient
- Yaldhurst outer suburb - ambient.
Figure 6.3 shows the annual average benzene concentrations measured at each of the monitoring sites. This indicates that the current guideline value for benzene is exceeded at one traffic site on Riccarton Road, which may not be representative of a person's typical annual exposure. The 2010 guideline value is currently exceeded at a number of traffic and residential sites. No annual averages were derived for the Riccarton Road florist indoor or outdoor sites because of incomplete sampling.
Based on a comparison of the 2001 results to the 1996-99 Ministry of Health data, Gunatilaka (2003) suggests that concentrations of benzene in Christchurch are decreasing, with roadside sites showing a 32% reduction, and ambient sites being around 13-15% of the 1998/1999 concentrations.
Concentrations of benzene have been measured in Nelson using both passive sampling and a DOAS continuous sampler. Results of the monitoring are detailed in Bluett and Peterson (2001). Sampling using the DOAS monitor was carried out for the period May to August, although data were missing for significant periods during this time. Based on the data available, an average benzene concentration for the sampling period of 6.8 µgm-3 was estimated. Passive sampling data indicated similar results, although some problems occurred with the sampling during June and July. As sampling was limited to winter months, extrapolation to an annual average was not possible.
6.5 West Coast
Passive sampling for benzene was carried out on the West Coast of the South Island during June, July and August of 2001 and 2002. All winter averages were within both the current and 2010 guideline values for benzene. The highest winter average concentration of 3.5 µgm-3 was measured in Reefton during 2001 (Figure 6.5).
6.6 Bay of Plenty
Concentrations of benzene have also been measured at a number of sites in the Bay of Plenty. Figure 6.6 shows the three-month and annual average benzene concentrations measured from August 2000 to July 2001. In most areas, the highest benzene concentrations were measured during the period May to July 2001. Annual average concentrations were within the guideline values, although the Mount Maunganui industry site concentrations were above the 2010 guideline values. Concentrations at the background site in Pongakawa were below the level of detection.