Handbook of Solvents - George Wypych - ChemTech - Ventech!

1080 Myrto Petreas
In short, biological monitoring should be used with specific objectives, such as to
evaluate exceedence of a reference or regulatory value; dermal or oral exposure not assessed
by personal monitoring; efficacy of protective equipment; etc. Accordingly, current,
recent or cumulative exposure may need to be assessed and, therefore, the appropriate
chemical (parent or metabolite) should be monitored in the appropriate specimen, collected
at the appropriate time, from the appropriate worker(s).
15.2.1.2 Types of samples used for biological monitoring
Of the various tissues/fluids that can be used for biological monitoring, the most common
are blood, urine and exhaled air because they are relatively easy to obtain.
Blood collection is the most invasive of the three and the chemical analysis may be
subject to interferences because of the complex matrix. Additionally, concern over hepatitis
and HIV infection, and confidentiality issues, make blood sampling less attractive for routine
collection. Nevertheless, concentrations of a compound of interest in blood are easier to
relate to concentrations at the target organ.
Analysis of urine samples allows elimination rates of the chemical or its metabolite(s)
to be ascertained. However, measurements in urine require specimen collection under a
schedule (first morning urine, or 24-hour sample) that can create logistical difficulties. The
concentration of the contaminant, or its metabolite(s), is usually corrected for the dilution of
the urine (specific gravity or, more commonly, creatinine correction) to be used as a measure
of dose.
Collection of breath samples is the easiest of the three methods. It is non-invasive; it
can take place almost anywhere; and the analytical matrix is usually very simple. The basic
assumption underlying breath monitoring is the existence of gaseous equilibrium between
the concentration of the vapor of interest in the alveolar air and in the arterial blood. This relationship
must be established for every solvent for which biological monitoring by exhaled
air analysis is considered. The apparent simplicity of breath sampling should not be overstated,
however, and the limitations and pitfalls should be identified before any large scale,
routine applications of breath monitoring can be envisioned. Since breath is a non-homogeneous
mixture of air coming from different regions of the lung with varying ventilation, perfusion,
and diffusion characteristics, some portion of the breath should be consistently
identified and tested for its relationship to the blood concentration.
The ACGIH only recommends measurements in exhaled air when: 7
• The chemical is poorly metabolized and, therefore, exhalation is the primary route
of elimination;
• Sampling can occur when the effect of time and other circumstantial factors can be
controlled;
• The sampling method is well defined.
15.2.1.3 Fundamentals of respiratory physiology
In order for any inhaled solvent vapors to enter the blood circulation, they need to reach the
alveoli, cross the gas-blood interface and dissolve in the blood. Gas is carried to the
gas-blood interface by airways, while blood is carried by blood vessels. Since these functions
take place in the lung, the essentials of respiratory physiology will be briefly reviewed.
The primary function of the lungs is to allow oxygen to move from the inhaled air into
the arterial blood and to allow carbon dioxide to move from the venous blood to the exhaled
air. Both oxygen and carbon dioxide move between air and blood by simple diffusion from
an area of high partial pressure to an area of low partial pressure. The barrier between air and
blood is less than 0.5 µm in thickness and has an area of between 50 to 100 m 2 . 8 This barrier
is very efficient for gas exchange by molecular diffusion, according to Fick’s 2nd law.