The rapid adoption by the car industry of catalytic converters for petrol engines that reduce the quantities of toxic nitrogen oxides and hydrocarbon pollutants entering the atmosphere has significantly improved air quality, particularly in busy towns and cities. However, this improvement comes at a price, according to Italian scientists who have studied the metallic fallout from catalytic converters.
Claudio Botrè of the University of Rome and Alessandro Alimonti of the Italian National Institute of Health in Rome and their colleagues explain that the increasing numbers of catalytic converters on the road has led to rising environmental levels of the metals used as the catalysts in these devices - platinum, rhodium, palladium, and iridium. The team has published their detailed findings in the International Journal of Environment and Health.
The team analysed air particulate samples collected from two typically busy sites in Rome over the winter of 2004-2005. They used mass spectrometry to determine the chemical constituents of the samples. Their initial findings confirmed that vehicle exhausts, as opposed to hospital incinerators and industrial sites, are the main source of platinum and related metals in the urban environment.
The researchers also confirmed the findings of an earlier study that suggests that platinum is present in vehicular pollution at four times the level of rhodium. The environmental evaluation of iridium used in catalytic converters provides the first benchmark for this pollutant as no detailed tests have been carried out previously.
In terms of public health, the researchers then looked at the way the platinum group metals interact with the natural antioxidant, vitamin C (ascorbic acid) and with a compound occurring in every cell of our bodies as a product of metabolic processes, the reduced form of nicotinamide adenine dinucleotide (NADH). They hoped to determine whether the metals from catalytic converters that have entered the atmosphere and been adsorbed, or trapped, on pollutant particles which can be breathed in could ultimately have a detrimental effect on health.
They used an electrochemical method to investigate how the platinum group metals from their particulate samples reacted with ascorbic acid and NADH. Their preliminary findings suggest that these metals can trigger deleterious reactions that decrease the amount of these two vital biomolecules, in the in vitro tests at least. They will need to carry out further investigations to find out whether the body's natural defences could cope with the potential harm caused by these metals.
Lead pollution has received considerable attention, with lead in petrol rightly banned across the EU. However, the emerging problem of platinum metal pollution must be considered in evaluating the benefits of vehicle catalytic converters. The researchers suggest that closer monitoring of increasing levels of catalytic metals in urban pollution is a matter of urgency. Epidemiological studies of the health effects on children of these metals are under way elsewhere with metal content in urine samples providing a straightforward method of monitoring exposure levels.