Study of environmental burden of lead in children using teeth as bioindicator
Introduction
Metals are certainly the most ancient toxic elements known by men. Anthropic intervention has changed their potential effects on health, particularly by means of transportation among several regions on earth through air, water, soil and food stuff (Goyer and Clarkson, 2001). In this work we deal with chronic incorporation of lead, a quite important, highly toxic and harmful metal. The data taking was focused on children from families belonging to low socioeconomics classes, living in a small, restrict and allegedly contaminated area in Sao Paulo city.
Gasoline in Brazil is unleaded since 1992. However, lack of rigorous control on the disposal to the environment of domestic and industrial waste, associated with the low recycling rate of batteries, makes lead an ever present contaminant and at non-negligible amounts (Franco-Netto et al., 2003). Additionally, lead is used in more than 200 distinct industrial processes.
Epidemiological and toxicological studies undertaken in individuals exhibiting lead concentration in blood, near or below the maximum recommended by the World Health Organization (10 µg dl− 1), surprisingly revealed that toxic effects are more intense in individuals belonging to low socioeconomics classes. In particular, learning difficulties, lack of concentration and memorization, and aggressive behavior have been reported (Smith et al., 1983, Canfield et al., 2003, Needleman et al., 1990, Wakefield, 2002). The most vulnerable individuals are children, particularly from the neonatal period until the pre-puberty.
These findings upgrade the importance of studying chronic contamination scenarios with low, non-critical lead quantities. In Brazil, as in many others countries, the great majority of studies refer to regions where acute and occupational contamination has been verified.
The south region of Sao Paulo city has been subject to intense and irregular populational occupation for more than 20 years, associated with lack of basic infrastructure. This region hosts the Guarapiranga dam, which belongs to a huge hydrographical basin located south of Sao Paulo city, covering an area of 643 km2 encompassing Sao Paulo city itself plus six neighboring villages. About 36% of the basin area (229 km2) with the dam inside is in Sao Paulo city. The Guarapiranga dam (G-dam, from now on) is responsible for water supply to 25% of Sao Paulo population, nearly 3.7 millions of inhabitants. The fringe surrounding the dam is irregularly occupied by 60,000 souls.
Measurements undertaken on sediment and particulate materials in the dam revealed concentrations of lead, copper, zinc and cadmium above internationally accepted limits. For lead in particular, although its content in water is within normal limits, the concentration in sediment is very high (Patella and Mozeto, 1999).
Humans' exposure to metals is commonly monitored through the analysis of urine, blood, hair and saliva. These bioindicators are easy to sample, and existing measuring techniques and methodologies are well established. However, blood and urine data provide information on recent exposures, that is, those occurring at times close to the sampling date. Furthermore, appreciable amounts of the contaminant could be gradually incorporated from a steady source, without an alarming increase of its level in blood (Fremlin and Edmonds, 1980). Hair and fingernail are considered medium-range bioindicators, associated with exposure times from a few months to years and providing, in the case of hair, more precise information on acute exposures (Aitio and Kallio, 1999).
According to the goals of the present study, i.e. chronic incorporation, it is necessary the use of indicators working as contaminant dumps through long periods of time (bioindicators for long-range exposures). In this regard, teeth fulfill nearly all of our investigation needs since: (1) they are easily obtainable from children; (2) present the same structure of bone and, therefore, they have the same metal affinity, and (3) their remodeling is slow; as a consequence, the contaminants clearance is much smaller vis-à-vis other organs (Rabinowitz et al., 1993). Therefore, teeth allow for both an exposure longstanding record and inferences on the contaminant content of the skeleton (Tsuji et al., 1997).
Section snippets
Apparatus
A Finnigan Mat (Bremen, Germany) model Element 1 high-resolution inductively coupled plasma mass spectrometer (ICP-MS) was used throughout. Teeth samples were ground with a cryogenic mill Model 6800 Freezer/mill (SPEX, Metuchen, NJ, USA). A laser particle size analyzer Model Mastersizer E (Malvern, Worcestershire, UK) was used for particle size measurements. For sample decomposition a closed vessel microwave oven, MARS 5 (CEM) was used.
Reagents, materials and solutions
We have used high purity de-ionized water (resistivity
Results and discussion
The sampling area corresponded to the surroundings of the Guarapiranga dam, from its rim up to a couple of kilometers inland, presenting a dense and irregular demographic occupation by families belonging to the lowest socioeconomics classes. Teeth were collected with the help of the Faculty of Dentistry, University of Santo Amaro, which maintains and operates an Odonto-pediatric office inside the studied area, offering gratuitous odontological services to its population.
The control area was
Conclusions and final remarks
- 1
The average concentration of lead in teeth from children living in the surroundings of the Guarapiranga dam (our case study) is approximately 40% higher than the one corresponding to the control region.
- 2
Considering gender, boys absorb 20% more lead than girls.
- 3
Lead concentrations are higher in molar and carious teeth.
- 4
Grouping the results in terms of gender, tooth type and condition, it is concluded that a carious molar of boys is a much more efficient contamination pathway for lead, resulting in
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