NIZNHNY
NOVGOROD UNIVERSITY
DEPARTMENT OF ECOLOGY
Summary
HUMANE
APPROCHES
TO
TOXICOLOGICAL EVALUATIONS
OF
INDUSTRIAL CHEMICALS
Made by
Loginov V. V.
Scientific advisor
d. b. s.,
prof. Gelashvili D. B.
NIZHNY NOVGOROD, 1999
There
are millions of chemical substances recorded in the scientific literature with
many more being added annually through the endeavors of chemists in industry
and academia (Tаble 1). Tens of thousands of these substances are used in
commerce, as demonstrated by the publication of inventories in the European
Economic Community under the Sixth Amendment to the Dangerous Substances
Directive and in the United States through the Toxic Substances Control Act
(TSCA).
The
enormous growth of the chemical industry, coupled with the potential for
increased exposure of the population to chemicala, has generated growing public
concern and an awareness of the need for correct safety aascsfunent. The
toxicological assessment, therefore, of the potential health hazards posed by
chemical substances to which humans and animals may be directly or indirectly
exposed Is a rational requirement of civilized society.
TABLE 1 Chemical
Substances Known
Group
|
Approximate
number
|
Documened
chemicals
(Chemical Abctracts)
|
7,000,000
|
Increase
per annum
|
400,000
|
EINECS
(European Inventory of Existing
Commerical
Chemical Substances)
|
95,000
|
ECOIN
(European Core Inventory)
|
34,000
|
Known
drugs
|
4,000
|
Known
pesticides
|
1.500
|
Over the last
40 years or so, the use of toxicology as a predictive science has developed
immensely. This growth has been stimulated by an increasing amount of
legislation that ensures that relevant toxiclty studies, which include
whole-animal studies, are completed on a variety of chemical substances.
The knowledge of whether a chemical
substance has the potential to poison a biological system, cause irritation on
contact with the external tissues or cause an allergic response, Is imiwrtant
in establishing a safer environment. An awareness of these properties assists
society in ensuring correct and safe procedures when people or animals are
exposed to chemicals.
Trade in chemicals is
international, and therefore understanding the hazards of chemical substances
and identifying those hazards on the label requires an international language
of hazard warning. Acute toxic effects derived from animal studies have been
the subject of standardization for classification and labeling for many years.
The language of the label-TOXIC, VERY TOXIC, HARMFUL, IRRITANT, CORROSIVE-is understood
by the international community.
While
society demands health and safety as prerequisites for the development,
manufacture, and use of chemical substances, society is also concerned with the welfare and humane treatment of
the laboratory animals used in toxiclty testing. This, of course, poses a
potential paradox since the complete assessment of the toxicity of chemical substances
involves the use of laboratory animals. Codes of practice have been established
in many countries to promote humane procedures. The Organisation for Economic
Co-operation and Development (OECD) haa made enormous progress in standardizing
toxicological testa to reduce barriers to trade caused by varying protocol
requirements between nations, and this has had a significant influence in
reducing the number of animals used in toxicological studies. The use of live
animals as experimental models is not in itself inhumane, although this view is
not shared by everyone.
In vitro systems that avoid
the use of live animals have been developed for predicting the mutagenic, and
possibly carcinogenic, potential of chemical substances, one such Is the Salmonella typhimurium reverse mutation
assay (Ames test). This has stimulated many toxicologists, biologists,
pharmacologists and biochemists to consider whether alternative in vitro/ex
vivo procedures could minimize the need for whole-animal studies in other areas
of toxicology.
A
primary objective for achieving general acceptance of any in vitro alternative
to an animal model for the assessment of potential risk to humans and the
environment is to have it accepted by regulatory authorities as a recognized
assessment of a toxic property; nowadays there are very few circumstances in
chemical manufacture, marketing, transportation, and use that do not come under
the auspices of a government department somewhere in the world.
In
short, in vitro alternatives need to satisfy scientific criteria for their
acceptability and need to satisfy the international regulatory community that
their use will not compromise assessment of risk or pose serious problems to
international trade in chemicals.
1. OCULAR
TOXICITY
The eye is one
of the most valuable and vulnerable of sense organs (Albino rabbits are used in
the test). Dusturbance of vision, injury to the eye, or even loss of sight due
to chemical or phisical damange must be recognized as a most traumatic
experience. It is the abhorrence of such events that necessitates the testing
of chemicals in order to reduce, and hopefully prevent, their occurrence in
humans. This method is the basic for most eye irritation testing today. New
chemicals and mixtures of chemicals pose a potential eye hazards to humans. The
nature of the hazards needs to be assessed because warnings about the potential
harm that a chemical can do to the eye only have credence if they are based on
valid information. Labeling all chemicals as hazardous would substantially
lessen the benefit of the warning label. Convincing workes and customers that a
hazards exicts and that there is a need for special care, including the use of
protective eyeglasses or goggles, has to be related to good extrapolation from
suitable model systems. The rabbit eye test has its liminations, but in our
view it is still the best practical way of assessing ocular damage and can be
conducted using a humane approach.
