During the last two years, a bromeliad that looks more like a tuft of grass and a lichen of a species tolerant to pollution, have been used in a systematic manner to detect the presence of heavy metals in the air of the city of São Paulo and of three municipalities in the industrial suburbs of São Paulo. Consequently, these small and fragile entities are serving as a data base in a study that has been carried out by researchers from the Nuclear and Energy Research Institute – IPEN. Their objective is to trace out a map of the sources of pollution by metals and to compare it with the profile of the industrialization and urbanization of the monitored region.
Among the locations researched is Ibirapuera Park, in the heart of the capital, an area cut across by tunnels and where there is intense traffic. There the presence of the chemical elements, zinc and lead, present from the burning of lubricating oils, was registered in a most accentuated manner. High concentrations of arsenic, barium, zinc and antimony, found in the samples coming from Santo André, an industrial suburb of the city of São Paulo in the ABC Region, and in Santana, in the north region of the city, also seem to be associated with vehicle sources, including diesel vehicles (barium and antimony).
In spite of Santo André being an industrial region, the collection area is also submitted to a high density of traffic. Cobalt was found in quantities much greater than the average of other collection points, in samples from the district of Sao Miguel Paulista, a region in which some metallurgical industries are installed. In the Dom Pedro Park, in the city center, where the traffic is extremely heavy, the main metal found was zinc, generally associated with vehicle emission to wear on the motor’s components and tires.
“The monitoring reflects the urban and industrial activity that are more strongly present in the region”, says Mitiko Saiki, from IPEN’s Analytical Laboratory for Neutronic Activation, and the coordinator of the research funded by FAPESP. For this study, the research team selected ten of the twenty three measuring stations for the quality of air belonging to the Technology of Environmental Sanitation Company (Cetesb), of the State Secretary for the Environment, in order to carry out the measurements: Santana, Dom Pedro Park, Ibirapuera Park, Congonhas Airport, Cerqueira César, Pinheiros, São Miguel Paulista, Santo André, São Caetano do Sul and Mauá.
Studies using bromeliads and lichens, known as vegetal-bio-indicators, for evaluating the impact of environmental pollution began to be carried out during the first decades of the last century, and, since then, various research works have been carried out, mainly in Europe. Over the last few years, Argentina, Chile, Mexico and Jamaica have also developed projects and published scientific papers with respect to the theme. Nevertheless, the evaluation of the impacts of the contamination of the air using plants has not substituted the physical-chemical methods for determining pollution levels. The vegetal bio-indicators function as an additional instrument, which has as an advantage the possibility of measuring various substances present in large areas and the simultaneous utilization of diverse areas. This is to a certain point a cheap method since it uses plants and lichens, but the result is obtained by way of the analysis of the samples carried out in nuclear reactors of accredited institutions for the use of this type of equipment.
The inclination towards this type of experiment with bromeliads began during the time that the researcher Ana Maria Graciano Figueiredo, from IPEN, visited Kingston, in Jamaica, as a consultant for a project in the area of analysis through activation with neutrons, financed by the Inter-American Development Bank (IADB). As Mitiko had already been researching lichens, they decided to work in a systematic manner in the collection of information that would lead them to mapping the pollution in the air for metals.
Powder and neutrons
In order to identify and quantify the chemical elements, the samples of plants are pulverized in a nuclear reactor and bombarded with a flow of neutrons. In this way radioactive isotopes of the elements that are to be determined are produced. The technique has as its main advantage the fact that close to twenty chemical elements can be detected with only the analysis of a small quantity of sample. Furthermore, it is a very precise and sensitive method, which allows for the detection of small concentrations of metals, of the order of parts per billion (ppb). For the bio-monitoring using Tillandsia usneoides, a bromeliad popularly known as goat’s beard and used in floral arrangements, the plants needed to be collected in non-polluted locations and then taken to the areas to be monitored. The bromelias were removed from within a forest well away from industries and highways, situated on private property in Mogi das Cruzes, a town some 63 kilometers from Sao Paulo.
