Environment and health

Benzene in the city

Benzene concentration levels in urban areas reach increasingly high levels the further south you travel in Europe. Such is the finding of a study carried out in six European towns by the Joint Research Centre's ERLAP laboratory. This makes the Commission's recent proposal for an "air quality" directive all the more pertinent. For the first time, the directive would put a limit on the presence of this carcinogenic compound in vehicle exhaust fumes.

The fight against benzene is about to be launched. Although the quantities of this volatile organic compound emitted by vehicle exhausts are small compared with some other pollutants (its presence is the result of the incomplete combustion of hydrocarbons in combustion engines), it is a known carcinogen and an important risk factor in leukaemia in particular. With no legal limit on benzene concentration levels, there had been few measurements to determine its presence in the air of our towns and cities.

It was to correct this situation that the European Commission's Directorate-General for the Environment (DG XI) asked the European Reference Laboratory for Air Pollution (ERLAP) - a body managed by the Joint Research Centre's Environment Institute at Ispra (I) - to undertake a major Europe-wide measurement campaign. Known as MACBETH, [1] the project was launched in six test cities across Europe from north to south: Copenhagen (DK), Antwerp (B), Rouen (F), Padua (I), Murcia (E) and Athens (GR). A number of national partners were involved in the various countries. [2]

The Radiello sensors

In order to measure pollution levels in urban environments, the ERLAP developed an innovative and particularly cost-efficient sampling technology. Comprehensive air quality measurements traditionally require quite sophisticated automatic devices whose recordings are automatically transmitted in real time for analysis. The high cost of these devices means that they are placed at only a limited number of locations. This limits the scope for monitoring air quality over large areas.

"In order to overcome this problem," explains Emile De Saeger, the ERLAP director, "we developed ultra-simplified pollution sensors, known as diffusion sensors, which can be used to detect various air pollutants. No bigger than a small test tube (7cm long, 1 cm in diameter), they contain an absorption material which is able to capture the pollutant by means of molecular diffusion. The cost of the Radiello sensor is minimal - about five euros - which means they can be installed over a very wide area. After being left for a few days, the samples are collected and the absorption levels analysed in a laboratory. Genuine pollution maps can then be drawn up."

In the street, the home and on the person

The Radiello sensors allowed the MACBETH researchers to carry out a triple analysis of benzene pollution in the six European towns. Observable atmospheric concentrations were measured at different locations in the town, in the home and directly on the person in order to measure the exposure of individuals.

"During the six observation periods, carried out during a five-day period on each occasion, fixed sensors were placed in different urban areas (100 sites per town), in the homes of non-smoking volunteers (50 inhabitants per town) and on the person of these volunteers. We monitored two groups of people. One group consisted of a sample of the population that would normally be subject to only average or low direct exposure to automobile traffic, as they spend a large part of their time indoors, notably students and their teachers. The other group were people whose jobs involve a high risk of exposure, such as bus and taxi drivers and highway maintenance workers.

Inequality of risk exposure

The MACBETH results were presented at the international conference on air quality in Europe,[3] held in Venice from 19 to 21 May 1999. They showed the extent to which the people of Europe are far from equal in the face of the benzene threat. Levels range from an average of 3.3 µg/m3 in Copenhagen to 24.9 µg/m3 in Athens. There is a clear increase in benzene pollution as you travel southwards across Europe. A number of variables must be taken into account to explain this difference, including, no doubt, traffic density and flows, the influence of climate and weather, lifestyles and the structure of the built urban environment.

There was another clear finding: benzene concentration levels are generally - and paradoxically - higher indoors than outdoors. This is a factor which must certainly be taken into account in future. For the rest, the harmful effects of certain high-risk jobs was confirmed.

The car and the town called into question

The MACBETH study lends support to the European Commission's policy on air quality. In December 1998, the Commission submitted a new proposal for a directive which, for the first time, will set a benzene concentration limit. The proposed objective is to reach what is seen as a precautionary limit of 5 µg/m3 urban air by 2010. "Our results show that meeting these concentration levels should not pose major problems in northern Europe," explains Emile De Saeger. "On the other hand, the alarming levels recorded in southern towns mean that a much more strenuous effort is going to be needed there." In this respect, the Commission's proposal includes a plan to assess progress in implementing the directive in 2004.

What weapons are available to the urban authorities in combating the benzene threat? These naturally relate to the complex debate on the place of cars in towns. Part of the solution can come from improving combustion engine technologies and the reduction of harmful emissions. On the other hand, draconian measures to limit traffic - such as those already applied in large cities such as Paris and Athens when pollution levels peak - have certainly shown their effectiveness. They have also met with a much more positive response among the population than had been expected. In any event, this is an issue which calls for reflection on both dissuasive policies, such as traffic flow measures and perhaps charging for vehicle access to towns, and the promotion of alternative means of transport.

Notes

[1] Monitoring of atmospheric concentration of benzene in European towns and homes.
[2] Fondazione Salvatore Maugeri (I), Miløundersøgelser (DK), Universidad de Murcia (E), Vlaamse Instelling voor Technologisch Onderzoek (B), Institut National de l'Environnement et des Risques (F).
[3] "Air quality in Europe: challenges for the 2000s": this conference was jointly organised by DG XI, the JRC and the Fondazione Salvatore Maugeri.

Contact
Emile De Saeger,
ERLAP
E-mail: emile.de-saeger@jrc.it