Module 3: Toxicology - Section 4: Biological Monitoring

TOX 4.2: Lecture: Biological Monitoring and Biological Effect Monitoring

LEGISLATION:

1. OHSA: Regulations for hazardous chemical substances 1995. (Open up the book "Regulations", and then open the book "Hazardous Chemical Substances Regulations", 1995).

   "an employer shall ensure that an employee is under medical surveillance if the employee may be exposed to a substance listed in Table 3"

   Table 3: Substances for which BEIs exist..

2. OHSA: Lead Regulations, 2001. (Open up the book "Regulations", and then open the book "Lead Regulations, 2001").

DIFFERENT TYPES OF WORKPLACE MONITORING:

Environmental monitoring:

Concentration of a substance in air, on surfaces, etc. (province of occupational hygiene).

Biological monitoring:

Concentration of a substance in body tissue /excreta.

Biologic effect monitoring:

Reversible physiological effects of a substance on an organ system.

Screening:

Early disease, or a marker of acquired or genetic susceptibility (overlaps with biological effect monitoring).

SUBSTANCES WITH BEIs IN TABLE OF THE HCS REGULATIONS:

Metals: arsenic*, cadmium, chromium VI*, mercury*, lead*;

Aromatic solvents: benzene*, ethyl benzene, chlorobenzene, nitrobenzene, phenol*, toluene*, xylene*;

Chlorinated solvents: Perchloroethylene*, trichloroethylene*, methylchloroform*;

Other solvents: carbon disulfide, dimethylformamide, methanol*, methyl ethyl ketone (MEK)*, methyl isobutyl ketone, n-hexane*, styrene;

Pesticides: parathion*, pentachlorophenol;

Miscellaneous: Aniline, carbon monoxide*, fluorides, furfural.

* You are more likely to encounter these in practice.

SUBSTANCES IN TABLE 3 FOR WHICH BIOLOGIC EFFECT MONITORING CAN BE DONE:

1. Cholinesterase* (organophosphate, carbamates);
2. Carboxyhaemoglobin* (carbon monoxide, methylene chloride);
   
   
   Question 2: How much carboxyhaemoglobin do smokers have? Why is this relevant to biological monitoring? (Answer)
   
   
3. Methaemoglobin (aromatic amines and nitro-compounds);
   
   
   Note: The iron in haemoglobin is normally in "ferrous" form, i.e. Fe²⁺. Methaemoglobinaemia is a pathological (cyanotic or "blue blood") state in which the iron is oxidised to the "ferric" form, i.e.Fe³⁺. (If you cant remember which way around this goes, suffice to say that "in methaemoglobinaemia the iron is chemically altered so that the molecule malfunctions".)
   
   
4. Zinc protoporphyrin* (lead);
5. Urinary enzymes e.g. beta 2 microglobulin for (cadmium), N-acetyl glucosaminidine (NAG) (lead);
6. Mutagenic / ? precarcinogenic changes.
   
   * Likely to encounter in practice.

BIOLOGICAL EXPOSURE INDEX (BEI):

1. ACGIH concept
   
   
   Question 3: What is the ACGIH? What is their relationship to the US government? (Answer)
   
   
2. The BEI is a reference level for occupational exposure
3. Linked to TLV for inhaled substances
   
   
   Task:: Revise your understanding of TLV.
   
   
4. BEI = concentration observed in a healthy worker doing (non-strenuous) work for 40-hour work week at TLV-TWA
5. Thus incorporates both a measure of exposure and of risk (via the TLV equivalence).
   
   
   Question 4: You find that two workers exposed to arsenic have urine arsenic concentrations of 60 µg/g creatinine and 300µg/g creatinine respectively. Describe the steps you would take and what you would tell the workers. (Answer)
   Question 5: What biological monitoring would you do for toluene? When would you take the specimen? What practical problems might you encounter in setting up a procedure for the regular monitoring of toluene? (Answer)