Hazard Assessment and Contaminated Sites - Dealing with Contaminated Sites: From Theory Towards Practical Application - page 527

The use of non-treated and vehicle-control groups aids assessment of effects due
to vehicle or excipients. When a vehicle is used to deliver the doses of the con-
taminant understudy (e.g., a lipophilic contaminant delivered in corn oil), the need
for vehicle-treated controls is paramount. Some parameters can be affected by ani-
mal handling (e.g., the serum enzyme ALT was raised in mice which were grasped
around the body compared with unhandled or tail-handled mice; Swaim et al. 1985 ),
so control animals should be treated in the same way as test animals.
Control animals must receive as much attention during the analysis and evalu-
ation process as do the treated ones as any untreated animal or group may exhibit
some signs of abnormality or drift from the norm for that species or strain.
Historical control data may be useful when evaluating the acceptability of
the “normal” data obtained from control groups (Haseman et al. 1984 ; Paynter
1984 ).
12.3.5.1 Mortality/ Survival
The separation of deaths caused by factors unrelated to exposure to the test contami-
nant (e.g., acute or chronic infections, age or disease-related degenerative processes,
anatomical abnormalities, negligent handling or accident) from toxicity-induced
deaths is important. All data relating to moribund or dead animals during their study
life, as well as the results of post-mortem examinations, should be scrutinised in an
attempt to make this distinction. The US EPA guidelines state that the highest dose
used in sub-chronic studies with non-rodents should not produce an incidence of
fatalities which would prevent meaningful evaluation.
Changes in the protocol during the course of a study can complicate the analysis
e.g., alterations in dosage levels can produce a confusing mortality pattern.
Any unusual mortality pattern should be explained by the test laboratory on
biological or toxicological grounds. If overall mortality is high (i.e., significantly
greater than expected for the particular colony and strain) for any repeat-dose study,
or for a particular group within a study, a credible explanation should be provided.
Deaths which are clustered at a specific time period may reflect a sponta-
neous epidemic disease situation of limited duration. High mortality associated
with infectious contaminant in treated groups, in the absence of such evidence in
the concurrent control group, could indicate an immunosuppressive action of the
contaminant being tested.
The effect of dietary intake on mortality needs to be considered. A contaminant
administered in the diet may make the laboratory chow more or less palatable, may
have a pharmacological stimulant or depressant effect on appetite, or may affect
the partitioning of the nutrients in the food. Likewise, decreased water consumption
(e.g., in the case of an unpalatable contaminant administered in the water) will lead
to reduced food consumption. These effects may significantly influence longevity
since it has been clearly shown in animal species that long-term dietary restric-
tion very significantly increases lifespan (e.g., Tucker 1979 ). Conversely, excessive
ad libitum intake of highly nutritious diets can reduce lifespan compared with the
expected average lifespan for an animal species/strain.