Appendix 3: Background information on hazardous air contaminants

Contaminant	Health effects	Classification		Unit risk x 10-6			Various guidelines (µg/m3) (annual averages unless otherwise stated)
Contaminant	Health effects	IARC*	*US EPA (potency)**	WHO	US EPA	CARB	UK	EC	TWA/ 100	WHO	US
Benzene	Haemotoxic; genotoxic; carcinogenic	1	A (medium)	4.4-7.5	8.3	29	18 (now) 3.6 (goal)	10 (now) 5 (2010)	18	-	-
1,3-Butadiene	Neurological; irritation of eyes, throat, lungs and nose; mutagenic; carcinogenic (?)	2A	B2 (medium)	-	280	170	2.4	-	24	-	-
Formaldehyde	Irritation of eyes, throat, nose and respiratory symptoms; nasal cancer	2A	B1 (medium)	Very low	13	6	-	-	9.2	100 normal 10 hypersensitive (30-min)	-
Acetaldehyde	Irritation of eyes, throat, nose and respiratory system; nasal cancer	2B	B2 (low)	15-90	2.2	2.7	-	-	3600	2400 (24-hour)	9 (RfC)
Benzo(a)pyrene	Dermatitis; photosensitisation; eye irritation; cataracts; lung cancer (?)	1	B2 (medium)	87,000	-	-	-	-	-	-	-
Mercury**	CNS; gastrointestinal; respiratory system; kidney	2B(m) 3(I)	C (medium) D (low)	-	-	-	-	-	0.1(al) 0 25(I) 1.0(ar)	1(I)	0.3(I) (RfC) 0.3(I) (REL)
Chromium VI	Respiratory; gastrointestinal; liver; kidney; immune system; blood	1	A (high)	11,000-130,000	1200	150,000	-	-	0.1-0.5	-	0.0023
Chromium III and metal		3	D	-	-	-	-	-	5.0	-	-
Arsenic (inorganic)	Gastrointestinal; haemolysis; central and peripheral NS; eyes; skin; mucous membrane	1	A (high)	1500	4300	1500	-	-	0.1	-	0.41 (REL)
Arsine		1	A (high)	1500	4300	1500	-	-	1.7	-	0.055 (RfC)

* IARC classes and US EPA equivalents are as follows.

IARC	Descriptor	USEPA
1	The agent (mixture) is carcinogenic to humans. The exposure circumstances entail exposures that are carcinogenic to humans.	A
2A	The agent (mixture) is probably carcinogenic to humans. The exposure circumstances entail exposures that are probably carcinogenic to humans.	B1
2B	The agent (mixture) is possibly carcinogenic to humans. The exposure circumstances entail exposures that are possibly carcinogenic to humans.	B2, C
3	The agent (mixture or exposure circumstances) is not classifiable for humans.	D
4	The agent (or mixture) is probably not carcinogenic to humans.	E

** Abbreviations for mercury: Organic (o) = [methyl (m), aryl (ar), alkyl(al)]; Inorganic (I) = elemental and other inorganic compounds.

For more information about these contaminants, please read Air Quality Technical Report 13.