This article throws light upon the nine criteria’s to be considered for evaluating biomarkers. The criteria’s are: 1. Biological Specificity 2. Clarity of Interpretation 3. Time of Responses 4. Permanence of Response 5. Reliability 6. Methodological Considerations 7. Relative Sensitivity 8. Validation in the Field 9. Linkage to Higher Level Effects.

Criteria # 1. Biological Specificity:

It important to know which classes of organisms the biomarker may be used on.

The inhibition of the enzyme acetyl choline esterase (AChE) can be applied throughout the animal kingdom, whereas the induction of vitellogenin is confined to those vertebrates that lay eggs.

Criteria # 2. Clarity of Interpretation:

How clear cut is the endpoint as an indicator of exposure to anthropogenic stress? Can the endpoints be clearly distinguished from natural stresses? It is valuable to know the mechanism of re­sponse to the chemical in assessing this point.

Criteria # 3. Time of Responses:

The response temporal expression of different biomarkers can vary widely from nearly instantaneous to years. Depending on the type of study, slow or rapid manifestation may be desirable.

Criteria # 4. Permanence of Response:

Similarly, it is im­portant to know how long the response lasts. If it is transient, it may readily be missed. The inhibition of AChE, especially in blood, is a transient response and thus it is necessary to know when the exposure occurred to assess the importance of the degree of inhibition. In contrast, the inhibition of ALAD is only slowly reversed.

Criteria # 5. Reliability:

This can be considered under two headings:

(a) Environmental influences that modulate the organism’s response to a chemi­cal, and

(b) Inherent variation in the biologi­cal response to a given exposure. It is impor­tant to know the extent of all variation in or­der to have a reliable biomarker.

Criteria # 6. Methodological Considerations:

Important considerations here are precision (analytical reproducibility of the method) and cost and ease of the analysis. Although many reliable essays have been developed there is a need for standardisation, along the lines used in ana­lytical chemistry, so results from different labo­ratories are comparable.

Criteria # 7. Relative Sensitivity:

It is important that the biomarker be sensitive when compared to other endpoints, such as mortality or repro­ductive impairment, and it is important to know the relative sensitivity of this compari­son.

Criteria # 8. Validation in the Field:

For a biomarker to be useful in environmental assessment, it must be validated in the field. Organisms in the field are subjected to a wide range of variables that are usually accounted for or controlled in labo­ratory experimentation.

Criteria # 9. Linkage to Higher Level Effects:

A biomarker is more useful if there is clear linkage to ef­fects at higher levels of organisation. Studies on invertebrates have been particularly fruit­ful as population changes occur more rapidly than in higher species. In general, biomarker assays are particularly useful when they relate to toxic effect and not just exposure.

The most important reason for using biomarkers in environmental risk assessment is that they can give information on the effects of pollutants. Thus the use of biomarkers is comple­mentary to bio-monitoring which involves the de­termination of levels of environmental chemicals.