Humane approches to toxicological evaluations of industrial chemicals
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
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
|
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 %
|
|
(,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.