Appendix 4: Basis for the guideline values for the new air contaminants

Contaminant	Guideline values (µg/m³)		Implied risk (per 10⁶)	Levels for risk of 1 in 10⁶ (µg/m³)	Ambient levels (annual average, or as specified)	Comment
Contaminant	Ambient (annual average)	Basis	Implied risk (per 10⁶)	Levels for risk of 1 in 10⁶ (µg/m³)	Ambient levels (annual average, or as specified)	Comment
Benzene	10 (now) 3.6 (2010)	EC (now) UK (long-term goal)	44-75 (WHO) 16 (WHO)	0.13-0.23	~ 7 (urban) 20+ (traffic)
1,3-Butadiene	2.4	UK	17-72 (RIVM) 670 (US EPA)	0.03-0.14 0.0036	~ 1 (24-hour)
Formaldehyde	15	WHO (health) converted	196 (US EPA)	0.077	12 (17-day) ~ 30 (1-hour)
Acetaldehyde	30	WHO (health) converted	450-2700 (WHO) 66 (US EPA)	0.001-0.067 0.45	No NZ data US ~ (2-4)
Benzo(a)pyrene	0.0003	Risk of 2-3 in 10⁵ assumed acceptable	26 (US EPA)	0.00001	7-72 (24-hour)
Mercury (organic)	0.13	TWA/100	-	-	No urban data
Mercury (inorganic)	0.33	TWA/100	-	-	< 50 (7-day)
Chromium (VI)	0.0011	Assume risk of 1 in 10⁵ is acceptable (between WHO and US EPA)	12-140 (WHO)	0.000007-0.00009	No NZ data	Ignores dietary intakes
Chromium (metal and III)	0.11	100 x Cr (VI)	1.3 (US EPA)	0.00083	No NZ data	Ignores dietary intakes
Arsenic (inorganic)	0.0055	Risk of 1 in 10⁵ assumed acceptable (between WHO and US EPA)	8.3 (WHO)	0.00067	No NZ data
Arsine	0.055	RfC (US EPA)	24 (US EPA)	0.00023	No NZ data