Risk Assessment – Brief Introduction

Paracelsus statement “All substances are poisons, there is none that is not poison. The right dose differentiates a poison from a remedy” describes the central theme that underlies the processes of risk assessment and risk management. Any chemical given in excess can cause harm, while in moderation it can be of benefit. However, at a given dose one individual may be cured, another will see no effect, and a third one may die because of hypersensitivity to the substance. A variety of other effects may be seen between the extremes of death and no response.

Determining what constitutes a “safe” level of exposure becomes a difficult task when we consider the wide array of chemicals in existence as well as the variability of individual response to them. Two informations for determining acceptable exposure levels: 1) the toxic effects associated with exposure to the substance, 2) the level of risk the public or the user is willing to accept.

All human activities are associated with some degree of risk. It is defined as the probability (chance) that an adverse effect will occur under a specific set of circumstances. In the final analysis an individual will undertake a particular activity based upon his/her perception of the risk involved weighed against the apparent benefits that will be derived.

Regulatory agencies such as EPA, FDA and OSHA are involved in determining risk associated with chemical exposure. EPA, through a variety of environmental laws, regulates exposure to toxic substances that may be released into the environment. FDA is concerned with toxic substances added to foods and cosmetics. OSHA evaluates and regulates toxic substances in the workplace. One of the primary functions of these agencies is to establish guidelines and safe levels of exposure for toxic substances.

It must be noted that in reality, there is always some risk because of the differences in susceptibility and sensitivity of individuals to a particular toxic substance. Therefore, it is not possible for regulatory agencies to establish absolute, safe levels guaranteeing that no individual will ever develop an adverse effect. However, agencies can determine the circumstances and concentrations where the risk of an adverse response is extremely low, thus defining the level of exposure that may be considered safe.

There are two phases in the establishment of acceptable exposure levels; risk assessment and risk management. Information derived from these activities is used to determine the risk involved in exposure to toxic substances and how to best manage risk.

There are qualitative and quantitative definition for risk. These approaches are necessary to fully perceive and comprehend how risk are being established for safety purpose.

Qualitatively, risk at minimum degree must involve the possibility of an adverse outcome and uncertainty over the occurrence, timing or magnitude of that adverse outcome. Thus, risk is a combination of uncertainty and damage that may result. Hazard is the source of the risk, there must be a safeguards value to compensate possible hazardous effect to human health.

Risk = uncertainty + damage

Risk = hazard/safeguards

Risk as defined quantitatively may be formulated as follows:

Triplet: R {}, i=1,2,3…N

S represents scenario (what can happen?)

P represents probability (how likely is it that it will happen?)

X represents consequences (what are the consequences if it does happen?)


Kent, C. 1998. Basics of Toxicology. John Wiley & Sons, Inc. New York

Class material: Environmental Toxicology and Risk Assessment

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