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Pollution Ranking

The following is the pollution ranking scheme developed by Blacksmith Institute for assessing the pollution severity at identified dirty places around the world. The relative subjectivity of some of the factors considered is balanced by the expertise packed in Blacksmith Institute’s Technical Advisory Board.


The structure of the database of nominated sites has been upgraded and a number of new sites have been added. This brings the total number of sites in our database to nearly 400 but there remain many sites across the world that have not yet been identified. A focused effort is being put in place to expand the coverage. However, it is not expected that the database will be regarded as complete for some time yet. The 2007 World's Worst review is based on a better, but still incomplete, list of nominations.

A key factor in this year's process is that of representativeness. The Technical Advisory Board review recommended that the sites put to the full TAB for selection of the World's Worst should be representative in terms of both the types of sites in the database and also their geographical distribution. The long list has therefore been presented in the form of a matrix of candidate sites.


The scoring system involves an algorithm that takes into account basic selection criteria. This approach is based on basic hazard assessment logic that can be summarized as:


Each of these essential links in the causal chain is represented by criteria that are included in the scoring methodology presented below. Details of the factors and the weights attached to them have been reviewed and revised from the 2006 version, based on the advice of the Technical Advisory Board.

Revised Criteria


Factor #A1 - Severity of Toxin

Group A - Toxins that are not assessed as acute or systemic.e.g. organics such as toluene or xylene = 1

Group B - Organics that are probable carcinogens (USEPA Class 2 and 3) or substances with some systemic toxicity. e.g. VOC's, PAHs, PCBs, air pollutants such as PM10 and PM2.5 = 2

Group C - Known carcinogens or chmicals with significant systemic or organ system toxicity. e.g. vinyl chloride, benzene, lead, radionuclides, hexchromium, cadmium, organophosphate pesticides. = 3

Factor #A2 - Amount or scale of pollutant source

Limited = 1

Moderate = 1.5

Large = 2

These two factors are taken as multiplicative and so the overall score for this element is as follows:



Factor #B1 - Evidence of Human Exposure Pathway

Clear pathway = 1

Multiple Pathways = 2

Factor #B2 - Reliable Evidence of Health Impact

No = 0

Yes = 1

These two factors are taken as additive and so the overall score for this element is as follows:



Factor #C1 - Number of People Potentially Affected <10,000 = 1

10,000 to 100,000 = 2

>100,000 = 3

Factor #C2 - Level of exposure

Low = 1

Medium = 1.5

High = 2

Factors C1 and C2 are taken as multiplicative.

Factor #C3 - Large numbers of children particularly at risk

No = 0

Yes (e.g. play areas, schools) = 1

This factor is taken as additive to the other two and so the overall score for this element is as follows:

SCORE C = (C1xC2)+C3


Factor #D - Additional High Risk Element (TAB member discretion)

No = 0

Yes = 1

On the above basis, the total score is calculated as:

SCORE = [A1xA2] + [B1+B2] + [(C1xC2)+C3] + D

On this basis, the maximum score that could be assigned to a site is 17, as follows:

SCORE = [3x2] + [2+1] + [(3x2)+1] + 1

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