Environmental Health Criteria 214

HUMAN EXPOSURE ASSESSMENT
breast-feeding infants (Niessen et al., 1984; Davies & Mes, 1987;
Sikorski et al., 1990; Sim & McNeil, 1992). Organic chemicals found in
breast milk have high lipid solubility, resistance to physical
degradation or biological metabolism and slow or absent excretion
rates (Rogan et al., 1980). Breast milk represents a major route of
excretion of lipophilic chemicals for lactating women (Rogan et al.,
1980; Sim & McNeil, 1992). Concentrations of chemicals in breast milk
are a function of parity, age, body mass, time of sampling,
nutritional status, lactation period and fat content of milk (Rogan et
al., 1986; Sim & McNeil, 1992). Breast milk results are generally
standardized to milk fat levels.
Breast milk sampling represents a non-invasive method to estimate
body burden of contaminants in adipose tissue. The correlation between
contaminant concentrations in the lipid phase of milk and adipose
tissue is good (Sim & McNeil, 1992). External contamination is a
concern for breast milk samples; all sampling equipment should be
cleaned in a manner that will prevent contamination. Although breast
milk sampling is an applicable way to estimate population exposure to
chemicals that bioconcentrate, sampling is limited to lactating women,
who may or may not be representative of the population as a whole.
10.6.8 Adipose tissue
Exposure assessment studies using adipose tissue have been
limited primarily to ecological studies comparing fat from cadavers or
surgical specimens to general pollution levels. Adipose tissue
represents a long-term reservoir of lipophilic compounds that the body
slowly metabolizes and may release into the bloodstream. Unfortunately
there is no non-invasive manner to sample fat stores directly, and
many subjects see fat sampling as exceedingly invasive. The analytical
method and detection limit requirements determine the quantity of
adipose tissue necessary. In studies measuring body burden of dioxins
in fat, a minor surgical procedure was necessary to collect a 20 g
sample from healthy potentially exposed subjects (Patterson et al.,
1986). When a smaller sample size is sufficient (200 mg or less),
needle biopsies of fat stores in the buttocks can be used (Que Hee,
1993; Kohlmeier & Kohlmeier, 1995).
10.6.9 Faeces
Faeces are a highly fat-soluble medium that provides information
on compounds of high-molecular weight that exit the body via biliary
excretion and on unabsorbed chemicals that enter the body via
ingestion. Metals may also be monitored in faeces; however, it is
unclear whether the metals found in faeces represent absorbed or
unabsorbed elements (DiVincenzo et al., 1985; Vahter et al., 1991).
Although collection of faeces is regarded as non-invasive, very few
subjects are sufficiently motivated or interested in their collection
(Bihl et al., 1993).
10.6.10 Other media
Several additional biological media have been used for
determination of biomarkers of exposure including tears (e.g.,
Ellegard, 1997), nasal lavage and nasal plugs (Steerenberg et al.,
1997), sputum (e.g., Pizzichini et al., 1997) and semen (e.g., Sram et
al., 1996). In most cases, these studies have focused on biomarkers of
inflammation as indicators of exposure to airborne oxidants.
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