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
| 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.
| 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. | -- |
| Candidate Cause | Specific Effects | Result | Score |
|---|---|---|---|
| Metals | Increased relative weight | Implausible: no known mechanisms | -- |
| Increased DELT | Plausible | + | |
| Decreased percent mayflies | Plausible | + |