In brief
Biological monitoring measures how much of a chemical has actually entered the body in a sample of blood, urine or breath; it shows absorption through the skin and the real effectiveness of PPE better than workplace air measurement. In Turkey, a binding biological limit value is defined only for lead in blood; for other substances, the workplace physician decides based on international references. For the result to be meaningful, the right biomarker and the right sampling time are essential.
What is biological monitoring, and how does it differ from air measurement?
Workplace air measurement shows the amount of a substance in the air the worker breathes. Biological monitoring shows how much of the substance has actually entered the body: it measures the substance itself in blood, urine or breath, the metabolite it is converted into in the body, or the effect it produces. The two methods do not replace each other; they complement each other.
There are three situations in which biological monitoring is better than air measurement:
- Absorption through the skin. Substances marked "Skin" in Annex 1 of the Regulation on Health and Safety Measures in Work with Chemical Agents can pass into the body through the skin in significant amounts. Even if the airborne value is low, a worker working without gloves can receive a high dose.
- The real effectiveness of PPE. A mask that does not fit the face or a glove that lets liquid in does not show up in air measurement, but it does in biological monitoring.
- Heavy work and poor hygiene. Breathing rate rises with heavy physical work; eating or smoking at the workplace increases intake by the hand-to-mouth route.
The regulation defines a biological limit value as the upper limit of the concentration of the chemical agent and its metabolite in the appropriate biological medium and of the effect indicator (Art. 4). Art. 12 on health surveillance states that health surveillance includes biological monitoring and the necessary examinations.
The binding biological limit value in Turkey: lead in blood
The only substance for which a binding biological limit value is defined in Annex 2 of the regulation is lead and its ionic compounds. Blood lead level is both the biological monitoring method and the decision criterion for this substance.
| Criterion | Value | Consequence |
|---|---|---|
| Lead in blood, binding biological limit value | 70 µg Pb/100 ml blood | May not be exceeded |
| Any worker's blood lead level | Above 40 µg Pb/100 ml blood | Medical surveillance is carried out |
| Lead in air (time-weighted average over 40 hours a week) | Above 0.075 mg/m³ | Medical surveillance is carried out |
For lead-related risks in battery, soldering and lead paint removal work, our articles on galvanising and electroplating and welding fumes are also useful guides.
Which test for which exposure?
Biological monitoring is not possible for every chemical. The table below summarises the examples most often encountered at workplaces and the sampling times accepted in international practice. The final decision rests with the workplace physician.
| Exposure | Example work | Sample and biomarker | Sampling time |
|---|---|---|---|
| Lead | Batteries, soldering, paint removal | Lead in blood | Not critical (accumulates) |
| Toluene | Paint, adhesives, printing | Toluene or o-cresol in urine | End of shift |
| Xylene | Paint, varnish | Methylhippuric acid in urine | End of shift |
| n-Hexane | Adhesives, rubber | 2,5-hexanedione in urine | End of the last shift of the week |
| Styrene | Polyester, composites | Mandelic and phenylglyoxylic acid in urine | End of shift |
| Benzene | Fuel, some solvents | S-phenylmercapturic acid in urine | End of shift |
| Trichloroethylene | Metal degreasing | Trichloroacetic acid in urine | End of the last shift of the week |
| Hexavalent chromium | Plating, stainless steel welding | Chromium in urine | End of the last shift of the week |
| Cadmium | Pigments, solder, batteries | Cadmium in urine | Not critical |
| Metallic mercury | Measuring instruments, lamp recycling | Mercury in urine | Before shift |
| Organophosphate and carbamate pesticides | Spraying | Cholinesterase activity in blood | Pre-season baseline and during the exposure period |
| Carbon monoxide | LPG forklifts, heaters, foundry | Carboxyhaemoglobin in blood or CO in breath | End of shift |
For solvent-related risks, see our article on solvent vapour exposure; for spraying work, see safety in pesticide application; for carbon monoxide, see carbon monoxide from heaters and stoves.
Why is sampling time so important?
A urine metabolite test is planned according to how quickly the substance is eliminated from the body. Solvent metabolites are excreted within hours; if the sample is not taken at the end of the shift, the exposure of the last few hours is missed. Some substances accumulate over the week; for these, the last shift of the week is used. For metals that remain in the body for a long time, such as lead and cadmium, sampling time is not critical.
