Page 43 - Veterinary Toxicology, Basic and Clinical Principles, 3rd Edition

10 SECTION | I General

VetBooks.ir Effectively communicate the total risk process
Risk communication

and risk characterization to all stakeholders

Risk research Risk assessment Risk management
Understanding the 1 Hazard identification Risk management
mechanistic linkages 2 Exposure, dose and decisions incorporate
between sources of response assessment the results of risk
toxicants, exposure, 3 Exposure assessment characterizations and
dose and response public health, economic
4 Risk characterization
social and political
5 Identification of considerations
research needs

Action
Identification of research needs

FIGURE 1.2 Risk paradigm for evaluating potential health impacts of a toxicant.

relevant to human situations. The exposure response developed earlier for providing guidance for controlling
assessment involves characterization of this relationship as it occupational exposures, the intake of contaminants
may pertain to likely levels of human exposure. The expo- in food, and the safety of pharmaceutical agents. Prior
sure assessment quantifies, either retrospectively or prospec- to World War II, the primary focus was on adverse
tively, the likely duration and intensity of human exposure health outcomes that caused functional impairment such
to the hazardous agent. The risk assessment element brings as decreased respiratory function. As will be discussed
together information from the other three elements in an later, the issue of carcinogenic responses received limited
integrated manner to characterize risk, as illustrated in attention prior to World War II. The approach to develop-
Fig. 1.1. Risk is defined as the probability of occurrence of ing guidance for the control of toxicants was based on
an adverse health effect from exposure to a hazardous agent the assumption that a threshold exists in the exposure
at a specified duration and intensity of exposure. As an (dose)-response relationship—just as Paracelsus had
aside, especially in Europe, the word hazard used as risk has discussed. The threshold exposure response relationship
been defined in the United States. Safety is defined as being is shown in Fig. 1.3 along with four other relationships:
a condition with a high probability of freedom from any sublinear, linear, supralinear, and a U-shaped or hormetic
increase in adverse health outcome when the agent is used function. Note that both scales in this schematic rendering
in a specified manner. Obviously, both safety and risk are are logarithmic.
relative in recognizing that it is not possible to ensure abso- There is an on-going debate in the scientific commu-
lute freedom from some small level of risk. As the control nity over the merits of threshold versus linear, no-
of hazards and risks has improved, in part through more and threshold models for describing exposure-(dose)-response
more stringent regulations, scientists and society at large are relationships, especially for carcinogenic hazards. I was
increasingly faced with the challenge of how low is low first introduced to this debate in 1965 by one of my
enough. Such decisions should be informed by scientific colleagues at the AEC, the late Paul Henshaw, a pioneer
knowledge. However, it is important to recognize other fac- in cancer biology and radiation effects research. He called
tors that need to be considered. my attention to a paper (Henshaw, 1941) he had published
The more formalized risk analysis approaches that on the use of tolerance dose in radiation protection.
were developed starting in the 1970s built on approaches During the last decade, there has been increased