What are the Problems Associated With Exposure Risk Assessment?

Exposure risk assessment and guidelines for determining which risks are acceptable or the limits up to which a particular exposure is safe are in a state of utter confusion. Regulatory agencies, like Environmental Protection Agency of the United States of America wrestle daily and inconclusively with the problem.

Often administrative authorities direct the regulatory machinery to check the use of chemicals which are unsafe and it is left to the regulatory machinery to determine what chemicals are unsafe and up to which limits the use of the chemical has to be permitted. Plenty of discretionary powers are allowed to these agencies which are often subject to pressures and counter pressure for the contending sides to influence the official decision to their advantage.

1. Expert Uncertainty:

Scientific methods are often unable to provide reliable evidence which clearly indicate when the level of exposure becomes dangerous to humans or to other forms of life, or what chemicals are capable of causing late and latent effects which are considered hazardous. In most of the cases appropriate tests have not been conducted so far.

And often in cases where the required tests have been carried out experts may disagree over the interpretation of the data. Discretionary judgements have to be used to answer the public enquiry. Sometimes we are simply unable to determine the exact limits of acceptable exposures as we lack the technology required for the same.

For example, a toxic blood level for Lead has been considered to be between 20-25 micrograms per decilitre of blood. More recent research indicates that Lead blood levels as low 10-14 micrograms per decilitre in children and fetuses could be harmful.

However, 20-25 microgram per decilitre remains the most acceptable value for two practical reasons: firstly most commonly used tests cannot detect Pb-levels lower than 20 micrograms per decilitre and secondly that the drugs used to remove Lead from blood stream do not work well below this level (Annonymous 1987).

2. Problem of Disappearing Threshold:

Extremely sensitive technology now enable scientists to detect hazardous substances in increasingly smaller and smaller concentrations in living systems and various components of the environment. That these concentrations are entirely harmless cannot be said with any certainty. If the living system detoxifies and eliminates them the process does place some strain on the system, howsoever, small it may be.

Thus, the threshold concentration levels of many toxic substances are coming down and down as new and more sophisticated technologies are developed. It becomes difficult, therefore, to ascertain which of the threshold concentration level should to be used to regulate the use of the chemical in society (Rosenbaum 1991). Moreover, with gradually lowering threshold of concentration the cost of regulating or restricting the use of the chemical concerned rises dramatically.

For instance, after reducing almost 85% of a toxic metal from waters of a canal it could cost almost half as much or more to remove an additional 5 or 10%. In practice, once the risk threshold earlier presumed by Policy-makers is questioned all measurable concentrations of the substance are supposed to be harmful in one way or other.

To eliminate any probability of risk from such substance authorities may have to eliminate it completely from the system – a demand which is extra-ordinarily expensive and almost impossible to be complied with. And if a compromise has to be made between the risk assessment or the damages caused and benefits that accrue from the use of the chemical what criteria should be used to regulate the threshold levels (Anonymous 1987)?

3. Questionable Nature of Inferences Drawn from Data on Toxicity Studies:

Observations on the toxic effects caused by chemicals to a living system are usually based on experiments carried out on test animals which are a rich source of controversy and confusion. In these studies test animals are exposed to the chemical substance under controlled conditions, the effects produced are carefully monitored and the risk are extrapolated to probable effects which the chemical causes to humans.

Due to obvious reasons (such as inherent differences between the human and animal system) it is quite likely that human system may not give the same responses as shown by animals. Animal studies become particularly controversial when the effect of very low level of exposures for long durations is to be determined (Doniger, 1978). Obviously the risk in such cases shall be small but how small? Scientists cannot use enough animals to eliminate the possibility of errors in determining the effect of very low levels of exposures.

For example, to show with 95% confidence that a low dose of a substance shall cause cancer in one case out of a million, it would require experiments involving six million animals. Instead of doing so, scientists have to use higher doses with relatively few animals and extrapolate the results, through statistical models, to the effects of low doses on humans. The result can vary wildly and could often make the study meaningless. The scientist uses his discretionary judgement which can vary from one scientist to another (Williams 1976, Annonymous 1987).

4. Political Bias:

Given enormous discretionary powers the machinary responsible for regulating the use of chemicals the selection of chemicals considered hazardous and the determination of the acceptable levels of exposures is often governed by socio-economic and political forces (Revelle, 1981). Impressed by ill health effects of a particular type caused by a Toxic Material in Environment and Exposure Risk Assessment particular chemical a complete ban may be ordered on it although the risk may be as little as less than one incidence per million. Other chemicals which may be much more dangerous may not be cared for at all.

For example, during the Carter Administration, the White House ordered the Occupational Safety and Health Administration (OSHA) to treat any suspected carcinogen as a proven health hazard until tests prove it to be harmless.

Moreover, the substance was considered to be a suspect for inducing benign or malignant tumours if it has been shown to be so even in a single laboratory study. During the Reagan administration things changed in USA. The Occupational Safety and Health Administration was required to obtain a more convincing proof before the substance could be considered a suspect and much more information was called for to put restriction on its use (Revelle, 1981).

5. Limited Nutrality of Scientific Judgement:

As many opportunities exists in the process of exposure risk assessment to make discretionary decisions for the scientists their role becomes more important. Normally scientists are expected to exercise their judgement uninfluenced by socio­economic and political conditions.

However, a scientist is also a part of the society. He has to live in it. There is every likelihood that his judgement may be tainted by current presumptions and thinking of the society plus his own notions about the use, risk and benefits of the chemical concerned. Thus, important decisions could be taken simply on the whims and fancies of a few scientists (Francis, 1986).