| Air Quality Criteria | WNP Processing Plant Air Discharge Assessment | 4397169-66885702-113 | 16/06/2022 | 9 Sensitivity: General 3 Air Quality Criteria 3.1 Introduction The Ministry for the Environmental (MfE) Good Practice Guide for Assessing Discharges to Air from Industry (Industry GPG)11 sets out an order of priority for the use of various air quality assessment criteria, as follows: ● Air quality standards contained in the Resource Management (National Environmental Standards for Air Quality) Regulations 2004 (NESAQ) ● New Zealand Ambient Air Quality Guidelines (NZAAQG) published by the Ministry for the Environment12 ● Regional Air Quality Guidelines (RAAQG) ● World Health Organisation air quality guideline (WHO AQG) concentrations (where appropriate). The Industry GPG recommends, in the absence of suitable New Zealand or WHO standards and guidelines, the use of other international assessment criteria such as: California Office of Environmental Hazard Assessment Reference Exposure Limits (OEHHA REL) and US EPA reference concentrations (RfC). US EPA RfCs are regarded as annual averages, while the California OEHHA publishes both 1-hour (acute) and annual (chronic) RELs. The Waikato Regional Plan defines RAAQG for a range of air contaminants, which are presented in Section 6.3 of the plan. The RAAQG concentration limits are the same as the published NZAAQG. 3.2 Assessment Criteria for Mercury A summary of the relevant health-based assessment criteria for mercury is presented in Table 3-1. There are no NESAQ for any of the monitored contaminant discharges. A NZAAQG of 0.33 μg/m3 has been published for inorganic mercury. The NZAAQ is comparable to the US EPA’s RfC of 0.30 μg/m3 and the US Agency for Toxic Substances and Disease Registry (ATSDR) chronic minimum risk level (MRL)13 of 0.20 μg/m3. The lowest annual guideline level for mercury of 0.03 μg/m3 is published by OEHHA14. In contrast the WHO annual average guideline15 for mercury is 1 μg/m3. OEHHA has also proposed both 8-hour average and 1-hour RELs for mercury of respectively 0.06 μg/m3 and 0.6 μg/m3. However, the 8-hour average REL is not based on acute health effect but on the cumulative chronic effect of repeated daily exposures to mercury for 8-hours per day over many years16. The 1-hour average OEHHA REL is based on a single study of the observed developmental effect that daily exposures to mercury vapour had on the offspring of pregnant rats. During the study pregnant rats were exposed to mercury for 1 to 3 hours per day over their pregnancy. The OEHHA 1-hour REL is based on the lowest mercury concentration at which an adverse effect was observed in the offspring divided by an 11 Ministry for the Environment, 2016. Good Practice Guide for Assessing Discharges to Air from Industry 12 Ministry for the Environment, 2002. Ambient Air Quality Guidelines. 13 https://wwwn.cdc.gov/TSP/MRLS/mrlsListing.aspx 14 OEHHA TSD for Non-cancer RELs December 2008 (Updated July 2014) Appendix D. Individual Acute, 8Hour, and Chronic Reference Exposure Level Summaries. https://oehha.ca.gov/media/downloads/crnr/appendixd1final.pdf 15 https://www.euro.who.int/__data/assets/pdf_file/0004/123079/AQG2ndEd_6_9Mercury.PDF 16 The subjects in the study on which the guideline is based on were exposed to mercury for 13.7 to 15.6 years
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