Distribution and Effects of Chemicals in Communities and Ecosystems - Organic Pollutants: An Ecotoxicological Perspective - page 85

r

c

h

Stressed

Reversible Irreversible

Healthy

Homeostasis Compensation Noncompensation Death

B5

B4

B3

B2

B1

Physiological Condition
Pollutant Concentration

fIgure 4.4 Relationship between exposure to pollutant, health status, and biomarker
responses. Upper curve shows the progression of the health status of an individual as expo-
sure to pollutant increases; h, the point at which departure from the normal homeostatic
response range is initiated; c, the limit at which compensatory responses can prevent develop-
ment of overt disease; r, the limit beyond which pathological damage is irreversible by repair
mechanisms. The lower graph shows the response of five different hypothetical biomarkers
used to assess the health of the individual. (Reproduced from Depledge et al. 1993. With
permission from Springer-Verlag.)

following the interaction of DDT or pyrethroids with Na + channels, although these
are changes that may also be caused by the operation of other toxic mechanisms.
These will also be treated as mechanistic biomarkers in order to distinguish them
from other responses that are only biomarkers of exposure (e.g., the induction of
certain enzymes that can occur at low levels of exposure before any toxic effects are
manifest). Mechanistic biomarkers (see Table 4.2 for examples) have potential for
measuring adverse effects of chemicals in the field—effects that may be translated
into changes at the population level and above.