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CADDIS Volume 3: Examples & Applications

Worksheets: Little Scioto River, OH

Mechanistically Plausible Cause

Does a plausible mechanism exist for increased metals to cause the observed effects?


Analysis

Table 22. Plausibility of different effects.
Specific Effect Mechanism References
Increased relative weight No known mechanism
Increased DELT Metals cause fin erosion and lesions. PB, Zn, and Cu cause deformities 1,2,3
Decreased percent mayflies Metals cause lethal and sublethal effects on invertebrates 4,5

Discussion

Decreased percent mayflies and increased DELT can be linked to metals contamination. No plausible mechanism is known by which increased metals leads to increased relative weight.

Evidence Scoring Table:
Finding Interpretation Score
A plausible mechanism exists. This finding somewhat supports the case for the candidate cause, but is not strongly supportive because levels of the agent may not be sufficient to cause the observed effect. +
No mechanism is known. This finding neither supports nor weakens the cause for the candidate cause. 0
The candidate cause is mechanistically implausible. This finding strongly weakens the case for the candidate cause, but is not convincing because the mechanism could be unknown. --

Table 23. Mechanistically plausible cause scores for metals.
Candidate Cause Specific Effects Result Score
Metals Increased relative weight Implausible: no known mechanisms --
Increased DELT Plausible +
Decreased percent mayflies Plausible +

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