RESPONSIBILITY SHARING AND EXPLICIT AND IMPLICIT INDICATION OF RISKS CAUSED BY INTERACTION AMONG POLLUTANTS

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  • SHOJI Tetsuya
    School of Frontier Sciences, The University of Tokyo
  • KOMAI Takeshi
    Institute for Geo-Resources and Environment, National Institute of Advanced Industrial Science and Technology

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Other Title
  • 汚染物質間の相互作用に起因するリスクの責任分担とリスクの明示・暗示

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Abstract

Interaction among pollutants can be assessed by the equation, r1/μ=Σrj1/μ=Σ(xj/Aj) 1/μ, where xj and Aj are, respectively, the content and the standard value of Pollutant j in a polluted material; rj=xj/Aj and r are, respectively, the over-content ratio of Pollutant j and the total over-content ratio; μ is interaction index (Shoji, 2006). The interaction is none (independent) at μ grarr; 0, negative at 0 < μ < 1, complementary at μ=1, and positive at μ > 1. When the equation is applied for assessing environmental risks caused by interaction among pollutants from multiple sources, it seems to be adequate that responsibility for the risks is shared by the sources proportionally to their over-content ratios in mixed polluted materials. This sharing rule causes, however, some absurdities: e.g. 1) in the case that pollutants have no interaction, all sources have to bear always the responsibility, if a source discharges a pollutant whose over-content ratio exceeds 1, 2) when a source increases his over-content ratio, and consequently a total over-content ratio exceeds 1, the other sources have to share the responsibility, 3) in the case that pollutants interact positively, mixing of pollutants having over-content ratios lower than 1 makes possibly the total over-content ratio higher than 1, and 4) in the case that pollutants interact negatively, mixing of pollutants having over-content ratios higher than 1 makes possibly the total over-content ratio lower than 1. The negative interaction, which causes the fourth absurdity, may be apparent in practice, and is clearly explained by stacking of influence points (i.e. organs injured by pollutants, global warming caused by green house gasses etc.), for each of which pollutants interact complementarily. For example, under the condition that the over-content ratio of Pollutant 1 for the second influence point is 5 times of the ratio for the first influence point, and that the over-content ratio of Pollutant 2 for the first influence point is 5 times of the ratio for the second influence point, the safety/risk boundaries of the first and second influence points intersect at the point where both over-content ratios of Pollutants 1 and 2 are 5/6, and hence the total safety/risk boundary forms a shape concave toward the origin. If the over-content ratio of Pollutant 1 for the third influence point is 1.5 times of the ratio for the first influence point, and the over-content ratio of Pollutant 2 for the third influence point is 1.5 times of the ratio for the second influence point, the safety/risk boundary of the third influence point passes between the origin and of the intersect point. This means that it frequently fails to notice the third influence point whose safety/risk boundary crosses the safe domain of the first and second influence points, when the interaction between the pollutants is not taken into account. Even if the safe domain of the third influence point includes completely the safe domain of the first and second influence points, the third influence point should not be ignored, because the total over-content ratio in a case of three influence points is higher than that in a case of two influence points in the risky domain of the third influence point.<br>

Journal

  • Geoinformatics

    Geoinformatics 17 (4), 219-230, 2006

    Japan Society of Geoinformatics

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