For the sample to be reliable, follow these rules:
- The urine sample is taken outside the production area, after workwear has been removed and hands washed. With metals, external contamination gives misleading results.
- The container provided by the laboratory is used; the name, date, time and shift are written on it.
- Very dilute or very concentrated urine affects the result. The laboratory applies a creatinine correction; unsuitable samples are repeated.
- The sample is delivered under the storage and transport conditions in the laboratory's instructions.
- A short information form is completed with the sample: the work done that day and that week, the PPE used, smoking, medicines and non-work exposures (such as home renovation, shooting, hobby soldering).
We plan tests with authorised laboratories and health facilities; we set the sampling time together according to the shift rota.
How are the results interpreted?
A single result only has meaning in context. The following questions are asked when interpreting it:
- Individual or group problem? If the results of several workers doing the same job rise together, the problem lies at the source; if one worker has a high result, their working method, PPE or hygiene habits are examined.
- What is the trend? A value below the reference but rising year on year shows that controls are weakening.
- Are there confounding factors? Smoking affects cadmium, benzene and carbon monoxide biomarkers. Some biomarkers may be affected by diet, medicines or alcohol use.
Art. 12 of the regulation lists what to do where a biological limit value is exceeded or an adverse health effect due to exposure is found: the worker is informed, the risk assessment is reviewed, measures are reconsidered and, if necessary, the worker is moved to another job without exposure. The health of other workers exposed to the same substance is also checked.
An individual result is health data. Only the fitness-for-work result and, where necessary, an anonymous group summary are passed to the employer; the worker has the right to see their own results. For the rules on sharing, see our article on workers' health data and data protection (KVKK).
When is biological monitoring pointless?
The regulation requires health surveillance to be carried out where valid techniques exist to detect disease and effects (Art. 12/1-c). In the following situations, other methods are chosen instead of biological monitoring:
- Irritant gases with local effects. Ammonia, chlorine and acid vapours do not accumulate in the body; they have no valid biomarker. Air measurement and monitoring of complaints are the basis.
- Substances without a biomarker. If there is no reliable method, testing gives false reassurance.
- If sampling time cannot be arranged. For a substance with a short half-life, a sample taken at the wrong time is a wasted test.
- Screening without a purpose. Requesting a "heavy metal panel" for everyone without carrying out a risk assessment and air measurement is not recommended, because it is unclear what will be done with the result.
Six steps to set up the programme
- Complete the chemical inventory and the chemical risk assessment.
- Determine the level of exposure with air measurements.
- Let the workplace physician choose the biomarker, sample type, timing and reference value. Workers are informed before this work begins (Art. 12/1-ç).
- Where needed, take a baseline value at pre-employment; tests such as cholinesterase are only meaningful when compared with the person's own baseline.
- Let the physician set the periodic schedule. There is no fixed frequency for these tests in the legislation; the level of exposure and previous results are decisive. For general examination frequencies, see our article on periodic examinations and tests.
- Feed back the results to the worker, the group summary to the employer and the findings into the risk assessment.
In its health surveillance service, Bursa Sistemer OSGB plans biological monitoring based on the chemical risk assessment. For risks specific to chemical and plastics businesses, see our chemicals and plastics page.
Frequently Asked Questions
Is biological monitoring mandatory for every chemical?
No. In Turkey, a binding biological limit value is defined only for lead, and medical surveillance is mandatory under the conditions in Annex 2. For other substances, the workplace physician decides whether biological monitoring is needed based on the risk assessment and air measurement results.
What happens if blood lead level is above 40?
A value above 40 µg Pb/100 ml blood requires medical surveillance under Annex 2. 70 µg/100 ml is the binding limit. The source is investigated, measures are reviewed and, if necessary, the worker is moved to a job without exposure.
Why is the urine sample requested at the end of the shift?
Solvent metabolites are excreted from the body within hours. A sample taken at the end of the shift reflects that day's exposure; a sample taken the next morning shows exposure as lower than it really was.
Can the employer see biological monitoring results?
An individual result is health data and stays with the workplace physician. The employer sees the fitness-for-work result and, where necessary, a group summary without names; the worker has the right to see their own results.
An exposure-based test plan, pre-employment and periodic examinations, confidential health files and an examination schedule tracked per person.
Bursa SİSTEMER OSGB Technical Team — written from the field experience of our OHS specialists and workplace physicians. Legal information is valid as of the publication/update date; contact us for an assessment specific to your business.