2. SYSTEMIC
TOXICITY
In testing for
acute systemic toxicity, it is our opinion that in vitro test systems are
unlikely to replace in vivo studies. The principle of the test method and
procedures generally recommended have been reviewed by many, recently by
Organisation for Economic Co-operation
and Development. The rat and mouse are the species of choice because
they are able to display a full range of clinical signs of toxicity. The test
substance is administered by the most appropriate route (either oral, dermal,
or inhalation) to small groups of animals at a range of draduated doses. The
formulations of substance and volume administered are standardized as far as
possible to avoid the confounding effects of minor protocol variation. Acute
systemic toxicity studies assess the relationship between the dose of a
substance and adverse effects, its toxicity relative to other substances of
know toxicity, the specific clinical
sings of toxicity, the physiological systems affected, and often an indication
of the mode and potential mechanism of toxic action. Such information may help
the clinical to diagnose and treat adverse effects when they occur in humans
using specific antidotes. The humane approach employed in most industrial
laboratories is he use of the minimum number of experimental animals and the
use of euthanasia when toxic effects are detected. In our own laboratory, with
experience of a number of different types
of industrial chemicals, many substances are defined adequately by a
limit dose or rangefinding study. Indeed, following acute exposure, a
relatively small number of substances produce observable adverse systemic
effects (Table 2).
TABLE 2
|
Toxic Categories Following
Acute Oral and Dermal Dosing Studies
in the Rat
|
Oral
|
Category
|
Dermal
|
65%
|
Low toxicity
|
66%
|
(>2000 mg/kg)
|
|
(>2000 mg/kg)
|
29%
|
Harmful
|
24%
|
(200-2000 mg/kg)
|
|
(400-2000 mg/kg)
|
5%
|
Toxic
|
9%
|
(25-200 mg/kg)
|
|
(50-400 mg/kg)
|
0.8 %
|
Very toxic
|
0.9 %
|
(<25 mg/kg)
|
|
(,50 mg/kg)
|
The use of
fewer laboratory animals, coupled with a less rigid adherence to the need for statistical
precision, is a rational approach that will allow assessment of toxicity hazard
and heme prevent human suffering.
3. CUTANEOUS
TOXICITY
Skin contact
is probably the most common form of exposure to industrial chemicals.The most
common in vivo approach to determine such potential is based on the method of
Draize et al. In the Draize skin test the animal of choice is the albino
rabbit. The skin, like many other organs, is complex is born structure and
function. Substances that interact with this tissue can produce different toxic
effects. The skin represents tissue that will allow more readly the development
of a variety of in vitro and ex vivo systems to assessirritancy and
corrosivity. However, the complexity of the immunological system means that
contact allergy may not be as readily stadied using in vitro tecniques.
The preceding section of
this chapter have deal with the areas of ocular toxicity, acute sustemictoxicity,
and cutaneous toxicity, and a common theme has emerged. There is, in our
opinion, no immediate likelihood of in vitro alternatives replacing laboratory
animals in the assessment of acute effects caused by chemical substances.
Society demands of the
toxicologist a high degree of certainty in determining health hazards, with a
minimal tolerance of error. Toxicologists, therefore, need to be cautious that,
in their search for alternatives to laboratory animals, they do not reduce the
predictive quality of toxicological assessment to the point where people will
be put at risk.
Selection of a hazard label
is particularly dependent on knowing the relative systemic
toxicity through the estimation of the median lethal dose (LP50) and the
irritant class. The vast majority of chemicals have been classified by data
derived from toxicity studies in laboratory animals and, in our experience,
with only a small number of chemicals producing adverse acute effects in the
acute toxicity tests (Fig. 1). Thus, if there is to be an in vitro alternative
to studies in laboratory animals that will have a role in international
labeling and classification, it must be very well validated against the animal
model. This difficulty should not, however, preclude the use of in vitro tests
per se, although it will certainly have a modifying influence on the rate at
which they gain acceptance by regulatory authorities.
|
|
a
SYSTEMIC - oral
(10%)
- dermal (8%)
IRRITATION - skin
(20%)
- eye (21%)
SENSITISATION -
skin (31%)
|
|
FIGURE 1 Acute toxicity studies (outcome of ICI experiments, 1976-1983). (a)
Proportion of studies, (b) Proportion of studies with effects, (c) Proportion
of all studies.
The
chemical industry is most concerned for the health and safety of people who may
be affected by its products and activities. The toxicologist is pivotal in
producing the data that can help reduce risks by improving the knowledge and
understanding of the hazardous properties of chemical substances. The use of
laboratory animals to investigate these hazards is unavoidable until such time
as in vitro alternatives have proven ability to predict the dangers to humans.
LITERATURE
1. Jackson S.J., Rhodes C.,
Oliver G.J.A. Humane approaches to Acute Toxicity Assessment of Industrial
Chemicals. // Toxic Substances Journal. 1989. pp.279-299.
2. O Flanerty E.J. Dose
Dependens Toxicity. // Commenis Toxicology. 1986. Vol.1. pp. 23-34.
3. Toxicological
Evaluations. Potential health hazards of existing chemicals. BG Chemie. Berlin.
1990. 341 p.
|