A T. usneoides has already been in use for some time in other tropical regions as a bio-indicator of atmospheric pollution because of its morphological and physiological characteristics. As it does not have roots, it presents all of its foliar surface area covered by a structure known as scales, whose principal function is to absorb water and mineral salts from the atmosphere. In this manner the plant can accumulate pollutants present in the environment. The samples collected at Mogi das Cruzes were placed hanging about one meter from the ground in a support adapted for rotation by the wind, in such a way as to guarantee homogeneous contact with the air pollutants. After two months of exposure, the bromeliad samples were removed for analysis and substituted by fresh plants, thus guaranteeing the continuous monitoring at the chosen locations for a period of twenty four months.
The bio-monitoring with the lichen named Canoparmelia texana – a species chosen because it is found in many Brazilian towns and cites, except along the coast – is carried out at the very location where the trees are found on which they themselves are born and grow. The lichens are symbiotic organisms composed of a fungus and one or more algae. This association forms a common thallus, without roots, which in order to grow mainly depends upon the mineral nutrients present in the atmosphere. Since the C. texana is more abundant in polluted environments than in clean ones, this characterizes it as a specific indicator of pollution. When its competitors disappear from the environment, it finds itself in an unoccupied habitat and, due to its high tolerance to pollution, occupies on large sections of the trunks of trees, as can well be observed in parks, squares and the university campuses of large cities.
In Brazil there are some 2,800 species of lichens already listed, but data for a mapping of the distribution of the elements indicating the levels of pollution does not exist. According to Mitiko, periods of rain or drought will not influence the measurement carried out by the lichens because the growth of this vegetal organism is extremely slow, around 0.5 to 3 millimeters per year. In order to make a comparison, samples of C. Texana were collected in non-polluted areas located at four points within the Intervales State Park, an Atlantic Rain Forest reserve some 270 kilometers from the city of Sao Paulo.
The lichen is removed from the tree using a titanium knife so that there will not be any contamination of the material. Lichen is a microscopic world that is made up of insects, spiders webs and moss. So that this task is always carried out to the same standard, Mikito held a course at the Botanic Institute of the State Secretary for the Environment. After the samples were cleaned in distilled water and dried by a process called lyophylization (dehydration carried out at low temperature) which last for sixteen hours.
The bromeliads, removed from the monitoring stations every two months, were taken to the laboratory and dried in an oven at 40°C. After they were dried, the plant samples were ground up and placed in clean plastic satchels. The envelopes, containing between 150 and 200 milligrams of material, were then placed in the atomic reactor to be irradiated and analyzed. The research had the participation of students with grants from the National Research and Development Council (CNPq) and of researchers from the Botanic Institute. Although the project has already been completed, studies are still in progress.
In the current phase, the collection points are being widened to include all of Cetesb’s 23 monitoring stations. In reality, these measures complement the control carried out by the São Paulo environmental agency, which makes use of other parameters such as the volume of sulfur dioxide (SO2 ), inhalable particles, the volumes of nitrogen dioxide (NO2), carbon monoxide (CO) and ozone (O3), in order to measure the pollution in the air.The results obtained by the team from IPEN have already attracted the interest of environmental consulting companies. One of them, installed in the city of Rio de Janeiro, intends to make use of the bio-indicator plants and lichens to measure the impact caused by a treatment station of industrial liquid effluent on the health of the neighboring inhabitants. The data collected in the study will also be presented in October at IPEN during a workshop that will bring together researchers from Latin America, which is being sponsored by the International Atomic Energy Agency and by the institution itself.
The utilization of bio-indicator plants that accumulate metals for the biological monitoring of urban pollution in Sao Paulo (nº 02/00418-0); Modality Regular Line of Research Assistance; Coordinator Mitiko Saiki – IPEN; Investment R$ 35,628.00 and US$ 11,815.00 (FAPESP)