Unleaded Petrol Reduces Dioxin Levels in Air
by Dr Chris Winder
One interesting spin-off from taking lead out of petrol
has been the reduction in other contaminants being emitted from cars. For example,
unleaded cars produce less dioxins and related compounds, recognised as being highly toxic
compounds.
Because the lead in petrol can end up in the engine oil, additives were
added to petrol to encourage the lead to discharge from the engine in the exhaust gases.
These additives, called scavengers, include ethylene dichloride, pentachlorophenate and
ethylene dibromide. The lead oxides formed in internal combustion are converted to more
volatile lead chlorides and bromides, and out into the exhaust they go.
In 1986, dioxins and related compounds were measured in used motor oil
in Germany.' In 1987 came the first direct evidence of dioxins and related compounds in
car emissions, based on tailpipe measurements taken from four Swedish cars running on
petrol containing 0.15 g/L (grams per litre) tetramethyl lead and 0.1 g/L ethylene
dichloride as a scavenger. Levels of 20-220 picograms of toxic equivalents of dioxins were
emitted for every kilometre driven. Levels of dioxins in two other cars running on
unleaded petrol were below the level of detection (that is, less than 13 picograms of
toxic equivalents of dioxins for every kilometre driven).
Two other studies repeated and confirmed these measurements, finding:
1 picograrn of toxic equivalents of dioxins for every kilometre driven
for cars using unleaded petrol, and up to 39 pg/km in cars running on leaded in a New
Zealand study; '0.36-6.3 pg/km (unleaded), 1.1-3.6 (leaded) and not detected in diesel
vehicles, in a study in Sweden.'
While these numbers are variable, they indicated that the use of
chlorinated scavengers in leaded petrol do increase emissions of dioxins and related
compounds to air. The original Swedish study suggested that cars using leaded fuel in
Sweden emitted 10-100 g of toxic equivalents of dioxins a year. The incremental decrease
that will occur from cars using unleaded petrol is one unforeseen benefit from phasing out
leaded petrol.
References
- Ballschmiter, K, Buckert, H, Niemczyk, R, Munder, A and Swerev, M. Automobile exhausts
versus municipal waste incinerators as sources of the polychlorodibenzodioxins (PCDD) and
-furans (PCDF) found in the environment. Chemosphere IS: 901-915, 1986.
- Marklund, S, Rappe, C, Tysklind, M and Egeback, KE. Identification of polychlorinated
dibenzofurans and dioxins in exhausts from cars run on leaded gasoline. Chemosphere 16:
29-36, 1987.
- Bingham, AG, Edmunds, CJ, Graham, BW and Jones, MT. Determination of PCDDs and PCDFs in
car exhaust. Chemosphere 19: 669- 673, 1989.
- Marklund, S, Andersson, R, Tysklind, M, Rappe, C, Egeback, KE, Bjorkman, E and
Grigoriadis, V. Emissions of PCDDs and PCDFs in gasoline and diesel fuelled cars. Chemosphere
20: 5530561, 1990.
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