Lead detection in paint

Saturnism is a disease caused by lead poisoning. This poisoning usually results from ingestion or inhalation of dust from paint containing lead salts. This type of paint is usually encountered in older housing (until 1948), as lead is currently prohibited as an additive to paint.

A legislative framework aimed at combating social exclusion sets an obligation for action to prevent child saturnism by requiring that the concentration of lead in paint be controlled. Article 3 of the order of 12 July 1999 concerning diagnosis of the risk of intoxication from the lead contained in paint, implementing article R. 32-2 of the Public Health Code, states that “the lead will preferably be measured using a portable X-ray fluorescence device”. This non-destructive analysis method allows instantaneous detection of lead in a coating.

The material to be analysed is excited by an input of energy, to obtain a spectrum in which the presence of the line characteristic of lead can be recognised and quantified. The measurement principle is as follows: the gamma photon emitted by a radionuclide interacts photoelectrically to eject an electron from an atom of the target. De-excitation of the atom to return it to its equilibrium state, leads to emission of an X-ray photon (X-ray fluorescence), the energy of which is characteristic of the element to be analysed (lead). The X-ray photons emitted are counted by a detector and their number is proportional to the number of atoms per unit surface area of the element looked for. Measurement precision is currently 0.058 mg of lead per cm2 of surface.

The appliances, which are portable, use sources of cadmium 109 (half-life 464 days) or cobalt 57 (half-life 270 days). The activity of these sources is about 400 MBq.

In 2004, a new type of device came onto the market, containing no radioactive source and using an electrical generator working on the same principle as the emission of X-ray fluorescence photons.

These various devices are used by a wide variety of organisations, mainly consulting firms, architects, surveyors, solicitors, real estate agents and building managers. The ASN therefore ensures that the appliances offer radiation protection guarantees appropriate to the conditions of use and sets obligations on the users for handling and storage of these appliances, in order to prevent unauthorised loans and theft.

Uses of radioactivity in molecular biology
Molecular biology is a scientific discipline which studies the molecules carrying the hereditary message:
• deoxyribonucleic acid (DNA). DNA carries genetic information, because it has the particularity of replicating and being transmitted to the descendants. It has a data storage role;
• ribonucleic acid (RNA). RNA plays a key role in synthesising proteins. It is the messenger of the genetic data (gene transcription).
In these molecules, molecular biology analyses the structure of the genome and its alterations (mutations) as well as the mechanisms of the normal and pathological expression of the genes. The term molecular biology is sometimes used to designate gene study techniques.
These techniques include:
• the Southern technique, developed by the British researcher E. Southern in 1975. It is used to identify and observe a DNA sequence or a gene without isolating it;
• the Northern technique, in which the process - identical to that of the Southern technique - is applied to RNA;
• the Western-Blot reaction which is used to look for antigenic (for example viral) proteins or antibodies, in particular in blood serum.

These techniques use a nucleic probe or an antibody marked with a radioactive isotope allowing identification, visualisation and quantification by autoradiography, in other words by obtaining an image produced on a photographic film (or emulsion) placed in contact with the preparation, through the radiation of the radioactive marker. For example, in the case of marking of a DNA or RNA probe, an atom of radioactive phosphorus (32P or 33P) or radioactive sulphur (35S) is incorporated into a nucleotidic sequence. The activity levels involved are about 2 to 4 MBq;

For in vivo marking techniques, thymidine marked with tritium (3H) is generally used for DNA and uridine marked with tritium for RNA. The activity levels employed are about 10 to 100 MBq.

Although radioactive marking techniques are common, in certain cases, other "cold" marking methods (in other words without radionuclides) can also be used to visualise macromolecules. These are for example fluorescent, chemical or bioluminescent markers, or detection of the {enzyme-substrate} complex using colorimetry.